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000
FXUS63 KGRR 240313
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1113 PM EDT Tue Apr 23 2024

.KEY MESSAGES...

- Scattered Showers and Storms This Evening

- Widespread Freezing Temperatures Wednesday Night

- Showers and Thunderstorms Over the Weekend, Warmer

&&

.UPDATE...
Issued at 926 PM EDT Tue Apr 23 2024

The frontal zone is shifting southeastward through the Kalamazoo
to Lansing region. The atmosphere has been stabilizing steadily
over the past hour and the storms have shown a weakening trend.
The storms will push through the Jackson region by about 04z with
the winds turning northerly behind it. We will continue to feature
diminishing POPs for the remainder of the night. Overnight lows in
the 30`s is supported by the latest model trends.  &&

.DISCUSSION...
Issued at 335 PM EDT Tue Apr 23 2024

- Scattered Showers and Storms This Evening

Scattered diurnal showers and storms expected this evening
underneath the cold pool and trough aloft should quickly fade
toward midnight. However a few showers could linger past midnight
in far eastern sections (Hwy 127) related to a secondary sfc
trough rotating south through ern Lwr MI.

Clearing skies follow from north to south on Wednesday as cold
dry air mass pours in, with sunny skies emerging by early
afternoon as sfc dew pts drop into the teens north and 20s south.

- Widespread Freezing Temperatures Wednesday Night

Guidance has been consistently showing high probabilities for
sub freezing temperatures early Thursday morning as sfc high
settles overhead with sfc dew pts of 15 to 20 in place. There are
some questions regarding cloud cover with the potential for
patches of mid and high level clouds floating through the
northwest flow aloft. At this time those clouds do not look too
extensive or thick and the timing is very late at night.

Coldest temps in the mid 20s per NBM are expected to be over the
nrn and ern portions of GRR CWFA with temps 29-32 anticipated
near and south/west of GRR. Will post an areawide Freeze Watch
now given the already high potential.

- Showers and Thunderstorms Over the Weekend, Warmer

Cold high pressure will bring more freezing temperatures on Friday
morning, before moving east with return flow of warmer and moister
air beginning Friday afternoon and continuing through the weekend.

THe large scale pattern features persistent western CONUS troughing
with rising heights to the east. Gulf inflow in the deep southwest
flow across the east-central U.S. should help fuel an axis of
potentially heavy rains across the greater Mississippi Valley and
occasionally into Lower Michigan as surface lows track through the
western Great Lakes.

ALthough there are the usual timing issues with individual
shortwave troughs, ensemble data indicates that the highest chances
for rain/thunder appears to be Friday night and again during Sunday
with a potential break in the rain coming early next week under
shortwave ridging.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 726 PM EDT Tue Apr 23 2024

An approaching wave of low pressure will encounter an unstable
airmass over Southwest Lower MI leading to several hours of
thunderstorm potential this evening. Around 04z the storms should
be pushing southeast of KJXN. There will be a sharp wind shift
dropping down from the north on the backside of these storms which
will impact the TAF sites. Local gusty winds and some hail will be
possible with any stronger storms. MVFR clouds will flow in behind
the system but they are predicted to break up and become scattered
closer to daybreak.

&&

.MARINE...
Issued at 335 PM EDT Tue Apr 23 2024

South-southwest winds to 30 kts will shift northerly tonight
behind a passing cold front and could even briefly flirt with
gales. Small Craft Advisory remains in effect through 8 PM
Wednesday.

Winds and waves subside quickly Wednesday night into Thursday as
surface high pressure settles in, then winds increasing out of
the southeast late Thursday night into Friday.

Southerly flow should prevail over Lk MI through most of the
upcoming weekend as a warmer/more humid air mass arrives. It`s
quite possible the southerly winds will be strong enough to
require small craft advisories, at least at times. Other marine
threats over the weekend could include occasional thunderstorms
and areas of fog as dew points above 50 arrive atop chilly water
temps in the mid 40s.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Freeze Watch from late Wednesday night through Thursday morning
     for MIZ043>046-050>052-056>059-064>067-071>074.
MARINE...Small Craft Advisory until 8 PM EDT Wednesday for LMZ844>849.

&&

$$

UPDATE...MJS
DISCUSSION...Meade/Ostuno
AVIATION...MJS
MARINE...Meade