Area Forecast Discussion
Issued by NWS Central Illinois
Issued by NWS Central Illinois
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589 FXUS63 KILX 140804 AFDILX Area Forecast Discussion National Weather Service Lincoln IL 304 AM CDT Tue May 14 2024 .KEY MESSAGES... - The majority of central Illinois is forecast to see greater than a half inch of rain through Wednesday morning. Localized areas (10 percent or less) could see 2 to 3 inches of rain or more, with runoff causing further rises in rivers and streams. - More rain is forecast from Thursday into Friday. Though the chance of over 1 inch is only about 20-40% for any particular location, wet soils will result in much of the rainfall being converted to runoff. && .DISCUSSION... Issued at 304 AM CDT Tue May 14 2024 Early morning water vapor imagery reveals a low pressure center over northern Missouri, with modest southerly flow ahead of the low working to slowly pull moisture northward. The latest analyzed precipitable water values range from 1.2 to 1.4 inches, with modest MUCAPE values of no more than a few hundred J/kg. Forecast soundings display an ideal saturated profile through much of their depth although with a bit of drying in the mid levels, with the minimal CAPE distributed in a "long, skinny" fashion. Combined with the continued approach of the upper low as well as daytime heating, this should yield an opportunity for showers and thunderstorms producing rain at moderate to heavy rates. Initially, look for showers bubbling up near and west of the Illinois River near and north of a zone of deep moist convergence where 100-200 J/kg of MLCAPE resides with little cap. In addition, the cluster of showers and thunderstorms moving into southern Illinois from southeastern Missouri may clip southeastern portions of the ILX CWA beginning within the next 2-3 hours. During the daytime, coverage of showers and storms is forecast to be greatest south of I-74 with coverage decreasing from north to south beginning about 3-4 pm. Coverage of the moderate to heavy showers will be spotty. Though most will measure at least a half inch of rain between now and Wednesday morning, about 25% of locations will probably measure less than that. Localized swaths could receive 2-3 inches of rain or more. The rainfall, especially where heavy, could result in further rises on area rivers and streams. Precip chances have been extended into tonight and Wednesday near the Indiana state line, as CAMs and deterministic global models are fairly consistently showing continuation of at least light precip to the west of the low slowly departing along the Ohio River valley. After a brief dry period Wednesday evening and perhaps early Thursday morning, notable precip chances return for Thursday and Friday as another fairly weak short wave trough makes its way across the Plains toward the Midwest. The joint probability of SBCAPE > 250 J/kg and sfc-500mb shear > 30 kt is only around 10-15%, but that is a bit more than for the present system. Still, severe weather probabilities are low for the Thursday-Friday event as well. Fortunately, the rainfall threshold probabilities are also lower than for the current system. The probability of an inch of rain during the entire 48 hour period from Thursday morning to Saturday morning is around 20-40%. Even so, each successive rain event serves to add to the saturation of soils and result in quicker runoff. The 00z GFS shows a closed low moving out of Missouri Friday evening with rain continuing most of the day Saturday. This solution appears to be a bit of an outlier, though it`s not the only solution with rain continuing so low precip chances are included for Saturday via the NBM. Low precip chances continue through the Sunday-Tuesday period as well, with uncertainty regarding timing of fast moving short-wave troughs in the presence of at least some instability for shower and storm development. It`s unlikely that this entire period will be wet, but it`s difficult to nail down exactly when the rainy periods will be. AAT && .AVIATION... (For the 06z TAFs through 06z Tuesday Night) Issued at 1136 PM CDT Mon May 13 2024 Initial challenge will be timing of low MVFR or IFR ceilings. Most thus far have been associated with the lingering showers near KBMI/KCMI and these are lifting northward, but some breaks in the clouds further south have quickly filled in with stratocumulus. Evening HREF guidance shows a 60-80% chance of ceilings below 3,000 feet overspreading the terminal sites between 06-09Z, and ceilings dropping to IFR within an hour or two afterward. Slow improvement is expected Tuesday afternoon, with best chances of rising back above 2,000 feet at KPIA/KBMI in the evening. Showers will become widespread again in the 12-18Z time frame and continue through late afternoon, before diminishing to scattered showers. Any of the showers from late morning through afternoon will be capable of a few lightning strikes, but confidence is too low/sparse to pin down a specific time frame for inclusion. Geelhart && .ILX WATCHES/WARNINGS/ADVISORIES... None. && $$