Conversion from Celsius to Fahrenheit can be accomplished by clicking on the underlined "°C" symbol next to the large temperature value in the "Current Conditions" box. It can also be found in the "Text only" mode at the bottom left of the page under "Imperial Units". The conversion formula is °F = °C x 9/5 + 32 or, in reverse, °C = (°F - 32) X 5/9.

Generally, temperatures rise through the day and fall through the night and a forecast for a day or night period will include the highest or lowest temperature expected. However, the sudden arrival of warm air at night or cold air during the day can trigger different temperature trends. An asterisk (*) is posted next to the temperature value when there is an "abnormal temperature trend" for the affected forecast period. An abnormal temperature trend is defined as a temperature drop of at least 3°C during daytime or a temperature rise of at least 3°C during night time.

The presence of an asterisk is intended to alert the reader to the fact that an "abnormal temperature trend" is expected during the forecast period. A complete description of the temperature trend can be found in the forecast details located below the icon summary.

"Yesterday's Precip", in the "Historical Data" table on the "Current Conditions and Forecasts" page, is a total of all the types of precipitation that may have fallen on the previous day including: rain, drizzle, freezing drizzle, freezing rain, hail and snow.

The unit used to express "Yesterday's Precip" is millimetres. Therefore any snow that has fallen is melted and this amount of liquid water is recorded in millimetres and added to any other amounts from other forms of precipitation (i.e. rain). Even if snow was the only type of precipitation to fall on the previous day, the snow is melted and the water equivalent is reported in millimetres.

Rain, drizzle, freezing rain, freezing drizzle and hail are usually measured using the standard Canadian rain gauge, a cylindrical container 40 cm high and 11.3 cm in diameter. The precipitation is funnelled into a plastic graduate which serves as the measuring device. The liquid precipitation is normally measured in millimetres.

Usually, the snow amount or the depth of accumulated snow is measured using a snow ruler. The measurements are made at several points which appear representative of the immediate area, and then averaged. Snow is normally measured in "centimetres".

To calculate the water equivalent of snow, we melt the snow captured in snow gauges like the Nipher snow gauge. This Nipher gauge is designed to diminish the turbulence around the opening of the gauge and positioned high enough above ground to prevent most of the blowing snow from entering the gauge.

In many snow events a ratio of 10 to 1 can be applied to the amount of snow to determine its water equivalent. In other words, 1 centimetre of snow is equivalent to about 1 millimetre of water once the snow is melted. This means that in many snowfall situations (on days when only snow fell), you can simply change the units from millimetres to centimetres on the "Yesterday's Precip. Total" on a specific location's weather page to get a reasonably good idea of how much snow fell.

However, this 10 to 1 snow to liquid ratio is not exact. Exceptions include very fluffy snow (snow that has less water once melted) where the snow to liquid ratio could be 15 to 1 or higher (i.e. 1.5 centimetres of snow would melt to provide 1 millimetre of water). At the other extreme, the snow can be heavy and wet resulting in a snow to liquid ratio of around 5 to 1 (i.e. 0.5 cm of snow would melt to provide 1 mm of water).

We also have a map giving snow depths (snow on the ground). It is available from http://weatheroffice.gc.ca/analysis/index_e.html.

Environment Canada employs manned and automated weather stations located across Canada to collect temperature, rain and snow fall amounts, wind direction and speed and barometric pressure. As precipitation rates constantly change with time and because weather systems are moving, measurements may differ considerably when taken at different times and/or at different locations. Consequently, precipitation amounts can vary throughout a city or region, and may be significantly different at your location compared to the weather station report.

Main error sources in precipitation estimates include the presence of tall objects (like trees and buildings) exposed to the wind direction which could either increase or decrease the amounts collected in the gauge. The nature of the terrain and immediate surroundings could also have some effects on accumulation on the ground (partial melting, precipitation soaking into the ground). Thus, the position of the instrument is very important in order to get the most accurate reading. In the case of snow for instance multiple samples even over a small area must be averaged.

Despite all the precautions and a precise calibration there are always errors related to instrument design and limitations. For example, trace amounts of precipitation, less than 0.2 mm, are not recorded by the instruments. Wind shaking the gauges can cause a false reading, including giving a precipitation measure when none has been received. Strong winds can prevent rain or snow from entering the gauge, thus giving inaccurate readings. Computer system malfunctions can also occur and affect data transmission.

Wind chill is the cooling effect of the wind in combination with low temperatures. When it is windy, we feel colder because our skin temperature is lower. This sensation of cold is what the wind chill index quantifies: as such, the index is not a real temperature and is expressed without units, even though it is calibrated according to the Celsius temperature scale.

Environment Canada's wind chill index gives you a good idea of the temperature which, with a quasi calm wind, would give your face a sensation of cold similar to that caused by the actual temperature and wind. Wind chill also estimates the risk of your getting frostbite (a severe injury caused by cold). You will find more details in our wind chill Web site.

