How can a weather forecast be deceiving?

While taking an effort to stay informed about the current news, weather is one item that is frequently changing.  Most weather models run four times a day, every six hours, and are based upon the current conditions when the model is running.  Forecasts that are shown in the morning can easily differ from what is shown in the evening.  For instance, a model can run when it’s cold and snow covered in the morning and drift towards a cold forecast, but if the snow melts by the afternoon, the following run will paint a different picture.  Most weather forecasts that are received while on-the-go from your mobile device are refreshed based on recent weather model runs.  This could lead to deceiving forecasts that look odd at first glance and further the need to stay up to date.

First, a look at the different types of forecasts:

Short-Range Forecasts are forecasts that range from zero to 36 hours which provide information on the nearest term happening.  In this timeframe, examples of what you would see include: storm warnings, sharp temperature drops, high waves/marine warnings, or aviation conditions.  Meteorologists often update these forecasts with extensive discussions as often as the model runs.

Photo: Forecast provided from the National Weather Service including near-term warnings and small descriptions -- Captured on March 29, 2020. (Courtesy of the National Weather Service)

Medium-Range Forecasts are forecasts that range around three to seven days.  These forecasts can determine temperature trends or expectations throughout the work-week.  These forecasts are useful for sharing when an umbrella is necessary or when you can expect sunshine again.  The confidence lowers in medium-range forecasts and there is more variability to be expected.

Photo: Extended forecast that displays expectations for the work week, and are subject to change as forecast models run.  (Courtesy of Wunderground)  

Long-Range Forecasts are forecasts that typically depict a probability of temperatures and precipitation chances in a given area 6-10 days in advance, or 8-14 days in advance.  You will find these outlooks depict broad information on trends that are expected based on historical data.  This will tell you whether to expect warmer, colder or normal temperatures for a given timeframe.  Likewise, you will see if normal, wetter or drier conditions are expected.

Photo: 6-10 day outlook that displays precipitation probability from April 3-7, 2020.  (Courtesy of NOAA)

Extended Outlooks are generalized forecasts that can depict probability similar to Long-Range Forecasts but for given single months, multiple months or seasons.  Arguably, some long-range forecasts can still fit in as an outlook, given that it is a probabilistic forecast rather than a deterministic approach.  These can be useful to planning a vacation, determining the best time to plant a garden, or to various elements of farming.

Photo: One month temperature probability outlook, valid for April 2020.  (Courtesy of NOAA)

While there are many forecasts that are displayed and accessible to the general public, these examples below depict Short-Range Forecasts and how they can be deceiving:

Example 1:
Currently at 2pm in Mid-February: 39 degrees and sunny
High: 43, Low: 28; Clouds and Snow Showers

This can be deceiving because we understand that we can’t see temperatures that high when it’s snowing.  While this is a description, it may appear on your mobile app as a snowflake icon with a high temperature of 43.  If you look deeper, you’ll see the low temperature and perhaps an hourly forecast that will tell you when to actually expect the snow showers to occur.

Example 2:
Currently at 8am in October: 58 degrees and cloudy
High: 62, Low: 33; AM Clouds and PM Sun/Windy

We are used to seeing the highest temperatures at the time of peak heating, which typically occurs in the afternoon.  This forecast suggests that the low temperature will be 33 degrees, and the high temperature is going to be 62 degrees.  In times of strong warm advection and overnight cloud cover, we can actually see temperatures rise overnight and be warmest in the very early morning hours.  The drop in temperatures is a result of a cold front passing and ramping up the wind speeds along with bringing in higher pressure and sunshine.

Example 3:
Currently 3pm in June; 62 degrees cloudy and windy
High: 84, Low: 60; Sunny and warm, Chance of a thunderstorm in the afternoon

While the time of this forecast seems to be when the temperature would be the warmest, the particular timing of the thunderstorm was in the afternoon.  Warmth starting early in the day lead to rapidly rising air and formed storms quickly in the afternoon hours which lead to rapid cooling following its passing.

Example 4:
Currently at 2am in January; -6 degrees and calm
High: 18, Low: 0; Clear and cold

This is a forecast provided to a large area that covers a handful of small towns and the temperature taken at this location was in a remote place.  The location experienced stronger radiative cooling than the model could depict, and showed a 6 degree difference from what was forecasted.  Once the local temperature was lower than forecasted, a special weather statement was issued to correct the issue.  In this case, a mobile-app may not refresh with the new forecast and show differing values.


While these forecasts depict what can be present on a mobile app at a given time, there are many cases to see a deceiving forecast.  Some mobile apps may refresh after a model run is performed and can automate a forecast for a given area.  This does not mean that they will refresh right away.  It is important to read further beyond the icons that are listed, and take into account hourly forecasts and descriptions attached to the forecast.  Professional meteorologists also write discussions on forecasts in the near and far term, which are updated nearly as often as a model runs.  The best practice is to stay informed about the big picture, and keep track of local happenings to be aware of what you could experience once you walk out your front door.

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 ©2020 Meteorologist Jason Maska