Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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581 FXUS63 KLOT 010136 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 836 PM CDT Tue Apr 30 2024 .KEY MESSAGES... - Wind gusts 50 mph or higher possible around/just after midnight as a line of decaying showers/isolated thunderstorms moves across the area. - Gusty westerly winds to 30 mph Wednesday. - A couple periods of showers and thunderstorms mid to late week, most notably Wednesday night into early Thursday morning, then again late Thursday night into Friday morning. && .UPDATE... Issued at 836 PM CDT Tue Apr 30 2024 Recent radar trends across southern Iowa show that a cluster of generally discrete supercells proceeded by disorganized convection toward the Des Moines area has congealed into a more organized MCV near Ottumwa. Unlike as was depicted in earlier CAM guidance, this organization does not display a cohesive MCS signal. Expectations are for the current MCV to track just south of east into the relatively more favorable convective environment. This would bring the track along or just south of the far southern CWA. Concerns of a potential small wake low with 50mph+ winds remain valid, but the smaller footprint of organized convection and weaker cold pool/trailing meso-high suggest the overall threat is waning. Farther north, residual mid-level forcing may be able to maintain some lingering isolated showers and storms across most of northern Illinois through the overnight hours. Given the existing low-level dry airmass and only gradual nocturnal surface decoupling in the warm sector, any (decaying) shower/storm would still be capable of producing gusty winds at the surface. Kluber && .DISCUSSION... Issued at 308 PM CDT Tue Apr 30 2024 Through Wednesday Night: The primary forecast focus and concern is regarding what the HRRR and several other models are showing late this evening into the early overnight hours, which is the potential for wind gusts 50 mph or higher. As showers and a few thunderstorms move into the western area late this evening, they will be in a weakening phase and as they dissipate across the local area, the models are showing the potential for strong winds mixing to the surface. Of note with the HRRR is that it has been doing this consistently, run after run today. There is a narrow time window of strong winds via a low level jet and whether the models are mixing into this low level jet or trying to develop a wake low is not clear. Confidence is low for how this will evolve and trends with convection across IA will need to be monitored into this evening. Have bumped up winds tonight, with gusts into the 30-35 mph range but if what the HRRR and some of the models are showing does continue in later runs this evening, its possible a short duration wind headline may be needed. The models show these stronger winds diminishing in the predawn hours. Winds turn westerly Wednesday morning and now appear to be a bit stronger than previously expected, especially along and north of I-80 where wind gusts to 30 mph are possible. Winds slowly turn northwesterly Wednesday afternoon with speeds/gusts slowly diminishing in the mid/late afternoon. This may allow a lake breeze to develop into northwest IN by late afternoon but confidence is low for a lake breeze into northeast IL late Wednesday afternoon. The next system will bring a chance of showers and possibly a few thunderstorms to the area late Wednesday night into early Thursday morning. Confidence is fairly low for coverage and its possible that much of the area may remain dry, with the best chances across the northwest cwa. cms Thursday through Tuesday: Warm air advection driven showers (and some embedded thunderstorms) may be ongoing across portions of northern/northwestern IL at the start of the period Thursday morning as a surface warm front lifts northward into the area. However, the focus for this early morning warm air advection driven convection is expected to shift north of the area through midday as the surface warm front continues its northward shift towards the WI state line. Thereafter, a primarily precipitation free afternoon is anticipated, as we await our next good potential for showers and storms with an approaching cold front later Thursday night into Friday morning. While most areas may end up dry Thursday afternoon, temperatures could end up varying considerably across far northeastern IL (northern Chicago suburbs). This is due to fact that Lake Michigan may slow the northward progression of the warm front into WI near the lake, thus resulting in continued persistent cool east-southeasterly winds through the day. In such a scenario, temperatures Thursday afternoon would be held down in the lower 60s near the lake in far northeastern IL, while areas to the south of the warm front experience summer-like temperatures (in the low to mid-80s) and breezy south winds. Mild weather will continue into Thursday night as our area remains locked in the warm sector of the surface low tracking northward across the upper Midwest. This low is forecast to occlude over northern MN and far southwestern Ontario into early Friday morning. As it does so, the attendant surface cold front will slide eastward into our area very late Thursday night into Friday. A period of showers, and a few embedded thunderstorms, is likely to accompany this front, with the highest chances (60-80%) coming early Friday morning. We will need to continue to monitor the potential for any hydrologic concerns during this time frame, especially given the recent heavy rainfall the area has experienced. However, signs continue to point at the heaviest rainfall amounts potentially remaining west of the NWS Chicago forecast area in closer proximity to the track of the surface low. The rain threat is expected to end from west-to-east on Friday following the cold frontal passage. Thereafter, temperatures are favored to return closer to normal going into the weekend. Another approaching disturbance may result in another period of precipitation late Saturday into Saturday night, but the signal for this is not all that strong at this point. Otherwise, slightly warmer temperatures are favored into early next week with the overall weather pattern continuing to look rather active across the central CONUS. KJB && .AVIATION /00Z TAFS THROUGH 06Z WEDNESDAY/... Issued at 617 PM CDT Tue Apr 30 2024 Aviation Key Messages: - Decaying SHRA moving across the area late tonight - A period of strong (>40 kt) south-southwest wind gusts possibly accompanying the decaying SHRA, with at least 25-30 kt range gusts appearing probable - Potential for a period of MVFR CIGs early Wednesday, primarily at RFD - Diminishing winds turn northwest late Wednesday and eventually light northeast later Wednesday evening Surface winds will continue to back to the southeast early this evening, in response to low pressure currently moving east across the mid-Missouri River Valley. Area of strong/severe TSRA across IA-NW MO-KS are expected to weaken quickly as they move east this evening and outrun better instability to our west. Decaying showers will likely make it into northern IL, though may be only for a brief period especially farther east into the Chicago metro terminals. Of greater interest, has been multiple successive runs of the HRRR CAM, which had shown a consistent signal for very strong west- southwest winds of 40-50+ kts associated with the decaying showers. Latest (22Z) HRRR run has backed off these higher wind magnitudes, though along with other guidance continues to suggest a period of gusty winds near 30 kt overnight. Will continue to monitor trends with convection to our west and any associated enhanced winds. Forecast soundings indicate a period of MVFR ceilings are possible behind a cold front which will move through the area pre-dawn, with a better signal farther west/northwest for KRFD than our other terminals. These should erode after sunrise Wednesday, with breezy west winds expected. Winds are expected to diminish and veer northwest late in the day as surface high pressure spreads into the area, and then shift northeast later Wednesday evening. Ratzer && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...Small Craft Advisory until 7 PM CDT Wednesday for the IL nearshore waters. Small Craft Advisory until 1 PM CDT Wednesday for the IN nearshore waters. && $$ Visit us at weather.gov/chicago