870
FXUS63 KGRR 231925
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
325 PM EDT Mon Sep 23 2024

.KEY MESSAGES...

- Rain Tonight through Tuesday

- Dry and mild Wednesday into Friday

- Rain chances arrive for next weekend with uncertainty

&&

.DISCUSSION...
Issued at 325 PM EDT Mon Sep 23 2024

- Rain Tonight through Tuesday

Shortwave trough amplifies across the Great Lakes region tonight
and Tuesday with a surface low tracking across Lower Michigan.
Leading edge of steadier rain is currently across central and
southern Ill/Ind and moving northeast. Just a slightly slower
adjustment for the arrival of the rain was made in the grids with
the rain arriving just after midnight across the south and
reaching the northern zones by daybreak.

The path of the surface low suggests the better warm sector
instability should remain south and east of the forecast area on
Tuesday although there could be some embedded thunder across
roughly the southeast half of the forecast area.

The deeper moisture moves east with the steadier rain ending
during the evening. Showers and drizzle could linger past midnight
along with lake effect rain showers near Lake Michigan in
northerly flow.

- Dry and mild Wednesday into Friday

The vast majority of the rain chances with the Tuesday wave should
have moved out by Wednesday morning. An isolated shower can not be
ruled out in the morning as the upper trough axis will be swinging
through at that time. Conditions will be drying out and temperatures
will warm into the 70s.

We should then see dry and mild conditions persist through at least
Friday. We end up in a col region for this period with the low
departing to our NE, upper ridging to our NW and SE, and a low
complex to our SW. This pattern with amplified features will get
blocked up for a bit as they will all be battling each other.
It seems that the ridge to our NW will be the dominating feature for
our area. 850 mb temperatures in the low to mid teens C will support
highs well into the 70s approaching 80.

- Rain chances arrive for next weekend with uncertainty

How long the dry weather remains and when the rain starts moving in
are a bit uncertain. What looks to bring the next chance of rain in
will be what is left of the tropical system that is forecast to
develop and move through the Gulf. This system will eventually be
absorbed by the upper low complex that is forecast to dig over the
Arkansas region. How this interaction takes place, and how each
system rotates around each other is the biggest uncertainty.

There does seem to be a decent amount of agreement that the main
upper low will rotate the leftovers of the tropical system to the NW
before it can reach our area. There are many various solutions to
when the rain moves in, and even if it does. Rain chances in the
official forecast begin Friday night and continue into next Monday
with this in mind.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 133 PM EDT Mon Sep 23 2024

Stratus with origins from Lake Huron with the flow from the NE has
been over most of the terminals since this morning after clouds
had briefly cleared out. This stratus is eroding at the edges from
the North and is lifting elsewhere. We do expect conditions to
improve gradually through sunset, with the eastern sites likely
keeping the clouds in, even if they go VFR.

Overnight, clouds will thicken up again where they are able to
clear out. A few rain showers will become possible after 06-08z,
with more widespread showers moving in after that. Low clouds and
mist with also move in across the area bringing conditions down to
LIFR-VLIFR. Once these conditions move in late tonight/Tuesday
morning, it will likely stick around for the remainder of this
forecast period through 18z Tuesday.

&&

.MARINE...
Issued at 325 PM EDT Mon Sep 23 2024

Winds will be mostly northerly the next couple days and remaining
below 20 knots for the most part. There could be some choppy waves
near Big and Little Sable Points otherwise winds and waves should
not pose a hazard to small craft.

Instability over the lake on Tuesday and Tuesday night could be
favorable for waterspouts but those have not been added to the
forecast at this point.

&&

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

&&

$$

DISCUSSION...Ostuno/NJJ
AVIATION...NJJ
MARINE...Ostuno