


Area Forecast Discussion
Issued by NWS Central Illinois
Issued by NWS Central Illinois
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802 FXUS63 KILX 241045 AFDILX Area Forecast Discussion...Updated Aviation National Weather Service Lincoln IL 545 AM CDT Sat May 24 2025 .KEY MESSAGES... - Below normal temperatures persist, with several days of highs ranging from the mid 60s to low 70s. There are a few light rain chances Sunday into next week, with the best chance being on Tuesday (40-50%). Severe thunderstorms are not expected. && .DISCUSSION... Issued at 254 AM CDT Sat May 24 2025 A low-impact forecast period continues across central IL, with the main forecast concern being occasional light rain chances. Early Sat AM, satellite imagery showed ample mid/high cloud cover overspreading the ILX CWA, helping to keep temps warmer than Fri AM, in the 50s as of this writing. A pleasant late spring day is in store across the region today as broad, weak sfc high pressure (1022- mb) nudges in. High temps rise into the low 70s, while winds will be light, and dewpoints only in the 40s result in afternoon RH values between 30-40%. Another synoptically-enhanced lake breeze arrives late this evening. Unlike previous occurrences, this one isn`t expected to be too breezy, but will result in the onset of northeasterly winds overnight. For Sun into early next week, IL will find itself positioned between a deepening sfc low over the southern Plains and sfc high pressure over the Great Lakes. Periods of weak ascent from the system to our southwest will have to work against persistent, (relatively) dry, northeasterly flow due to the high pressure to the north. This pattern leaves me thinking that the model blend PoPs are generally overdone. However, one period where forcing looks sufficient to include low chance (20%) precip mention is late Sat night into Sun, when models show an east-west oriented band of low-level FGEN forcing. This forcing is initially focused north of I-74, but does slide south Sun afternoon. Fcst soundings never fully saturate, but do appear to be near saturation throughout the day. So, in a deviation from previous forecasts, PoPs were expanded northward on Sun, now including a 15-30% chance across the entire CWA. On the flip side, for Monday, the sfc high sinks closer to the area and most guidance suggests precip stays just southwest of the ILX CWA. The forecast blend kept 20-40% PoPs south of a Galesburg-Paris line, but if current trends hold I`d expect these PoPs to lower in the coming days. By Tues, the shortwave responsible for the southern Plains system lifts into the mid-MS Valley, shunting the sfc high pressure a bit northeast and providing the best chance for rain during this forecast period (40-50%). Forecast soundings and instability progs only show weak instability, but perhaps enough for a few rumbles of thunder (MUCAPE values of a few hundred J/kg). Total QPF amounts through Tues night are light, with just a 30-50% chance to exceed 0.25" north of I-72, and a 50-70% chance to the south. Skies will be partly to mostly cloudy each day through Tues, with seasonably cool temps as highs continue to range from the mid 60s to low 70s each day. For the latter half of the work week, the forecast will be influenced by the evolution of a closed upper low over the northern Plains/upper Midwest, which is expected to be slow to evolve. Guidance eventually slides this upper low to the east, at which point ensembles show an amplifying upper pattern with long wave troughing developing over the eastern US while a separate upper low cuts off off the coast of SoCal. The closed upper low traversing the upper Midwest will result in some mention of precip in the forecast during the latter half of the week. At no point in this pattern is there a clear signal for strong southwesterly flow across the Midwest, which means temps will be slow to warm and the svr storm threat stays low through the week. The probability of high temps above 80F is below 50% each day through the end of May (though the probs are around 40-50% for the western half of the CWA by Sat May 31). Normal high temps for late May are in the upper 70s/near 80F. Erwin && .AVIATION... (For the 12z TAFs through 12z Sunday Morning) Issued at 543 AM CDT Sat May 24 2025 VFR conditions prevail through the period, along with an easterly wind component. Winds should stay below 10 knots. Broken mid-level cloud cover will be prevalent throughout the period. There is a low chance (15%) of light rain towards the end of the period (06-12z), but did not feel this warranted a precip mention in the TAF. Erwin && .ILX WATCHES/WARNINGS/ADVISORIES... None. && $$