Expert Forecast Opinion

717
FXUS63 KDTX 092349
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
649 PM EST Tue Dec 9 2025

.KEY MESSAGES...

- A Winter Weather Advisory is now in effect tonight through Wednesday
afternoon north of M-46. Snowfall totals of 3 to 6 inches are
expected.

- Areas south of M-59 will see a changeover to rain Wednesday
morning that keeps snowfall totals in the 1 to 4 inch range.

- Snow tapers off Wednesday afternoon with temperatures dropping
into the teens Thursday morning.

- Active pattern continues late this week-weekend with potential for
additional round of light accumulating snow and sub-zero morning
wind chills.

&&

.AVIATION...

Widespread MVFR ceilings with pockets of IFR exist ahead of a winter
system arriving later this evening. Snow is expected to pick up
around 03Z or shortly after with a potential for heavy snow in the
05Z to 09Z resulting in widespread IFR to LIFR conditions. P-type
starts as snow for all terminals with an expectation across PTK and
the southern Detroit terminals for a transition to wet snow/rain mix
around 09Z. IFR to LIFR conditions hold through tomorrow morning and
possibly into early afternoon. A cold front will pass through
tomorrow bringing increasing southwest wind late tonight and then a
post frontal gusty northwest wind by early afternoon. Northwest gusts
may reach 30 knots at times. The front will also bring a changeover
back to snow showers by around 13Z with any light snow showers or
flurries tapering off through tomorrow afternoon.

For DTW...Higher snowfall rates with LIFR conditions remain favored
between 04Z and 09z tonight before transition to wet snow/rain mix
by around 09Z. Transition still carries some uncertainty if colder
temperatures prevail. Snow showers then become favored after 13z
with decreasing precipitation trend through the late morning and
afternoon. A wind shift to NW is currently expected between 17 and
19Z Wednesday with gusts up to 30 knots at times.

DTW THRESHOLD PROBABILITIES...

* High for ceiling at or below 5000 ft through the forecast period.

* High for precipitation type as snow this evening and overnight.
Medium for a transition to rain or rain/snow early tomorrow
morning, then high for a transition back to snow after 12Z
tomorrow morning.

* Low for ceiling/visibility at or below 200 ft / 1/2 mile overnight.

&&

.PREV DISCUSSION...
Issued at 411 PM EST Tue Dec 9 2025

DISCUSSION...

Aside from some lingering snow showers/freezing drizzle across the
north, main forecast update this afternoon was the southward
expansion of the Winter Weather Advisory down to the I-69 corridor.
The 12z model suite showed a notable southward shift in the surface
low track, especially in the hi-res data, with the low pressure
center shifting as far as 200 miles south compared to previous
cycles. This draws the freezing line down toward the I-69/M-59
corridors, allowing a longer duration of snow with lower chances of
rain mixing in across the Saginaw Valley/Thumb region. Details
discussed below:

1. Areas along/north of the M-46 corridor: A Winter Weather Advisory
remains in effect, with snowfall forecasts trending up. With the
track of the surface low now projected to be along/just south of
this corridor, it is positioned favorably in the northern quadrants
of the low to see all snow for a longer duration. Further, there is
banding potential given the strong convergence signature along the
warm front and steep mid-level lapse rates (3-6km AGL lapse rates
over 7 C/km) that would act to constrict and strengthen the frontal
circulation. Peak snowfall rates of an inch per hour are possible,
primarily between midnight to 6am, with snowfall totals of 3 to 6
inches likely. If banding does develop, we will come close to the
6"/9 hr Warning threshold (e.g. 12z.HRRR solution). A short-fused
upgrade to a warning may be needed as observations warrant,
especially given that these areas have fallen short of forecast
highs this afternoon (still in the upper 20s vs low 30s forecast).

2. I-69/M-59 corridor: The Winter Weather Advisory has been expanded
to include counties along the I-69 corridor (including cities of Owosso,
Flint, Lapeer, Port Huron). Southern shift of the freezing line
supports a longer duration snow with wet bulb zero heights holding
aob 2 kft for the majority of the precipitation event. A brief
transition to rain is possible, timed around the morning commute,
before changing back to snow mid-day as the system moves into Ontario
and its cold front settles through the cwa. Rates in excess of a
half inch per hour will be plausible, with a high liquid content to
the snow (wet snow) as temperatures are near the freezing mark (31-
33 degrees likely). The slight elevation difference of the Irish
Hills may warrant additional southward expansion to the advisory into
Oakland County, where projected snowfall totals are in the 2-4 inch
range.

