813
FXUS63 KAPX 241034
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
634 AM EDT Sun Aug 24 2025

.KEY MESSAGES...

- Showers, thunderstorms, and waterspouts...oh my!

- Chilly, fall-like weather for early this week; watching potential
for frost??

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 404 AM EDT Sun Aug 24 2025

Northwest flow overtaking the central US...thanks to upper ridge
settling back into the western/SW US, between an upper low in the
Gulf of Alaska and downstream 551dm upper low near James Bay. A lobe
of PV digging southeastward into the Upper Midwest attm, with a much
colder air mass in its wake across the central Canadian Prairies
(850mb temps at or below +4C)...though several niblets of PV hanging
around the Upper Great Lakes attm. Unusual (+2 standard deviations
from the mean) surface low over James Bay, with a cold front
stretching from here into the OH Valley, denoting the back edge of
warmer/more moist air...and some continued convective activity.
Meanwhile, scattered showers are spreading southeastward across the
Upper Midwest in the presence of aforementioned PV maxima and much
colder air aloft, sufficient to generate shallow convection.

Expect the upstream PV maxima to swing through this morning into
early afternoon, dragging a potent front through the region,
instigating an uptick in shower activity across northern Michigan
this afternoon, particularly downwind of the Great Lakes, as lake
surface temps around 20C, give or take a couple degrees, will be
sufficient to generate overlake instability with the incoming cold
air mass. As cold advection deepens the cloud layer today, expect
some thunderstorms will develop this afternoon across the area,
especially across NE Lower with the better forcing along the front.

Primary Forecast Concerns through Tonight:

Thunderstorms this afternoon... expecting cold advection in the
lower/mid levels to result in deeper convective clouds and potential
for more vigorous convection, even into the realm of ice nucleating
temps aloft...supportive of an electrical threat with the showers
this afternoon. Primary timeframe of concern will be between 15z and
00z as the trough axis sharpens up...which could lead to better
forcing for ascent right along that boundary this afternoon across
NE Lower in particular as we go deeper into the afternoon. Some of
the more aggressive guidance soundings (the ones with more distinct
cold advection aloft) suggest we could generate as much as several
hundred J/kg of surface based cape along the front (lake-based
instability notwithstanding). Do have some concerns some of the
convective activity on the Sunrise Side could get a little spicy, as
there are some signals for strong low-level CAPE that could enhance
stretching this afternoon, despite having little directional/speed
shear in the low-levels. (Waterspout potential is pretty high...do
have to think landspouts can`t be entirely out of the question...)

Any storms today could be a bit gusty, though think hail is a
greater threat (probably smaller hail, noting that there`s not
necessarily a ton of CAPE aloft in the hail growth zone...and some
soundings suggest little to none, if it doesn`t cool enough aloft).
Additionally...with pwats increasing again along the boundary
(perhaps approaching 0.8in or so), do think a few spots could see
some good soaking rains later this afternoon into tonight. Some
probabilistic guidance hints at a 50 percent shot of 6-hr rainfall
totals around an half inch this afternoon/tonight across NW Lower
within the more focused lake effect rain showers/bands we are
expecting to set up, though wind directions, for what it`s worth,
look to shift around a bit through the night, which could keep
QPF a little less focused.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Issued at 404 AM EDT Sun Aug 24 2025

Days 2-3 (Monday-Tuesday)...Behind the primary trough axis Monday
morning, expect another lobe of troughiness to drop through the
region during the afternoon, though details are a little unclear
attm on specific niblets within the broader trough axis. Either way,
think this will keep things unsettled into the start of the work
week. It should be colder on Monday as well, with the coldest temps
aloft overhead (850mb temps around 4-6C). Highs could struggle
to break 60 where clouds hang on the longest (i.e., NW flow
lake effect areas), but not impossible we start to get into
subsidence and clearing late. This will result in a chilly
night Monday night, with lows likely dropping well into the
40s, and even upper 30s across NE Lower MI, away from the better
chances for clouds. Would not be surprised to see some of the
typical interior cold spots get down into the mid 30s where it
clears out.

Ridging builds in Tuesday, with perhaps a brief reprieve from the
showery weather, though it should remain on the cool side with a
cold start likely. Attm...signals point toward the attendant surface
high remaining to our southwest as another lobe of PV starts to drop
out of Hudson Bay/central Canada...which could keep winds a little
stronger across our region for purposes of overnight lows Tuesday
night...though latest signals seem to be hinting at a weaker
pressure gradient for us attm. Think another night of lows well
into the 40s is possible, and mid to upper 30s could certainly
be achievable away from the lakes, where better radiational
cooling is likely, given a standard 20-25 degree diurnal curve
for this time of year. Think we will need to keep a close eye
on frost potential at least Tuesday night, but possibly Monday
night as well.

Days 4-7 (Wednesday-Saturday)...

Slightly warmer weather returns Wednesday beneath ridging...ahead of
another potential trough axis looking to approach the area just
beyond midweek. Still a lot of time to sort out the details, which
are a bit messy attm, but there are some signals pointing toward the
troughing trying to hang out in our region/New England going into
the end of the week. If the trough axis ends up far enough
east...certainly possible we could end up under the influence of
ridging and high pressure for the last weekend in August...but
again, this could certainly change in the coming days.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 634 AM EDT Sun Aug 24 2025

Rain showers will increase in coverage and intensity through this
morning into this afternoon as troughing slides over the region.
Mainly VFR conditions will persist through this afternoon, with the
exception of a stronger shower or storm passing over a TAF site and
temporarily dropping conditions to MVFR/IFR. While there is high
confidence in showers today, lesser confidence exists in storms
impacting particular TAF sites during a certain time -- thus, PROB30
is utilized in the TAFs to account for this potential. MVFR CIGs
look to move in late this afternoon and evening associated with
increased low-level moisture and aforementioned showers. West-
northwest winds around 10 kts will gust to around 20 kts at times
through this afternoon.

&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory from 6 AM to 8 PM EDT Monday for LHZ345.
     Small Craft Advisory from 2 AM Monday to 2 AM EDT Tuesday for
     LHZ346>348.
     Small Craft Advisory from 6 AM to 8 PM EDT Monday for LMZ341.
     Small Craft Advisory from 5 PM this afternoon to midnight EDT
     Monday night for LMZ323-342-344.
     Small Craft Advisory from 6 AM to 8 PM EDT Monday for LSZ322.
     Small Craft Advisory from 7 PM this evening to midnight EDT
     Monday night for LSZ321.

&&

$$

SHORT TERM...FEF
LONG TERM...FEF
AVIATION...DJC