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Tuesday March 27, 2018

Assignment: Predict the 24 hr maximum temperature (deg F) for St Louis, MO (KSTL)

Heavy rain, including the possibility of thunderstorms, is forecasted for parts of the Midwest on Tuesday. In St. Louis for example, the NWS has issued a flood watch, with predicted precipitation amounts as high as nearly 4 inches. The high temperature may peak early in the day and then slowly decrease for the rest of the day. So let's predict the Tmax for St. Louis and see what happens.

Question: On a normal day, the temperature increases into the mid or late afternoon. For St. Louis on Tuesday, what two big factors may prevent that from happening?

What Happened?

The rain fizzled in St. Louis, with less than 0.5 inches reported. But the high temperature was only 59 F, held down by two big factors. First, the overcast skies and light rain kept the temperature almost constant through the morning hours. Second, a fairly strong front passed through, bringing in a cooler air mass and immediately dropping the temperature. Look at the observations, and you'll see that at 11 am there was a temperature of 58 F, with winds from the southwest. But then the front passed through and one hour later the temperature had dropped to 52, with northwest winds at 13 mph. Also, remember that the two U.S. models disagreed on the high temperature, and in this case the NAM was right, and the GFS was way too warm.

Forecasts for St Louis, MO (KSTL)
Forecaster Tmax, deg F (error) Comment Day Score