SOME BIG BANGERS?

SOME STRONG TO SEVERE STORMS POSSIBLE, ESPECIALLY SOUTHEAST WEDNESDAY

A deep low pressure will travel across Iowa today, bringing a conditional threat of severe thunderstorms. Further southeast, a tornado outbreak is expected today and tonight from parts of the lower Mississippi Valley into the Mid-South and lower Ohio Valley. Numerous tornadoes, along with multiple long-track EF3+ tornadoes, appear likely. In addition, tornadoes, severe wind gusts, and very large hail will be possible across a broad area from north Texas northeastward to the southern Great Lakes. A rare high risk outlook (5 of 5) is in place from southern Illinois into SE Missouri and western Kentucky.

Locally, all of my region is under at least a level 2 slight risk of severe storms, with a few of my eastern counties included in the enhanced level 3 outlook that extends eastward into Chicago, Indianapolis, and Springfield. While hail and strong winds are likely to be the dominate modes of severe weather, there is a chance of a couple tornadoes, especially where the flow is strongly backed near an advancing warm front. Here, some surface based updrafts might allow tornadic development.

It appears there are two windows for severe storms. The first is tied to a strong warm front that arrives early Wednesday morning in my southern counties. Robust warm air advection has created widespread showers and storms overnight that will be ongoing Friday morning. The 3k shows a couple well-formed bands ahead of the front and surface low in SW Iowa around 5:00AM. These storms will be elevated, and the primary threat is likely to be hail. Pea to penny size is possible in spots. Closer to the warm front, there could be some storms more rooted to the surface that might deliver strong winds as well.

The warm front continues to advance northward Wednesday, and coverage of showers and storms will decrease by midday. At 2:00pm some sunshine is likely near and south of I-80 where temperatures are close to 70. Later in the day, the warm front passes into Wisconsin where even the north should poke into the mid 60s for a time. The far south may even reach the upper 70s.

A notable change will be the humidity, which will be at the highest levels of the year, with dew points near and south of I-80 in the range of 65-68, quite juicy.

That is critical because it drives healthy instability, with CAPE values on the 3k well over 2,000j/kg. from EC and SE Iowa into central Illinois.

At this point, (early Wednesday afternoon), a cold front will advance into eastern Iowa encountering the CAPE setting the stage for what could be a short window for a second round of strong to severe storms. This is highly contingent on heating after morning storms depart, (especially south of HWY 30).

The area to watch for storm development Wednesday afternoon is on the edge of the most unstable CAPE where the incoming cold front impinges upon it.

The 3k is hinting at that between 2-3PM. However, I'm not at all confident in the second round of severe weather. It's quite possible the morning storms will take a lot of the starch out of the atmosphere. The cold pool generated may also slow the warm front up. That and the fact it will be moving through early afternoon before peak heating could be the kiss of death for afternoon storms locally.

That said, with the front racing east, any window for any afternoon severe weather looks brief, beginning around 2:00PM in eastern Iowa and ending in my counties in Illinois by 6:00PM. If storms do fire, there is some tornado threat along with hail and high winds. But again, it's possible development could hold off until just east of my region, more towards central Illinois. We will need to watch that warm front and the mesocale details that result from ongoing storms Wednesday morning for any alterations in the threat at that time.

Last but not least, it does appear that most locations will get a good soaking the way things are setting up tonight. Here's what models are suggesting for rain totals through Wednesday evening. This includes anything that fell overnight.

The EURO

The 3K NAM

The GFS

The HRRR

Cooler weather follows the system, with highs mainly in the 50s Thursday-Saturday. There's a chance of a some showers late Friday, especially Friday night in the southeast half of the region, as we are sideswiped by another system tracking up the Ohio Valley. Once it departs Saturday, it opens the door to NW flow and another cold front Sunday. That should be followed by several days of below normal temperatures next week.

That's all for now, roll weather....TS