Please visit our new wind chill Web site. It contains a wealth of information on wind chill and our new program. In particular, this site gives you access to an on-line wind chill calculator and a downloadable program to calculate the wind chill index and the humidex.

Wind chill is indicated in current conditions only when the temperature is 0°C or lower, with a wind speed of 2 km/h or more. In general, wind chill is mentioned in a forecast only if it is expected to be significant, that is to say, if wind chill is expected to be -25 or colder, with a forecast wind speed greater than 10 km/h.

This is because the wind chill and the humidex are indices and not physical quantities. In other words, these quantities are calculated, not measured. Even though these two indices are calibrated according to the Celsius temperature scale, we do not put °C after their values to emphasize the fact that they are not temperatures.

Note: In imperial units, the wind chill and the humidex indices have different values because, in these units, they are calibrated according to the Fahrenheit temperature scale.

The dew point is a measure of the humidity content in the air. Dew point is short for dew point temperature. It indicates the amount of moisture in the air. It is the temperature to which the air must be cooled, keeping pressure constant, to become saturated. When the difference between the air temperature and the dew point temperature is large, the air is dry and the relative humidity is low. As the air temperature is cooled to the dew point the relative humidity increases and reaches 100% when the two temperatures coincide.

The best way to understand the dew point notion is to visualise how dew is formed on a clear fall morning, for example. Dew occurs as a result of the air gradually cooling overnight. In the late afternoon, the air holds a certain quantity of water vapour (humidity). During a clear night, however, the earth's surface loses radiational heat rapidly and cools; consequently, air in contact with the earth's surface is forced to cool while the atmospheric pressure remains the same. After a certain period of cooling off, the air reaches its saturation point and if it cools any further, we witness an excess of humidity that condenses and forms dew. The temperature at which condensation starts occurring is what we call the dew point.

The percentage of humidity or relative humidity is the quantity of water vapour the air contains compared to the maximum amount it can hold at that particular temperature. It is expressed as a fraction of the maximum moisture the air can hold, at the same pressure and temperature, before water droplets start forming clouds or dew (if close to the ground). For example, a relative humidity of 60% means that the air contains 60% of the maximum moisture it could contain at the present temperature. Note that the warmer the air, the more moisture the air can hold. A relative humidity of 60% feels comfortable when it is 20 degrees, but a lot less comfortable when the temperature reaches 30 degrees. Because the air can contain a lot more moisture in 30-degree weather than in 20-degree weather, we feel the effect of humidity a lot more when the temperature reads 30 degrees even though the relative humidity (percentage) is the same.

For more information regarding the relative humidity, consult our fact sheet on humidity.

The humidex is an index (a computed value as opposed to something measured) devised to describe how hot or humid weather feels to the average person. The humidex combines the temperature and humidity into one number to reflect the perceived temperature. It takes into account these two important factors that affect summer comfort. It is therefore a better measure of how stifling the air feels than either temperature or humidity alone. A humidex of 40 with, for example, a temperature of 30 degrees means that the sensation of heat when it is 30 degrees and the air is humid is more or less the same as when it is 40 degrees and the air is dry. We must be careful not to depend on this interpretation alone: it is a mere indication of physiological reactions, not an absolute measure

For more information regarding the relative humidity and the humidex, consult our fact sheet on humidity.

The humidex is particularly significant when its value is greater than 30. We only display humidex values of 25 or higher for a location which reports a dew point temperature above zero (0°C) and an air temperature of 20°C or more. Below this value, the humidex is too close to the air temperature to be considered significant.

The Humidex formula is based on the work of J.M. Masterton and F.A. Richardson at the Atmospheric Environment Service (now MSC) of Environment Canada in 1979. It is a standard for Canada, but variations are used around the world. The dew point temperature should be given in kelvins (temperature in K = temperature in °C + 273.1) for the formula to work. The magic number 5417.7530 is a rounded constant; it's based on the molecular weight of water, latent heat of evaporation, and the universal gas constant.

e = vapour pressure in hPa (mbar), given by:
e = 6.11 * exp [5417.7530 * ( (1/273.16) - (1/dewpoint) ) ]

h = (0.5555)*(e - 10.0);
humidex = (air temperature) + h

Note that the values associated with the discomfort of the humidex are generally for the outdoors. The Canadian Centre for Occupational Health and Safety recommends another index for indoors. For more information, visit:
http://www.ccohs.ca/oshanswers/phys_agents/humidex.html

Program designed to calculate the humidex
Environment Canada offers a program that helps calculate the humidex from temperature and dew point data. This program, called Chilldex, also allows you to calculate the wind chill from the wind speed and temperature. You may download this calculator from this page: http://www.msc.ec.gc.ca/education/windchill/
calculator_e.cfm

Atmospheric pressure tendency is defined as the characteristic and the amount of the change in station pressure (pressure measured at the altitude level of a given reporting observing station by opposition to the pressure measured at the sea level) in the three hours preceding the observation. The pressure tendency is usually included in weather reports every three (3) hours. The characteristic is the nature of the pressure change and can be coded according to eight (8) possible trends (such as: increasing steadily, steady, falling rapidly, etc.). The pressure amount is the net change of pressure over a period of three (3) hours and is determined in hectopascals (hPa) to the nearest tenth.

