Awaiting the arrival of a season-ending cold front

Despite a very late start, summer did end up rearing its ugly 3-H head (hazy, hot, and humid) the past few weeks. Though there were a few brief respites in August, the end of last week into the first half of the weekend did me in. I am over the heat and especially the humidity.

We are now in the midst of a short respite from the humidity, but temperatures are already rebounding behind Saturday's cold front and humidity will also make a return tomorrow, and especially Wednesday. As highs reach back into the 90s those days, we'll see the heat index back near 100 on Wednesday afternoon.

HOWEVER, I'm now highly confident, perhaps even giddy (much like a Memphis Tiger football fan after a very solid moral victory), that a season-ending cold front will kick summer to the curb later this week. A strong autumn front will dive south this week, passing through the Mid-South on Thursday. By this weekend, high pressure originating in Canada will dominate the U.S. from the Rockies to the east coast. The first freezing temperatures of the season will be found in the northern U.S. Snow will fall in the northern Rockies. And fall will begin! If you don't have outdoor plans this weekend, make them.

Saturday morning's projected low temperatures according to the GFS computer model.  These numbers are backed up by the European model as well.

Saturday's projected high temperatures according to the GFS computer model.

With a front of this magnitude, it's worth considering the possibility of severe weather, especially considering we go from a heat index near 100 Wednesday to lows near 60 less than 48 hours later. In this case, the passage of the front appears to be early in the day on Thursday, which is not the best timing for a severe weather threat. Also, with the main dynamics of the low pressure system going by to our north, that is where the main severe weather threat will be focused, as per the Storm Prediction Center severe weather risk for Wednesday shown below. By Thursday, thunderstorms are likely along the front, but severe weather is not expected, including here in the Mid-South.

The fall cold front will bring a risk of severe weather to our north on Wednesday, but no severe weather is anticipated Thursday in the Mid-South.

Beyond this week, the long-range outlooks favor near to below normal temperatures well into September. In fact, below normal temperatures are highly likely into the first half of next week according to NOAA's Climate Prediction Center, as shown below. By the time we start seeing any chance of above normal temperatures again (and I'm not predicting this), the average highs will be in the lower 80s. So while highs well into the 80s are still entirely possible, anything higher than that looks unlikely after this Wednesday. Thus my proclamation that with the arrival of this week's major cold front, summer is done - put a fork in it. Check out our forecast for the details on what I expect with the cold front, and more importantly, behind it.

The NOAA temperature outlook for Sep 13-17 (Saturday through  Wednesday) indicates well below average temperatures east of the Rockies, excluding the FL peninsula. For the Memphis area, there is a 70% chance that temps will average below normal. Average highs during this period are in the mid 80s and lows in the mid 60s.

Are you ready for fall or do you wish summer could hold on a little longer?

Erik Proseus, MWN Meteorologist

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