About the Forecast Products

• Always Check the date: Automated processes fail on occasion and making plans based on last week's weather doesn't usually turn out well.
• Read the documentation: As with many technical disciplines, meteorology uses terms that have specific meanings. Misunderstandings are often the result of poor communication on the meteorologist's part, or misinterpretation on the user's part.
• Forecasts are sometimes wrong, and sometimes very wrong: This is likely evident to even the most casual critic, but the accuracy of a forecast depends on the location, season and synoptic situation. In general precipitation amounts are the least reliable forecast variable, and winter the most difficult season to forecast especially in mountainous regions like Yukon
• Rules of thumb are meant to be broken: As often as not, following rules of thumb will lead to confusion and incorrect assumptions. For more on why they are so prevelant, read this article. This is not to say that all rules of thumb are wrong, but it's important to understand when rules of thumb aren't applicable.

• Fire Weather Forecast:  The fire weather forecast is produced daily at 0900 PDT and updated at 1400 PDT from late May until late August. This is the only product that is created by a human every day. The contents are geared to fire managers and wildland fire fighters but most of the forecast is general enough to be useful to the general public. See below for definitions of some commonly-used terms.
• Present Conditions: This links to a text file containing the most recent reported weather conditions for Yukon airports as well as Wildland Fire Management (WFM) weather stations. Most stations record weather at the beginning of each hour, but WFM stations only report twice daily outside of the fire season due to limited solar power availability. Make sure to check the time beside each observations.
• Downloadable data: This links to comma-separated files for each of Wildland Fire Management's remote weather stations. Each file is only updated twice daily so hourly conditions are not available, but recent past conditions are. In the winter when less sunlight is available for power it isn't uncommon for a station to fail to report for a day or two. FIRE_MANAGEMENT_YYYYMMDD_AM.csv contains data for all stations from 1300 PDT the previous day to 0500 PDT that morning. FIRE_MANAGEMENT_YYYYMMDD_PM.csv contains data from 0500PDT to 1300PDT.
• 500 mb Maps:  The 500 mb level is approximately 5km above the earth's surface. This is high enough that friction from the ground does not significantly influence weather patterns, and low enough that important features such as highs, lows and fronts can be identified and tracked. These maps are useful for predicting general trends over the next several days. They are not sufficient by themselves to forecast for any specific location with any accuracy.
• Clouds and Precipitation These maps come from the Canadian Meteorological Centre's GEM regional and GEM global models. The precipitation data are corrected for the bias at each station: If a model routinely over or underpredicts precipitation this constant is removed. They show the average cloud cover and accumulated liquid precipitation from the previous 12 hours. The cloud cover maps can be slightly misleading because they don't give any information about cloud height: A day with high overcast cirrus clouds will look the same as one with low, opaque, precipitating stratus clouds. The precipitation is good to see regional trends, but the amounts should not be taken literally. At best, the models only have a horizontal resolution of 15km, so a day with 30-50% scattered showers in the summer will often appear to be widespread (80-100%) rain. The clouds and precipitation product is useful but, as with other products, needs to be supplemented with other information.
• Surface Weather This product is automated, but is tailored to the unique characteristics of each station. The forecast temperature, relative humidity, wind and weather are plotted at 3-hourly intervals out to 5 days. This type of presentation is called a Station Plot and is commonly used to show present or forecast conditions. See below for more on how to read a station plot.
• Surface Wind The wind product is automated, but the data are extensively corrected for each forecast location. Yukon is a mountainous region and weather models often can't "see" the valleys and ridges that influence wind speed and direction. The wind product here corrects for these errors and shows wind speed and direction for numerous locations, mostly valley bottom along highway corridors. The values are generally quite close to reality at the forecast locations, but because of the extensive corrections may not be valid for surrounding locations. This applies especially to areas far above the valley floor.
• Three hour trend forecasts As with the wind, these data are extensively modified for each forecast location. 3-hourly forecasts of temperature, wind and precipitation are provided in tabular form out to 5 days. 6-hourly forecasts are provided from days 5-16. Some rules of thumb are used here which frequently improve the forecast, but do at times make it worse. At the bottom of each page is a verification of the forecast issued 5 days ago: The last 3 columns show the difference between forecast and observed Temperature, wind direction and wind speed.

• High: A closed area of high pressure that is usually associated with fair weather.
• Low:  A closed area of low pressure that is usually associated with unsettled weather.
• Ridge : A ridge shaped protrusion of high pressure. Often (but not always) associated with clear, stable, dry and, in the winter, cold conditions.
• Trough:  A trough shaped protrusion of low pressure, often extending from a low. During the summer surface troughs are often associated with instability and thundershowers.
• Cold Front:  A boundary where colder air is overtaking warm air. Often associated with gusty winds and showers or thundershowers. Due to the mountainous terrain in Yukon cold fronts tend to get broken up and are relatively rare.
• Warm Front: A boundary where cold air is retreating and warm air replacing it. Often associated with lowering cloud base and showers or thundershowers. As with cold fronts, warm fronts are relatively rare in Yukon.
• Probability of Precipitation (POP): The probability of measurable precipitation (greater than 0.1mm) occurring in a given geographical area. The POP is associated with a time frame, usually 3,6 or 12 hours.
• Inversion: An increase in temperature with height. A sign of stable air; Frequently occurs overnight in valleys when skies are clear. During the winter before freezup inversions frequently keep valleys cloudy/foggy while skies are clear and sunny on surrounding ridges.
• Synoptic:  A spatial scale on the order of 1000km to 10000km. Useful when talking about approaching low pressure systems or ridges.
• Rain (R) vs. Showers (RW):  Rain implies more widespread precipitation coming from non-convective cloud. Showers imply spottier precipitation coming from predominantly convective cloud.

Page design last updated on Jan 17, 2012