611
FXUS63 KDTX 091345
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
845 AM EST Tue Dec 9 2025

.KEY MESSAGES...

- An active mid-week stretch begins this morning with a fresh coating
  to 1.5 inches of new snowfall, locally up to 2 inches.

- Areas of light freezing rain/drizzle on top of new snow possible
  midday as temperatures rise above freezing.

- Snowfall resumes tonight, then changes over to mostly rain for the
  majority of the region early Wednesday morning.

- A Winter Weather Advisory is now in effect tonight through
  Wednesday afternoon from M-46 north where new snowfall totals of
  3-5 inches are expected.

- Colder air returns Wednesday evening.

- Daily snow chances exist from Thursday onward.

- The next arctic airmass arrives over the weekend with potential for
  sub-zero morning wind chills.

&&

.UPDATE...

Narrow band of moderate to heavy snow is making its way across SE
Michigan with visibility readings as low as a quarter mile. The
narrow nature of the band is a product of steep mid-level lapse
rates, with 3-6km agl lapse rates of 7.8 C/km sampled by the 12z
KDTX RAOB. Indications are for most areas to see a quick burst of
snowfall rates in excess of a half inch per hour, while the
residence time of this band over any one location is limited given
its eastward propagation around 35 mph. In general a quick 0.5-1
inch is expected before the band quickly exits into Ontario between
15-16z (10a-11a local). Water vapor imagery does show a more
enhanced area of ascent that spans from nrn lower MI into the
Thumb/Saginaw Valley, but the advertised development of snow showers
behind the main line has yet to materialize. With that in mind,
thinking snow totals in the Thumb are more likely to be in the 1.0-
1.5" range with decreased confidence to reach 2". Nudged snowfall
totals down a touch in the Thumb as a result.

Dry slot is evident in both the sharp cutoff in radar returns and
satellite presentation. Latest upstream observations are not showing
a widespread freezing drizzle scenario, but have seen a few sites
come in with UP (e.g. KBTL most recently). Will maintain the
inherited patchy freezing drizzle mention.

&&

.PREV DISCUSSION...
Issued at 605 AM EST Tue Dec 9 2025

AVIATION...

A series of low pressure systems keep aviation weather active today
through mid week. A fast moving lead system brings a short period of
snow to SE Mi terminals this morning until quickly exiting eastward
early this afternoon. Upstream observations at forecast issuance
indicate a rapid reduction into IFR visibility with the band of snow
which then transitions to MVFR ceiling and patchy freezing
drizzle/mist. Borderline IFR/MVFR boundary layer visibility in the
dry slot/warm sector of the system supports maintaining a few hours
of -FZDZ until passage of the surface warm front by late afternoon.
MVFR ceiling then becomes IFR this evening as upstream clouds across
the Midwest and TN/OH valleys fill in across Lower Mi ahead of the
next stronger low pressure system. A longer period of heavier snow is
punctuated by SW wind gusting near 30 knots from late evening
through tonight. The snow becomes mixed with rain as far north as FNT
as the surface low moves about over MBS toward sunrise Wednesday.

DTW THRESHOLD PROBABILITIES...

* High for ceiling at or below 5000 ft today and tonight.

* High for initial precipitation type as snow this morning before
  transitioning to a light freezing drizzle/mist this afternoon.

PREV DISCUSSION...
Issued at 400 AM EST Tue Dec 9 2025

DISCUSSION...

A very complex and thermodynamically sensitive setup commences this
morning due to two multi-faceted wintry clippers affecting Southeast
Michigan during the next 36 hours.

The speed max tied to the first clipper system is currently digging
through Wisconsin based on GOES vapor imagery (Channel 9). Preceding
adiabatic ascent-driven snowfall has quickly filled in over
Southwest Michigan early this morning. This wave of snowfall expands
across the rest of the state (from west to east) over the next
several hours, leading to minor accumulations for the forecast area.
Latest consensus model data shows consistency in a fresh coating
south of I-94 to around 1.5 inches further north by midday. Isolated
totals up to 2 inches are possible across the northern half of the
CWA (north of M-59). This upper bound is contingent on the
appropriate balance between peak moisture advection and proximity to
the track of the VortMax. Hi-Res guidance differs from most global
solutions in handling the axis of maximum QPF (greater than 0.20
inches). Generally, the coarser models are more bullish across The
Thumb region, while the CAMs are more dispersive throughout the
northern half (to even two thirds) of Southeast Michigan. Most of
the event snowfall should occur along the front-end of the system,
between 07Z and 17Z. The bulk of the fluffy snow accumulations will
occur during a 2-4 hour period with peak rates between 0.25 and 0.50
inches per hour.

