263
FXUS63 KGRR 161744
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
144 PM 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 /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 139 PM EDT Fri Aug 16 2024

Widespread MVFR and occasional IFR ceilings and visibilities from
earlier are slowly improving, with some sunshine trying to spread
into the area from the southwest. While conditions should spend
most of the afternoon VFR at most locations, showers and scattered
thunderstorms are expected to begin redeveloping by mid afternoon,
primarily affecting northern and eastern areas. A more widespread
line of storms is likely this evening - generally between 6pm and
10 pm - to move in from Lake Michigan and sweep across Lower
Michigan. Behind this line of storms, winds shift a bit to come
from a due west direction and thunderstorms taper off to hit-or-
miss showers. This showery pattern, with steadily worsening MVFR
or even IFR ceilings and visibilities overnight and continuing
throughout much of the day Saturday with only very limited
improvement expected.

&&

.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...AMD
MARINE...04