Area Forecast Discussion
Issued by NWS Central Illinois
Issued by NWS Central Illinois
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342 FXUS63 KILX 280552 AFDILX Area Forecast Discussion...Updated Aviation National Weather Service Lincoln IL 1252 AM CDT Sun Apr 28 2024 .KEY MESSAGES... - Flood Watch in effect tonight for locations along and north of a Rushville to El Paso line. Several rounds of thunderstorms with excessive rainfall rates may lead to flash flooding. - Another round of strong to potentially severe thunderstorms expected Sunday evening. Highest severe probabilities will be focused west of I-55. && .UPDATE... Issued at 711 PM CDT Sat Apr 27 2024 Complex convective scenario unfolding this evening. Currently have a blossoming area of showers and isolated storms from near St. Louis northeast to Danville. This is occurring in a region of modest instability and weak deep layer shear, so not anticipating much more than brief heavy rainfall and cloud to ground lightning strikes over the next few hours as this festers in a focused region of moist convergence. To our west, the main severe convective line of interest stretches from west central MO into southeast IA. This has formed in an area of moderate instability (MLCAPE near 2k J/kg) and deep layer shear of 40+ kt. This line is expected to continue its northeastward motion this evening, reaching our far northwest CWA around 10-11 pm. The farther east the line pushes, the less favorable the thermodynamic environment becomes. Still, there appears to be a few hour window where severe thunderstorms will be possible late this evening, primarily northwest of the IL River. If storms can remain surface based all severe hazards would be in play given curved low level hodographs and sufficient instability for severe level wind gusts and hail. Heavy rain and localized flash flooding are also concerns, given the convergent nose of a strong low-level jet setting up over the western CWA tonight. With the instability and high moisture levels already in place, deep convection and high rain rates (1-2"/hr) seem to be a good bet. 1-hr flash flood guidance is around 1.5", and these should be approached at least on a localized basis. The current Flash Flood Watch has the region of concern covered, so not anticipating any changes to the watch at this time. 25 && .SHORT TERM...(Tonight through Sunday) Issued at 323 PM CDT Sat Apr 27 2024 A warm and humid airmass has overspread central Illinois this afternoon...with 19z/2pm temperatures in the middle to upper 70s and dewpoints hovering in the middle 60s. A slow-moving cold front is poised well upstream from central Iowa southwestward into Kansas and will serve as the focus for strong to severe convection over the next several hours. Regional mesoanalysis shows SBCAPEs in excess of 3000J/kg ahead of the front from southeast Iowa to Texas. With 0-6km bulk shear of 35-45kt within this zone, all CAMs indicate convection rapidly blossoming this afternoon. Meanwhile further east across central Illinois, instability/shear are not as impressive and the region is still experiencing synoptic subsidence as a result of short-wave ridging aloft. Am therefore only expecting widely scattered thunderstorms within the broad warm sector across the KILX CWA through the remainder of the afternoon into early this evening. Most models suggest thunderstorms will begin developing further east into the Illinois River Valley after 03z/10pm in response to a strengthening low-level jet oriented from Oklahoma northeastward into Missouri. HREF indicates low probabilities for severe wind/hail as far east as the Illinois River this evening, so think current Slight Risk area west of I-55 has a good handle on the severe potential. Aside from the potential for scattered damaging wind gusts and large hail, there is increasing concern for heavy rainfall and flash flooding across the W/NW CWA. With precipitable water values increasing to 1.50-1.75 and several CAMs suggesting training thunderstorm cells within the instability axis ahead of the front, have opted to issue a Flood Watch for locations along/north of a Rushville to El Paso line. Think storms will be efficient rain-makers...with excessive rainfall rates of over 2 inches per hour possible. Given the wet soil conditions, think this additional rainfall could lead to scattered flash flooding...particularly in flood-prone and urban areas. Further east into central Illinois, the precip will be much more scattered in nature tonight...with locations along/south of I-70 staying mostly dry. Barnes .LONG TERM...(Monday through Next Saturday) Issued at 323 PM CDT Sat Apr 27 2024 Convection tied to the nocturnal LLJ will shift eastward and weaken considerably late tonight into Sunday morning as it outruns its energy source. As a result, am expecting overcast conditions with showers and perhaps a few thunderstorms along/west of I-55 on Sunday. Further east, windy and dry conditions will prevail along and east of the I-57 corridor. The next round of strong to severe convection will fire along the cold front across Iowa/Missouri late Sunday afternoon...then gradually push into west-central Illinois during the evening. Think a damaging wind/large hail risk will exist as far east as I-55 before the storms weaken as daytime instability wanes. Still need to keep an eye on the far E/SE CWA mainly east of I-57 Monday afternoon as the potential still exists for a few strong storms along the departing cold front. Once the front passes, a return to warm/dry weather is anticipated for Tuesday. After that, an unsettled week is ahead as a series of disturbances brings periodic rain chances Wednesday through Friday. Temperatures will warm back into the upper 70s/lower 80s by mid-week before slightly cooler/drier conditions arrive by next weekend. Barnes && .AVIATION... (For the 06z TAFs through 06z Sunday Night) Issued at 1245 AM CDT Sun Apr 28 2024 Scattered to numerous showers and thunderstorms were over central IL since mid evening and lifting northeast with strong SSW to southwest low level jet around 45 kts. This convection has lifted ne of SPI and about to lift ne of DEC airport. HRRR model has been handling this convection fairly well and utilized it with this aviation forecast package. Convection to lift north of CMI and BMI between 07-08Z but be close to PIA on the IL river through 11Z. IFR to MVFR ceilings and vsbys expected at times with thunderstorms, lowest at PIA. Continue LLWS overnight until sunrise with 2k ft SW winds 40-50 kts weakest at PIA. Looks like a break in convection during the day Sunday with VFR conditions generally expected. South to SSW winds will increase to 17-24 kts with gusts 28-34 kts developing between 13-14Z and then weaken some by sunset Sunday but still gusting around 25 kts during Sunday evening. Another batch of convection forecast to spread eastward ahead of an approaching cold front by late Sunday evening after 03Z/10 pm Sunday with MVFR conditions possible again with band of showers and thunderstorms. 07 && .ILX WATCHES/WARNINGS/ADVISORIES... Flood Watch until 10 AM CDT this morning for ILZ027>031-036-037- 040-041. && $$