In the web-site www.weatheroffice.gc.ca the pressure tendency provided within the "Current Conditions" is simply the characteristic (rising, falling and steady) of the change in station pressure (as described above). To know how much the pressure has changed (or the amount) one needs to go to "Past 24 hour Conditions" and make the determination by subtracting the hourly pressure values for the desired period.

The UV Index gives information about the level of UV rays (or ultraviolet radiation) that reach the surface. UV rays are those sun rays that can cause sunburns. Long-term exposure to UV rays has also been associated with skin cancer and cataracts.

The forecast UV Index is the maximum level of UV radiation that can be expected to reach the surface on a given day (today or, in afternoon forecasts, tomorrow). The UV Index is included in the text of the public forecast whenever it is expected to be 3 or more, i.e. when the index can reach the "moderate" category.

In Canada, the UV Index normally ranges from 0 to 10 (it can reach higher values further south), and is also expressed in categories, as follows:

Normally, we only indicate the wind in the text of the forecast (it does not appear in the icons) when the wind is expected to be at least 20 km/h. Lighter winds vary too much from one location to another to make it possible to forecast them with accuracy.

In meteorology, the wind is always given with the direction it is blowing from, using geographic cardinal points. A north wind is therefore a wind blowing from the geographic north.

The probability of precipitation (POP) is the chance that measurable precipitation (0.2 mm of rain or 0.2 cm of snow) will fall on any point of the forecast region during the forecast period. For example, a 30% probability of precipitation means that the chance of you getting rained over (or snowed over in winter) is 3 in 10. In other words, there is a 30% chance that rain or snow will fall on you, and, therefore, a 70% chance that it won't. It must also be noted that a low POP does not mean a sunny day: it only means a day where the chance of rain or snow is low.

This fact sheet explains the Probability of Precipitation: http://www.msc.ec.gc.ca/cd/probability_e.cfm.

Rules for including the POP in forecasts changed in 2001. The forecast POP is only indicated when it is expected to be from 30% to 70%, inclusive. You can find more details on this page.

This fact sheet should help you understand our forecasts.

Synopses were discontinued in September 2001. We have conducted public and media opinion research and we found that 85% of the media did not even read the synopsis. In addition, pages giving the synopses had low traffic. Since we rely heavily on the media to broadcast our bulletins, if the media do not use a bulletin, this bulletin becomes a candidate for cancellation. This allows us to focus on higher-priority services.

We have not completely terminated the total functionality of the synopsis, however. When we anticipate that some significant weather conditions are going to affect certain regions of the country, we issue special weather statements to inform the concerned population of the situation. By issuing these special weather statements, we hope to satisfy the need for descriptive information on the general weather situation when circumstances call for it.

You can also look at analysed weather maps to get displays of weather systems. In particular, the maps in the "Complete" column will give you a more extensive picture of the weather features that influence the northern hemisphere.

Environment Canada does not directly provide this information. However, in association with the Lung Association of Nova Scotia and St. Mary's University, Environment Canada provides a chart of pollen and spores in the Halifax area on this page : http://www.ns.ec.gc.ca/weather/pollenenglish.html.

You can also, in season, find pollen information for a number of Canadian cities from The Weather Network's Web site at http://www.theweathernetwork.com/

You need to refer to the climate normals, namely the monthly and annual means derived from a variety of meteorological factors (i.e. temperature, degree days, hours of bright sunshine, rain and snow fall, humidity and winds, as available). The normals can be found at this address: http://www.climate.weatheroffice.ec.gc.ca/
climate_normals/index_e.html

The tables of climatological normals also show, when available, temperature, precipitation and wind records for each month.

This information is available for a number of Canadian cities through the Canadian Climate Normals; see the previous question.

The Canadian Meteorological Centre has several web sites. The weather site is maintained by the Operations Branch, and provides information about the current condition of the atmosphere, and output of our models to predict its future state. What you won't find on these pages is any information about the past; this is considered climatological data. For questions on climatological topics, please consult our colleagues in the Climate and Water Information Branch.

For information regarding a region of Canada, please consult our regional climate contacts.

You may also try the Canadian Institute for Climate Studies (not part of Environment Canada).

You can find this information, and much more, at the link given below. (When you are at this link, to find historical weather information, click on "Climate Data"):

http://www.climate.weatheroffice.ec.gc.ca/
prods_servs/index_e.html

If you can't find the needed data at the link above, we may be able to provide it on a cost-recovered basis. Further climatological information is available from Environment Canada's regional climate centres. For more information, contact the regional office serving your area - link to http://www.climate.weatheroffice.ec.gc.ca/
contacts/index_e.html. Where available, the user-pay Climate Source service, accessible at 1-900-565-1111, gives you quick, direct access to this office.

Please refer to the previous two questions.