The area of lowest expected snow totals, Washtenaw, Lenawee, and
Monroe Counties, will also be the most susceptible to a period of
light freezing rain/drizzle. Drier and warmer westerly mid-level
flow (as addressed in the last several discussions) will erode ice
nuclei and frozen hydrometeor concentrations by midday. Lower column
forcing weakens by then, therefore lingering 2-3 kft stratiform
cloud depths should only be capable of inconsequential freezing
drizzle atop fresh snowpack. FRAM data is lean on ice QPF which
justifies minimal coverage of measurable ice accretions. Assuming
the southern three counties receive even just a thin coating of new
snow this morning, they should be spared from transportation
impacts, especially once 2m temperatures climb above freezing. In
the lower likelihood scenario exhibiting a lack of accumulating snow
and a slower rise in temperatures above freezing, there could be
minor travel concerns.

Given forecast totals at/below 2 inches, and negligible icing
amounts, no headlines were issued for today`s clipper. Note that
areas of light icing (up to a thin glaze) are also possible
northward, up to the I-69 corridor.

As for tonight into Wednesday, QPF has generally trended upward with
broader coverage of higher snow accumulations, attributed to a
second clipper system that follows in quick succession. Lots of
variability in modeled snow amounts relative to minute differences
in latitude before the system`s cold front clears through, roughly
between 15Z and 18Z. A preference toward snow as the dominant
precipitation type (compared to rain) is evident in the latest model
adjustments, revealing potential for the highest event totals over
the central portion of the forecast area. However, this setup is
highly sensitive to the track of the surface low and its
accompanying warm advection belt. Southwest flow tonight might allow
lows to hold above freezing along the Michigan/Ohio border. A
changeover to rain is then expected to bleed northward early
Wednesday morning after earlier re-saturation aloft degrades. As
this process unfolds heading into sunrise, locations that cling to
snow longer will see a drop in SLRs amidst 33-34F snowfall.

A Winter Weather Advisory has been issued for tonight through
Wednesday afternoon from M-46 north where new snowfall totals of 3-5
inches are expected. This grouping will be aided by the lowest
probability of a changeover to rain, prior to the passage of the
cold front and related cold advection. Although the included
counties will be offset from the QPF bullseye, the preservation of
snow throughout the second clipper event should lead to the highest
overall snowfall totals. This assumption relies on forecast
thermodynamic profiles holding relative to the positioning of the
baroclinic zone. Short-notice adjustments to headlines may be needed
later today to expand the advisory southward should the warm sector
progression underperform. Even just an hour or two of partitioning
peak QPF to snow (instead of rain) between M-59 and M-46 could lead
to a spike in snowfall totals worthy of an advisory.

Post-frontal airmass could spur a few flurries, but conditions
should largely dry out Wednesday evening with temperatures falling
back below normal into the extended forecast period. Some lake
effect snow will be possible Thursday, but low-level cyclonic flow
trajectories are not favorable for widespread lake effect for
Southeast Michigan. Still some solutions that brush a third clipper
past southern Lower on Friday, and latest NBM PoPs reflect this. The
next release of arctic air slams in Saturday with a drop-off in 850
mb temperatures and potential for sub-zero morning wind chills each
morning.

MARINE...

A warm front is lifting through the Central Great Lakes this morning
producing snow. Wind gusts look to reach at least 30 knots across
all marine waters, with brief gales even possible in the 12-15z
Tuesday time frame.  A larger and stronger low pressure system is
then on track to move through Lower Michigan Tuesday night into
Wednesday producing widespread snow and even rain over Lake St.
Clair and Lake Erie. The southwest low level jet ahead of the looks
to be very strong, and low level profiles may not warm quick enough
to stabilize the near water surface. Thus, it is looking like a
short period of gales will occur over western Lake Erie, with even
brief isolated gusts to gales over Lake St. Clair. On the flip side,
with the water temp near freezing over the nearshore waters and some
ice development, it may be just enough to limit mixing and keep
gusts to gales less than 3 hours. 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 will then support
strong northwest winds Wednesday afternoon and early Wednesday
evening. Isolated, brief gusts to gales remain likely, but the cold
advection is exhausted quickly and the pressure gradient relaxes by
Thursday morning. With the short duration and the marginal nature of
the gales, elected not to issue gale watch and small craft
advisories carry right into Wednesday night. The cold airmass (850
MB temps in the negative lower teens/around -10 C) looks to persist
to close our the work week, supporting moderate winds and scattered
snow showers.

&&

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

Lake Huron...Small Craft Advisory until 4 AM EST Thursday for LHZ421-422-441>443.

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.

&&

$$

UPDATE.......MV
AVIATION.....BT
DISCUSSION...KGK
MARINE.......SF


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