Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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014 FXUS63 KLOT 100538 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 1238 AM CDT Fri May 10 2024 .KEY MESSAGES... - Period of quiet and warmer weather on Friday, followed by another chance of showers Friday night. - Periods of showers and possibly some thunderstorms early next week. && .DISCUSSION... Issued at 239 PM CDT Thu May 9 2024 Through Friday night: After our break in rainfall, our next batch of showers continues to quickly shift/develop eastward into the area early this afternoon in association with the next mid-level impulse now shifting into northwestern IL. These showers will persist across much of the area through the remainder of the afternoon before gradually tapering off from northwest to southeast across the area this evening. While the thunder threat with this activity will remain low, we cannot rule out a few storms across our far southern counties in central IL and IN late this afternoon. Either way, no severe weather is expected. Drier weather is expected during the day Friday as we await our next weather maker shifting southward across the Upper Midwest. Partly cloudy/sunny afternoon skies will allow inland temperatures to rebound back into the mid to upper 60s. However, conditions look to become favorable to allow an afternoon lake breeze to develop along the northeastern IL shores. While the lake breeze may not move more than 10 to 15 miles inland prior to sunset, onshore easterly winds will keep conditions a few degrees cooler along the lakeshore Friday afternoon. Our next chance of rain will come Friday night as the next fast moving and compact impulse digs southeastward across the western Great Lakes. This looks to be a quick hit (2 to 4 hours) of mainly some showery activity with an approaching surface cold front, though steepening lapse rates could also support a couple of embedded thunderstorms. The quick movement of the precipitation should keep total amounts rather low, so we really do not look to have any major hydro threats with this activity. KJB Saturday through Thursday: The rain chances forecast for Friday night will clear the area by daybreak Saturday. Surface high pressure building in from the south and steady height rises aloft will then bring pleasant Spring conditions to the area for the weekend. Temperatures will be rather seasonable on Saturday with highs forecast in the middle and upper 60s, lower 60s closer to the lakeshore. A tight pressure gradient behind the departing storm system will bring breezy NW winds to the area on Saturday. As the surface high moves across the Tennessee Valley Saturday night into Sunday, the mild return flow will pull highs into the middle and upper 70s to close out the weekend, again with a hefty breeze expected during the day. An upper trough looks to move across the central Plains and lower Midwest Monday into Tuesday. The surface response will be a low pressure center that medium-range guidance can agree will pass to our south. Nonetheless, broad upper forcing in a moisture-rich profile will lead to rain chances across our domain early next week along the storm`s northern flank. An ample amount of MUCAPE north of the low could bring us some elevated thunderstorms as well, although heavy rain may be the most appreciable concern. This wave will hang out in the region through Tuesday with another wave moving in right behind for midweek ushering in what could be a somewhat active week ahead with lots of room for rain chances. Luckily, nothing overly impactful appears on the scope through the middle of next week. Doom && .AVIATION /06Z TAFS THROUGH 12Z SATURDAY/... Issued at 1238 AM CDT Fri May 10 2024 Aviation Key Messages: * Light northwesterly winds (around 5kt) this morning will back westerly and increase in magnitude (to 10-12kt) this afternoon. * VFR clouds based near 10kft this morning will transition to VFR cumulus based near 5kft early this afternoon. * A band of showers with northwesterly wind gusts as high as 30kt will swing through the terminals this evening (generally between 03-06Z). Discussion: The "widening" of the surface pressure gradient across the western Great Lakes along far eastern influence of a surface high diving into the Plains will allow for northwesterly winds at press time to continue backing westerly by early afternoon. Sustained speeds of 10-12kt this afternoon may be accompanied by a few gusts of 15-20 kt, though opted to withhold mention of gusts for brevity and the expectation for limited impacts to aviators. Broken mid-level clouds based near 10kft between two upper- level troughs early this morning should scatter by mid-morning, setting the stage for the development of a healthy cumulus field based near 5kft this afternoon. With forecast soundings showing appreciable depth and instability within the cumulus layer, a stray shower or two cannot be ruled out particularly between 20 and 00Z. For now, will withhold any formal mention of showers this afternoon in the outgoing TAF package given the expectation for a relatively limited coverage (not to mention the probability of occurrence being less than 20%). A vigorous upper-level shortwave and associated cold front will race southeastward across the Great Lakes this evening accompanied by a strongly forced band of showers. Chances for thunder appear to be less than 10% at the terminals owing to a loss of diurnal instability, though thunder may be observed earlier in the day further to the north in Wisconsin. With a pocket of dry air expected to be in place beneath cloud bases this evening, the band of showers may produce gusty northwesterly winds perhaps as high as 30 to 35 kt in spite of the development of a shallow near-surface stable layer. For this reason, opted to introduce targeted TEMPO groups for showers with northwesterly wind gusts to 30 kt at all terminals generally between 03-06Z (except GYY, as the showers are expected to arrive right 06Z). A few showers may continue behind the front as mid-level lapse rates steepen within the core of the passing upper-level wave. Borchardt && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...Small Craft Advisory until 3 AM CDT early this morning for the IL and IN nearshore waters. && $$ Visit us at weather.gov/chicago