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Area Forecast Discussion
Issued by NWS Central Illinois
Issued by NWS Central Illinois
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616 FXUS63 KILX 041934 AFDILX Area Forecast Discussion National Weather Service Lincoln IL 234 PM CDT Thu Jul 4 2024 .KEY MESSAGES... - Scattered showers (40 percent coverage) will continue north of a Macomb to Paris line through the remainder of the afternoon, but will taper off from the southwest with dry conditions likely (80-90 percent confidence) through most of the evening. && .DISCUSSION... Issued at 230 PM CDT Thu Jul 4 2024 This afternoon, a shortwave trough is noted lifting from central Illinois into northeastern Illinois with scattered showers occurring, mainly north of a Macomb to Paris line. Latest RAP suggests very weak instability is in place, less than 200 J/kg but forecast soundings show the instability does poke up above -10C at times and an isolated storm could not be ruled out. As upper wave continues to move northeast, subtle shortwave ridging will move in behind and should keep conditions dry late this afternoon through much of the evening. Late this evening and overnight, deep/closed H5 low is progged to dig across the Upper Midwest while attendant surface cold front sweeps across central Illinois overnight into early Friday morning. Showers and a few storms will accompany these features, spreading back into the Illinois River Valley likely around or just after midnight tonight, then across the remainder of central Illinois overnight. A narrow plume of weak instability (MUCAPE around 300 J/kg) will support a few storms, but the severe threat appears low given the unfavorable diurnal timing and weak instability. Precip amounts will be light overnight across central Illinois. NBM 75th percentile generally runs less than a tenth of an inch north of I- 70, with up to around a quarter inch south. Behind the departing cold front, slightly drier (low to mid 60) dew points will begin to advect across central Illinois along with slightly cooler temps. Expect highs in the upper 70s to low 80s across the area Friday afternoon. Despite the drier air, steep low level lapse rates and lingering low level cyclonic flow should drive some cold-air stratocumulus development Friday afternoon. Forecast soundings suggest instability may be several thousand feet deep allowing a few light showers or sprinkles to develop, especially near and north of I-74. Otherwise, dry weather is expected to prevail Friday and continue into Saturday as high pressure spreads from the central Great Plains Friday across the mid Mississippi Valley Saturday. Heat and humidity begin to work back across central Illinois Sunday as the ridge axis shifts to our east allowing return flow to overspread the area. Precip chances will return early next week as a deep upper trough slowly moves east across the region. Deubelbeiss && .AVIATION... (For the 18z TAFs through 18z Friday Afternoon) Issued at 1216 PM CDT Thu Jul 4 2024 Showers will taper off across central Illinois in the wake of a shortwave trough lifting into Indiana early this afternoon. Conditions should remain VFR the rest of today, but the I-72 corridor may briefly see MVFR at times over the next few hours. Additional showers and storms are possible overnight, but favored to stay south of the terminals. Light winds in place this afternoon will set up out of the south this evening and tonight followed by northwest Friday morning. Expect gusts around 20 kt to develop mid to late Friday morning. Deubelbeiss && .ILX WATCHES/WARNINGS/ADVISORIES... None. && $$