Area Forecast Discussion
Issued by NWS Central Illinois
Issued by NWS Central Illinois
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205 FXUS63 KILX 110203 AFDILX Area Forecast Discussion...Updated National Weather Service Lincoln IL 903 PM CDT Mon Jun 10 2024 .KEY MESSAGES... - Summer-like temperatures return by Wednesday and appear likely to stick around over much of the next two weeks. Thursday is expected to be the muggiest day this week, with afternoon heat indices approaching 100F west of the Illinois River. - There is a 30-50% chance of thunderstorms Thursday evening/night, some of which could be strong to severe north of I-72. && .UPDATE... Issued at 903 PM CDT Mon Jun 10 2024 Sprawling ridge of high pressure extending from Ontario southwestward to the mid-Mississippi River Valley will dominate the weather across central Illinois tonight...providing clear skies, light winds, and chilly temperatures. 02z/9pm readings have already dropped into the lower to middle 60s across much of the KILX CWA, with even cooler upper 50s noted near the Indiana border. Lowest dewpoints in the upper 30s/lower 40s are in place along/northeast of a Bloomington to Mattoon line and this is where the coolest overnight lows will be found. Based on rate of temp fall so far this evening, think lows will range from the lower 40s near the Indiana border to around 50 degrees across the far southwest near Winchester. Barnes && .DISCUSSION... Issued at 151 PM CDT Mon Jun 10 2024 The mostly cloudy skies that were present this morning continue to slowly scatter out, but the combination of cloud cover and northerly flow have kept temps in the mid 60s to low 70s as of 130pm/1830z. An upper trough remains in place over the eastern CONUS, with an associated cold front having pushed all the way south to the Gulf Coast. A 1018-mb sfc high pressure was situated over the Upper Midwest. That broad, weak sfc high pressure will remain in control through Tues. Light, southerly winds develop on Tues, marking the start of a warming trend. Highs return to near 80F tomorrow, which is closer to normal, while dewpoints remain seasonably low, in the 40s for most of the area. Into the latter half of the work week, height rises occur as ridging builds over the Four Corners region. Multiple disturbances progress around the north side of this ridge, moving through the northern Plains/upper Midwest. For the most part, precip associated with these disturbances is expected to remain north of the ILX CWA, but can`t rule out a glancing shower north of I-74 Tues night or late Wed night (~10% chance). The better chance (30-50%) for rain/storms is Thurs PM, when a cold front sags south into the area and interacts with a moist, unstable airmass. While the 500mb jet is progged to stay north of the area, it should still provide sufficient shear to support a chance for strong to severe t-storms. The Grand Ensemble depicts a 40-70% chance of having both surface-based CAPE greater than 1000 J/kg and deep layer shear over 30 knots north of I-72 Thurs PM. One factor that could limit the severe potential locally is the diurnal timing, as current guidance keeps storms north/west of the CWA until later in the evening (after 00z/7pm). Ensemble mean PWAT values are between 1.5-2", which is above the 90th percentile of the ILX observed sounding climatology, so locally heavy rainfall is also a concern Thurs PM. Aside from Thurs PM, precip chances are generally low (below 15%) through the upcoming weekend. The other forecast concern is the heat, and it appears that above normal temperatures will become a staple of the forecast beginning mid-week and continuing well into the extended. By Wed, highs push into the upper 80s/low 90s. Dewpoints will be climbing but won`t be too oppressive on Wed. By Thurs, however, dewpoints will range from near 70 west of the IL River to near 60 across far E IL. With highs in the low to mid 90s, that will result in peak heat indices around 100F west of the IL River on Thurs. The experimental NWS HeatRisk product (which uses wet bulb globe temperature) reaches "high" (level 3 of 4) for a few hours west of I-55 during peak heating on Thursday. For context on that specific category, "heat of this type represents a major risk to all individuals who are exposed to the sun and active, or in a heat-sensitive group". Conditions aren`t expected to be quite as oppressive Fri-Sat, with highs in the upper 80s/low 90s but with reduced humidity as dewpoints fall to the 50s or low 60s. That "respite", if it can be referred to as one, will be short-lived, with temperatures forecast to return to the mid 90s Sun-Mon, while dewpoints climb back toward 70. The CPC 6 to 10 and 8 to 14 day outlooks (valid June 15 to June 23) suggest that above normal temperatures are likely during that time (70-80% chance). Normal temperatures during that period are highs in the mid 80s and lows in the low 60s. Erwin && .AVIATION... (For the 00z TAFs through 00z Tuesday Evening) Issued at 632 PM CDT Mon Jun 10 2024 VFR conditions will prevail through the entire 00z TAF period. N/NE winds of around 10mph initially will become light/variable after sunset...then will eventually become SW at 5-10kt by Tuesday afternoon. Skies will remain clear this evening, followed by a gradual increase of high/thin clouds late tonight into Tuesday morning. After that, models show an upper-level disturbance tracking across the Northern Plains into the western Great Lakes. The associated surface trough/front will approach from the northwest late in the day, resulting in a band of mid/high clouds pushing toward the I-55 corridor by late afternoon. Barnes && .ILX WATCHES/WARNINGS/ADVISORIES... None. && $$