


Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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269 FXUS63 KGRR 100744 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 344 AM EDT Thu Jul 10 2025 .KEY MESSAGES... - Increasing chance for showers/storms late tonight-Friday - Showers/storms remain likely Saturday - Dry Sunday through Tuesday; Rain chances return Wednesday && .DISCUSSION... Issued at 344 AM EDT Thu Jul 10 2025 - Increasing chance for showers/storms late tonight-Friday The area cleared out nicely in the wake of the frontal passage on Wednesday. Night time microphysics satellite imagery does indicate some fog and stratus oozing to the SW from Lake Huron/Saginaw Bay with the flow from the NE. This all should burn off/mix out well this afternoon with plenty of dry air aloft and winds becoming better mixed. There are some indications that a shower could pop up over the eastern portion of the forecast area as the flow becomes light from the WNW, and collides with a lake breeze from Lake Huron. This is low enough for our area to leave out of the forecast as a silent 10% chance. Friday remains a bit of a challenge with regards to rain chances for the area, and resulting temperatures depending on how much cloud cover/rain ends up being present. The uncertainty has existed over the last couple of days in the models and ensembles all centered on a wave shown in the models expected to move east toward the area. The Euro and it`s ensemble members had a more defined wave a couple of days ago and beyond, and have trended weaker with it and rainfall that makes it to the area. Many of the shorter term models and ensemble means have continued to show a better defined wave remaining in tact, and providing somewhat of a decent soaking with it across most of the forecast area. We tend to favor a stronger wave and better chances for rain very late tonight and the first part of Friday. This preference is based on a better defined wave/MCV that is evident on regional radar imagery over the Plains, as compared to a weaker wave that is not correctly placed by the Euro out of the gate. The interesting thing about the Euro is it does advect a decent amount of instability ahead of the weak wave. The other short term models do advect as much instability, but still bring some. Per coordination with surrounding offices, it was felt that there is definitely enough justification for higher chc pops at this point, but not go any higher than that for now. Instability is somewhat weaker, and there is a stable low level layer, so severe weather is not likely. We will continue to monitor the trends with this wave. We could see a few showers and storms persist later Friday just along and north of a boundary/warm front located just south of the area and return flow helping to advect warmer and more moist air over the sfc boundary. - Showers/storms remain likely Saturday For the most part, the uncertainty does not look at have a big effect on the forecast for Saturday. This is because we see a fairly well defined short wave come in from the NW. This wave will support a well defined cold front at the sfc. The flow out ahead of it will advect additional warm and moist air up and over the area. The best low level jet/theta e axis will move over the area by 00z Sunday, with the front just to the west. There is good agreement that MU CAPEs will soar to around 2,000+ J/kg ahead of it. This will be the result of the theta e advection, and due to a diurnal boost. The low level jet over the area close to peak heating will help with low level shear and storm organization. On the bigger scale, deep layer effective shear values are forecast to be around 25 knots or so. The degree of instability ahead of the wave and sfc front is concerning. That may compensate a little bit for the lack of strong shear to provide some stronger storms. - Dry Sunday through Tuesday; Rain chances return Wednesday The front may linger over the far SE portion of the forecast area early Sunday, before it clears out, and all of the area will then dry out. We are looking at 2-3 days of dry and warm weather with a somewhat flat upper ridge building over the area. Temps will initially cool off a little bit, but will warm through mid week. The upper ridge is expected to build east of the area by Wednesday, allowing the next wave to approach the area, and bring the next chance of rain to the state. && .AVIATION /06Z TAFS THROUGH 06Z FRIDAY/... Issued at 138 AM EDT Thu Jul 10 2025 Skies have cleared out nicely at all of the terminals. This along with light winds is setting most of the area up for a round of fog toward daybreak this morning with the moisture that is left over from the rain at most of the sites, except KMKG. Have hit the eastern sites at KLAN and KJXN the hardest as they saw the most rain most recently. We have gone down to VLIFR there, and gradually improved conditions as you head toward KMKG where they did not have much rain. Once the fog burns off, we will just see some cumulus clouds as any low level boundary layer moisture mixes up and eventually out. Winds will remain under 12 knots from mainly the west and northwest. We will see some low-mid level VFR clouds likely move in late to the western terminals. This will be associated with the next wave moving in just after the valid time of this set of forecasts. && .MARINE... Issued at 344 AM EDT Thu Jul 10 2025 The beach/marine headlines that were in effect for late yesterday were able to expire on time at 2 am this morning as winds and waves dropped off sufficiently. Right now, it looks like we may be headline free until Friday night, but we could see a need for early Friday. There is a bit of uncertainty in place with regards to an upper wave coming in early Friday. There are some indications that winds may be a bit stronger Friday, if the upper wave stays stronger as it arrives. We will watch for this potential. No matter how the Friday wave ends up, late Friday through Saturday looks like headlines will be needed as the front approaches Friday night, and moves through later Saturday. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ DISCUSSION...NJJ AVIATION...NJJ MARINE...NJJ