THE HEAT & VERY HIGH HUMIDITY:
EXCESSIVE HEAT WARNING ALONG & NORTH OF U.S. 24 (ALSO INCLUDES BENTON COUNTY)
HEAT ADVISORY REST OF VIEWING AREA
Heat indices as of 2:03 p.m.
103* Danville, Illinois-Vermilion County Airport
102* Frankfort Municipal Airport
101* Attica (4 ESE Attica)
99* Fowler (2 ENE Fowler)
99* Rochester-Fulton County Airport
99* Peru-Grissom Air Reserve Base
98* Purdue University Airport
96* Monticello-White County Airport
96* Kokomo Municipal Airport
94* Crawfordsville Municipal Airport
93* Logansport-Cass County Airport
It will remain intensely hot over the next three days with highs, overall, at 91-96 with heat indices of around 106 to as high as 112. Even next week looks hot & humid. Highs will tend to run 88-93 with heat indices averaging 97-107 with very high humidity.
THE CAP & EVENTUAL INCREASING STORM DEVELOPMENT & COVERAGE.........STORMS AROUND EVERY DAY NEXT WEEK:
The clouds were bubbling up nicely this morning with even an isolated shower, but strong capping has strengthened & is taking over. This cap is a warm, dry layer in the troposphere that tends to come from the Plains & desert areas well to our west & southwest. The troposphere is the lower part of the atmosphere where weather occurs. We are at a lower elevation than the elevated Plains & desert areas, to that heat builds there & then moves northeastward & effectively puts a stout lid on the very humid, hot air that would normally fuel storms popping from any trigger in our area. This cap looks even deeper & stronger than it did yesterday in today's outlook!
Check out a projected cross section of the troposphere in the image below.
Note that the projected sounding this late afternoon in Tippecanoe County shows a very moist airmass near the surface & a sharp temperature difference between the ground & just below 5,000' ("850" on the chart). This may allow a few surface-based cumulus clouds to form, but beyond that, check how it warms & then just doesn't cool quickly as you go way up. Also, see how the red & green lines separate? That is the temperature & dew point far away from each other signaling dry air.
What is amazing is how incredibly unstable it will be with this intense heat & humidity near the surface. Surface instability will be an astounding +6000 J/kg of CAPE (energy). Given the intensely unstable surface airmass that is only further concentrated by the cap, if not for that lid, intense, pulsey storms with wet microburst potential would be the story. The outflow boundary & gravity wave perturbation left from the monster bow of severe storms to our west & southwest yesterday evening to last night would be the triggers. This is why you see "SEVERE" classified for this projected sounding on the left of this image. It shows that conditions would be good for pulsey, slow-moving severe storms, but we are just too capped.
Even the short-range high-resolution models do not even have a lick of an isolated shower or storm popping this afternoon. I liked keeping "an isolated random storm" in the forecast last night for today, but unless there is any local weakness in the cap, there will not be a thing. This will be the case despite us being absolutely loaded for a storm to pop.
We will still monitor for the afternoon-evening.
Even tomorrow, new data & projected soundings have us completely locked in a cap strong enough to prevent even an isolated storm from popping, despite being absolutely loaded with CAPE (energy) that would propel storm updrafts upward very quickly. This would be a pulsey, wet microburst, slow-moving storm situation. The NAM model projection has an even stronger cap tomorrow with still extreme CAPE from the intense heat & humidity near the surface.
I went ahead with my gut & kept a 20% coverage of storms for tomorrow to account for any weakness in the cap that would pop a randomly isolated storm. I noticed a weakness in the cap over southeastern Missouri & southern Illinois, so I felt better keeping that "isolated" wording in. Otherwise, it looks dry & very hot & humid with only a few to some scattered cumulus clouds.
We should see a few scattered storms make it into the area by Sunday. There may be a few early, then more later in the day, appears at the moment. The best potential is setting up over the northwestern half of the viewing area (northwest of Lafayette & West Lafayette).
Periods of scattered showers & storms are likely Monday-Friday of next week. They may organize or semi-organized into clusters & some lines at times, but the main wind fields for organized, widespread severe weather (at least right now) are setting up northwest, north & northeast of our area. We will continue to monitor.
Locally-heavy rainfall is possible with some localized totals of +4" possible for the Monday-Friday period.
Also, at this point, looks like 40% coverage of T-storms for the afternoon-evening of July 4th. This coverage may continue into the early night-time hours.