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Area Forecast Discussion
Issued by NWS Central Illinois
Issued by NWS Central Illinois
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660 FXUS63 KILX 061043 AFDILX Area Forecast Discussion...Updated Aviation National Weather Service Lincoln IL 543 AM CDT Sat Jul 6 2024 .KEY MESSAGES... - There is a 30% chance for thunderstorms west of the Illinois River Sunday evening, with more widespread showers and storms anticipated Monday into Tuesday. While severe weather is not expected, storms may produce heavy rain and gusty winds, especially Sunday evening. && .DISCUSSION... Issued at 201 AM CDT Sat Jul 6 2024 Tranquil weather conditions will prevail this weekend across central Illinois under the influence of surface high pressure. While cool advection is forecast to be weaker today with less afternoon wind than yesterday, subsidence and (weak) convective mixing will maintain seasonably dry (upper 50s to mid 60s dew points) low levels, with radiational warming this afternoon bringing highs to only the low 80s - still a little cooler than normal for this time of year. Tomorrow will be a bit warmer, however, as return flow overspreads the region ahead of a trough across the Plains. The 00z HRRR suggests some locations, mainly along and south of I-72, will warm to 90 or better, and this seems reasonable if mixing brings afternoon dew points into the 50s as the same model would suggest. Toward late evening, some storms are expected to fire to our west where a little more low level moisture leads to MUCAPE values over 2000 J/kg (as the 06.00z NAMNest and HRRR would have it). The piece of shortwave energy lifting northeast into western IL/eastern IA Sunday night could even spark a couple storms across our western counties, though more widespread garden variety convection isn`t expected until Monday afternoon. Right now, NAM forecast soundings suggest inverted-V soundings with steep low level lapse rates and notable mid level dry air Sunday evening across our west where EPS mean brings PWATs to 1.7" or higher (near the climatological 90th percentile), so conceptually precip loading in the feistier storms should make them capable of localized strong (40+mph) wind gusts in wet microbursts when they collapse. Even so, lack of wind shear has us expecting nothing sustained or organized, so the severe risk remains low (5%). Forecast soundings for Monday look even less concerning, with still an inverted-V and steep low level lapse rates in place, but a much more moist column above the LCL; this lack of mid level dry air leads us to believe downdrafts will be a little weaker compared to Sunday, and once again the anemic shear will preclude storm organization to result in a low (less than 5%) severe risk. Monday night into early Tuesday, another piece of shortwave energy lifting across the Prairie State will result in a LLJ currently slated to be strongest across our southern counties (mainly near/south of I-70) where a little more shear (NBM probs climb to 50- 70% for more than 30 kt 0m-500mb shear) can be expected for sustained storms. LREF mean PWATs there approach 2 inches early Tuesday, and with any training storms there could theoretically be some localized heavy rain totals; however NBM probs remain sub 20% for more than an inch by 12z (7am) Wednesday (morning), by which time the axis of this first trough should be departing. Throughout the rest of the work week, troughing is expected to linger across the eastern half of the CONUS in response to an amplifying ridge across the West. The significance of this is threefold: (1) we can`t quite rule out precip any day, though (2) severe potential will be low, and (3) temperatures and humidity should remain near or slightly below normal. Bumgardner && .AVIATION... (For the 12z TAFs through 12z Sunday Morning) Issued at 543 AM CDT Sat Jul 6 2024 High pressure will maintain continued dry conditions and winds (west-northwest through afternoon, then backing to southerly this evening) generally 10 kt or less throughout the forecast period. VFR will be the theme, though a sea of diurnal cu that develops after around 15z (10am) may initially be within the MVFR flight category, especially at BMI and CMI. Cloud bases, however, will be quick to lift to above 3kft by around 17z (noon) as the mixed layer deepens. Bumgardner && .ILX WATCHES/WARNINGS/ADVISORIES... None. && $$