Area Forecast Discussion
Issued by NWS Central Illinois
Issued by NWS Central Illinois
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991 FXUS63 KILX 240116 AFDILX Area Forecast Discussion...Updated National Weather Service Lincoln IL 816 PM CDT Sun Jun 23 2024 .KEY MESSAGES... - Hot and very humid conditions return Tuesday with heat index values between 100-105 degF, posing a risk for sensitive groups. - Multiple chances for thunderstorms span the middle-to-late portions of this week, bringing an attendant risk for severe weather and heavy rainfall. && .UPDATE... Issued at 816 PM CDT Sun Jun 23 2024 00z surface map indicated a ridge axis stretched north/south across IA and MO. This feature is forecast to shift east over central IL tonight, resulting in calm to light/variable winds and mostly clear skies. Somewhat drier air has worked into the area on brisk northwest winds this afternoon, with early evening dewpoints in the low/mid 60s. This should result in cooler overnight lows in the mid 60s. 25 && .DISCUSSION... Issued at 223 PM CDT Sun Jun 23 2024 Large-scale subsidence has settled in behind a departing upper-level trough and surface cold front. Cool, calm conditions are anticipated tonight as high pressure builds directly across central Illinois. While patchy fog is often associated with these types of synoptic patterns following a rain event, there is very little signal evident in forecast guidance. Beneath mostly clear skies, overnight temperatures are likely to crash into the mid 60s; some of the coolest readings in over a week. Our welcomed cool-down will quickly yield to a warming trend Monday and Tuesday. By then, an upper ridge axis will shift across the area in response to hot, Gulf air advecting northeastward into the Mid-Mississippi Valley ahead of a frontal zone. Temperatures will warm into the low 90s on Monday, then the low-to-mid 90s on Tuesday. Of the two hot days, Tuesday will feel more oppressive as a warm front lifts in and brings with it a surge of humid air. The current forecast for heat index values on Tuesday is 100-105 degF. This will put central Illinois in the conversation for its first Heat Advisory of the year, but with notable bust potential. An active weather pattern then returns Tuesday - Wednesday as a series of shortwaves breaks down the upper ridge and helps force a surface cold front into central Illinois. While the synoptic pattern looks favorable for multiple rounds of thunderstorms during this period, the timing will remain unknown until the hi-res guidance (ARW, HRRR, NSSL WRF, etc) begins to better resolve the upstream mesoscale pattern. And even then, guidance notoriously struggles to depict the evolution of MCS/MCV/outflow features. What we do know at this point, however, is that the ambient environment is conducive for severe weather and torrential rainfall given explosive CAPE profiles, just enough shear, and weak Corfidi magnitudes (better backbuilding-MCS potential). As alluded to above, any early- day convective debris on Tuesday could play spoiler to heat headlines. Cooler and drier conditions will settle into the region later Wednesday through Thursday as a ridge of high pressure builds across the region. Afternoon temperatures in the mid 80s will be most common, and these will be accompanied by low RH values. Additional rain chances exist by late week as progressive late June flow brings yet another cold front into central Illinois. Temperatures ahead of this front are once again forecast to spike into the 90s. MJA && .AVIATION... (For the 00z TAFs through 00z Monday Evening) Issued at 600 PM CDT Sun Jun 23 2024 A high pressure ridge currently stretched across IA and MO will shift east over central IL tonight. This will allow gusty northwest winds to diminish quickly this evening, then remain calm to light/variable through sunrise. As the high shifts farther east, SSE winds will eventually develop on Sunday. Skies to be mainly clear with scattered high based cumulus or alto-cu Sunday afternoon. 25 && .ILX WATCHES/WARNINGS/ADVISORIES... None. && $$