505
FXUS63 KAPX 202000
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
400 PM EDT Fri Sep 20 2024

.KEY MESSAGES...

- Rain/thunder chances through this evening

- Rain/storms Return Sunday

&&

.SHORT TERM /THROUGH SATURDAY/...
Issued at 359 PM EDT Fri Sep 20 2024

Pattern Synopsis:

Weak troughing will continue to slide over the Great Lakes this
evening and tonight as much stronger upstream troughing pivots
across the northern Great Plains through Saturday. Meanwhile, short
wave ridging looks to work over the region to start the weekend,
providing subsidence aloft to help temporarily build surface high
pressure across the Great Lakes.

Forecast Details:

Rain/thunder chances through this evening -- Scattered showers and
isolated thunderstorms will continue to work across northern
Michigan into this evening. While coverage has diminished some over
the last 1-2 hours, additional showers/storms may still initiate
across northern lower this afternoon. With a few hundred J/kg of
MLCAPE and around 30 kts of deep layer shear in place, a strong
storm or two cannot be ruled out -- but current confidence is that
these chances are low. Chances will diminish this evening into
tonight as the weak front moves through and forcing aloft becomes
less favorable with time. Otherwise, cloud cover will begin to clear
from west to east tonight, allowing for efficient radiational
cooling with weak/calm winds in place. Rainfall today is expected to
provide sufficient moisture to help patchy/areas of fog develop
later tonight into Saturday morning. After morning fog burns off as
diurnal mixing ensues, a summer-like day is in store for Saturday
with mostly sunny skies and high temperatures in the upper 70s to
mid 80s.

&&

.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
Issued at 359 PM EDT Fri Sep 20 2024

PATTERN SYNOPSIS/FORECAST:

Finally starting to see a bit of a pattern breakdown...with largely
zonal flow across the northern tier of the US...though southern
stream troughing over southern California trying to keep the ridge
in place over the southern Plains...further aiding in zonal flow
into the Midwest. Trough axis and attendant surface occluded front
punching through the Upper Great Lakes this morning...with a decent
plume of moisture (morning sounding pwats of 1.28" (compared to
0.37" a few days ago)) stretching northward into Canada...where
southerly flow remains strong between parent PV swirly over
Manitoba...and upper level ridge centered near Hudson Bay. For a
change...with this zonal pattern, starting to see some signals of
cold advection aloft across the northern tier of the country,
especially back over the Rockies, where 120+kt upper jet diving
southeastward is aiding in development of a decent blob of PV
there.

Troughing continues to plod through the Great Lakes
today/tonight...with ridging briefly returning for Saturday.
However...aforementioned blob of PV over the Intermountain
West/Canadian Rockies is expected to trek eastward this weekend,
approaching the Great Lakes for Saturday night into Sunday. Looks
like the upper low over SoCal will eject this weekend as
well...which could lend to a SW-NE oriented boundary setting up
across the Midwest for early next week. Beyond this...increasing
uncertainty in how things play out, as guidance is still struggling
on how troughing develops/moves through the Great Lakes toward
midweek next week...though signals do point to the potential of
troughing settling into the eastern US/Upper Great Lakes in some
fashion. Assuming this idea comes to fruition...this suggests things
should begin to cool down to more seasonable levels (perhaps a bit
below normal if we were to end up with upper troughing settling
directly overhead). Stay tuned to see if this idea does develop
further in the coming days.


Primary Forecast Concerns:

Rain/storms Sunday into Sunday Night.
Cold front drops into the area starting Sunday morning. Should be
some decent forcing along this front through the day...and do think
the boundary will stall out from NE to SW over the Great
Lakes...which could allow rain to stay focused over an area for
several hours. Think it will rain, too...given that the antecedent
dry airmass we thought we had over the area has not been able to
keep rain from getting to the surface today. Radar estimates suggest
that some areas today could have seen up toward a half inch in 6hrs,
which we haven`t heard reports on yet...so might have to wait till
tomorrow morning to find out for sure how well the moisture is
getting wrung out today...given that pwats will be similar on Sunday
as they are now (1-1.5 inches)...though forcing might be a little
better, which could be more favorable for rainfall production than
today. Not a ton of instability for deep convective purposes, though
do think we should have some thunder...with deep layer shear around
30kts being on the marginal side regarding storm organization
purposes. So not impossible there could be some stronger storms
Sunday...but nothing widespread by any means. Some concern for rain
to focus over part of NE Lower near Saginaw Bay as a low/wave
tracks up the boundary...where there could be better deformation to
promote better rainfall rates. Interestingly...some of the more
typically bullish guidance really wants to bullseye some 6-hr
rainfall totals around or in excess of an inch Sunday night;
probabilistic guidance is sort of hinting at better probabilities of
this as well (30-40 percent chance of 6-hr rainfall totals of an
inch or more Sunday night)...though admittedly, I`d prefer to play
things more conservatively than the going deterministic forecast
suggests, at least at this time.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 141 PM EDT Fri Sep 20 2024

Mainly VFR conditions are expected to persist across northern
Michigan TAF sites through this evening. Showers and a few embedded
thunderstorms will continue to work across the area this afternoon
before chances wane this evening. Any heavy showers/storms that pass
over TAF sites could briefly drop VSBYs to MVFR/IFR. Otherwise,
rainfall today followed by clearing skies and weak/calm winds
tonight is expected to lead to patchy/areas of fog development
across northern Michigan tonight. Drops to IFR/LIFR VSBYs will be
possible late tonight/early Saturday morning before lifting after
sunrise.

&&

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

&&

$$

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