There are a number of web sites that give information on these phenomena. Here are a few of them.
http://www.msc-smc.ec.gc.ca/education/elnino
http://www.pmel.noaa.gov/tao/elnino/nino-home.html (high bandwidth)
http://www.pmel.noaa.gov/tao/elnino/nino-home-low.html (low bandwidth)
http://www.msc-smc.ec.gc.ca/education/lanina

There are six (6) time zones across Canada. These time zones can be found at the following web site: http://inms-ienm.nrc-cnrc.gc.ca/time_services/daylight_saving_e.html

You may also try this URL for the time zones: http://www.canadainfolink.ca/time.htm

Most localities change to Daylight Saving Time. However, Saskatchewan is on Central Standard Time (CST) year round. It shares the same time observed by Alberta during the summer months (Mountain Daylight Saving Time) and observes the same time zone as Manitoba (Central Standard Time) for the winter months. See the previous question

UTC is the international abbreviation for Coordinated Universal Time. It is the local time at the Greenwich meridian (0°). The World Meteorological Organization (WMO) has adopted the UTC as the standard time for use in reporting of all meteorological data. Times in UTC sometimes get the suffix Z, i.e. 16Z. From the Z suffix came the mnemonic "Zulu" (as used in international marine communications standards).

(Reprinted from: http://www.eecis.udel.edu/~mills/leap.html)
GMT is a historic term which is now obsolete. It is today called Coordinated Universal Time (UTC). Universal time is the local time on the zero meridian which goes through the old observatory in Greenwich, London, UK.

If you are interested in knowing time more precisely than 1 second, then you have to make a difference between the following versions of universal time:

• UT0 is the precise sidereal local time on the zero meridian.
• UT1 is UT0 corrected by a number of periodic effects (UT0 has different "speeds" at different times of the year).
• UTC is a time defined not by the movement of the earth, but by a collection of atomic clocks all over the world. When UTC and UT1 drift apart for more than 0.9 s, a leap-second is inserted into UTC to correct this. The C in UTC stands for "Coordinated".
• UT2 is an even better corrected version of UT0 which is used in astronomy.

GMT is a term that was used before time was defined internationally by an atomic time reference in the late 1950s. People who talk today about GMT really mean UTC.

See table below for examples:

Daily at 00 UTC and 12 UTC, a snapshot of the atmosphere is taken, and made readable to our computers. This snapshot is called an "analysis". Using the analysis and other data as a starting point, a numerical simulation of the atmosphere is run (on a supercomputer) to predict the state of the atmosphere at various times in the future. The forecast maps are typically available about three hours after the snapshot data (at 03 UTC and 15 UTC). Forecast maps are labelled by the simulated hour of the model, and by valid date and time. Below is a sample title from a forecast map:

12 H FORECAST - PREVISION 12 h

V12Z WED-MER 09 AUG-AOU 00

This is a map showing a forecast valid at 12Z (noon UTC) on Wednesday, 9 August 2000 (the second title line.) The first title line means the forecast is for 12 hours after the collection time of the data on which the forecast is based; it is therefore based on data collected at 00Z, i.e. at midnight UTC on 9 August. This forecast would normally be available on the WWW around 03 UTC.

A zero-hour forecast indicates how the computer model "sees" the atmosphere at the beginning - the initial time or "zeroth" hour - of a numerical simulation. A 00H forecast map shows the initial values of the meteorological elements that the model calculates.

1 hPa = 1 mbar = 0.1 kPa. Hence, 1013.25 mbar = 1013.25 hPa = 101.325 kPa

Your barometer indeed reports pressure in inches of mercury (Hg). The conversion factor is approximately 33.9 hPa, or 3.39 kPa, per inch of Hg. So divide the pressure in kPa by 3.39 to get it in inches of Hg, or multiply the value in inches of Hg by 3.39 to convert it into kPa.

For North America, we have a map of the jet stream at http://weatheroffice.gc.ca/jet_stream/index_e.html. You can get to it by clicking on Analyses and Modeling.

Try http://ww2010.atmos.uiuc.edu/(Gh)/guides/maps/home.rxml
This site gives an introduction to weather map interpretation. Or you may want to visit :
http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/home.rxml

If you read French, you will also find some information on the La Girouette site; click on "Le quoi et comment de la météo". You may also try the education site InterMet. From the home page, click on Ressources éducatives.

We do not have this explanation on our Web site, but it can be found elsewhere on the Internet. You may try the following sites:

In English: Guide to Weather Symbols

Selected Weather Map Symbols - from the American Meteorological Society

Synoptic code Table, from a British site which is to be consulted in conjunction with this other site.

In French: Lire une carte météo (Cyberscol)

The "knot" is the unit used to describe the speed of the wind in Canadian marine forecasts. It is a measure of the wind speed in nautical miles per hour. One nautical mile is equal in distance to 1.852 kilometres.

The nautical mile is the traditional unit of marine navigation derived from the 360 degrees of latitude comprising the circumference of the earth, measured around the poles. There are 60 minutes of arc in one degree of latitude, and the nautical mile is defined as a distance equal to one minute of latitude, or one sixtieth of a degree, on the earth's surface.

