Sunrise 6:02 AM   Sunset 7:49 PM Moonrise 11:07 PM   Moonset 7:18 AM

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FXUS63 KILX 260325 AFDILX

Area Forecast Discussion...Updated Aviation National Weather Service Lincoln IL 1025 PM CDT Thu Apr 25 2024

KEY MESSAGES

- There will be multiple rounds of showers and storms Friday through the weekend. Some of the storms could be severe each day (5-15%). Much of the area west of I-57 can expect 1-2 inches of rain (50th percentile) through Monday morning, but localized amounts in excess of 3 inches (90th percentile) are possible particularly north of the Illinois River.

- Warm and windy conditions are expected this weekend. Daily highs will be near or into the 80s accompanied by breezy southerly winds gusting 30 to 40mph.

UPDATE
Issued at 844 PM CDT Thu Apr 25 2024

Latest regional radar mosaic indicated a band of showers and embedded thunderstorms stretched from northeast KS southeast into western TN, located in a zone of elevated warm advection. This lift and associated area of precip will shift northeast overnight, reaching our west central IL counties around daybreak. Instability will be much diminished by then, so mainly expecting showers with an isolated storm possible. Otherwise most of the overnight will remain dry with thickening high and mid level clouds. East- southeast winds to increase to 10-20 mph late as the MSLP gradient tightens between high pressure over the eastern Great Lakes and low pressure developing in the lee of the Colorado Rockies. These winds and the increasing cloud thickness will keep lows several degrees warmer than last night, mainly in the mid/upper 40s.

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DISCUSSION
Issued at 243 PM CDT Thu Apr 25 2024

This afternoon, low pressure is in place along the Front Range of the Colorado Rockies while a warm front stretches east across Kansas into southern Missouri. This low and attendant warm front will lift northeast tonight while a broad low level jet sets up across the mid Missouri Valley. Thunderstorms will expand in coverage in response to this feature and move east across IA/MO overnight and eventually expand into portions of Illinois Friday morning. These early day storms will outrun the stronger instability to the west and the forcing associated with the weakening/veering low level jet. As such, expect an initial round of showers with a few embedded non-severe storms to move across central Illinois through the mid/late morning and early afternoon hours. Additional showers and storms will be possible through the day as the warm front gradually lifts across central Illinois allowing dew points well into the 50s to overspread the area. The next round of strong to severe storms will initially develop within a narrow ribbon of moderately strong instability near the NE/IA state line and spread east overnight. These storms should be in a decaying state as they cross the Mississippi River given the unfavorable diurnal timing and as storms outrun the stronger instability to the west. Otherwise some elevated WAA driven storms will be possible Friday night.

Saturday continues to look like the better day for higher impact severe weather potential, though this threat is conditional as forcing continues to be nebulous with shortwave ridging overhead between the two main systems. Moderate to strong instability is expected to develop within the warm sector across portions of the mid Mississippi Valley Saturday afternoon. GFS indicates that up to around 2000 J/kg MLCAPE will develop during the afternoon, strongest across portions of the Illinois River Valley. MLCIN is expected to be minimal with capping around or weaker than 30 J/kg.
That being said, overall synoptic scale forcing for ascent will also be weak, in between the departing low over the Upper Midwest and ahead of the second low developing across the Great Plains. If we are able to overcome this and see convective initiation occur Saturday afternoon, deep layer shear of 35-40 kt will be sufficiently strong to support a few supercells with all severe hazards in play, especially west of I-55 where shear and instability are greatest.

Saturday evening and overnight, precip coverage will increase in response to a strengthening low level jet. Corfidi vectors fall off to 5kt or less and oppose the 850-300mb flow from NE Missouri into northern Illinois Saturday night. A corridor of heavy rain should result from both training and backbuilding storms Saturday night, though placement of the axis of heaviest rain may stay just to our west or clip only our far western counties (near the Illinois River Valley). 12-hour 90-95th percentile QPF from the NBM shows the potential for around 1.00-1.75 inches of rain Saturday night north of the Illinois River.

Sunday, second area of low pressure is progged to lift from Kansas into the Upper Midwest through the day. Guidance continues to advertise minimal recovery during the day Sunday across central Illinois due to ongoing convection and cloud cover early in the day. GFS for example only develops around 300-700 J/kg MLCAPE by Sunday afternoon. Sunday night, there are indications that portions of central Illinois could see a minima in precip amounts as the area is bifurcated by the main upper low lifting across the upper Mississippi Valley and a shortwave digging across the lower Mississippi Valley. Still, broad warm advection across the region will support a chance for additional showers and storms, especially during the evening and overnight hours. Trailing cold front has slowed down from earlier runs, now tracking across central Illinois more during the day Monday as opposed to Sunday night. Tail end of the front/col area slowly moves across central Illinois Monday afternoon and will support additional chances for showers and storms. Deep layer shear appears to weaken significantly Monday as the main upper wave lifts into Canada.

Daily chances for showers and storms continue into next week along with warm temperatures. A frontal boundary will push into and then stall over the region Tuesday through Wednesday or Thursday of next week and will serve as the focus for additional precip.
Expect daily highs in the 70s through this time frame.

Deubelbeiss

AVIATION
(For the 06z TAFs through 06z Friday Night)
Issued at 1025 PM CDT Thu Apr 25 2024

High pressure over the eastern Great Lakes will shift east tonight, as low pressure moves into the western Plains. This will keep east-southeast winds blowing around 10-12 kt overnight, then gust 20-25 kt on Friday when the gradient tightens. Mainly high cirrus in place through much of tonight, then lowering cloud bases after sunrise with the approach of a warm front. Ahead of the front, a band of showers is likely to affect all terminals late morning through much of the afternoon, producing MVFR ceiling and visibility. Showers should scatter out late afternoon, and with low confidence on clearing trends into the evening kept BKN MVFR ceilings in the forecast.

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ILX WATCHES/WARNINGS/ADVISORIES
None.

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