Next Few Weeks Bring Temp Swings

Tuesday September 2nd, 2014 -- Tuesday brought a cold front south across the Ohio River Valley resulting in morning convection across parts of Southern Illinois, though the strongest storms and heaviest rain stayed just to the north. Behind the front, dewpoints dropped into the upper 60's with temps in the upper 80's and dewpoints in the low to mid 70's still ahead of the front.

Radar depiction Tuesday afternoon showing cold front through Southern Illinois

With zonal flow set up aloft and the jetstream situated across the Upper Midwest, there's not much push in the atmosphere to get a cold front all the way through into the Deep South. Tuesday's cold front will return as a warm front by Wednesday afternoon which may result in isolated convection, mainly over Southeast Missouri, and a wind shift bringing south winds back by Wednesday afternoon. Low-level south/southwest flow will bring a return to heat and humidity, especially Thursday and Friday.

Wednesday afternoon, the most of the warm, humid air can be seen lifting into S. Illinois.

Thursday, core of heat and humidity is seen across the Red River/Lower MS River Valley. Cold air spilling into Plains.

The next big weather maker to impact Southern Illinois arrives Friday evening as a cold front. Upper air patterns show a shallow trough pushing south into the middle of the U.S. which will be enough to push the cold front through Southern Illinois. Showers and storms will become more abundant as the day wears on Friday with CAPE levels approaching 3000J/kg and PWats over 2", an isolated strong to severe storm may be possible. The limiting factor for more severe storm development will be a very weak wind field throughout the column. Showers and storms will linger into Saturday and diminish as the front moves south.

GFS 12Z (7AM) Saturday with widespread showers and storms over S. Illinois.

Cold air advection behind the front will bring temperatures down for the weekend. Sunday will be coolest day over the extended period with 60's in the morning and low 80's in the afternoon. 

Longer range charts continue to indicate that more warm air will move our way by mid-September. Warm is a general term as "warm spells" getting cooler and cooler as we begin to transition towards fall.

GFS 00Z Tuesday September 16th -- Large ridge building across the lower half of the U.S.

I've seen a lot of winter forecasts and predictions already starting to pop up on social media. While seasonal forecasts are popular with the public, they rarely show much accuracy. I personally don't care for seasonal forecasts because we simply lack accurate understanding of weather patterns that far out.