Thus one degree of latitude equals 60 nautical miles. It then follows that the earth's circumference in nautical miles is 360 degrees X 60 nautical miles, or approximately 21,600 nautical miles. (1 knot = 1.852 km/h, 1 km/h = 0.54 knot)

A Strong Wind Warning is an alert issued to advise mariners that marine wind speeds between 20 and 33 knots inclusive are occurring, or are expected to occur. The main purpose of the Strong Wind Warning is to alert near-shore mariners and operators of smaller vessels to strong wind conditions that may impact their operations. The terminology for this alert replaces the "Small Craft Warning" which was previously issued for the same wind speed criteria.

The terminology "Strong Wind Warning" is used to more accurately describe the nature of the alert, and it is less likely to be misinterpreted. As well, the definition of "small craft" is not entirely obvious and may be subject to misinterpretation.

To help maintain brevity the marine forecast will only include visibility if it is obstructed to the extent that it could potentially impact marine operations. One nautical mile is the threshold that has been determined by most mariners to be the critical threshold for their activities. Visibility, along with the associated obstruction, will be mentioned when it is expected to be one nautical mile or less. For fog alone, visibility is not mentioned in the marine forecast since the visibility statement at the beginning of the forecast states that the presence of fog alone implies visibility less than one nautical mile.

One of the objectives of the new marine program is to standardize the format, timing, and content of marine forecasts and warnings. To accomplish this there have been some regional changes. Although, in some cases, forecast issue times have changed, they will still contain current information. In the event of a change in forecast conditions for any marine area, an updated forecast for the marine area will be issued. This will ensure that the latest marine forecast information will be available to mariners regardless of initial issue time.

Further information can be found under Canadian Marine Weather Alerts, and Marine Weather Services. These pages include information about the marine warning definitions and marine forecast products issued by Environment Canada for each region, including forecast issue times and methods of access.

This is the ratio of an area of ice to the total area of water surface within the marine area.

The ice concentration describes the amount of ice coverage, measured in tenths, occupying the marine area. For example seven tenths ice concentration means that the marine area is 70 percent ice-covered.

Ice types are described based on the thickness of the ice cover within a marine area. For example, "new" ice refers to ice with a thickness less than 10 cm. "Grey" ice refers to ice with a thickness of 10 cm or more, but less than 15 cm. The ice description will state the predominant ice type first. The thickest ice type, if present, will be stated second. There may be other ice types present, but only the predominant and thickest types are mentioned in the ice forecast bulletins.

For more information about different ice types, please refer to the Canadian Ice Service website.

The iceberg limit is a general point-by-point description of the limit between areas of icebergs and no icebergs. However, sea ice may be present outside the iceberg limit.

Unknown number of icebergs indicates that icebergs are present over a marine area but the actual number cannot be determined due to the absence of any recent aircraft survey or ship observations over that area.

Many of our marine forecast areas can be split into two sub-areas in a forecast update. If you bookmark a particular marine area that has since become split into sub-areas and you return to the initial marine forecast area, the original bookmark will no longer work. The changed web address is a result of the "dynamic" division of the marine area into two areas for selection. Likewise, if the bookmark is applied to a sub-area which has since returned to a single marine area in a forecast update, the bookmarked address will not work properly on a return visit.

The recommended practice is to bookmark the web page with the "regional marine map" where a visitor can select one of many areas on the map.

For example, bookmark the page with the map for the Maritimes region of the Atlantic Coast, instead of the marine area "Cabot Strait - northern half" selectable from this map. This web page with the regional map is "static" in that the address doesn't change, just the definitions of the marine areas in the map.

The Canadian Hydrographic Service web site gives tide times for most Canadian sites for which tides are calculated. Once you are in the site, click on "Canadian Tide Tables", and then on "Select region of interest".

You can order products directly from the Canadian Hydrographic Service:

Hydrographic Chart Distribution Office
Department of Fisheries & Oceans
1675 Russell Road, P.O. Box 8080
Ottawa, Ontario K1G 3H6
Tel: (613) 998-4931
Fax: (613) 998-1217

You may also find more information through the Government of Canada's Marine Services On-Line site.

Try this web site for West Coast tides: http://www.tides.info

Environment Canada is not an official source for this data, however as a courtesy, approximations for sunrise and sunset are available on the city forecast page nearest your location. Official times for sunrise and sunset can be found on the Web site of the Herzberg Institute of Astrophysics of the National Research Council of Canada.

Web site options for calculating moonrise/moonset include: Timeanddate.com or the U.S. Naval Observatory site.

If you want a locality that does not appear in the list of cities, you will need to find its latitude and longitude. You can find these on the Canadian Geographical Names site of Natural Resources Canada.

The times posted for moonrise, moonset, sunrise and sunset are provided on this site solely as a courtesy by Environment Canada for general reference purposes. If, however, you are seeking official times, the Canadian authority for this information is the National Research Council (NRC) whose data can be accessed at: http://hia-iha.nrc-cnrc.gc.ca/sunrise_e.html. The standards used by the NRC for the generation of astronomical times conform to international practices for computing sunrise, sunset and times for related data. And these computed values may differ from the times posted on our site.

