Warm and rainy conditions to continue

Published 7:00 am Saturday, September 22, 2018

By Skip Rigney

We keep sweating here in south Mississippi like it is July or August instead of late September. Afternoon temperatures climbed into the middle 90s a couple of days this past week. Except for a few hours now and then, dew point temperatures remained elevated above 70 degrees, which is indicative of a very sticky, muggy air mass.

Summer has also been hanging on longer than usual for many of our neighbors to the north. In Bismarck, North Dakota, the daily average temperature was above normal on 13 of the first 16 days of the month. On Thursday the combination of high temperatures and humidities sent the heat index to 102 degrees in places as far north as Peoria, Illinois, and St. Charles, Missouri.

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The Northern Plains and the Midwest may not see heat like that again until next summer. A cold front sweeping southward out of Canada has ushered in a cool autumn air mass for those folks for this weekend. High temperatures are forecast to only reach the 70s from St. Louis to Cincinnati, the 60s from Chicago to Buffalo, and the 50s from Montana to Minnesota.

But, alas, that cool front just doesn’t have the push necessary to make it much further south than about Memphis. Over the next couple of days it will start moving back north as a warm front.

We will remain in an air mass that is warm and humid enough to support a chance of showers and thunderstorms as the sun heats the ground each day. Also, this weekend an upper low pressure system over the Gulf of Mexico will bring additional instability to the atmosphere over south Mississippi. The National Weather Service in Slidell forecasts a 50 to 60 percent chance of showers each day this weekend and through most of the coming work week. Rainfall totals over the next seven days are most likely to be in the one to two inch range.

The various computer weather models are in good agreement that the cool air will stay to our north through at least Thursday. But, there is significant disagreement among the models about how the wind patterns in the upper atmosphere will evolve as we head towards next weekend. Some models keep high pressure several miles above the southern U.S. If those models turn out to be correct, we will stay in warm and humid, air, although compared it won’t be as hot as this past week, because the high will be weaker. Other computer model runs predict that strong winds in the jet stream several miles high in the atmosphere will plunge southward from northern Canada, delivering a cool, dry air mass to the Gulf Coast by next weekend. But, even those models show the cool air only barely getting to us.

You can check the latest National Weather Service forecast from the Forecast Office in Slidell by using Google, or another Internet browser of your choosing, to search for “NWS Picayune” or “NWS Poplarville”. The disagreements between the various computer models indicate a more complex-than-usual atmospheric pattern. So, it makes sense to keep checking the forecast as the week progresses.