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Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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269 FXUS63 KGRR 150809 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 409 AM EDT Mon Jul 15 2024 .KEY MESSAGES... - Showers and storms move off to the east this morning - Another round of strong/severe storms this evening/tonight - Mainly dry after Tuesday && .DISCUSSION... Issued at 408 AM EDT Mon Jul 15 2024 - Showers and storms move off to the east this morning A very long lived mesoscale convective vort is moving through the forecast area this morning. This vort was formed last night in the northern plains and it reinvigorated convection yesterday evening on the Mississippi near the IA/WI line. It has not produced severe weather in our area, but it has produced flooding and a lot of lightning. We remain concerned about flooding in the Lansing metro area early this morning as the ground there has been saturated from recent rains and this activity has been producing 1-2 inch per hour rainfall rates. We do have areal Flood Advisories and Warnings that carry into the 800am to 1000am time frame. Flooding should recede fairly quickly this morning as it is more urban and small stream related. The showers and storms will likely clear to the east out of the GRR forecast towards 12z. In the wake of this activity we expect some clouds to linger much of the morning over at least half the forecast area from near and just north of I-96 southward. This will put a lid on how much heat we see today as the clouds do not clear out until towards midday. - Another round of strong/severe storms this evening/tonight The next focus is on our next round of thunderstorms which could be strong to severe. The HREF 4 hour max reflectivity which does well most of the time shows a surge of convection moving in after 800pm. It sweeps through the forecast area between 800pm and 600am. This round looks to hit many of the same areas as the current round (near and south of I-96). There is a signal for some severe weather in the same area given quite a few updraft helicity swaths moving through the area. MUCAPE values hit 2000-3000 j/kg along with 30-40 knots of deep layer shear so we will be monitoring once again for severe weather. We are in a slight risk from the SPC for the southwest half of the area (MKG to GRR to LAN) and points to the south. Can envision the slight line being bumped a bit north today, possibly up towards Alma to include points south down U.S. 127. - Mainly dry after Tuesday The front will progress south on Tuesday as an upper trough settles into the area. We have chance pops for showers in the forecast across the south on Tuesday. We may see some scattered showers on Wednesday with the upper trough, otherwise much of the rest of the week looks dry with high pressure settling in. && .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 408 AM EDT Mon Jul 15 2024 An overall fairly slack gradient is in place through Tuesday night, so wave height overall will be on the low side. The exception is the potential for a short duration burst of wind tonight associated with thunderstorms expected to sweep across Lake Michigan. Thunderstorms look likely this evening over the lake, which will likely kick up a wave field. This is one of our top problematic scenarios as the wind is short lived, but can be strong with overnight thunderstorm complexes and low level jets. We could be looking at waves that over perform into Tuesday morning. As of right now we have 2-4 footers in the forecast and we will have to see tonight what actually sweeps across the lake. Our next time frame of concern will be on Wednesday in a north flow behind a frontal passage. NAM winds look to be in the 10-20 knot range which should keep us just below advisory. The GFS however is showing more 15-25 which would push us into a Small Craft Advisory and Beach Hazards Statement. We will be watching for more consensus in speeds as this event closes in. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ DISCUSSION...Duke AVIATION...Duke MARINE...Duke