Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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581 FXUS63 KLOT 030554 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 1254 AM CDT Wed Jul 3 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 /06Z TAFS THROUGH 12Z THURSDAY/... Issued at 1254 AM CDT Wed Jul 3 2024 Forecast concerns for the terminals... - Showers and occasional thunderstorms to persist through the night - Lowering ceilings overnight as showers end with MVFR conditions expected but pockets of IFR possible - Ceilings improve Wednesday morning with VFR conditions through the rest of the period An area of showers continues to pivot across northern IL this evening as a cold front progresses over northern IA towards IL and eventually IN. While there was some thunderstorms within the area of showers earlier, the waning instability this evening has allowed that threat to diminish and therefore felt confident enough to remove formal TS from the TAFs. However, there is a narrow plume of instability west-central IL that could pool ahead of the front which may allow for a brief period of more robust showers and/or thunderstorms towards daybreak. Though, confidence on this new development occurring remains too low for a formal mention at this time. Regardless, showers should gradually taper from northwest to southeast after 09z leaving dry conditions for Wednesday. Ceilings will gradually lower in the wake of the showers overnight allowing MVFR ceilings to develop over the terminals. Though, there have been some pockets of IFR and even LIFR ceilings across IA where higher moisture has been present. The general thinking is that these IFR/LIFR ceilings should lift to the MVFR category as they move into northern IL, but cannot completely rule out a brief period of IFR conditions especially at RFD. The lower ceilings are expected to persist into Wednesday morning before scattering out between 15z-16z with VFR conditions expected from that point forward. Otherwise, expect south-southwest winds tonight to gradually become westerly and eventually more northwesterly behind the front Wednesday morning. Wind speeds may remain breezy at times with any showers, but should generally remain in the 8-10 kt range through Wednesday afternoon. Yack && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago