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