Nav Canada's Aviation Weather Web site is the official source for METAR reports, TAF forecasts, and graphical area forecasts (GFA) for the Canadian domestic air space. As a partner, their Web site can be found in our Links section. Environment Canada also provides an aviation package of Operational Model forecasts.

Complete and exhaustive information on Geosynchronous Operational Environmental Satellite (GOES) and Polar-Orbiting Environmental Satellite (POES) of the NOAA (National Oceanographic and Atmospheric Administration of the United States) can be found from the general satellite links below. (link with exit page to each)

• http://noaasis.noaa.gov/NOAASIS/ml/genlsatl.html
• http://ww2010.atmos.uiuc.edu/(Gh)/guides/rs/home.rxml
• http://ww2010.atmos.uiuc.edu/(Gh)/guides/rs/sat/img/vis.rxml
• http://ww2010.atmos.uiuc.edu/(Gh)/guides/rs/sat/img/ir.rxml
• http://ww2010.atmos.uiuc.edu/(Gh)/guides/rs/sat/img/wv.rxml
• http://ww2010.atmos.uiuc.edu/(Gh)/guides/rs/sat/img/cir.rxml

The satellite has two on-board imaging sensors (visible and infrared). Each sensor "sees" the same field of view; however, they differ in their sensitivity to various wavelengths of light.

The light detector for each sensor is a charged-coupled device similar (in concept) to that found on most video cameras. Light energy (photons) hits the detector and generates an electrical current that can be measured with sensitive electronics.

Visible light falls in the wavelength region that can be detected by the eye, hence the term optic or optical often used to describe this region. Because the use of electronics is integral to the functioning of the detector, the visible-light detector is frequently called an electro-optical (EO) detector or sensor.

Infrared (IR) light occupies a large band in the light spectrum. This is the type of energy that provides heat for your home and (non-microwave) oven. Infrared detectors can "see in the dark" by detecting the presence of "heat" given off by people and equipment. The detector used in infrared sensors is basically the same as that used for electro-optical sensors. It is, however, sensitive to wavelengths in a different region of the spectrum. This detector must be kept cold so that its own temperature does not generate false signals.

The satellite's EO sensor can detect clouds visible to the eye. This sensor is sensitive to light with wavelengths from 0.4 to 1.1 micrometres (or microns; one micrometre is equal to 10-6 metre or 1/1000 of a mm). The IR sensor is sensitive to light with wavelengths from 10.5 to 12.5 micrometres. It can detect high clouds even when they are very thin and not visible to the EO sensor. This is possible because high clouds are also very cold (they are composed of ice crystals).

IR stands for infrared. On an image, IR is usually followed by a wavelength in micrometres (e.g. 10.7). In the IR spectrum, clouds at different heights show up very well as differences in radiances (quantity of light energy detected) from ground level (radiances vary with cloud height). Radiances can then be converted into temperatures with some calculation. So what we see on an IR image is the distribution of temperatures as detected by the satellite's sensor, and the temperature in the legend corresponds to the temperature of whatever the satellite sensor "sees" (clouds at different heights, sea surface, earth surface).

VIS stands for visible. A VIS satellite image (taken in the visible spectrum) is a picture of the earth from space, just as you would see it if you were looking out the window from a spacecraft in orbit. During nighttime over the Americas, the picture is dark.

IR image: The legend indicates the relation between the colour and the temperature in degrees Celsius; please refer to the previous question.

VIS image: The colour on the legend at left (if present) is related to the reflectivity, i.e. the amount of light reflected (0-100%). Note that a visual spectrum satellite image is not a false colour one. Blue means that the particular part of the earth looks blue from where the satellite is, white means it looks white, etc. So a legend on these images is largely superfluous.

Is it a VIS image while it's nighttime over North America? A nighttime image of North America is dark because there is no visible light falling on that part of the planet. If you download the visual animation, you can watch sunrise or sunset move across the hemisphere (from east to west). At night, visual spectrum images are almost all black, so infrared is used at night.

Yes; you may find them at http://meteo.ec.gc.ca/satellite/index_e.html, towards the end of the page.

However, images of areas north of 60° look different because they come from a different satellite. Most weather satellites, including those we use for images of southern Canada, are in geosynchronous orbit. This means they revolve around the earth in 24 hours, at a very high (34,880 km) altitude over the equator. These satellites, therefore, remain over a fixed point of the earth (in south America for satellites that can view the Americas). Because geosynchronous satellites stay over the equator, the higher the latitude of the area we want to observe, the worse the view. As a result, to get useful pictures at the higher latitudes (north of 60°), we need a different satellite-a polar-orbiting satellite.

Instead of staying high over one place, a polar orbiting satellite moves very quickly (orbits in less than two hours), at much lower altitude (around 800 km). While geosynchronous satellites take a picture of an entire hemisphere (a disk showing the planet earth), polar-orbiting satellites are so low, they only take in a small swath below the satellite at each orbit. So to get a full-disk, one must-using software-"stitch" the swaths together. Because the strips are photographed at different times, the result is not a true image, but a composition.

