171
FXUS63 KGRR 131912
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
312 PM EDT Wed Aug 13 2025

.KEY MESSAGES...

- Dry And Comfortable Through Thursday

- Warming This Weekend With Several Chances of Showers/Storms

- Cooler Temps Return Early next Week With Rain Chances Continuing

&&

.DISCUSSION...
Issued at 310 PM EDT Wed Aug 13 2025

- Dry And Comfortable Through Thursday

The cold front is well clear of the area at this point with
plenty of cumulus development areawide. The post frontal airmass
is notably drier than the one we were in overnight last night.
However cannot rule out patchy fog near I94 (especially Battle
Creek and Kalamazoo areas) due to soil moisture being very high
from yesterday`s rain.

Tomorrow will be similar to today featuring daytime cumulus
development and dewpoints in the upper 50s to lower 60s. Combined
with highs in the low to mid 80s it will be a pleasant day Thursday.

- Warming This Weekend With Several Chances of Showers/Storms

The arrival of large scale ridging to end the week will mark a
notable warmup as 850 mb temps climb to the low 20s Celsius. This
will translate into surface highs in the upper 80s to 90s, with
dewpoints back into the 70s bringing the familiar mugginess back.

A cold frontal boundary will drift south through the weekend
bringing chances of showers and storms through the region. Ridging
will limit upper-level support though some ridge riding shortwaves
will assist in convective development Initially, a mid-level wave
will ignite storms across the lake, with storms favored to ride the
nose of the low-level jet into northern lower. The best chance for
these storms reaching our forecast area is near and north of US10.
As this front drifts south into Sunday, shower and thunderstorm
chances will expand into Central and Southern Michigan. The moisture
and hot weather will support ample instability, however dynamics are
poor with wind shear lacking as a result favoring convection remain
unorganized.

- Cooler Temps Return Early next Week With Rain Chances Continuing

The arrival of troughing early next week will mark a return to more
comfortable temperatures like we are seeing now. While the overall
ensemble means depict this troughing, cluster analysis shows that
uncertainty as to the extent (which would also affect frontal
placement) has some remaining spread. This would affect how much we
get to cool off. The aforementioned frontal boundary looks to stall
south of us which warrants some shower and thunderstorm chances for
this period, however confidence is low given the extended range. As
noted the frontal placement remains uncertain at this range, which
will become clearer with time.


&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 138 PM EDT Wed Aug 13 2025

Low clouds have taken longer to mix out/dissipate today than
expected, with MVFR cigs holding on at several sites. However,
satellite trends are favorable, and we should finally scatter out
within an hour or so (around 19z) at the remaining sites.
Generally light northwest winds diminish around sunset and shift
around to the north overnight. Winds in the boundary layer look
light enough that we will probably see some hints of low clouds
develop again after midnight, especially along the I-94 corridor
locations where heavier rain yesterday is keeping things very
moist in the lowest levels of the atmosphere. This won`t be a
repeat of this past night, though, and any MVFR-type cigs that may
develop should burn off quickly tomorrow morning.

&&

.MARINE...
Issued at 310 PM EDT Wed Aug 13 2025

Northwest winds in the 15-20 knot range will peak in intensity late
this afternoon before weakening and shifting around to the north
overnight and then offshore/northeast tomorrow. There remains a
window this afternoon for some 3-4 foot waves in our southern
coastal areas, with will likely produce a brief period of moderate
swim risk. Otherwise, the wind field remains fairly weak through the
end of the week before gusty southerly winds on Saturday start to
build waves again and may approach hazardous small craft
conditions.

&&

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

&&

$$

DISCUSSION...Thomas
AVIATION...AMD
MARINE...AMD