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FXUS63 KILX 021057 AFDILX

Area Forecast Discussion...Updated Aviation National Weather Service Lincoln IL 557 AM CDT Thu May 2 2024

KEY MESSAGES

- Level 1 (marginal) risk of severe weather continues from mid afternoon into mid evening from McLean, DeWitt, Logan and Sangamon counties west.

- Warm, more humid and breezy today with highs in the mid 80s, except closer to 80F by Galesburg. This will be the warmest day since Apr 14th over much of central IL.

- Numerous chances for showers and thunderstorms through Wednesday, though brief drier periods expected Friday night and Saturday morning and overnight Saturday night and Sunday morning.

DISCUSSION
Issued at 400 AM CDT Thu May 2 2024

Predawn surface map shows 1002 mb low pressure over southeast Nebraska with a warm front extending eastward over central MO and into sw IL. Very small/isolated shower and thunderstorm over eastern Shelby county and nw Macon county lifting ne ahead of warm front and along an old outflow boundary originating from convection that was near St Louis area Wed evening. Temps were in the mid 50s to lower 60s over central IL with mid 60s along and south of highway 50. Drier dewpoints in the low to mid 40s from Macomb to Rantoul north while more moist dewpoints in the lower 60s over Clay, Richland and Lawrence counties.

Latest CAMs show warm front lifting northward over central IL during this morning and only isolated convection possible as it moves through with much of morning being dry over the area. Breezy south winds by afternoon to bring warmer highs in the mid 80s over much of area, with Galesburg closer to 80F. Getting more humid too as dewpoints rise into the low to mid 60s across the area by midday and afternoon. Air mass gets more unstable during this afternoon as CAPES peak from 1000-1500 j/kg by mid afternoon with wind shear values of 15-25 kts, highest over western CWA SPC day1 outlook has marginal risk of severe storms from McLean, DeWitt, Logan and Sangamon counties west from mid to late afternoon into mid evening where wind shear values will be higher than in eastern IL. Isolated convection early this afternoon to become more scattered over the IL river valley by late afternoon. Higher chance of showers and thunderstorms spreads eastward during tonight as cold front moves thru central IL overnight. Lows overnight mostly in the lower 60s over central IL, but range from upper 50s nw of the IL river to near 65F se of I-70.

Best chances of convection will be over eastern IL on Friday especially Fri morning. Models have trended faster with pushing convection eastward during Friday afternoon and much of CWA should be dry by sunset Friday with just isolated showers near the Wabash river early Fri evening. We are not in any outlook for severe wx on Friday as wind shear and instability is weak. Cooler highs Friday in the low to mid 70s and becoming partly to mostly sunny over the IL river valley during Fri afternoon as drier air moves in behind the cold front.

A brief period of dry weather expected over most of area Friday night and Sat morning. Then a disturbances ejects eastward from the central plains and returns chance of showers and thunderstorms Sat afternoon/evening. A bit more instability develops Saturday afternoon especially sw CWA with CAPES around 500 j/kg and still rather weak wind shear values 15-25 kts. A few stronger storms possible from mid Sat afternoon into early Sat evening mainly sw CWA Highs Saturday in the upper 70s in central IL and near 80F in southeast IL. More humid again as dewpoints elevate into the lower 60s as day progresses.

Drier conditions expected overnight Sat night and Sunday morning though can not completed rule out an isolated shower or thunderstorm south of I-72. Diurnal heating could develop isolated to scattered convection late Sunday afternoon especially southern CWA, then convection chances increase northward during Sunday night into Monday as short wave moves into the mid MS river valley. Highs Sunday in the low to mid 70s in central IL and upper 70s southeast of I-70. CAPES increase to 500-800 j/kg Monday afternoon with wind shear values around 25 kts, so a few stronger thunderstorms possible Mon afternoon.

Stronger mid/upper level trof develops over the Rockies Sunday and ejects strong low pressure system into western ND by Tue morning.
Models agree on a swath of convection moving into IL later Monday night and Tuesday. CSU machine learning and CIPS analogs shows risk of severe storm on Tuesday into Wednesday over IL and will need to monitor this period. Highs Monday in the upper 70s and 80-85F Tue/Wed.

The Climate Prediction Center (CPC) 6-10 Day outlook for May 7-11th shows 60-70% chance of above normal temperatures over central IL with 40-45% chance of above normal precipitation. The 8-14 day outlook for May 9-15th also trending toward wetter conditions. So the mild and active wx pattern looks to continue next two weeks.

07

AVIATION
(For the 12z TAFs through 12z Friday Morning)
Issued at 555 AM CDT Thu May 2 2024

A warm front will lift north across central IL during this morning, with isolated showers and possibly a thunderstorm occuring. Current radar shows isolated showers from BMI and DEC eastward and lifting ne. Have VCSH to account for this next few hours. As warm front lifts north later this morning, East to ESE winds at 7-12 kts to turn south and increase to around 15 kts with gusts 23-28 kts by late morning and continue through the afternoon. Isolated convection to develop during mid and late afternoon with better chances of convection at PIA by late afternoon. MVFR conditions are possible as band of showers and scattered thunderstorms shift eastward across central IL during this evening, with MVFR ceilings likely overnight even as showers diminish from the west. SSW winds to diminish to around 10 kts during this evening and shift west to NW during overnight at 5-10 kts.

07

ILX WATCHES/WARNINGS/ADVISORIES
None.

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