Area Forecast Discussion
Issued by NWS Central Illinois
Issued by NWS Central Illinois
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216 FXUS63 KILX 040013 AFDILX Area Forecast Discussion...Updated Aviation National Weather Service Lincoln IL 713 PM CDT Fri May 3 2024 .KEY MESSAGES... - Near daily chances for showers and thunderstorms over the next week as a series of fronts advance across the region. The Tuesday through Wednesday period looks particularly active, with medium confidence in thunderstorms capable of producing all severe weather hazards. && .DISCUSSION... Issued at 127 PM CDT Fri May 3 2024 Current GOES WV imagery depicts a strong upper-level low positioned over western Ontario with more subtle shortwave energy ejecting out of the Great Basin. Model guidance remains in excellent agreement that shortwave energy lifts into the Northern Plains and Upper Midwest regions overnight, ultimately helping to force a synoptic cold front into western Illinois Saturday afternoon. A plume of low-to-mid 60s dewpoints is progged to advect northward ahead of the cold front, and SBCAPE values should be able to achieve 1000-1500 J/kg with CINH eroding in the presence of steep 0-3 km lapse rates (> 7.5 C/km). This all adds up to likely (> 60% chance) thunderstorm development Saturday afternoon along and ahead of the cold front. Coverage of Saturday storms could be limited by somewhat underwhelming deep-layer shear profiles, with much of the area at or below 30 kts in the vicinity of the cold front. Updrafts may struggle to become organized or struggle to stay organized, especially some of the early updrafts, and recent CAMs hint at this as well. Nevertheless, CAPE/Shear profiles are just good enough to support the potential for an isolated severe hail and wind threat. As storms move toward and east of I-55 Saturday evening, the severe potential should gradually fade. This will largely be due to the loss of daytime heating and the lack of a LLJ to help augment instability. This thinking lines up well with SPC`s Day 2 Marginal Risk, which ends the threat near the I-57 corridor. Flooding should not be a concern with the Saturday storm event. NBM Mean QPF is around 0.25", and this guidance only offers a 10% chance that rainfall exceeds 0.75", which is well below 3-hour flash flood guidance. The rest of the weekend through Monday should be fairly low drama, with the main frontal zones displaced just to our south. Attention quickly turns to the Tuesday - Wednesday timeframe as persistent, deep southwest flow envelops the region ahead of an elongated upper-level low. While we`re running lean on details at this timeframe, the synoptic pattern (kinematics/thermodynamics) being modeled supports a multi- day severe weather threat across portions of the Plains and Midwest. This strong signal in the global models is also reflected in the analogs and machine learning tools for severe weather potential. MJA && .AVIATION... (For the 00z TAFs through 00z Saturday Evening) Issued at 711 PM CDT Fri May 3 2024 VFR conditions should continue through most of the forecast period, though conditions will likely deteriorate locally along and west of I-55 near the end of the period as a broken line of thunderstorms develop with a cold front. Variable, but predominantly northeast, light winds will veer to southerly between 13z and 16z with some localized stronger gusts (along with heavy rain, small hail, lightning) possible with the line of storms. Bumgardner && .ILX WATCHES/WARNINGS/ADVISORIES... None. && $$