Area Forecast Discussion
Issued by NWS Central Illinois
Issued by NWS Central Illinois
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496 FXUS63 KILX 231754 AFDILX Area Forecast Discussion...Updated Aviation National Weather Service Lincoln IL 1254 PM CDT Mon Sep 23 2024 .KEY MESSAGES... - Widespread showers and a few thunderstorms will lift northeast over central and southeast IL this afternoon and tonight, with a good chance of showers lingering into Tuesday. Storm total rainfall will be greatest along and south of the I-72 corridor where 1 to 1.5 inches of additional rain is expected, with less than a half inch of rain west of the IL river. && .UPDATE... Issued at 1055 AM CDT Mon Sep 23 2024 A shortwave ejecting northeastward into central IL is spreading widespread rain northeastward into central IL this morning, with embedded heavy bands setting up near the I-70 corridor. Near the I-70 corridor, radar estimates of up to 2 inches have been noted over the past few hours, on track to extend into southeast portions of the forecast area near Effingham. Will need to watch for localized urban flooding issues if over an inch per hour occurs, but for the most part the rainfall still should be welcome with drought conditions in the area. Have increased precipitation amount projections and increased to categorical PoPs late this morning and early afternoon for portions of the area south of I-72, however PoPs continue to taper off to slight chance for much of the area north of I-74, mainly west of Bloomington. Instability still looks to be weak today for most of the area, until this evening when the warm sector nudges northward into areas up to around the I-70 corridor, which could bring several hundred J/kg and more prevalent thunderstorms to near I-72, as well as perhaps some strong to severe thunderstorms close to the I-70 corridor. Otherwise, mild highs around 70 for much of the area, and into the mid 70s south of I-70 look on track for today, with light easterly winds. 37 && .DISCUSSION... Issued at 400 AM CDT Mon Sep 23 2024 Predawn surface map shows 1012 mb low pressure over nw AR with a frontal boundary extending through southeast MO, far southern IL and nw KY and extending to 1009 mb low pressure over sw Ontario province peninsula. North to NE winds over CWA have brought in cooler temps in the low to mid 60s, except upper 60s from I-70 southeast. Dewpoints still fairly moist in the low to mid 60s, except upper 50s to near 60F nw of the IL river. An area of very light rain showers had tracked eastward over central portions of CWA past few hours. Radar mosaic shows bands of convection over central and southern MO and extending sw of there, tracking ne. IR satellite imagery shows mostly cloudy to overcast skies over CWA with low stratus decks below 1k ft common se of Peoria. Latest CAMs take low pressure from nw AR northeast to sw IL and near MO border by sunset as it deepens a bit. This will likely spread showers ne over central/se IL during late morning or afternoon with isolated thunderstorms possible over southern CWA. Seasonably cool highs today in the lower 70s over much of CWA, with upper 60s possible from Springfield sw and mid 70s over the Wabash river valley. Low pressure deepens to around 1006 mb as it tracks ne over se CWA tonight and to near the eastern IN/lower MI border by sunset Tue. This will likely continue showers and isolated thunderstorms over central and se CWA tonight into Tue morning, and diminishing from the west during Tue afternoon. SPC day1 outlook has marginal risk of severe storms for hail and wind south of Clay, Richland and Lawrenceville counties late this afternoon and evening where instability is higher (MLCAPES above 1200 j/kg) and some wind shear of 30-35 kts. If the warm front gets further north into southeast IL this evening, that area se of I-70 may get a few stronger cells too. SPC day2 outlook keeps marginal risk east of the Wabash river on Tuesday. Lows tonight in the upper 50s to near 60F over northern CWA and mid 60s in southeast IL. Highs Tue around 70F to lower 70s in central IL and mid 70s se of I-70. Very isolated light showers could linger Tue evening especially in eastern IL with pops less than 20%. Otherwise drier wx expected Tue night thru Wed night as surface low pressure pulls away from area while upper level trof and cutoff low digs into MO/IL by dawn Wed. Cooler lows Tue night in the low to mid 50s in central IL and upper 50s in southeast IL. Highs Wed in the mid 70s with partly to mostly sunny skies over the IL river valley in nw CWA and still mostly cloudy skies lingering in southeast IL. The cutoff low around 570 dm drops down into the Ozarks of northern AR by dawn Thu while a strong tropical system lifts northward over the eastern Gulf of Mexico and toward the FL big bend region later Thu. ECMWF, GEM continue to show qpf into central and especially southern IL by Thu afternoon/evening while GFS has it mainly over southern IL Thu afternoon and Thu night. We have 20-30% pops from I-72 south Thu morning and then slight pops northern CWA Thu afternoon with 30-40% pops from I-72 south Thu afternoon. A bit milder highs Thu/Fri in the mid to upper 70s. The cutoff low meanders over the lower MS river valley late this week and pulls the remnants of tropical system nw into TN river valley Fri and being absorbed as it tracks over the lower Ohio river valley Fri night. This will likely spread more showers into central/se IL later Fri and Fri night and continued good chances of showers this weekend as cutoff low weakens over the mid MS and lower Ohio river valleys. Still quite a bit of differences with deterministic models with the 00Z run and previous run so stayed close to a blended forecast. WPC is giving 1-2 inches of rain over central and southern CWA from Thu afternoon through early next week with higher amounts (several inches of rain) in sw IL into MO. 07 && .AVIATION... (For the 18z TAFs through 18z Tuesday Afternoon) Issued at 1254 PM CDT Mon Sep 23 2024 IFR cigs are predominant along the I-72 corridor as an area of rain and embedded heavy showers spreads over the area. To the north, MVFR cigs and scattered light showers are in place, but it appears northward shift of the precipitation shield should take place this afternoon and evening, spreading the IFR cigs northward. As the center of this system ejects northeastward close to the I-72 corridor late this evening, scattered thunderstorms should approach the I-72 terminals, so have included a period of VCTS. IFR cigs look to continue through 18Z before significant improvement, except at KPIA which should see some improvement by around 16Z. Winds E 5-10 kts this afternoon, becoming light and variable near the low center, then winds shifting to NW Tuesday morning around 15Z as the low moves off to the northeast. 37 && .ILX WATCHES/WARNINGS/ADVISORIES... None. && $$