3. South of M-59 to the Ohio border: no headlines are in effect as
there is still confidence in a transition from snow to rain early
Wednesday morning. This cuts down on snowfall totals toward 1-2",
and will help limit impacts as the changeover is anticipated prior
to the morning commute. The period of snow p-type still could
see rates of a half inch per hour to result in quick accumulations,
although with a melting/compaction component given the warm temps. A
lull in precip is expected in the warm sector Wednesday morning as
temperatures climb into the mid-30s before falling in the afternoon
as the low drags its cold front through Lower Michigan. This will
support a changeover back to snow as the system`s cold front settles
through Lower Michigan, with an additional dusting of snow possible
Wed afternoon.

Synoptic precipitation tapers off Wednesday afternoon as the low
pushes further into Ontario, leaving northwest flow in its wake that
becomes breezy (30-35 mph gusts). Robust mid-level dry slot strips
most of the moisture from the DGZ to prevent lake effect activity
from surviving this far away from the lakes Wed evening. The one
exception will be near the Lake Huron shoreline where lake effect
snow showers may linger through the evening. Temperatures fall below
freezing by early evening and continue to plummet into the teens by
Thursday morning as the thermal trough clips across Ontario. Any
residual water (storm total liquid of 0.4-0.6 for reference) will
freeze given these temperatures. Wind chills in the single digits are
expected Thursday morning.

Quieter conditions are in store Thursday as high pressure builds
briefly into the Ohio Valley, but the broad longwave troughing
pattern remains a favorable storm track for additional clipper
systems and arctic air late week-this weekend. Additional snowfall
accumulations and sub-zero wind chills are the main concern.

MARINE...

Strong southerly winds of 20 to 30 knots this afternoon over the
Central Great Lakes. Isolated/stray gusts of 32-35 knots
even reported by a couple ships over Lake Huron. A surface trough
tracking through will allow for winds to diminish and veer to the
southwest-west this evening, as milder air also streams in.

A larger and stronger low pressure system remains on track to move
through Lower Michigan tonight into Wednesday, producing
widespread snow and even rain over Lake St. Clair and Lake Erie. The
southwest low level jet ahead of the low looks to be very strong
(40+ at 925 MB/50+ knots at 850 MB) toward the southern Michigan
border. Still a very difficult call on the near lake surface
stability over over the nearshore waters of western Lake Erie, as
peak south-southwest winds look to be around 12z Wednesday. With the
water temp near freezing over the nearshore waters and surface dew
pts rising into the low to mid 30s, anticipate just enough limited
mixing to keep gusts to gales less than 3 hours, as winds also look
to be more southwest/offshore. As usual with offshore flow nearing
gales, there will be heighten concern for low water conditions
across the western basin of Lake Erie.

Rush of cold air behind the passage of the low in the afternoon
will then support strong northerly winds Wednesday afternoon and
early Wednesday evening. There is now another model support to
expected frequent gusts to marginal gales over most of southern Lake
Huron, and will go ahead with a gale warning. 850 MB temps lowering
to -16 C over northern Lake Huron will promote deep mixing and lake
induced troughing, which should keep gusts to gales going over the
open waters of Lake Huron, at least through midnight, before winds
gradually diminish through the rest of the night into Thursday
morning. However, a 500 MB low tracking south along the
Ontario/Quebec border will re-enforce the cold air, and should
maintain sufficient mixing/gradient over Lake Huron to support gusts
in the 25 to 30 knot range out of the northwest during Thursday.
Surface ridge building in for Thursday evening/night will lead to
much lighter winds, which should linger into Friday as a wave of low
pressure track through the Ohio Valley. None-the-less, an
Arctic front is on track to move through Friday night, with
sporadic gusts to gales possible over Lake Huron during the weekend
as 850 MB temps plummet to -20 C, supporting snow squalls and
freezing spray as well.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory from 10 PM this evening to 4 PM EST
Wednesday for MIZ047>049-053>055-060>063.

Lake Huron...Small Craft Advisory until 4 AM EST Thursday for LHZ422-443.

Gale Warning from 11 AM Wednesday to 3 AM EST Thursday for LHZ363-
462>464.

Gale Warning from 11 AM to 11 PM EST Wednesday for LHZ421-441-442.

Lake St Clair...Small Craft Advisory until 4 AM EST Thursday for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 4 AM EST Thursday for LEZ444.

&&

$$

AVIATION.....AA
DISCUSSION...MV
MARINE.......SF


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