At present we receive NOAA polar orbiting satellite data, and we post images of most of Canada northern regions, including the Yukon, Northwest Territories and Nunavut.

Try the European Meteorological Satellite Association at: http://www.eumetsat.de/en or try the Intellicast image at http://www.intellicast.com/Global/satellite/Current.aspx?location=PLXX0055

Our satellite images are generated from large data sets which are archived on a private server. There is no software in place, or any plan to implement any software, to allow the public to extract arbitrary data from the archive system. For older images you may try NOAA's National Climate Data Center (United States), which offers a fairly good historical archive on-line. Click on the "Historical GOES Browse Server" link on http://www.ncdc.noaa.gov/oa/satellite.html.

Full disk images are updated every three hours, other GOES images are updated every half hour, while HRPT images are updated as they become available. (This is what the *, ** and *** footnotes refer to in the satellite image page).

R. The radar echoes that you see on these areas are not caused by precipitation: they are echoes caused by "ground clutter", i.e. surface features like mountains, hills or tall buildings. Areas of ground clutter can be identified on radar animations: on animations, echoes caused by precipitation move while those caused by ground clutter do not.

Go the National Radar Project site, where you'll also be able to consult the Frequently Asked Questions.

For information on the basics of radars and target detection, interpreting radar imagery and exploring their applications in forecasting and severe weather prediction, go to these sites:

http://ww2010.atmos.uiuc.edu/(Gh)/guides/rs/rad/home.rxml
http://ww2010.atmos.uiuc.edu/(Gh)/guides/rs/rad/basics/cltr.rxml (clear air returns)

Weatheradio Canada is a nationwide network of radio stations broadcasting weather and environmental information 24 hours a day, in both official languages and directly from Environment Canada's storm prediction centres.

Most Weatheradio Canada transmitters broadcast on the VHF public service band using one of 7 frequencies: 162.400, 162.425, 162.450, 162.475, 162.500, 162.525, or 162.550 MHz.

For more information about Weatheradio Canada

Please see our Employment Opportunities link under "About Us".

It is permissible to have, on your page, a link to one or more of our pages. However, to avoid any confusion, we would appreciate it if you would let your visitors know they are going to leave your site to enter ours.

The information produced by the Government of Canada is copyrighted. However, since the information and the data on our web pages are for general use, we grant you permission to reproduce on your site, for non-commercial purposes, the information found on our public pages, provided that you clearly acknowledge Environment Canada as the source of this information.. Remember that the data and information remains copyrighted to the Government of Canada, and all copyright laws apply. You can find more information, including information concerning reproduction for commercial purposes or for publication, on the Important Notices and Disclaimers page of The Green Lane.

Please try to turn off the graphics by clicking on the words "Graphics off" found near the bottom of our pages. This reduces the size of a page and should accelerate downloading for people who have slow connections to the Internet.

We also offer a service for cellular telephones and pocket computers. You will find details of this service at http://weatheroffice.pyr.ec.gc.ca/pda/introduction_e.html

Environment Canada with headquarters in Ottawa-Hull, is a scientific Department of the Government of Canada. It has a network of WWW servers known as The Green Lane. The Department is divided into "Services." The Meteorological Service of Canada (MSC) is the one providing Canadians with weather and climate information to enhance their safety and quality of life. The service has a national headquarters (located partly in Toronto and partly in the National Capital Region), a national weather centre, the Canadian Meteorological Centre or CMC (located partly in Toronto, partly in Dorval, QC), and Regional Centres across Canada.

The CMC takes care of the data which needs to be collected from across the country and around the world. The CMC uses this data in its computer models of the atmosphere to produce predictions of what the atmosphere will look like in the future (up to six days). The Regional Centres produce and issue weather warnings and regional routine forecasts like those for aviation, the public, marine users, travel or recreation. They monitor the weather in the region, produce special weather statements and advisories for weather of interest or potential risks, provide a broad range of commercial services for private clients, and provide briefings to the local media. In addition, they collect and redistribute local data.

Browser caching options on your computer control how and when your browser displays or downloads images from our web server. The animations on the Environment Canada (EC) "weatheroffice" web site are shown as a series of individual images, like a slide show. If you set your browser's cache options to download images ¨on every visit¨, then each run through the slide show will trigger a new transfer of every image in the series.

With Microsoft Internet Explorer browser, look in Tools/Internet Options/ General /Settings. Under ¨Check for newer versions of stored pages¨ a selection of ¨automatically¨ should solve the problem. This change would also substantially accelerate your web activities by reducing the amount of data downloaded to your computer from the web sites you visit. Users of the mozilla-firefox browser will not encounter this problem, since the faulty setting has been removed as this browser ¨automatically¨ defaults to the proper setting.

