90 Degrees Overnight in Portions of South Central North Dakota

At 235 am CDT, 7 miles south of St. Anthony, temperatures quickly rose into the 90s with 8 foot corral walls being blown 25 feet from their railroad ties. What could cause such an increase in temperatures in the middle of the night with very strong winds? This can be explained using the graph below. The right hand curved line represents the temperature in the atmosphere, with the surface at the bottom of the graph and the upper levels of the atmosphere at the top. The further to the right this line goes, the warmer the air. At 2 am CDT, the model was depicting 84 degree air at about 3,000 feet above the ground, compared to surface temperatures in the upper 50s. The left hand curved line represents the dewpoint in the atmosphere. The greater the distance between the two lines, the drier the air is. As can be seen below, the air was very dry in the lower atmosphere.

With the presence of elevated shower activity in the area, rain that did fall from nearly 10,000 feet quickly evaporated, increasing the downdraft. As the downdraft approached the surface it mixed the very warm temperatures just slightly off the ground to the surface, while also compressionally warming the air as it sank. As a result, you have 90 degree temperatures at the surface.

However, what about the winds? On the right hand side of the graph are wind barbs. Each small line is 6 mph, each long line 12 mph, and each pennant 58 mph. Simply add the lines and pennants to get the wind speed. As is shown below, 63 mph winds from the southwest were just off the surface. Therefore, the downdraft mixed the winds to the surface as well. Two thermometers 7 miles south of St. Anthony recorded temperatures of 90.5 and 94.6 degrees at 235 am CDT with very strong winds reported and corral damage. At an observation site near Flasher, winds increased slightly, but the temperature rose to 86 degrees overnight!!!



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