Area Forecast Discussion
Issued by NWS Central Illinois
Issued by NWS Central Illinois
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042 FXUS63 KILX 141052 AFDILX Area Forecast Discussion...Updated Aviation National Weather Service Lincoln IL 552 AM CDT Sun Jul 14 2024 .KEY MESSAGES... - Hot and humid conditions through Monday, with highs in the low to mid 90s and heat indices in the 100s. - An unsettled pattern continues with occasional disturbances producing periodic thunderstorm chances through Tuesday, some of which could be strong to severe. - Much cooler air and a stretch of mostly dry weather is expected from Wednesday into the weekend. && .DISCUSSION... Issued at 235 AM CDT Sun Jul 14 2024 A multi-day stretch of oppressive heat and humidity is the top weather headline across central IL through early next week. Upper level ridging remains anchored over the Four Corners region, while weak sfc high pressure sits over the SE US and lower sfc pressures are present over the upper Great Lakes. This sfc pattern will result in continued southwesterly flow and WAA through Monday, continuing a gradual warming trend. The pattern supports continued MCS activity primarily north of the ILX CWA, and three are ongoing at the start of the forecast period (N IL, cntrl MN, SD). The one over cntrl MN is expected to progress SE towards N IL by mid-morning. CAMs have not been handling the mature MCS over SD well (which is also tracking SE). Most CAMs have it dissipating in a few hours, but it seems likely to maintain beyond that. It still seems like a stretch that this system would persist all the way to IL, but it bears monitoring, and it could transition into a remnant MCV that leads to scattered t-storm develop this afternoon/early evening. Confidence in the evolution of these features is quiet low. The other avenue via which scattered showers could development is WAA, focused mainly across IA/MO where t-storms have formed recently (as of 2am/07z), but this activity could clip west-central IL this morning. While we`ve been monitoring the potential for these MCS to provide some cooling cloud cover, the latest model guidance makes it seem like widespread cirrus is unlikely, with cloud cover generally forecast to be partly cloudy or less. So it`s full steam ahead on those hot/humid conditions today, with highs in the low to mid 90s and heat indices of 100-105 degrees. The heat peaks on Monday, as temps warm a few degrees relative to Sunday and heat indices push into the 105-110 degree range. The nighttime periods will also offer little relief, as heat indices stay in the mid to upper 70s. A heat advisory remains in effect area wide through Monday evening. Additional convective development appears possible Sun night as a LLJ ramps up and 850mb moisture axis focuses over northern parts of IL. As has been the case with all of the previous MCS activity, CAMs suggest the bulk of the precip stays north of the ILX CWA, with areas near/north of I-74 having the best chance of seeing any rain Sunday night. Into early next week, a deeper upper low digs towards the Great Lakes, sending a cold front pushing towards the ILX CWA which will break the heat wave and provide a chance for thunderstorms Mon night (mainly north of I-72) into Tuesday. Forecast soundings for Tues continue to show a highly unstable environment ahead of the cold front, but with varying levels of deep layer shear depending on the guidance source. At any rate, the deep layer shear vectors are nearly parallel to the front and forecast soundings show steep low- level lapse rates resulting in DCAPE values over 1000 J/kg. Collectively, these factors favor upscale growth of t-storms and if a severe threat develops it would likely be a wind threat. The exact area at risk will depend on the frontal timing, but for now it appears the threat will be focused south of I-72 Tues PM. There is also some potential for locally heavy rain/isolated flash flooding, with PWAT values forecast to approach or exceed 2" and deep layer flow oriented to the boundary resulting in the potential for training convection. The forecast for the latter half of the work week and into the weekend remains largely unchanged. As the front gradually shifts SE, precip could linger near/south of the I-70 corridor on Wed, but otherwise mostly dry conditions will prevail into the weekend. Large sfc high pressure develops behind the front and slowly sinks southeast, reaching IL by Friday. Below normal temperatures remain highly likely from Wed into the weekend, with highs near 80F which is about 5-6 degrees below normal. Erwin && .AVIATION... (For the 12z TAFs through 12z Monday Morning) Issued at 551 AM CDT Sun Jul 14 2024 Southwesterly winds prevail through the period, with gusts around 20 knots from mid-morning through the afternoon. VFR conditions should largely prevail, although some isolated ground fog could result in MVFR visbys at KCMI through 13z. The main challenge this period was low confidence regarding multiple thunderstorm chances and whether or not they will reach the terminals. A line of storms is tracking into northern Illinois as of this writing, and could impact the northern terminals (KPIA/KBMI/KCMI) between 13-16z if the line does not dissipate before then. If these thunderstorms do reach the terminal, expect reduced visibility, MVFR ceilings, and gusty northeasterly winds. Another rounds of thunderstorms is possible overnight, late in the 12z TAF period. Again, confidence in how these thunderstorm chances evolve is lower than normal. Erwin && .ILX WATCHES/WARNINGS/ADVISORIES... Heat Advisory from 1 PM this afternoon to 8 PM CDT Monday for ILZ027>031-036>038-040>057-061>063-066>068-071>073. && $$