Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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400 FXUS63 KLOT 021953 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 253 PM CDT Tue Jul 2 2024 .KEY MESSAGES... - Showers/storms expected to reach the I-39 corridor this evening, then decreasing in coverage and intensity as they attempt to move east toward/east of the I-55 corridor. - Typical July warmth and humidity through the week with periodic chances for showers and storms late Wednesday night through Friday && .DISCUSSION... Issued at 253 PM CDT Tue Jul 2 2024 Through Wednesday: After a persistent area of WAA-forced elevated showers north of I-80 this morning, the last few showers should be lifting north of the WI state line within the next hour. Otherwise, mostly sunny skies are expected through sunset as temps rise into the low to mid 80s for all areas except the northern tier of counties. A mid-level wave just west of Kansas City early this afternoon will interact with a plume of higher theta-e air into central and eastern Iowa late this afternoon, fostering quickly growing convection into a generally linear MCS within the next few hours. The resulting convection is expected to track into a substantially less favorable environment around and east of the Mississippi River this evening into the early overnight hours as moisture decreases and mid-level lapse rates remain rather marginal for sustained organized convection. Expectations are for the convection to slow and weaken into a band of showers with some embedded thunder as far east as the Chicago metro. Poor low-level thermodynamics will limit the amount of surface- based convection, but a narrow reservoir of 1000+ J/kg DCAPE nosing northeastward ahead of the convection early this evening could support a few strong wind gusts as far east as the I-39 corridor. Additionally, PWATs over 2" combined with weak backward propagating vectors and deep layer shear vectors only slightly oblique to the forcing may result in brief training and subsequent localized rainfall amounts of 1-2" across the western CWA. After the early overnight hours, residual convection and scattered showers will gradually drift southeastward as a cold front approaches from the northwest late tonight into Wednesday morning. The cold front should clear the southern CWA by late afternoon, with a vast majority of the CWA in line for a partly cloudy day with highs in the mid to upper 80s. Kluber Wednesday Night through Tuesday: A surface frontal boundary is expected to settle across downstate portions of IL and IN Wednesday night. This front is likely to remain the focal point for convective activity Wednesday night, especially south of our area. While our local weather looks rather quiet Wednesday night, conditions will remain on the warm and muggy side, with overnight lows only falling back into the mid to upper 60s. The remnants of some of Wednesday night`s convection will try to shift northeastward into parts of the area Thursday morning as a mid-level impulse tracks into the area. While a period of showers does look to be a good bet, especially for areas south of I-80 Thursday morning, poor lapse rates over our area will likely curtail the threat of thunderstorms through the morning. Following the morning activity, a low (~30%) chance for some afternoon and evening thunderstorms exists. However, with the surface frontal boundary looking to remain south of the area until later Thursday evening and night, current thinking is that there will be a good amount of dry time for any outdoor 4th of July plans. Expect temperatures during the day to be in the low to mid 80s. The next mid-level trough will shift eastward across the Upper Midwest late Thursday night into Friday morning. As it does, a surface wave of low pressure will lift northward into the western Great lakes while driving a surface cold frontal boundary eastward across our area into Friday morning. While the timing of this feature moving across our area will not be diurnally favorable, we will have increasing chances for a period of showers and thunderstorms late Thursday night into Friday morning. Some showers, and possibly a few scattered storms may also linger into Friday afternoon across far northern sections of IL into WI as the central of the upper trough shifts overhead. Slightly cooler temperatures are expected, with highs generally in the upper 70s to low 80s. The weather heading into the weekend overall does not look too bad at this time. It appears that we could have a good deal of dry time Saturday into Sunday before our chances for showers and thunderstorms begin to increase again with the approach of the next weather impulse late Sunday into Monday. Expect temperatures to be in the low 80s Saturday, and into the mid 80s for Sunday. KJB && .AVIATION /18Z TAFS THROUGH 00Z THURSDAY/... Issued at 1254 PM CDT Tue Jul 2 2024 Key Aviation Messages: - Gradual wind shift from SSE to SSW early this evening. - SHRA with possibly some embedded TS late evening and early overnight. A mid-level wave over central Kansas is expected to spread a period of SHRA and perhaps some embedded TS across the area late this evening into the early overnight hours. Confidence in occurrence and associated coverage of TS at the Chicago terminals remains low enough at this time to maintain a PROB30 mention roughly in the 06- 09Z window. However, have included a short period (02-04Z) of VCTS at RFD where elevated instability will be notably higher this evening. Isolated to widely scattered -SHRA may persist to around sunrise Wednesday ahead of an approaching cold front. A period of post- frontal MVFR ceilings will follow through late morning before ceilings SCT and lift into VFR levels through the afternoon. SE/SSE winds over 10 knots will begin to gust over 20 knots this afternoon while gradually veering SSW through this evening. Winds will begin to favor west of 180 degrees sometime in the 23-01Z window, especially with the development of a veering LLJ. Winds will further veer SW overnight and WNW behind the cold front after daybreak Wednesday. Kluber && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago