666
FXUS63 KGRR 132314
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
714 PM EDT Tue Aug 13 2024

.KEY MESSAGES...

- Fair and mild weather through Wednesday night

- Showers and storms possible Thursday through Saturday

&&

.DISCUSSION...
Issued at 319 PM EDT Tue Aug 13 2024

- Fair and mild weather through Wednesday night

We are expecting conditions to remain dry for most areas for the
entire period through Wednesday night.

There is still a small chance of a sprinkle this afternoon along the
lake breeze boundary where just enough convergence could pop a
shower. We are seeing the low level moisture from the lower levels
this morning mixing out, resulting in high cumulus bases and a good
dry sub-cloud layer.

Otherwise, upper ridging will build over the area tonight and hold
through Wednesday night when the ridge axis will be directly
overhead. This will suppress cumulus development more than the past
couple of days, along with the lower levels not seeing any kind of
noticeable moisture return.

- Showers and storms possible Thursday through Saturday

  The mild weather will come to an end as the high pressure is
shifted eastward as an deepening upper level low moves through the
upper mid west beginning Thursday. Successive waves will swing
through the region Thursday through Saturday. There is some
discrepency on timing however, there will be slightly anamolous
moisture associated with this system with PWATS in the 1.5 to 2 inch
range.  Subtropical moisture along with some mid level warm air
advection will aid in the heavy rain threat Thursday through Friday.
There still is some question on where the heaviest precipitation
will be but the heaviest looks to be through the southwest corner of
the state currently.

 While there will be a dry slot on the back side of the wave on
Friday,  the upper level low is expected to trek through lower
Michigan allowing for good vort maxes and mid level instability
Friday into Saturday. That, along with daytime heating should allow
for the potential for afternoon showers and thunderstorms Friday and
Saturday.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 703 PM EDT Tue Aug 13 2024

Diurnal cumulus in the 5-6kft range will dissapate shortly after
sunset leaving clear skies. These combined with light winds and
shallow moisture set the stage for patchy MVFR radiation fog from
7-13z. Traditional blended guidance is overdoing surface
dewpoints, and as a result is likely overdoing the extent of
overnight fog and how low visibilities get. As a result, have
moved the prevailing BR group to a TEMPO as impacts look to be on
an occasional basis instead of prevailing. Any fog that does form
dissipates quickly after 12-13z Wednesday. VFR then prevails with
only few cirrus and light winds Wednesday as high pressure sits
over the area.

&&

.MARINE...
Issued at 319 PM EDT Tue Aug 13 2024

We are looking at low impacts for both mariners and swimmers through
Wednesday. High pressure will keep the general winds under 10 knots
through Wednesday afternoon. Lake breezes are expected the rest of
today and Wednesday afternoon, which could sneak up above 10 knots a
little locally.

Winds will start to increase Wednesday night and especially on
Thursday ahead of the incoming front from the S/SE. Small Craft
Advisories and Beach Hazards are likely at that point. Winds will
become more SW-NW Friday and over the weekend, occasionally causing
hazardous conditions with winds and waves.

&&

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

&&

$$

DISCUSSION...NJJ/Ceru
AVIATION...Thomas
MARINE...NJJ