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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS63 KGRR 211126
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
726 AM EDT Sun Apr 21 2024

.KEY MESSAGES...

- Elevated Fire Danger Today, Cold Tonight

- More Rounds of Frost/Freeze Risk Midweek

- Typical Unsettled Spring Weather This Week

&&

.DISCUSSION...
Issued at 334 AM EDT Sun Apr 21 2024

- Elevated Fire Danger Today, Cold Tonight

As expected, frost and freeze issues tonight are low due to the
stratus deck in place across lower Michigan. Have seen a few sites
briefly dip below freezing during breaks in the clouds but the time
frame for any one site is short.

Clouds exit with the departure of the low level moisture field this
morning resulting in a breezy day with plenty of sunshine. These
breezy conditions with gusts to 30 mph and clear skies will promote
strong mixing allowing afternoon RH values to fall into the 25-30
percent range, especially east of US131. These combine to create an
elevated fire danger across much of the area with conditions
approaching red flag warning criteria, especially across Mid-
Michigan. Highs today will be in the low to mid 50s.

Temperatures fall back into the upper 20s to 30s tonight as winds
die off and few clouds expected. Given marginal temperatures for
frost/freeze criteria and dry conditions hampering frost potential,
will not be issuing any sort of headline with this package. Will
defer to the subsequent shift for headline decisions.

Monday then continues to warm with highs in the 60s as the thermal
trough across the area exits to the east. Clouds increase ahead of
our next system but mostly sunny skies still generally expected.

- More Rounds of Frost/Freeze Risk Midweek

After a few warmer nights, a reinforcing shot of cold air descends
on Lower Michigan for the middle of the week. Many growers in our
area will be watching with concern as temperatures look like they
will drop into the upper 20s in some of the areas with the most
sensitive fruit tree conditions. Tuesday and Wednesday nights will
be the area of concern, but Wednesday Night will probably end up
being the coldest, as the surface ridge axis moves overhead and
winds in the column drop to near-zero. The cloud forecast will need
to be watched closely as any low clouds that form will keep things
warmer, but at this point that is looking unlikely, so favorable
radiational cooling conditions are expected.

- Typical Unsettled Spring Weather This Week

Overall the weather pattern this week will be a typical spring
rollercoaster. A northern stream wave will briefly pull up some
warmer air with marginal (<500 j/kg) instability Monday night and
Tuesday, producing some rain and maybe a few rumbles of thunder. A
cold front then drives through Tuesday night setting the stage for
the chilly midweek weather. The rollercoaster continues late in the
week as an upper wave ejects from the four corners region of the
Southwest and moves toward the Minnesota/Wisconsin area - driving
another airmass replacement into our area as warm and moist air
rushes northward. This airmass will be warm enough that we could see
temperatures approach 70 even under cloudy conditions. Depending on
the diurnal timing of any embedded shortwaves, as well as any breaks
in the clouds, we will likely be looking at thunderstorm risks as
all of Lower Michigan comes firmly under the influence of deep
southwesterly flow by Saturday. Currently models are keeping
instability around/less than 1000 j/kg, but the specific details
will matter for any severe weather risks, and these will clarify as
we get closer in time.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
-- Changed Discussion --
Issued at 727 AM EDT Sun Apr 21 2024

The back edge of the low clouds currently stretches from Kalamazoo
to near Lansing as of 7AM, with clearing skies already being
observed in Grand Rapids and Muskegon. This clearing will continue
southeast and overtake the other TAF sites within an hour or so.
Expectations continue for plenty of sunshine today - resulting in
VFR conditions everywhere. Gusty winds from the west will develop
by late morning and continue through the early evening hours,
before winds calm again and set the stage for another chilly
spring night.
-- End Changed Discussion --

&&

.MARINE...
Issued at 334 AM EDT Sun Apr 21 2024

Winds and waves remain below levels hazardous to small craft today
with 10-15 knot winds and 2-4 foot waves expected. A small craft
advisory will likely be needed from later in the day on Monday
through Wednesday as winds ramp up ahead of our next system.
Initially strong south to southwest winds ramp up ahead of a cold
front with strong northerly winds behind it. Guidance suggests that
gales are not off the table, but chances are low at present (20-30
percent). We will continue to monitor.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.

&&

$$

DISCUSSION...AMD/Thomas
AVIATION...AMD
MARINE...Thomas