Area Forecast Discussion
Issued by NWS Central Illinois
Issued by NWS Central Illinois
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338 FXUS63 KILX 291747 AFDILX Area Forecast Discussion...Updated Aviation National Weather Service Lincoln IL 1247 PM CDT Sat Jun 29 2024 .KEY MESSAGES... - Scattered thunderstorms may redevelop this evening along a cold front, though the probability is low (< 30% chance). If storms do redevelop, they could carry an attendant severe risk with 60 mph wind gusts and quarter-size hail. - A stretch of drier, cooler and less humid weather will arrive late tonight and span through Monday. Sunday night lows will dip into the upper 40s in some spots. - A surge of seasonably hot and humid conditions returns by the middle of next week with daily chances for thunderstorms Wednesday - Friday. && .UPDATE... Issued at 1007 AM CDT Sat Jun 29 2024 After a couple morning thunderstorms, some breaks of sunshine across much of the ILX CWA is allowing radiational warming to bring temps up quickly (not that we were particularly cool to begin with) into the mid 80s already by 10am. The airmass in place is characterized by mid 70s dew points, with a PWAT of 2.17 inches and 3344 J/kg MUCAPE on the morning raob - more than sufficient instability for heavy thunderstorms. Fortunately, low-mid level warm advection from the west later this morning into early afternoon will strengthen the cap evident on the morning sounding, limiting potential for convection except with the cold front, along which a few CAMs are suggesting convection will develop between 4 and 6pm...sliding east and out of our area by 11pm. At this point, the greatest model agreement in storms during that time period is near and east of a Bloomington to Effingham line, where HREF neighborhood (radius = 20 km) probabilities for >40dBZ surpass 50%. Bumgardner && .DISCUSSION... Issued at 1242 AM CDT Sat Jun 29 2024 Overnight thunderstorm activity was limited by an upstream MCS in central Missouri, and we begin today with plenty of convective debris overhead. With a MCV tracking along I-70, it`s unlikely that we get enough sunshine to erode CINH this afternoon. Any convective initiation that occurs is going to have to do so this evening on the cold front. Up until this point, CAMs had been lackluster on the convective potential later today, but the 06z HRRR is now resolving a line of storms pushing southward along the front after 21z/4pm. Deep-layer shear (< 30 kts) should limit an organized/widespread event, but moderate instability (2500-3000 J/kg MLCAPE) and dry air entrainment could result in a few pulsey updrafts capable of large hail and strong downbursts. As with any conditional threat, convective trends will need to be monitored throughout the day. Anomalous surface high pressure will settle into the Northern Plains tonight, gradually building into the Great Lakes region by Sunday night. Seasonably cool temperatures will accompany this modified Canadian airmass, yielding afternoon highs in the mid- to-upper 70s and overnight lows in the 50s. A few spots may even dip into the 40s Sunday night. Record low temperatures are not in serious jeopardy of being broken, but an impressive cool down nonetheless. Temperatures bounce warmer by Tuesday as low-level winds veer southwesterly behind departing surface high pressure. Typical summertime heat and humidity will then pool ahead of a cold front, which is forecast to drop through the region Tuesday night into Wednesday. Mid-range guidance remains in fair agreement of the surface front washing- out over the area Wednesday night as the main upper-level forcing becomes displaced too far to the northeast. This stalled-out front may provide a focus for heavy rainfall with the synoptic pattern bearing some resemblance to a Maddox setup for flash flooding, with slow 850-300mb flow (30 kts) and multiple shortwave impulses running parallel to the surface front in an environment where PWATs eclipse the 99th percentile of early July climatology for 24 hours. Notable spatial/timing differences among blended and ensemble guidance with respect to frontal passage are causing the NBM to smear chance PoPs (40-60%) through much of the midweek period, with a signal for drier weather returning by next weekend. MJA && .AVIATION... (For the 18z TAFs through 18z Sunday Afternoon) Issued at 1241 PM CDT Sat Jun 29 2024 Scattered thunderstorms have developed early, courtesy of a weak boundary and a bit more sunshine than expected which eroded our capping inversion. DEC and CMI have already reported thunderstorms, which should be moving out of the area in the next hour or two. Additional development is less certain given the strengthening cap further west, though wind shear will be increasing along the cold front as it moves southeast through the area late this evening. Given expected limited coverage (30-50%) along that front and continually shifting model output, we`ve included a prob30 for a few hours (roughly 22z Sat to 02z Sun, or 5-9pm CDT) this evening to message that potential, which is highest once again at CMI and DEC. Behind the front, an abrupt shift and uptick in winds is forecast with frequent gusts near or over 20 kt expected for several hours before winds gradually become more steady around 10-13 kt toward Sunday morning. Bumgardner && .ILX WATCHES/WARNINGS/ADVISORIES... None. && $$