246
FXUS63 KGRR 140522
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
122 AM EDT Wed May 14 2025

.KEY MESSAGES...

- Scattered Showers and Storms Through Wednesday

- Severe Thunderstorms Possible Thursday Evening/Night

- Breezy Friday With Showers Friday Night into Saturday Morning

&&

.DISCUSSION...
Issued at 329 PM EDT Tue May 13 2025

- Scattered Showers and Storms Through Wednesday

Instability driven by a mid-level cold pool will bring scattered
showers and thunderstorms over the next 24-30 hours. There will be a
diurnal component to this, as is common with these events, with
better coverage in the afternoon/evening each day. There is also a
signal for greater coverage late this afternoon into the early
evening across the western half of the CWA as the advancing lake
breeze collides with easterly flow.

Little in the way of capping is present, with around 1000-1500 J/kg
MUCAPE supporting the potential for thunder this afternoon and
Wednesday. Shear is minimal, at or below 15 knots. Strong storms are
not expected, but isolated small hail or gusty winds is not
completely out of the question in a stronger updraft. The better
risk is for locally heavy rainfall as storm motions will be slow
given weak flow aloft. Precipitation winds down Wednesday Night as
the upper-low moves away.

- Severe Thunderstorms Possible Thursday Evening/Night

The potential for the most impactful weather in the current package
is Thursday evening/night. A mid-level wave in conjunction with a
cold front will initiate storms across Wisconsin Thursday afternoon.
These storms will move east reaching West Michigan sometime Thursday
evening and move across the area through late Thursday Night.

The parameter space is favorable for severe storms with our area
seeing an overlap of both good forcing and the best instability.
Over 1500 J/kg MLCAPE and over 2000 J/kg MUCAPE are possible given
dewpoints in the 60s under steeper mid-level lapse rates. Deep layer
shear around 30-40 knots will be favorable for organized storms
with ample SRH to support the potential for rotating hodographs.
Damaging winds, large hail, and tornadoes are all possible in this
environment.

However some uncertainty to the exact timing, coverage, and
intensity of storms exists. Guidance varies on when exactly storms
arrive affecting their potential strength. Also, storm mode is
uncertain. Can the storms over Wisconsin grow upscale into a QLCS
by the time they arrive? Or do they remain at least semi-discrete
supercells, the difference having implications for tornado
potential. The extent of the EML and mid-level dry air on CIN is
also a factor to monitor. Overall, while uncertainty remains as to
if and how severe weather occurs, there is the potential for a
significant severe weather episode across the region Thursday
night. People should monitor the forecast over the next few days.

- Breezy Friday With Showers Friday Night into Saturday Morning

Behind the front, gusty conditions are expected in the cold air
advection pattern. Wind gusts in excess of 30 mph are possible. A
surface trough then crosses the area later Friday through Saturday
morning with an upper-low overhead. This will likely bring at least
scattered rain showers across the area. By this weekend, highs will
fall to near 70 under the aforementioned trough.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 121 AM EDT Wed May 14 2025

IFR conditions will become widespread overnight with areas of LIFR
by daybreak. THere will be a slow improvement during the morning
to MVFR with scattered showers and isolated thunderstorms during
the afternoon into early evening.

&&

.MARINE...
Issued at 739 PM EDT Tue May 13 2025

Bottom Line Up front: A Marine dense fog advisory has been issued
for the nearshore waters of Lake Michigan.

The biggest hazard for the next 24 hours will be the formation of
dense fog overnight into tomorrow. Weak winds with a stagnant air
mass and warm cooling condensing air will allow for air over Lake
Michigan to settle allowing for dense fog to form over most of
Lake Michigan. Webcams showing fog forming offshore as of 730 PM.
This fog will thicken overnight. Weak winds will allow this fog to
persist through the morning hours. The lake breeze could bring
this fog inland during the daytime late tomorrow morning. The
dense fog will slowly lift and dissipate tomorrow though patchy
dense fog could linger into early Wednesday afternoon.

Winds and waves will remain non hazardous through the next few
days. There is some concern for lingering showers early this
evening in the nearshore waters. There will be more of a concern
Thursday evening as a line of storms could bring strong winds
followed by winds gusting over 30 knots and waves building over 4
feet on Friday and Saturday.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Dense Fog Advisory until 2 PM EDT this afternoon for LMZ844>849.

&&

$$

DISCUSSION...Thomas
AVIATION...Ostuno
MARINE...Ceru