Area Forecast Discussion
Issued by NWS Central Illinois
Issued by NWS Central Illinois
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021 FXUS63 KILX 182000 AFDILX Area Forecast Discussion National Weather Service Lincoln IL 300 PM CDT Wed Sep 18 2024 .KEY MESSAGES... - A few more days of high temperatures close to 90 degrees are on tap, which is about 10 degrees above normal for this time of year. - Chances of decent amounts of rain are highest early next week, especially across the Illinois River valley, though not enough to significantly impact the drought. && .SHORT TERM... (Through Friday) Issued at 300 PM CDT Wed Sep 18 2024 Scattered high clouds continue to spread eastward across the forecast area this afternoon, with most of the diurnal type development off to the west. 250 mb humidity plot off the RAP model suggests a period of mostly cloudy conditions west of I-55 this evening, though cirrus thins out as it gets further into eastern Illinois. Behind it, another period of mostly clear skies is expected for much of Thursday. Not a lot of change with the first cold front that moves through Thursday night and Friday. Forecast soundings remain on the drier side below 7000 feet ahead of the front Thursday evening, and several of the synoptic and high-res models show a significant weakening of the rain after it crosses the Iowa border after midnight. Will keep a mention of likely PoP`s across the far northwest CWA, with rain chances quickly dropping off eastward, but still around 30% as far east as Decatur late night. Still a couple more very warm days ahead, with highs Thursday and Friday again in the upper 80s to around 90 degrees. Geelhart .LONG TERM... (Saturday through Next Wednesday) Issued at 300 PM CDT Wed Sep 18 2024 Morning models continue to advertise that the persistent blocking pattern will begin to break down this weekend. The remnant low off to our east makes it about as far as the New England coast before drifting south again, but this should allow the upper ridge to break down as the low currently off the California coast swings through the 4-corners region. The earlier cold front never truly gets through the mid-Mississippi Valley, and will drift back northward this weekend as the low weakens somewhat and moves into the Plains. Most of the rain activity with this system appears to be in the Saturday night into Monday time frame. The European model is on the slower end of the guidance, with several of its ensemble members lingering rain through Monday night, and even keeps showers into mid week as a sprawling upper low forms over the central Plains. Both the GFS and Canadian models are more progressive and develop the midweek upper low more over Minnesota or the Lake Superior region, but also with a potential tropical system over the Gulf of Mexico which could complicate things. For now, the Tuesday/Wednesday period will largely be with "silent 20" PoP`s. In terms of amounts, time-lagged LREF ensembles show precipitable water values peaking around 1.5-1.6 inches Sunday afternoon, a little above the 90th percentile in climatology for the first day of autumn. Probabilities of 24-hour rainfall over 1 inch remain in the 25% range across the Illinois River valley off both the NBM and the time-lagged LREF. With the hard ground, the gradual amounts would be more favorable for soaking in, though more rainfall would be useful. Geelhart && .AVIATION... (For the 18z TAFs through 18z Thursday Afternoon) Issued at 1201 PM CDT Wed Sep 18 2024 VFR conditions to continue the next 24 hours, with a period of high-based (above 20kft) ceilings through about 08-09Z. Winds will mainly be out the south and 5 knots or less. Geelhart && .ILX WATCHES/WARNINGS/ADVISORIES... None. && $$