The humidity will still be low, but lack of a breeze will make it feel warmer than the 76-81 high expected.
A few fair weather cumulus will fade & some high/mid clouds will begin to increase from the west late as rain fades northeast & east of approaching warm front.
Heavy storms with flash flooding rainfall should blow up in Missouri & Iowa tonight, then form a very large complex of rain & storms that rides east & southeast along & just north of the warm front.
Our clouds will thicken tonight & our temperatures plateau as rain approaches. Lows will run in the 50s to 60.
Wave of showers will pass in the morning, through midday period with an average of 50% coverage. After that, rainfall coverage should run 25-30% for the remainder of the day with a few isolated to scattered showers.
I changed the wording from "rain" to just "showers" because it no longer looks like a solid mass of rain, but more broken. I also took out any mention of thunder, as it appears any thunder or storms will stay west & southwest of our viewing area.
It should overall be mostly cloudy to cloudy. Showers raining through the cool dry air of the morning hours will cause temperatures to have a hard time warming tomorrow. There will be nil warm air advection, given the light southeast wind & the clouds will be around all day.
So, highs should only run 70-76 with around 73 in the Greater Lafayette area.
Rainfall totals look to vary from 0.40" in the northwest to trace to 0.02" to the far east. Amounts will taper with eastward extent through the area.
Tomorrow night, temperatures will not fall much at 64-69 for lows as it become humid with warm front making progress east & northeastward.
Severe storms in Iowa, northern Missouri & northwestern Illinois should move eastward along/near the front & weaken. These should pass our area late Friday night-early Saturday morning.
As for Saturday itself, a good chunk of it will be dry after some early morning showers/storms.
However, new storms should fire in the late afternoon-evening along the warm front & ride southeastward along it into Saturday night.
Isolated severe storms are looking possible, given the heating with highs 85-90 & very humid conditions of tropical dew point of 74-77 with a south wind at 15-25 mph.
An upgrade to Slight Risk could occur if we manage to pull a bit more higher wind fields southeastward to sideswipe out area a bit.
There is currently no severe risk listed for our area by SPC for this time period, but I think future updates will show a Marginal Risk at least for part of the area.
Once those storms pass, we should see a break for a good chunk of Sunday with hazy, hot, humid conditions with south to southwest winds 15-25 mph & highs near 90 to as high as 94. Heat indices will run 98-105. Skies will be partly cloudy.
The high dew points will partially be a product of the winds blowing over west soils of eastern Missouri & southern Illinois where a total of 2-6" of rainfall will have fallen mainly Friday morning.
Storms could fire in the late afternoon-evening on outflow boundary of storms from Saturday night. An isolated severe storm cannot be ruled out, though it does not look like the potential of isolated severe is as high as Saturday late afternoon-evening-night.
Sunday night-Monday morning look very warm with lows only at 72-76 with southwest winds 10-20 mph all night with oppressive dew points of 71-75.
I only went for a few isolated storms Monday with partly cloudy skies, southerly winds 15-25 mph, highs around 90 to as high as 94 & heat indices 97-103. I cut the heat indices only very slightly on account of a tiny bit more dry air mixing down with the winds.
Monday night will be warm, dry & oppressive with lows only at 72-76 with southwest winds at 10-20 mph.
Tuesday looks dry, breezy, partly cloudy, hazy, hot & humid with highs around 90 to as high as 94 with heat indices upper 90s to as high as 103.
It is a little bit unclear what is exactly going to transpire Wednesday-Friday. I say this due to a lack of clarity regarding when a potential one complex or two complexes of storms could pass.
This would likely occur with the front sagging back southward some & then moving back northward.
So, I would like to just keep it status quo for now to avoid flip-flopping. Let's just go with around 90 to as high as 94 Wednesday, Thursday, the drop it to upper 80s to 90 Friday with humid conditions throughout. We will keep lows in the 70s.
I will also keep a 45% storm coverage in for Thursday late & Friday, as well.
On the edge of this heat wave near the front, we may very well have multiple complexes of storms nearby or in the area over the weekend & into Labor Day. However, exact track in the "Ring of Fire" & exact timing is in question. It is also unclear how many could affect at least part of the viewing area.
It looks very warm to hot & humid to very humid, however, with brisk south to southwesterly winds & oppressive overnight lows of 68-75.
Some severe weather cannot be ruled out for any of the complexes of storms that can get into the area. See how we are right on the edge of the stronger flow aloft (IN ANIMATION BELOW). This is also the edge of the hot upper ridge or "Ring of Fire".
So, we will need to watch these complexes of storms even though the best wind fields & shear for severe storms will be in the Dakotas to Minnesota, Iowa to Wisconsin & Michigan.
Other than one brief cool-down, see how the hot upper ridge overwhelmingly dominates our weather much of the time up to September 22?
This means lots of days of above normal temperatures in September, until late in the month.
The only way this could change is if we see a major Pacific hurricane move way to the north, combine with a normal mid-latitude storm & create a big storm system or even a "bomb". This would completely disrupt the upper flow in the Northern Hemisphere, which would change this forecast. This has happened before, so we will monitor. With this El Nino Modoki taking shape, Pacific hurricane occurrence will be pretty high now-October.
Trouginess begins to come in late month, so it should cool below normal for several days. However, notice how the strong upper ridge never really goes away south our area? This could re-expand & bring many above normal temperature days as we start October.
This looks a lot like September 2002. However, I think September 2018 will probably show more green & some blue in the High Plains & northern Rockies to account for the big cool down there late month.
I am on-board with warmer than normal September.
I originally thought the warmer early part & cooler late part would equal out to "normal" temperature-wise for the month. However, the warmth looks to win out.
September 2002 precipitation looked like this. I am shooting now more for a bit above normal here overall due to storms early in the month & then wetter weather late month. However, there will be lots of dry time in-between.
Originally, my thought was pretty dry first, then wet late bringing "normal" precipitation overall for the month.
Interestingly, the wetter than normal weather in September 2002 from Ohio to Louisiana was due to tropical systems, not storm systems or frontal boundaries.