059
FXUS63 KDTX 070713
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
313 AM EDT Tue Oct 7 2025

.KEY MESSAGES...

- Turning much cooler today with areas of showers.

- Cool and dry conditions last through the end of the week.

- Frost is possible Wednesday night and Thursday night.

&&

.DISCUSSION...

Deep layer frontogenesis has held nearly stationary during the night
from Iowa/nrn Illinois into Lake Huron, which has kept the more
widespread shower/scattered thunderstorm activity generally
northwest of an Owosso to Sandusky line. Deep layer moisture
transport and isentropic ascent has been sustaining another region
of widespread showers across the Ohio Valley. Localized subsidence
between these features has in turn held most of the southern half of
the forecast area precip free through the late night hours.

A veering of the mid level flow toward the west-northwest across the
nrn Great Lakes today will help slowly drive the deep layer frontal
zone across Se Mi. System relative isentropic analyses suggests
continued frontal forcing across the northern portions of the
forecast area this morning while slowly sinking south, with continued
weak mid level instability overhead. Model solutions indicate an
increase in upper divergence within the right entrance region of an
upper jet streak this afternoon which should sustain some semblance
of deep layer frontogenesis across a good portion of Se Mi,
supporting rain chances into the afternoon over much of the area.
The instability axis is forecast to become aligned generally along or
just southeast of an Adrian to Detroit line toward early afternoon.
This is likely to coincide with the surface cold front (projected to
be over the I-69 corridor by daybreak) as it is forecast to move from
Detroit to Toledo between 16Z and 19Z. This suggest precip chances
across the far south may be more tied to convective potential along
the lower portions of the tropospheric front as opposed to the more
persistent deep layer frontal ascent farther north. Upstream
observations and model projected surface temperatures indicate
temperatures dropping into the 50s behind the cold front. Some
rebound in morning temps are possible across the northern Saginaw
Valley where late afternoon dry air advection will allow some diurnal
recovery.

More progressive flow will drive strong high pressure into the Great
Lakes region from the northwest tonight into Wednesday, downstream
of a building mid level ridge over the Upper Midwest and northern
Ontario. Northerly flow in advance of the low level anticyclone will
provide a sustained period of cold and dry air advection tonight
into Wednesday. 850mb temps are forecast to plunge to 0 to -1c
across much of Se Mi on Wednesday, limiting daytime highs to the mid
50s to low 60s. Nam soundings do indicate that a Lake Huron moisture
flux on Wednesday will result in at least an interval of strato cu,
particularly across the thumb. Shallow convective depths will hinder
any lake effect rain. The duration of cloud cover will be limited by
an aggressive push of dry air. This will open the door to clear
skies Wed night/Thurs morning, warranting lows in the 30s which will
give many areas their first frost of the season. The large high
pressure system will gradually drift east of the region by the end of
the work week, allowing a gradual moderation in temperatures under
clear skies.

&&

.MARINE...

Post frontal cold air advection today as 850 MB temps fall into the
low single numbers to near zero. A period of wind gusts up to 30
knots is expected across northern Lake Huron this evening with the
increased boundary layer before winds slowly diminish and veer north-
northeast on Wednesday as expansive high pressure arrives. Despite
winds diminishing, the northerly flow will lead to larger waves over
the southern Lake Huron basin Tuesday evening into Wednesday, with
small craft advisories needed during this time for the nearshore
waters as the cold airmass leads to unstable low level profiles
conducive to good wave growth with the long north-northeast fetch.

&&

.HYDROLOGY...

Frontal forcing has held nearly persistent across the Saginaw Valley
and northern thumb region during the overnight. Combination of radar
and a few gauge reports suggest rain totals already between a half
to three quarters of an inch, with some localized areas over an
inch. There is expected to be a little more of a southward shift in
any additional heavier rain during the day. Given the current
observational trends and recent model guidance, locations south of
the I-69 corridor will likely see rain totals range from just a
tenth to a half inch.

&&

.PREV DISCUSSION...
Issued at 1205 AM EDT Tue Oct 7 2025

AVIATION...

Showers and scattered thunderstorms expand farther across SE Mi late
tonight as a cold front moves NW to SE across the area. Coverage is
near peak in the MBS area at forecast issuance which steadily fills
in while moving toward DTW by early morning as the front moves
overhead. The system also brings solid coverage of MVFR ceiling
spreading southward with the front but also spreading in from IN/OH
northward into the DTW area which then quickly fills in toward PTK
and FNT while trending into IFR all areas. The best time window for
thunderstorms at MBS and FNT is for a few hours after midnight
followed by greater uncertainty toward the DTW corridor where storms
may not occur until early to mid morning. Ceiling is also first to
improve toward MBS mid to late morning while MVFR ceiling and post
frontal showers linger longer toward DTW, however a return to VFR is
projected at all locations by 21Z into Tuesday evening.

For DTW/D21 Convection... There is a low chance (30%) for
thunderstorms to impact the DTW airspace late tonight through mid
morning.

DTW THRESHOLD PROBABILITIES...

* High for ceiling 5000 ft or less late tonight and Tuesday
  morning.

* Low for thunderstorms late tonight and Tuesday morning between 10z
  and 14z.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Small Craft Advisory from 10 PM this evening to 10 PM EDT Wednesday
     for LHZ421-441>443.

     Small Craft Advisory from 10 PM this evening to 4 PM EDT Wednesday
     for LHZ422.

Lake St Clair...None.
Michigan waters of Lake Erie...None.
&&

$$

DISCUSSION...SC
MARINE.......SF
HYDROLOGY....SC
AVIATION.....BT


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