919
FXUS63 KGRR 141128
AFDGRR

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

.KEY MESSAGES...

- Hail and high winds Thursday Evening then gusty winds on Friday
  into Saturday

&&

.DISCUSSION...
Issued at 328 AM EDT Wed May 14 2025

Another day of mostly afternoon showers and thunderstorms today
as the upper low results in some diurnal enhancement of the
showers. Coastal fog is possible near Lake Michigan this afternoon
if winds come onshore.

The main forecast concern remains the severe weather potential
Thursday evening. An upper trough moves east with cyclogenesis
across the Dakotas and the sfc low deepening to near 980 mb as it
moves into Minnesota. An advancing cold/occluded front moves into
the moist and unstable air mass across Lower Michigan traversing
the forecast area roughly between 8 pm and 2 am.

Shear profiles show potential for organized severe with
sufficient mid level lapse rates for deep updrafts and low level
helicity sufficient for rotating updrafts. Main threats are large
hail, damaging downbursts and transient tornadoes. The severe
threat winds down after midnight as the deep moisture exits to the
east.

Friday should be breezy with a good amount of sunshine, though
ensemble members are far from settled whether this will be a day
with gusts around 30 mph or 40-45 mph. A shortwave trough rounding
the base of the low and a proximate cold front may touch off a
quick round of showers late Fri evening, perhaps thunderstorms in
Southern Michigan given the potential for instability rebuilding
to 500-1000 J/kg.

Saturday does have the potential to be another breezy day,
though the magnitude of peak gusts is still questionable among the
ensembles, dependent on the pressure gradient between the low over
the northern Great Lakes and the high over the SE US.

Canadian sfc high builds in early next week with potential for
scattered frost Sunday night and Monday night.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 728 AM EDT Wed May 14 2025

Areas of IFR conditions at 12z will gradually improve during the
morning to MVFR with scattered showers and isolated thunderstorms
during the afternoon into early evening.

&&

.MARINE...
Issued at 328 AM EDT Wed May 14 2025

No changes to the fog advisory, although it may need to be
extended if winds are not strong enough to disperse it this
afternoon. Dew points in the upper 50s and 60s will continue
through tonight so fog will continue, but increasing winds on
Thursday could mitigate dense fog.

Strong thunderstorms are possible THursday evening then winds
behind the storms on Friday of 20 to 25 knots will build waves
greater than 4 feet into Saturday.

&&

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

&&

$$

DISCUSSION...Ostuno
AVIATION...Ostuno
MARINE...Ostuno