Area Forecast Discussion
Issued by NWS Central Illinois
Issued by NWS Central Illinois
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002 FXUS63 KILX 010441 AFDILX Area Forecast Discussion...Updated Aviation National Weather Service Lincoln IL 1141 PM CDT Tue Apr 30 2024 .KEY MESSAGES... * Band of showers/thunderstorms is expected to decay as it moves into our CWA tonight, with highest shower/storm chances near the IL River Valley. * Above average temperatures expected through the next 7 days, warmest temps Thursday with highs expected to be well into the 80s. * Another round of showers and thunderstorms expected Thursday night into Friday morning. && .UPDATE... Issued at 847 PM CDT Tue Apr 30 2024 A broken line of convection continues to track eastward across Iowa this evening. While the storms were originally rooted in an instability axis characterized by MLCAPEs of 1500-2500J/kg, they are beginning to outrun their energy source as the airmass further east is much more stable. Latest SPC mesoanalysis shows MLCAPEs of only 50-100J/kg along/west of the Illinois River...and even lower further east. CAMs have consistently shown the storms weakening considerably as they spill into the Illinois River Valley toward midnight, and see no reason this trend will not be realized. As a result, think scattered showers/thunder will impact locations west of the I-55 corridor between 11pm and 2am...with the activity diminishing to just a few showers as it reaches I-55 after 2am. Current forecast has a good handle on the situation and requires no major update at this time. Barnes && .DISCUSSION... Issued at 244 PM CDT Tue Apr 30 2024 Water vapor imagery early this afternoon depicts a vigorous, negatively tilted shortwave trough moving east across the northern Plains toward the Upper Mississippi Valley. Strong/severe thunderstorms are forecast to develop over western/central IL late this afternoon in association with this trough. Axis of moisture and instability with this system is rather narrow and while it will likely advect eastward toward the Mississippi River later this afternoon and evening, it seems likely that it will get narrower and eventually pinched off with convection likely to outrun the better instability as it moves into western Illinois. In addition, the upper trough will pass north of the area with no real height falls and strong synoptic ascent progged to pass north of the CWA. Given all of this, the expectation is that storms will be in a weakening phase by the time they reach the Mississippi River or very soon there after. The greatest threat of severe weather will likely remain west/northwest of our CWA. Interestingly, there has been a consistent signal in CAM guidance depicting the potential for strong to potentially damaging wake low winds tonight as this area of convection decays moving into Illinois. Conceptually, this would make sense as wake lows tend to form when adiabatic warming on the backside of a convective complex is unable to be offset by evaporative cooling from precip (precip shield progged to weaken/dissipate over IL). There`s a high degree of uncertainty on how well CAMs can forecast a rare scenario like this. While the CAM guidance has mostly been across northern IL and perhaps our far northwestern CWA with the strongest winds, it is worth noting that in addition to the highly uncertain ability to accurately predict the occurrence of this mesoscale phenomena, there would be a high degree of spatial uncertainty about where it could occur. Given this, our northern CWA is close enough to warrant monitoring for a potential period of strong wake low driven winds tonight. Weak cold front will clear the area early Wednesday morning with clearing/partial clearing and another day of above average temperatures and comfortable humidity expected Wednesday. Front is progged to return north as a warm front Wednesday night, but strongest forcing and moisture return will lie west of our CWA. Have maintained some chance pops for showers/storms Wed night into early Thu morning, especially across the IL River Valley for this potential scenario. Another vigorous trough is expected to emerge over the northern Plains Thursday with the associated surface lo lifting north into the Upper Mississippi. This should place central and southeastern Illinois in the warm sector of the cyclone with strong southerly winds likely driving temps into at least the mid 80s. While likely shy of daily records, these temps are unseasonably warm and more typical of June than early May. Cold front will sweep across the area Thursday night into early Friday morning. Medium range guidance has been trending gradually quicker with the frontal passage and it would appear that the best chances of showers and storms will be Thursday night. Have maintained some low pops Friday afternoon, particularly across southeastern IL where some afternoon convection could redevelop if the front doesn`t clear these areas in time. Above average temperatures are expected through the weekend into early next week. Generally looks like most of the weekend will be dry with better shower/storm chances returning early next week as western long wave trough reloads and ejects another shortwave east into the mid-section of the nation. - Izzi && .AVIATION... (For the 06z TAFs through 06z Wednesday Night) Issued at 1141 PM CDT Tue Apr 30 2024 One small cluster of decaying convection continues to make its way eastward toward the Illinois River Valley late this evening. Based on radar timing tools, have maintained thunder at KPIA from 05z-06z. Will also maintain a period of -SHRA at KBMI after 06z, but will only mention VCSH at the other terminals as the precip area is rapidly shrinking. Winds will initially be S at 10-15kt, then will veer to S/SW after the dying showers pass. Winds will then swing to the W/NW after FROPA Wednesday morning. Barnes && .ILX WATCHES/WARNINGS/ADVISORIES... None. && $$