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Area Forecast Discussion
Issued by NWS Central Illinois
Issued by NWS Central Illinois
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774 FXUS63 KILX 062316 AFDILX Area Forecast Discussion...Updated Aviation National Weather Service Lincoln IL 616 PM CDT Sat Jul 6 2024 .KEY MESSAGES... - Scattered thunderstorms are possible west of the Illinois River on Sunday (20-30% chance). Severe weather is not expected. - Precip chances persist across much of the area Monday-Tuesday (20-50% chance), then shift to southeastern Illinois on Wednesday as the remnants of TS Beryl approach the Ohio Valley. && .DISCUSSION... Issued at 212 PM CDT Sat Jul 6 2024 Weak, broad sfc high pressure, with MSLP values around 1016-1018mb, continues to slowly shift east across the mid- Mississippi Valley, and should shift east of Illinois tonight. Diurnal Cu will fade this evening, resulting in mostly clear skies through the evening. A shortwave over the northern Plains has led to storms forming across the Plains, and these are expected to track towards the Upper Midwest. CAMs depict most, if not all, of this activity staying north/west of the ILX CWA as it passes by during the pre-dawn hours of Sunday, but the far northwest portions of the CWA could be clipped by this precip activity. This disturbance will also result in mid/high cloud cover increasing west of I-55 after midnight. A trough over the central Plains will gradually shift east through early next week, resulting in occasional scattered precip chances through Wed. The most favored area for precip will shift east each day, beginning with areas west of the IL River on Sunday, peaking area-wide on Monday (30-50%), shifting east on Tues (20-40% east of I-55), and lingering but diminishing on Wed (20% chance near/east of I-57). While it`s difficult to completely rule out an isolated strong storm or locally heavy rainfall this time of year, overall the probability of such hazards is quite low. That`s in large part due to tropical system Beryl, which will prevent gulf moisture from advecting into the Midwest, as well as prevent EML advection out of the SW US. Ensemble mean PWAT values across central IL with this wave are in the 1.50-1.75" range, which is above normal but not excessive, with such values being below the 90th percentile of the ILX sounding climatology. The lack of an EML really limits the instability values, with MUCAPE values generally below 1000 J/kg each day Mon-Wed. Additionally, upper level heights gradually start to rise on Tues-Wed as the main upper trough starts to lift northeast. The one exception is Sunday, with modest instability (around 1500 J/kg) developing west of the IL River, although shear values are marginal (less than 30 knots). Most CAMs do show some storm development across west-central IL, aided either by previous t-storm outflows or an MCV lifting out of MO. Unfortunately pinpointing the specific placement of either of these mesoscale features is a low confidence venture. The 06.12z run of the HRRR indicates some spotty higher wind gusts out of the Sun PM storms, however it`s forecast soundings appear significantly overmixed, and thus have disregarded this signal for now. Perhaps the presence of an MCV can locally enhance shear values across west- central IL tomorrow afternoon and allow for better storm organization, but otherwise the prospects of severe weather are looking quite slim. Late Wed into Thurs, the remnants of Beryl are progged to curve northeast towards the Ohio River Valley. Most guidance still keeps the system and the bulk of its associated rainfall south of the ILX CWA. The "cone of uncertainty" does extend as far north as the I-72 corridor, illustrating the typical track error of such systems at this range. Adding to the difficulty is the fact that there could be a tight northern gradient to the precip with this system. The NBM PoPs did seem too low compared to other ensemble guidance, so in coordination with neighboring offices to the south/east, PoPs were raised. Significant temperature swings are not expected over the next week, with highs generally in the mid/upper 80s and lows in the mid/upper 60s. Erwin && .AVIATION... (For the 00z TAFs through 00z Sunday Evening) Issued at 616 PM CDT Sat Jul 6 2024 VFR conditions through the forecast with scattered diurnal cu dissipating this evening, then redeveloping Sunday morning. High pressure will shift over the area tonight, resulting in light winds. After the high pushes off to our east Sunday morning, winds will set up from the south/southwest around 10 kt. 25 && .ILX WATCHES/WARNINGS/ADVISORIES... None. && $$