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Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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986 FXUS63 KGRR 150606 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 206 AM EDT Mon Jul 15 2024 .KEY MESSAGES... - Showers and Thunderstorms this evening and again Monday night - Diminishing Rain Tuesday then Cooler and Dry to End the Week && .UPDATE... Issued at 1003 PM EDT Sun Jul 14 2024 Bottom line up front: A storm system will be moving across Lake Michigan and through southern lower Michigan, mainly south of the I 96 corridor, overnight bringing a chance for large hail and damaging winds. The other concern overnight is the potential for flooding, especially in low lying regions along and adjacent to the I 94 corridor in areas that recently received heavy rainfall. A remnant MCV or, mesoscale convective vortex, is currently moving through southern Wisconsin and northern Illinois. This storm system is expected to move across Lake Michigan around midnight and then make its way across Southern Lower Michigan. While the system has shown some signs of weakening, super cells have formed with the main threat being large hail and damaging winds. While the Bulk shear is only between 35 to 40 kts, it is orientated with the bookend vortex which increases potential for updraft and mesocyclone strength which, coupled with the large CAPE values, 1500 J/KG in mixed CAPE and 1200 J/KG in DCAPE, will create an environment for severe storms. As this system has moved through WI, there have been reports of heavy rainfall with reports of 2 inch per hour rates. Considering the recent rainfall that inundated the region, flood guidance is around 1.6 inches. So flooding is a concern, especially in low lying regions and regions near bodies of water. The regions of most concern is south of I 96, especially along the I 94 corridor and along and west of US 131. && .DISCUSSION... Issued at 354 PM EDT Sun Jul 14 2024 - Showers and Thunderstorms this evening and again Monday night Chose to roughly follow the HREF forecast for POPS tonight since it seems to be a decent compromise for the wide range of solutions in the CAMs. The idea is that convection will initiate in the next few hours across Iowa and southern Wisconsin as an MCV moves through an area where the airmass fully recovered from last night`s convection. The storms move east and expand into another MCS in WNW flow with the southern half or third of the forecast area with likely POPs and some risk of severe weather, mostly downburst winds. These storms should be clearing the eastern forecast area around 06Z followed by a break in the action before the next round arrives Monday afternoon as heights being to fall and surface cold front settle south, with an MCS expected to form somewhere upstream across the Dakotas or Minnesota and dive SE into Wisconsin, northern Illinois and eventually southwest Lower Michigan. The general signal in the synoptic pattern has been there for several days, but the details on the mesoscale have been quite variable and uncertainty remains. It seems the main threat will be strong downbursts in a progressive type derecho regime with the highest chance for severe winds across the southwest forecast area, late afternoon Monday into Monday night. - Diminishing Rain Tuesday then Cooler and Dry to End the Week The cold front continues to get shoved southwards early in the day Tuesday, then shower chances diminish by the afternoon. Upper troughing moves in overhead with a weak shortwave presenting low rain chances Wednesday afternoon across north central lower Michigan. Surface high pressure builds in from the west Wednesday evening with dry weather to persist through the end of the week. Noticeably cooler conditions expected starting Tuesday following the passage of the cold front Monday. Highs near 80 Tuesday, then into the 70s through the end of the week. Dewpoints will also fall resulting in less humid conditions. Overall, expect pleasant and quiet weather with comfortable temperatures and plenty of sunshine to end the week. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 206 AM EDT Mon Jul 15 2024 A round of showers and thunderstorms is moving through the TAF sites at 06Z. Aviation conditions are a mix of VFR and IFR given the storms are not widespread. The round of showers and storms that are over the TAF sites at 06z will gradually work to the east through 12z. After about 12z, the precipitation should be moving off to the east into Southeast Lower Michigan. This will leave the TAF sites in a likely area of MVFR ceilings for much of the morning. After 18z, we should see a period of VFR through the afternoon before the next round of storms which will move in after 00z Monday evening. At this point have VCTS in the TAF for Monday evening. && .MARINE... Issued at 354 PM EDT Sun Jul 14 2024 Winds and waves will continue to stay below hazardous levels for mariners and swimmers, except for the potential for some strong thunderstorms this evening and again Monday night. THese storms could create locally higher waves and wind gusts over 35 knots. Some areas of marine fog are also possible through Monday. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ UPDATE...Ceru DISCUSSION...Ostuno/Thielke AVIATION...Duke MARINE...Ostuno