Area Forecast Discussion

KEY MESSAGES

- Warmer today, with a slight chance (15-25%) for isolated thunderstorms this afternoon/evening in northwest IL. Additional chances of storms are forecast late evening in northeast MO, southeast IA, and west-central IL. Some small hail and locally gusty winds will be possible with these storms.

- Widespread showers and storms will move through the area Thursday into Friday. Some of these storms may be strong to severe, with a Level 1 of 5 risk of severe storms for eastern Iowa, west-central Illinois, and northeast Missouri.

SHORT TERM /THROUGH TONIGHT/

Issued at 238 AM CDT Tue Apr 21 2026

Early morning water vapor shows a weak shortwave over eastern South Dakota in the northwest flow aloft. VAD winds at DMX/DVN show a rather strong southwest LLJ (>45kts) advecting warmer temperatures into the CWA. At the surface, a weak low was seen over southwest MN with a warm front extending east over northern IA and then southeast over portions of eastern IA. As a result, temperatures at 2 am were already around 15 degrees warmer compared to this time yesterday.

A noticeably warmer and somewhat breezy day is on tap today, with southwest winds boosting temperatures well into the 70s area-wide. Forecast soundings even show deep mixing to 800 mb in our western third, suggesting a few locations may even hit 80 degrees despite the high clouds.

Attention then turns to passing shortwave/weak boundary moving through during peak heating. A rather strong EML will be in place for much of the daylight hours today effectively keeping a lid on any convection. That being said, enough cooling aloft and convergence along the boundary should allow for some isolated/scattered activity to form after 2 pm as it sags southeast into northern IL. This is supported by half of the CAMs now, and I have maintained slight chance PoPs (15-25%) across northwest and north central IL for this occurrence, which may need to be raised in later updates this morning. Highest coverage should be just to our east where better lift will exist. With rather steep mid level lapse rates, any storms that do form will pose a small hail/gusty wind threat, but should remain below severe levels due to weak deep layer shear. Another subtle elevated theta-e boundary is forecast to set up shop along and just south of Hwy 34 in Iowa tonight. This is also where an MUCAPE gradient will be situated per the 00z HREF supporting a few isolated thunderstorms. In collaboration with our southern and western neighbors, have introduced some slight chance PoPs (10-30%) for this. Small hail, heavy rain, and gusty winds will the primary threats and will quickly diminish after 9pm.

LONG TERM /WEDNESDAY THROUGH MONDAY/

Issued at 320 AM CDT Tue Apr 21 2026

Persistent ridging will remain in place through Wednesday evening, allowing for dry and warm conditions to continue. Temperatures Wednesday are forecast in the upper 70s across the region will be above- normal.

An upper level trough will displace this ridging Thursday, allowing for more active weather Thursday and Friday. A strong surface low is expected to move into the northern Plains. Ahead of the low, southerly flow will continue to advect warmer temperatures and moisture northward. This will allow for instability and shear on Thursday, with SBCAPE values of 700-1000 J/kg and deep-layer shear of 25-30 knots across the region. With the increased moisture and instability, showers and even a few storms are likely (80-100% PoPs). These showers and storms, some of which may be strong to severe (SPC level 1 of 5 severe risk), will be ahead of the cold front Thursday night into Friday morning. Following frontal passage, Friday will have more seasonable temperatures.

The remainder of the period will be characterized by a persistent upper level low sitting over south-central Canada, allowing for westerly flow over the region. Seasonable temperatures will return as this low persists. Towards the end of the period, a shortwave will propagate through on Monday, bringing another round of rain.

AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 1217 AM CDT Tue Apr 21 2026

VFR conditions to prevail through the period. Strong low level winds just above the surface are forecast through mid- morning and will continue LLWS mention until 14z. DVN VWP currently shows 46kts at 1400ft. Southwest winds will increase this morning as we begin to mix down stronger winds aloft, with occasional gusts over 20kts. A weak frontal boundary will drop southeast early afternoon and evening, with an increase in mid level clouds primarily at MLI/BRL. Winds to turn WNW late in the period and decrease under 10kts.

DVN WATCHES / WARNINGS / ADVISORIES

IA...None. IL...None. MO...None.