There is usually nothing wrong with our images. We can download them on the systems we have at the CMC without problems. If you have difficulties viewing some elements at the site, we are unlikely to be able to help you unless it is a problem on our server. Your best bet is to consult internet resources on the various types of software available, e.g. Netscape Help or Internet Explorer Support.

If you still think you should ask us about a problem viewing a given image or animation, please include the exact URL of the image you are having difficulty with, and a description of your system, namely the hardware (how much RAM), the operating system (name and version, for instance Windows 95b), the browser (name and version), the plug-ins and the helpers (name and version) you are using. This will help us solve the problem.

Link to our RSS (Really Simple Syndication) weather service is located at the bottom of our "5 day weather" pages. This will link you directly to the free subscription service if your browser supports RSS feed. For more details on our RSS service, please visit our "Weather on the Go" page.

Yes, weather information has now been added to the Government of Canada Wireless Portal as a new service for web enabled mobile devices. Links to the mobile service are located at the bottom of our 5 day weather pages on weatheroffice or point your mobile web-enabled device to the following address: http://wap.gc.ca.

If you link to our RSS (Really Simple Syndication) weather service located at the bottom of our "5 day weather" pages and you see the XML file instead of opening the RSS reader window, your web browser does "not" support RSS feed. For more details on our RSS service, please visit our "Weather on the Go" page.

You went through the entire FAQ, and you didn't get an answer to your question. Have no fear, email is here!

The Vancouver 2010 Olympic and Paralympic Winter Games are less than six months away! Explore our new 2010 Winter Games page to access:

• Olympic Venue weather conditions and forecasts
• Historical climate information for the 2010 Winter Games period
• Current road conditions
• Canada2010.gc.ca - the official Government of Canada 2010 Winter Games Website

As the exclusive provider of weather services, Environment Canada's detailed weather forecasts, warnings and information will guide crucial operational decisions during the 2010 Winter Games. This data will also help prepare athletes for competition, promote fairness, and keep Olympic spectators, tourists and local residents safe.

Stay tuned! As the 2010 Winter Games approach, new resources will be added to Weatheroffice's 2010 Winter Games page.

Accurate and timely marine forecast information is now available as a RSS (Really Simple Syndication) feed. Receive updates to the latest forecast and warnings for your marine area when you subscribe to Environment Canada's RSS Marine Weather Feed! One RSS feed contains the following information:

• Marine Watches and Warnings:

  Notification of Warning/Watch events including Ice warnings from issue time to the time it is ended.

• Forecasts:

  Forecast weather conditions including winds, waves, weather & visibility and outlooks for up to 5 days.

To facilitate access to this service, our "Forecast" tabbed page in the marine weather section of the web site has a RSS link near the bottom of the page.

Users of the "Current Conditions and Forecasts" section will quickly notice the introduction of several improvements. The primary change is the inclusion of a sixth and seventh day in the forecast period. Other minor adjustments to the web page have been made in response to the ongoing feedback from our users. To summarize, the changes include:

• Introduction of a sixth and seven day in the forecast.
• Full text is always available beneath the icons to reduce button clicks.
• Highlighted temperature values in the icon summary when no high or low temperature is stated where temperatures rise or fall abnormally.
• In morning forecast updates, the low temperature value for tonight is moved to the next day icon box since the occurrence of the lowest night temperature typically occurs near day break.
• In afternoon forecast updates, this low temperature adjustment is also applied to the third day of the forecast period.

Improvements to the lightning detection pages of our site have just been implemented. These new pages enable users to select "regional" geographic areas of interest which are updated hourly. In addition, the areas of lightning are smaller covering 40 square kilometres instead of the previous 80.

Visit our lightning detection section to see the recent improvements! Comments regarding these changes can be made by visiting Contact Us.

Users of the "Marine Info" forecast section will quickly notice the introduction of new improvements. Environment Canada's marine forecast products can now be accessed by selecting areas of interest from regional maps. These redesigned pages provide mariners, boaters and sailors with:

• marine warnings and watches highlighted on national and regional maps.
• maps that enable users to select an area of interest which brings them to a suite of marine weather and ice products accessible from one page.
• "tabbed browsing" to select a variety of info products for the marine area of interest.
• access to weather reports from a network of buoys and coastal weather stations located on interactive maps.
• links to related content through the Marine Services On-Line portal and other web pages.

Improvements to the "weatheroffice" web site's left menu and forecast pages are here! In order to serve these ever popular web pages more effectively, a new design has been introduced to make them easier to scan and navigate. These comprehensive changes based on usability testing have brought many improvements. They include:

Navigation

• "New" left menu using easy to understand terminology
• Simpler terms and shorter list of menu choices
• Expandable menus for related content
• Improved navigation by using "Forecast Quick Link" found at the top of the Canada and forecast pages

Presentation

• Forecast icons - organized in one row for the 5 day period
• Details of forecast are selectable for each forecast period
• Simpler style for easier scanning adopted in the page layout

Content

• Content grouped as Current Conditions, Forecast and Historical Data
• Grouping of related content with the use of "more info" menus for each group
• New icons developed through the input of client groups