FROM THE STOVE TO THE FRIDGE...
We've got some big changes coming on the thermometer in the next 24 hours, just in time for the official start of fall. Before I get to the potential of near record heat, a couple comments about the past weekend. First and foremost, a recap of the rains which in the SW half of my area were significant and beneficial from several rounds of storms both Saturday and Sunday. Here's the Doppler estimates of what fell. Many areas from I-80 south picked up 1-3" totals over the two day period. Even larger amounts were measured in a band from SE of Des Moines to roughly Ft. Madison.
Here's what fell in Sunday's storms.
The rains were a reason to celebrate from SC Iowa to WC Illinois, an area suffering from moderate to extreme drought conditions. Some places in the extreme drought category in southern Iowa saw more rain in 36 hours than they had in the previous 3 months.
Unfortunately, some of the downpours came with hail and high winds. Here's some storm reports compiled by the NWS around the central Midwest. There were 2 distinct bands of concentrated severe weather.
This radar image shows two clusters of severe storms rolling through parts of SE Iowa and WC Illinois around 9:15 Sunday evening (significant hail was found in both). Within the red rectangular box a tornado watch is in effect over southern Iowa.
That disturbance quickly departed Monday leaving sunshine and mild temperatures with highs of 80-84 degrees to start the week.
ONE DAY SHOT OF HEAT...
Tuesday a short lived burst of heat arrives on the scene allowing temperatures to reach 90 in much of the area, perhaps 94 in a few spots.
Readings that warm would be close to the records for the date.
RECORD HIGHS FOR TUESDAY SEPTEMBER 20th.
Burlington.........94 in 2018
Moline...............94 in 2017
Cedar Rapids...93, in1931
Making matters worse will be dew points that are likely to reach or top 70.
That's expected to create heat index values in the mid to upper 90s which will make for a very steamy September day, especially with winds only in the 5-15 mph range.
A capped atmosphere will allow abundant sunshine and no threat of storms despite some decent instability.
A BIG CHANGE TO FALL...
Tuesday night a potent cold front will dive into the region bringing with it a sharp change to cooler conditions by late Wednesday. Moisture is expected to be minimal so only a slight chance of rain is indicated with the frontal passage. If showers do develop they are likely to be post frontal, light in nature, and focused on the area south of I-80. Here's what models are suggesting for rain totals Tuesday night through Wednesday night.
THE NBM (national model blend)
The Weather Prediction Center
Winds do pick up Tuesday night behind the front and will usher the cooler air in from north to south Wednesday. Temperatures and humidity will steadily decline during the afternoon as the cooler drier air mass gets established. Highs should range from about 70 north to 80 in the south before slowly falling in the afternoon.
Thursday morning (the first day of fall), lows should dip into the 40s north of I-80 and be in the 40s areawide Friday morning. It's possible a few places in the NW could reach the upper 30s, a sign of the times. The NBM (national model blend) shows this for lows Friday morning.
The 12K NAM is the coldest with some frost potential in the north Friday morning. For now this is an outlier and likely too cold.
Highs both Thursday and Friday should be contained to the 60s. perhaps as much as 30 degrees cooler than what we see Tuesday. Figure in lows in the 40s Friday morning and its quite possible that temperatures 45-50 degrees cooler will prevail from our warmest highs Tuesday to our coolest lows Friday.
There's also a chance that a few showers could sneak into the area Friday but there is still some doubt on the timing and coverage. Afternoon or evening currently looks most likely with only light amounts expected.
Overall the next two weeks look very much on the dry side with the GFS showing rainfall departures like this from now through October 5th.
Okay, fire up for what looks to be a 90 degree day over much of the region. I can't say for sure but this could be the last 90 degree reading of the year. In fact, it's not far fetched to think it may be another 6+ months before temperatures are this warm again. Roll weather...TS