UPDATE
Issued at 813 PM CDT Thu Sep 19 2024

This evening, a trough of low pressure stretches from central Minnesota across central/SW Iowa back into Kansas. Showers and storms are expected to increase in coverage ahead of this feature as a low level jet strengthens late this evening. Convection is still on track to move into portions of the lower to mid Illinois River Valley after midnight tonight. 00Z ILX sounding showed a fairly dry column with very weak instability (MLCAPE less than 100 J/kg). While the LLJ may advect some instability into the area, it should remain fairly weak overnight, less than 500 J/kg MUCAPE, which will keep storm intensity in check. Coverage should begin to diminish east of the Illinois River as the LLJ veers and weakens late tonight.

Deubelbeiss

SHORT TERM
(Through Late Friday Afternoon)
Issued at 250 PM CDT Thu Sep 19 2024

Skies remain mostly sunny across the forecast area this afternoon, with just a few high-based cumulus recently developing from Decatur southward. Looking upstream, surface analysis showed the cold front extending from west central Minnesota into south central Kansas. Scattered convection should expand across Iowa this evening as the front pushes further east, though morning high-res models continue to advertise a weakening trend as the showers/storms move southeast to the Illinois River valley.
Highest PoP's remain focused west of I-55 and mainly in the post-midnight period. By sunrise, what's left of the rain should generally be in areas near and southwest of Decatur, with the forecast area expected to be dry by about 10 am.

Some scattered redevelopment is possible early Friday afternoon ahead of the front, which by midday should be located near the Illinois River. Latest SPC Day2 outlook maintains a level 1 severe risk across east central Illinois. Parameters overall don't look especially impressive, but 1000-1500 J/kg of MLCAPE and peak heating would favor a few strong to severe storms. Anything that forms should quickly weaken toward sunset.

With the front seeing an arrival later in the day, temperatures in the upper 80s will be common once again. However, more of a moisture surge ahead of it will result in a heat index in the low-mid 90s ahead of the front.

Geelhart

LONG TERM
(Saturday through Next Thursday)
Issued at 250 PM CDT Thu Sep 19 2024

Prominent upper low seen on water vapor imagery south of San Francisco this afternoon is still progged to reach the Desert Southwest early this weekend, before tracking northeast. With the persistent upper level high over Texas flattening but not completely going away, a front will lay out from the Texas panhandle into the western Great Lakes region Saturday night.
Little movement in this boundary is expected until Tuesday, when the low has finally opened up and the associated wave gets kicked eastward as a deepening trough digs into the upper Mississippi Valley. Latest NBM highlights about a 60-70% chance of greater than 1 inch of rain north of I-72 during this period, with only a 20-30% chance south of I-70. Rain chances will be highest Sunday and Sunday night (60-80% range). However, showers will remain in the forecast through Monday night, finally fading on Tuesday with the front pushing east.

Getting toward midweek, the models build a rex block pattern over the Rockies and nudge it eastward toward Thursday. However, both the GFS and European models close off a sprawling upper low over the Great Lakes or mid-Atlantic states, which persists into late week. This would put us in the position of being too far west for any significant wraparound showers from the low, but too far east for the heat building underneath the ridge. Thus, midweek temperatures in the mid 70s would be more common. Blended guidance does have some silent 20 PoP's for Wednesday and Thursday right now, but dry conditions should prevail.

Geelhart

AVIATION
(For the 06z TAFs through 06z Friday Night)
Issued at 1153 PM CDT Thu Sep 19 2024

Scattered thunderstorms have developed across portions of central and southwest Iowa this evening, but has been very isolated so far further east. Latest guidance has backed off on storms moving into central Illinois late tonight into Friday morning, but a few weakening showers may still reach this far east. Have removed the tempo for precip owing to the lower confidence in showers/storms reaching central Illinois but maintain a VCSH mention for some isolated activity. Otherwise, expect south winds overnight to veer to the SSW Friday ahead of an approaching cold front, then to the NW Friday afternoon and evening behind the front. Winds will continue to veer to the N/NE Friday evening as high pressure builds across the region.

Deubelbeiss

CLIMATE
Issued at 947 AM CDT Thu Sep 19 2024

Rainfall over the last 30 days across much of central and southeast Illinois has been about 25% or less of normal, with the impacts of post-tropical Francine mainly limited to parts of Richland and Lawrence Counties southward. Going back 2 months, only a few pockets generally along the I-72 corridor have had above normal rain, though far enough back that its impacts have largely faded. Burn bans have been implemented in Crawford, Richland and Lawrence Counties.

This morning's Drought Monitor introduced D1 (moderate) drought conditions across the southern third of the state generally near/south of I-70, as well as in west central Illinois from about Havana to Quincy. While prospects of some decent rain have been increasing for the weekend and early next week (>50% chance of over an inch of rain north of I-72), prospects south of I-70 are more in the 20% range, with only a 40-50% chance of even a half inch. Latest CPC 8-14 day outlook for September 26 to October 2 lean near or slightly below normal for rainfall.

Geelhart



ILX WATCHES/WARNINGS/ADVISORIES
None.