153
FXUS63 KGRR 251158
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
758 AM EDT Fri Jul 25 2025

.KEY MESSAGES...

- Showers and Storms Remain in the Forecast Today/Saturday

- Another Chance for Showers and Storms on Monday

- Cooling Off Mid Next Week

&&

.DISCUSSION...
Issued at 349 AM EDT Fri Jul 25 2025

- Showers and Storms Remain in the Forecast Today/Saturday

Shower and thunderstorm chances continue today through Saturday as
a surface boundary remains in the area. The front is located from
near the tip of the thumb to near Mt. Pleasant to Muskegon at
300am. The front will continue to sag southward today and become
stationary across Southern Lower Michigan this afternoon. Building
instability and convergence along the front will set the stage for
shower and thunderstorm development. SREF 3hr probabilities for
precip would indicate our best chances are along I-94 this
afternoon, especially from AZO to the east. HREF shows a bit more
of the forecast area in play today based on 4hr max reflectivity
progs...roughly from I-96 southward. Convection will likely be
pulse variety with some isolated strong winds possible as cores
crash a few hours either side of max heating.

Isolated to scattered activity is possible tonight as the boundary
remains in place. This activity may be aided by a weak low level
jet that some of the models indicate may interact with the
boundary. By morning the boundary looks to be taking on warm
frontal characteristics so given these factors at least scattered
showers and storms can be anticipated.

On Saturday, the day will likely start out with the aforementioned
showers and storms due to the nocturnal low level jet. The HREF
showers redevelopment occuring during the afternoon over much of
the area. Almost the entire forecast area looks to have chances
for showers and storms with the northwest CWA towards Ludington
having the lowest chances.

SPC has placed the area in a Marginal Risk for severe weather on
Saturday. Overall feel chances are low for severe weather today
given weak deep layer shear. Pulse severe or MCV driven activity
would be our main chance today. A little better threat exists on
Saturday as deep layer shear nudges towards 30 knots.

- Another Chance for Showers and Storms on Monday

Another chance for showers and storms exists on Monday. The ECMWF
has been consistent on bringing a shortwave trough through the
area aloft during this forecast period along with a surface cold
front. MUCAPE looks to be in excess of 2000 j/kg, however shear
looks to be more marginal at 20-25 knots. Bottom line, the deep
summer pattern continues with occasional showers and storms.

We will remain warm and humid at least into Monday. Temperatures
will likely peak on Monday when some areas will likely eclipse 90f
again.

- Cooling Off Mid Next Week

A cooling off can be expected mid next week as a large upper low
over Eastern Canada drifts southward into the Great Lakes. Our
heights will fall and 850mb temperatures cool off from about +20C
on Monday to the lower teens C by Thursday. Our forecast highs on
Thursday will be back into the 70s.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 758 AM EDT Fri Jul 25 2025

Stratus and fog are scattered across Southwest Lower Michigan at
12z. We expect these low clouds to lift rather quickly this
morning with improvement expected by 15Z. This afternoon we may
see scattered shower and thunderstorm develop again at most TAF
sites, especially between 18z and 23z. VFR weather is expected for
the most part this afternoon and evening outside of
showers/storms. Status and fog are likely again tonight after 08z
or so. Winds will be light, under 9 knots through the period.

&&

.MARINE...
Issued at 349 AM EDT Fri Jul 25 2025

Limited marine concerns today through the weekend with a light
wind regime in place. Today through Saturday a weak stationary front
will be located across the Southern Great Lakes providing a slack
gradient, followed by ridging on Sunday. Winds in BUFKIT overviews
generally look to be 10 knots or less. Correspondingly wave
heights are forecast to be 2 feet or less from today through
Sunday.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Air Quality Alert until midnight EDT tonight for MIZ037>040-
     043>046-051-052.
MARINE...None.

&&

$$

DISCUSSION...Duke
AVIATION...Duke
MARINE...Duke