852
FXUS63 KGRR 161513
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1113 AM EDT Fri Aug 16 2024

.KEY MESSAGES...

- Periods of Showers/Storms through Saturday

- Showers ending Sunday then fair and cool next week

&&

.UPDATE...
Issued at 1049 AM EDT Fri Aug 16 2024

The cluster of thunderstorms moving onshore near Muskegon is shown
by the latest HRRR to track eastward over the next couple of
hours. The storms are basically forming along a low level
boundary in that region which extends down into parts of Kent
County. Aloft there is some upper level divergence and instability
was advecting into the west side of the convection. We did raise
the probabilities for thunderstorms for the expected track of the
storms. Waves have increased around the convection and some values
were nearing 4 feet. Guidance suggests that they will gradually decrease
on the backside of the storms. We ensured a moderate swim risk
exists into the afternoon mainly north of Holland.

 &&

.DISCUSSION...
Issued at 322 AM EDT Fri Aug 16 2024

- Periods of Showers/Storms through Saturday

We are currently in a lull in shower activity. However, a
thunderstorm complex near Chicago is slowly moving ENE toward
Lower MI and may graze the southern cwa early this morning.
Additionally, new convective development over central Wisconsin is
moving east and if it holds together could impact the western cwa
within a few hours.

Low pressure over northwest WI is pushing an occluded front across
the eastern portion of that state and an upper low is sending
minor short waves east toward MI. As a result, mesoanalysis shows
in uptick in shear and mid level lapse rates approaching Lake MI.
We`ll likely see some storms develop by 09z. Even so, shear isn`t
all that high and so svr storms aren`t expected early this
morning, but it wouldn`t be out of the question.

By mid morning, we`ll be in another lull as the first short wave
moves east. The next short wave will approach toward 00z and so
we`ll see an uptick in showers/storms by late afternoon.
Generally, progd shear values are less than 25 kts this afternoon
and so while we`ll likely see storms from late afternoon through
this evening, we`re leaning toward them being non severe.

The next short wave to rotate through the flow will arrive
Saturday morning and we`ll see another uptick in showers/storms
then that will carry through much of the day. Once again, limited
shear will render the storms non severe.

- Showers ending Sunday then fair and cool next week

The rain should be ending by Sunday night as the upper trough axis
and surface low finally kicks out to the east. Fair weather with
below normal temperatures can be expected next week as northwest
flow regime brings in surface high pressure of Canadian origin while
the heat and humidity remains bottled up across the SW CONUS.
Overnight lows will drop into the 40s in rural areas both Monday and
Tuesday nights.

There is a slight chance of showers by the end of next week as
another upper trough approaches from the northwest, but moisture is
limited.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 728 AM EDT Fri Aug 16 2024

MVFR conditions with some patchy IFR can be expected early this
morning then clearing will move in from the west with conditions
alternating between VFR and MVFR/IFR at times in heavier showers
and thunderstorms this afternoon and evening. Southeast winds
around 10 knots will go southwest by 15Z.

&&

.MARINE...
Issued at 322 AM EDT Fri Aug 16 2024

Wind and waves will remain below advisory criteria through
Saturday as low pressure settles over the region. Isolated to
scattered thunderstorms will remain in the forecast, though, and
be a marine/beach hazard.

Waves will increase a bit by Sunday and a Small Craft Advisory may
be needed then.

&&

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

&&

$$

UPDATE...MJS
DISCUSSION...Ostuno/04
AVIATION...Ostuno
MARINE...04