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Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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399 FXUS63 KGRR 140557 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 157 AM EDT Sun Jul 14 2024 .KEY MESSAGES... - Round of Thunderstorms Possible Overnight into Early Sunday - Late Sunday Storms Possible Mainly Near/South of I-96 - Strong to Severe Storm Chances Monday - Dry and Cooler End of the Week && .UPDATE... Issued at 1003 PM EDT Sat Jul 13 2024 Storms approaching the western shore of Lake Michigan will continue to work toward lower Michigan over the next few hours. A southern surge toward Milwaukee and northern Illinois starting to drive the risk for severe weather overnight a little further south. Best instability at mid lake closer to South Haven and points south and this should be where our greatest risk for any severe winds are well after midnight. Overall severe risk seems pretty low for most of west Michigan overnight. Still watching though the impact the trailing MCV in Southwest Minnesota will have on storms by Sunday morning that could lead to increased risk of heavier showers persisting over the same areas. && .DISCUSSION... Issued at 315 PM EDT Sat Jul 13 2024 - Round of Thunderstorms Possible Overnight into Early Sunday The first period of interest to watch will be late tonight into Sunday morning. While severe weather is unlikely, thunderstorms containing heavy downpours and some locally gusty winds are possible. An isolated instance of damaging wind gusts around 60 mph is possible mainly across the lakeshore counties. An MCV is moving through north central WI this afternoon. Additional scattered storms are occuring in MN. The primary feature to watch into this evening and tonight will be where the MCV goes and what, if any, additional storm development could occur along, ahead of, and/or behind this feature. The 12z CAMs depict various outcomes, with some suggesting little to no thunderstorm activity overnight into Sunday morning, but the HRRR often has a superior handle on convective mode and timing (and will also give a nod to the 00z NAM 3km, which did well with location and extent of storms in MN this morning). The MCV will head into an unstable environment in eastern WI albeit with weak deep layer shear. In Michigan, our deep layer shear looks poor even at 06z (less than 20 kts), but does bump up to around 30 kts by 12z as we do see a modest 30kt LLJ aim toward the region. Around and after 06z, the HREF 4hr max dBZ with neighborhood probability for over 40 dBZ (within 20 km of a point) tops out around 50% across the CWA, indicating that a fair amount of the membership has heavier storm activity over us but a fair amount doesn`t. Again, am leaning on the better performing guidance for this forecast period. Given the orientation of the MUCAPE gradient overnight, could envision storm activity across northeastern and east central Wisconsin moving E/SE over Lake Michigan and into west central Lower Michigan, with additional backbuilding thunderstorms possibly occurring as the LLJ feeds them. Will also be watching for MCS development likely across MN overnight that could catch up to existing activity in WI and press toward Lake Michigan, arriving mid morning Sunday. If this scenario occurs, some heavy amounts of rain with localized street/poor drainage flooding is not out of the question. While some gusty winds could occur (primarily 40-50 mph), the 24 hr HREF LPMM tells the bigger story that the late night and morning storms could easily lay down 1" or more in spots. While location and geographic coverage is tough to pin down, the favored area is the lakeshore but this does extend toward US 131 also. - Late Sunday Storms Possible Mainly Near/South of I-96 Better upper level synoptic support will be in place Sunday evening and night as an upper jet with left exit region divergence moves in. At 500 mb, another shortwave trough is shown in WI at 00z Monday and a LLJ of 35-40 kts is forecast to move over northern IN. A stationary boundary is slated to be draped over the state during this time as well. Deep layer shear around 30 kts with SBCAPE of 2500 J/kg and PWATs of 1.8"-2.0" should be supportive for thunderstorms especially toward late afternoon and evening, and given the stronger wind fields aloft there is a better risk for damaging wind gusts and hail especially from I-96 to the south. The storms will be efficient rain producers, with yet another risk for 1" or more of rain in spots. - Strong to Severe Storm Chances Monday Another hot and humid day Monday with 850mb temps at 20C and dewpoints surging into the mid 70s. A mid-level wave will push a cold front through the region Sunday afternoon to Tuesday morning while a warm front extends from MN/IA eastward towards northern IL. To our west, thunderstorm activity will start off north of the warm front and along/ahead of the cold front and will track eastwards into WI and MI. Across our area substantial instability will build to 3000+ J/kg with PWATs surging to 2+ inches ahead of the front with bulk shear to 40 to 50 knots. Much of the setup will be resultant on how prior convection evolves Saturday night and Sunday night, therefore a fair amount of uncertainty exists on where the exact corridor of thunderstorm activity will track. However, generally the most likely corridor looks to be upstream convection across MN/IA/WI propagating toward southwest Michigan during the late afternoon to evening hours. Damaging wind gusts are the primary threat. - Dry and Cooler End of the Week Upper troughing settles in over the region and cold air advection brings in more comfortable conditions. Surface high pressure will scour out any lingering moisture, so expect dewpoints back into the 50s. Plenty of sunshine into the end of the week apart from typical diurnal cumulus. High temps in the 70s starting Wednesday. && .AVIATION /06Z TAFS THROUGH 06Z MONDAY/... Issued at 157 AM EDT Sun Jul 14 2024 The incoming shower and tstm activity has been weakening but we may still have some brief MVFR/IFR vsbys in any of the heavier rain showers over the next few hours. The thunder risk looks to be restricted to areas south of I-96. After the current activity passes through/wanes, attention turns to the storms currently near MSP. These storms should be arriving in west Michigan toward daybreak and may produce IFR vsbys in heavy rainfall through Noon before diminishing/exiting this afternoon. Most of this afternoon currently looks dry/VFR however additional storms are possible after 00Z MON. Was not confident enough to include thunder in the tail end of the TAF period of Sunday evening but this is something to watch going forward. && .MARINE... Issued at 303 PM EDT Sat Jul 13 2024 Little wave action is expected for the remainder of today and tonight given light winds. However, waves do look to pick up into the 2-3 ft range Sunday as southwest winds increase to 10-20 kts. At this point it does not look like winds will be strong enough or waves high enough to reach SCA. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Air Quality Alert until midnight EDT tonight for MIZ050-056-057- 064-071. MARINE...None. && $$ UPDATE...Maczko DISCUSSION...Hoving AVIATION...Meade MARINE...Hoving