Model data is split on what will trigger a few storms tomorrow.
This one, the the HRRR, suggests the outflow boundary from big complex of storms over Wisconsin & northern Illinois to northeastern Iowa will be the trigger. This would mean, they would track northwest to southeast over the area.
Some others suggest it will be a plume of deep tropical moisture axis moving up from the south that will be the trigger with outflow boundary remaining in Illinois. These cells would move south to north over the area.
There is also considerable disagreement on how many cells will pop based on magnitude of capping & instability & whether a few will pop in just the late afternoon-evening or a few at various times during the day.
Regardless, I'd like to keep 25% coverage of showers/storms for tomorrow to keep it consistent. I have honed in on the PM in previous forecasts, but let's have it 25% all day. If I feel more confident that more than just isolated storms will pop in future data, I will increase the coverage.
Skies look partly cloudy with highs in the 80s with muggy dew points of 70-73 with heat indices rising well into the 90s (with a south to south-southwest wind at 10-15 mph.
On Saturday, the main concentration of rain & storms should stay in Illinois (with isolated severe risk).
Here, after a mostly sunny start, skies look to turn partly cloudy.
I'd like to keep the 30% rainfall coverage up for Saturday late afternoon-evening.
Models suggests little if anything here at any point Saturday, but it would not surprise me to see some spotty storms in the western half in the PM. I like 30% over lesser coverage because there is an outside chance that some of the better rainfall coverage in Illinois could try to sneak in.
It will be a warm, muggy day with highs in the 80s to 90 with heat indices well into the 90s with south-southwest wind at 10-15 mph (after morning lows in the mid to upper 60s).
The remnants of Tropical Storm Imelda pivoting northeastward through Oklahoma to Missouri, along with moisture from Tropical Storm Lorena in Mexico will make for a band of heavy rainfall along & just behind our cold front Sunday.
Looks like the heaviest will occur late afternoon to evening with a few storms on the leading edge of the band of rain, then steady rain with southwest winds 10-25 mph initially followed by shift to northwest at 8-15 mph.
It is possible that we eek out a dry Sunday morning before rainfall moves in.
Thinking highs in the 70s & muggy conditions, but locations in our eastern half could see 80-82 before the rainfall.
1-2" of rainfall is possible Sunday with heaviest 3-5" rains setting up west & southwest of our viewing area.
Much of the rain should be out of our area Sunday night, though I kept low potential of a few showers Monday morning, followed by partly cloudy skies & highs in the 70s with a drop in the humidity.
Main reason for heavy rainfall over the Corn Belt now to the end of the month are the tropics, specifically the Pacific. Blocking ridge in the Southeast with the endless heat wave there & cold, wet upper low in the eastern Rockies to Northern Plains will pull & guide tropical moisture into the Midwest.
3-7" rainfall now to the end of the month is likely from Kansas & Missouri to Wisconsin.
Here, a total of 1.75-3.50" is possible with 1-2" of that potentially Sunday.
Wetter than normal regime the rest of September for us.
Temperatures will average a bit above normal for the rest of the month with the cold air northwest of us & the endless summer southeast of us (& summer returns to New England after quite early frosts & freezes).
The first few days of October may see lows dip into the 30s & 40s, but warm spurt will follow, followed by very brief cool snap THEN an even bigger warmer spurt in mid-October with the return of summer.
Drier pattern should return.
After a wet snap, then a cold snap for a bit of late October (with frost & freezing), the very end of October to early November still looks warm, wet & stormy.
How I currently foresee end of October-early November (below).........strong upper jet (stronger than even indicated below) nearby by, deep moisture, multiple storm system & warm air. It all points to warm, wet, stormy pattern with unusual, potential record warmth in the Southeast & early season winter storms in the Rockies to northern Plains with also early season soaking heavy rainfall deep into California, southern Nevada & Arizona.
We will monitor.
BIG change is expected in late November with significant cold snap possible with first less than 1" snow at West Lafayette & perhaps a bit more elsewhere with cold temperatures like January (single digit lows possible).
Wet pattern will be over.
However, I do see it turning mild getting into at least the first part of December.
I don't see any real winter weather after that until latter December. That is when the first substantial snows may fall with sustained intense cold with single digit lows.