Day 4
I hope you enjoyed the deviation from the cold air with yesterday’s post on severe thunderstorms and tornadoes. Today, we’re back to highlighting the impending cold air outbreak. Below is a graphic created from the Global Forecast System (GFS) numerical weather prediction model (NWP). It is taken from the 12UTC (6 AM CST) run1 from 4 January 2010 and is valid2 at 12 UTC (6 AM CST) Friday, 8 January 2010. In other words, this is a good approximation as to what the NWP model is predicting for overnight low temperatures Thursday night/Friday morning (for locations in central time zone). The temperatures contoured are predicted 10 meters above ground level temperatures, which means locations where the winds are calm and the sky is clear, the surface temperature will most likely be even colder.
A couple of things to note about this forecast.
- The temperatures are in degrees Celsius. For those who don’t like math3, -30C = -22F ; -20C = -4F ;
-10C = 14F ; 0C = 32F ; 10C = 50F ; 20C = 68F ; 30F = 86F. - The green color fills are the liquid equivalents for any precipitation that has fallen during the previous 6 hours4.
- Almost everywhere is below 0C (32F). The only places where this isn’t the case is the west coast, extreme southern Texas, and the peninsula of Florida (which will most likely experience below freezing temperatures the following night).
(Image Courtesy of the NWS National Centers for Environmental Prediction Central Operations)
2 The valid time of a forecast is the time at which the NWP model is making a prediction. For example, the 48 hour forecast made by a computer model that is started at 6 AM on 1 January would be “valid” at 6 AM on 3 January (because it is 48 hours later than when the NWP model started).
3 If you didn’t catch on, for every 10C increase in temperature, the resultant increase in degrees Fahrenheit is 18.
4 This means that if snow was the precipitation type, the amount color filled would be the amount of water that is contained in the snow that has fallen. In other words, take the amount of snow that fell during the past 6 hours, melt it, and the resulting value is your liquid equivalent.
