Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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556 FXUS63 KLOT 142001 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 301 PM CDT Tue May 14 2024 .KEY MESSAGES... - Showers and embedded thunderstorms will continue through around sunset roughly south of a Pontiac to Valparaiso line. - A narrow axis of heavy rainfall (20-30% chance of >1" of rain) resulting in localized flooding remains possible through this evening over locations that experienced heavy rainfall across Livingston, Ford and Iroquois counties on Monday. - Chances for showers and thunderstorms will return on Thursday, followed by warming temperatures into the weekend. && .DISCUSSION... Issued at 300 PM CDT Tue May 14 2024 Through Tonight: We remain under the influence of an upper-level low over central Missouri this afternoon, with the associated surface low over far western Kentucky. An ongoing light rain band near the IL/WI state line will gradually dissipate over the next few hours as mid/upper forcing begins to wane north of the exiting low. Focus then settles on an active mid-level deformation axis stretching from near Pontiac ENE toward South Bend this afternoon. This axis has roughly aligned with an exiting (and stalling) surface boundary in an area with locally higher low- level instability after some morning sun. While overall surface- based instability is modest at best, marginal lapse rates and low LCLs will support a general axis of broken showers and embedded storms that should persist through sunset. The main concern is on localized flooding for areas that experienced heavy rain across east-central Illinois on Monday. Had considered a targeted Flash Flood Watch for Livingston, Ford and Iroquois counties through early evening, but the expected small footprint of higher convective rates supported more of a tactical gridded/graphical forecast approach. Would not be surprised if an areal Flood Advisory is needed at some point through early evening, but the likelihood of a Flash Flood Warning remains under 30%. If a Flash Flood Warning were needed, the most favored area would be from southeast Livingston into northwest Iroquois counties where the highest axis of rain on Monday has resulted in a Flash Flood potential with rates as little as 1"/3hr this afternoon. Overall activity will only slowly shift southeast through the night as the upper-level drifts east, with some showers lingering into Wednesday morning south of a Watseka to Rensselaer line. Kluber Wednesday through Tuesday: Other than a few spotty showers lingering early Wednesday morning (as noted above) dry conditions are expected the rest of the day on Wednesday as mid-level ridging builds overhead in the wake of the departing low. This should also allow for warmer temperatures compared to today, especially well inland from the lake in Illinois where low to mid 70s are expected if clouds can clear out. Continued northerly flow will keep temperatures cooler near the lake and further inland across northwest Indiana where highs likely still struggle to warm out of the upper 50s to mid 60s. As mentioned in previous discussions, confidence in the details decreases with time in the extended forecast period due to a greater degree of variability in the handling of a cut-off low across the desert southwest as it drifts east and whether it remains south of the area or phases with the broader upper jet near the region late week into the weekend. There is, however, a continued signal for dissipating convection (storm clusters/MVC/etc) to to approach the area heading into the day on Thursday which could result in renewed convective development during the afternoon/early evening period. At this range conditions do not appear favorable for severe weather given generally weaker shear/instability parameters this far north. Additional showers/storms may continue into Friday though again will be dependent up on the southern stream cut-off low/shortwave. While a dry forecast can`t be guaranteed over the weekend there is perhaps a bit better signal for increased precipitation chances early next workweek. Temperatures also look to trend warmer each day with highs back into the upper 70s to lower 80s by the weekend (with the exception of lake adjacent areas). Petr && .AVIATION /18Z TAFS THROUGH 00Z THURSDAY/... Issued at 1226 PM CDT Tue May 14 2024 As an upper-level low drifts south of the area today, MVFR ceilings will persist through the afternoon before becoming SCT this evening. A few -SHRA are expected to develop as far north as northwest Indiana mid-afternoon through early evening and may brush the MDW vicinity. Otherwise, NE/NNE winds of 10-15 knots are expected though the period. Kluber && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...Small Craft Advisory until 7 AM CDT Wednesday for the IL and IN nearshore waters. && $$ Visit us at weather.gov/chicago