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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS63 KGRR 211942
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
342 PM EDT Sun Apr 21 2024

.KEY MESSAGES...

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- Frost Threat Tonight; Milder on Monday

- Rainshowers Tuesday

- Cold Air Returns Midweek

- Another Chance of Precipitation Next Weekend
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&&

.DISCUSSION...
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Issued at 340 PM EDT Sun Apr 21 2024

- Frost Threat Tonight; Milder on Monday

The frost/freeze threat the last two nights has been marginal due
to cloud cover and winds, but there`s less of each tonight so have
issued our first Frost Advisory of the season. (Minus the
northern row of the CWFA which has not yet been activated for
headline issuances.)

The sfc dew points are expected to come up somewhat once the
deeper mixing of the dry air mass ceases around sunset. Clear
skies will promote effective decoupling of the boundary layer
giving a better chance of sfc winds becoming calm for a longer
duration and over a broader area than the last couple nights.

Sub-freezing temps are certainly possible in some areas early
Monday, but feel the duration/coverage will be too limited to go
with a Freeze Warning. Coordinated headline with DTX/IWX.

Synoptic warming takes place on Monday as the current upper
trough lifts out and a brief period of shortwave ridging occurs
ahead of the next upper trough approaching from the northwest.
Elevated fire weather conditions may develop in the afternoon as
temps rise into the lower 60s inland from Lk MI and SW winds
increase to 15-25 mph. Shower risk arrives and ramps up later
Monday night from northwest to southeast as the next frontal
system approaches.

- Rainshowers Tuesday

 A large, primarily isentropic, upper level system will move through
the region Tuesday into Wednesday. There is a decent short wave
associated with this system. Latest mid range models show a decent
low level jet associated with this system, upwards of 55kts at
925mb. Latest ensemble means only give a few hundred J/kg of CAPE.
Latest runs show a dry mid level, a weak mid level inversion, and
lack of deep moisture. Given these conditions, there is only a
slight chance for thunderstorms Tuesday into wednesday.

  Otherwise, expect for periods of rain late Monday evening through
Wednesday as a cold front moves into and through the region.

- Cold Air Returns Midweek

  The brief respite of warmth will short lived and cold air behind
the before mentioned front moves into the area Wednesday night.  A
large upper level ridge building over the central Untied states will
supply dry, cold downsloping flow that will dominate the weather
pattern through mid week. 850mb temps are ranging from -4C to -7C
currently. This will drop temperatures around 10 degrees below
normal Wednesday and Thursday.   Another frost/freeze potential is
possible Wednesday and Thursday mornings, especially since the mid
to low level will be dry, there will be strong sfc high pressure and
dense cold air at the sfc. These are favorable conditions for
frost/freeze events.

- Another Chance of Precipitation Next Weekend

Warm air advection in the wake of the midweeks cold will bring
Michigan back into Spring with a low level system potentially moving
through the upper levels late next week. A decent boundary ahead of
it between that and the retreating high pressure could allow for
streaming gulf moisture into the region. There are questions on
timing  so solutions are varied. However, there remains a chance for
showers and storms next weekend.
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&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 111 PM EDT Sun Apr 21 2024

Sunny skies and gusty winds will continue today. The gusty winds
will slacken and become calm around sunset with calm winds
overnight. While there is some low level moisture that will be
present between 07Z to 13Z there shouldn`t be enough to allow for
fog. If some does develop it will be patchy and not enough to
reduce visibilities. Gusty winds from the west will develop by
late morning tomorrow.

&&

.MARINE...
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Issued at 340 PM EDT Sun Apr 21 2024

Southerly winds start to ramp up later Monday afternoon and
especially Monday night as a frontal system begins to approach
from the west. Small Craft Advisory conditions expected to develop
first north of Whitehall late Monday, then spread south over the
rest of the nearshore waters on Monday night. An Advisory will
likely need to be carried all the way through Wednesday as the
flow veers southwest Tuesday then shifts northerly behind the
front Tuesday night and Wednesday. Can`t rule out some gale force
gusts at times between Monday night and Wednesday, but confidence
too low at this time for a Gale Watch.
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&&

.GRR WATCHES/WARNINGS/ADVISORIES...
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MI...Frost Advisory from midnight tonight to 8 AM EDT Monday for
     MIZ043>046-050>052-056>059-064>067-071>074.
MARINE...None.
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&&

$$

DISCUSSION...Meade/Ceru
AVIATION...Ceru
MARINE...Meade