161
FXUS63 KGRR 181854
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
254 PM EDT Wed Sep 18 2024

.KEY MESSAGES...

- Warm and Dry into Tomorrow

- A Few Showers Possible Friday

- Rain Potential Remains From Sunday into Early Next Week

&&

.DISCUSSION...
Issued at 254 PM EDT Wed Sep 18 2024

- Warm and Dry into Tomorrow

Upper level ridging in place will continue dry conditions through
tomorrow night. With 925 mb temperatures around 20 and an
inversion in place temperatures are expected to fall into the
50s tonight and 50s to low 60s tomorrow night. There is a
signal for fog to develop again around daybreak along the I-94
and 127 corridors looking at soundings and HIRES guidance. Copy
and paste today for tomorrow with highs in the low to mid 80s
across the area.

- A Few Showers Possible Friday

Upper troughing will finally try to make some headway into the Great
Lakes Friday. Strong low and mid level jets over Wisconsin Thursday
will weaken as they advance eastward Friday. A weakening surface
cold front, initially helping fire some robust convection across
Wisconsin Thursday, will press east into Michigan Friday with a
dying line of showers during the morning and no instability to work
with. That said, the front is forecast to slow down and perhaps just
wash out over the region. Depending on how far it advances, there is
a chance that some surface based or at least elevated instability
(perhaps a few hundred J/kg) could develop ahead of it by late in
the day or evening, supporting a thunderstorm or two, though odds
are not great. Overall, it seems the likely evolution on Friday will
be a fading line of showers crossing the lake in the morning,
bringing a few hundredths of an inch of rain to the lakeshore, then
possibly a few additional showers / isolated storm during the
afternoon or evening mainly west of US 127, with heavy amounts not
expected.

- Rain Potential Remains From Sunday into Early Next Week

After a dry day Saturday, the upper pattern evolution Sunday into
early next week is still a bit in question, though good agreement in
the 500 mb pattern is shown between the ECE and GEFS means. An
upper low across the Desert Southwest region this weekend is
forecast to eject northeastward and potentially phase with upper
troughing across the Northern Plains and Upper Midwest Sunday. In
general, this will lead to a strengthening low level jet across the
Midwest that should finally help bring better low level moisture to
the region as PWATs increase to the 1.50"-1.75" range Sunday into
Monday (perhaps lingering into Tuesday). There may be a warm front
lifting through the area in that time frame as well. Given synoptic
scale support for precipitation, there could be periodic
thunderstorms as well if destabilization takes place. The ECE
probability for 0.50" or greater from Friday into Tuesday (bulk of
that starting Sunday) is 80% across most of the region, which is a
fairly high probability. Raising that threshold to 1.00" or greater
is showing about a 50% probability.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 114 PM EDT Wed Sep 18 2024

A similar setup for fog to impact the terminals appears in place
for early Thursday morning. Model guidance (GFS LAMP, HRRR
soundings) does suggest fog is most likely at AZO, BTL, LAN, and
JXN especially in the 09z-13z time frame. Like today and
yesterday, much of this may take until 14z-15z to totally mix out
and dissipate. The HRRR soundings show less in the way of
saturation at the surface than what occurred today, so maybe the
1/4 mile visibilities will be less commonplace.

&&

.MARINE...
Issued at 254 PM EDT Wed Sep 18 2024

Light onshore winds along the lakeshore will become more easterly
overnight and to the southeast Thursday morning. Toward the
afternoon expect winds to shift more onshore and continue the
diurnal pattern into Friday morning. Wind pick up slightly up to
15 knots Friday with the potential for showers and storms Friday
morning and afternoon. Winds and waves are expected to remain
below Small Craft Advisory thresholds into next week.

&&

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

&&

$$

DISCUSSION...Hoving/RAH
AVIATION...Hoving
MARINE...RAH