Area Forecast Discussion
Issued by NWS Central Illinois
Issued by NWS Central Illinois
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946 FXUS63 KILX 201838 AFDILX Area Forecast Discussion National Weather Service Lincoln IL 138 PM CDT Mon May 20 2024 .KEY MESSAGES... - Multiple rounds of severe weather are expected over the next few days with portions of the forecast area in a slight risk (level 2 of 5) today, moderate risk (level 4 of 5) Tuesday, and slight risk (level 2 of 5) again Wednesday. - Summer-like heat and humidity will be in place Tuesday. High temps will be near 90 degrees with dew points approaching 70 degrees. NBM probs for high temps exceeding 90 degrees are 50-70 percent north of the Illinois river and south of I-70. Probabilities generally run 20-40 percent in between. && .DISCUSSION... Issued at 133 PM CDT Mon May 20 2024 This afternoon, an elongated area of low pressure stretches from the OK/TX Panhandle region into MN. Aloft, an MCV is lifting across southern WI while a shortwave trough is lifting across the IL/MO state line near St. Louis. Forcing in minimized across central Illinois in between these features, and CAMs have been inconsistent in placement and timing of any potential convection across central Illinois. The general theme, though, has been for isolated to widely scattered storms with the best chance late this afternoon into the evening. HREF LPMM shows a few bullseyes of 2-4 inches of rainfall which is plausible if storms do develop given the slow nature of the storms (storm motions to the NE around 20 mph) and the high moisture content. Surface dew points are well into the 60s across most of central Illinois and PWats are progged to increase to around 1.5 inches today. Tonight, low pressure will consolidate over KS/NE and lift into the Upper Midwest Tuesday. A broad warm sector characterized by temps near 90 degrees, dew points approaching 70s degrees, and MLCAPE values in the 2000-2500 J/kg range will develop across portions of IA/MO/IL Tuesday with the highest values along and west of I-55. Deep layer shear will be strong across most of this warm sector with 0-6km bulk shear values of 35-45 kt superimposed over the strongest instability. Moderately strong capping will also be in place keeping the local area dry much of the day Tuesday. Capping should begin to erode Tuesday evening as the main H5 shortwave trough and surface cold front push across the Mississippi River Valley. A line of thunderstorms should accompany these features as they push across central Illinois mid to late Tuesday evening. The severe threat will be greatest as storms enter the western counties of the forecast area near or shortly after peak instability for the day, but the severe threat will gradually diminish with time as we move past sunset allowing instability to weaken and as storms move further ahead of the strongest forcing along the cold front. The cold front will slowly push across central Illinois late Tuesday night and will still be over portions of east central Illinois Wednesday morning. Severe weather appears possible once again Wednesday, especially across portions of east central/SE Illinois along a cold front that is slowly pushing through the region. Guidance indicates that a narrow corridor of moderately strong instability (MLCAPE 2000-2500 J/kg) will develop ahead of the front by around midday. Moderately strong deep layer shear continues to support stronger or severe storms Wednesday afternoon and evening. Frontal boundary is progged to stall along portions of the Ohio River Valley Thursday and Friday and will support additional showers and storms across the region, especially south of I-72 in central Illinois. A series of shortwaves riding atop the surface boundary will keep precip chances going across central Illinois through the weekend. Deubelbeiss && .AVIATION... (For the 18z TAFs through 18z Tuesday Afternoon) Issued at 1255 PM CDT Mon May 20 2024 VFR conditions are expected to continue through most of the 24 hour period through 18Z/1 pm Tue across the central IL airports. However an isolated thunderstorm could (20% chance) impact the PIA early this afternoon and along I-74 terminals early this evening from 23Z-02Z. Breezy SW winds 13-17 kts with gusts around 25 kts through mid afternoon, will veer south and subside to around 10 kts or less around 00z/7pm. South winds increase to breezy levels again after 15Z Tue with speeds near 15 kts and gusts around 25 kts. 07 && .ILX WATCHES/WARNINGS/ADVISORIES... None. && $$