Sizzling Heat Continues...

by KDLT Weather
July 16, 2012 12:07 AM

Another scorcher of a day Monday with highs well above the century mark for many of us.  Surprisingly though, these numbers were still several degrees off from breaking any records.  But unlike the past 3 or 4 years, triple digits have been a pretty common site around here with the three digit numbers starting in June and haven't let up in July.  So far, many areas have already reached their average yearly number of 100 degree days and we still have the hottest 6 weeks of the year to go.  Check out a few select cities and stay cool because it is going to be one hot week.

                                                       



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The heat has returned, but one would debate whether it left in the first place. Sunday’s high temperatures topped out in the 100s throughout much of the Missouri River Valley. Pierre was the hot spot with a high of 108 with slightly cooler temperatures east of the James River Valley. In fact, Sisseton only topped out at 89 Sunday Afternoon.

This map isn’t an unfamiliar sight, though. It seems that Valentine, Winner, Chamberlain, and Pierre break the century mark every day during this time of year. It isn’t uncommon for our eastern cities to have heat indices that break the century mark, but what’s keeping actual temperatures in the east from getting that high?

The current weather set-up explains this perfectly. One of South Dakota’s most notorious weather features is the wind; but it plays a much bigger role in our every day lives than just blowing our hair around. In this part of the country, a change in wind direction can lead to a significant change in temperature.



Obviously, a southerly wind would bring warmer air than a northerly wind; but I’m talking about a much smaller change in direction. Notice that Sunday night’s winds were out of the southeast. This southeasterly flow brings very humid air from the Gulf of Mexico, spreading moisture across the area it moves north and west. Notice in the map below, dew points are higher in the southeast and much lower across the west. Even though winds are out of the southeast in all of these locations, most of the air is dried out by the time it makes it to places like Pierre and Mobridge.



What does this have to do with actual temperatures? Air with higher dew points, or higher moisture content, cannot heat as quickly as it would if the air was dry. This, along with soil moisture content, dictates how temperatures will change throughout a given day. With drought conditions being much more excessive in the west, temperatures easily broke 100.

With winds forecast to shift out of the southwest on Monday; temperatures will likely surpass Sunday’s highs. Air brought in by southwesterly flow will be dry as it originates from areas like Colorado and Nebraska—nowhere near a body of water like the Gulf of Mexico. This drier air will easily replace the moist air over the east, allowing temperatures to increase dramatically throughout the day. Be sure to tune into KDLT and KDLT.com to find out when the next wind shift will come and if it will bring relief from this extreme heat.