042
FXUS63 KDTX 292001
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
301 PM EST Sat Nov 29 2025

.KEY MESSAGES...

- A Winter Storm Warning and Winter Weather Advisory are in effect
for widespread 5 to 8 inches of snowfall. The heaviest snowfall
rates are expected this evening.

- Below normal temperatures continue through next week. Highs in the
20s and overnight lows in the teens will be prevalent from Monday
onward.

- Light accumulating snow is forecast Monday night and Tuesday
morning with 1 to 2 inches possible for Metro Detroit and areas
south.

- Dusting of snowfall or light snow accumulation will possible late
Wednesday ahead of an approaching cold front.

&&

.DISCUSSION...

Satellite imagery and reflectivity mosaic this afternoon depicts a
low pressure system digging into portions of western Missouri with
baroclinic leafing and warm advection expanding to the north and
east into the Great Lakes region. The low pressure system is
forecasted to track from near Kansas City this afternoon through
Chicago tonight and into the Saginaw Bay vicinity by 12z Sunday.
There is high confidence that precipitation type will remain snow
throughout the event. No significant differences were observed in the
most recent model data and no changes have been made to the
headlines or forecasted snow amounts.

Gradually sloped 288-314Ks system relative isentropic ascent will
continue to overspread Southeast Michigan late this afternoon
providing for top down saturation and increase in accumulating
snowfall rates. Plan view perspective of isentropic surfaces support
a relatively diffuse frontal structure over the region with any
upright features fairly transient. Cross sections show a differing
story rather abruptly after 21-00z with an impressively deep column
UVV response emerging from coupled upper level jet dyanmics and
absolute vorticity advection. The breadth of the deep uvv response
is impressive encompassing all of the forecast area. Will also need
to watch for the arrival of the nose to the low level jet that will
clip areas south of I 69 between 01-05Z this evening. It is in this
ascending branch/eastern flank that could bring some of the highest
snowfall rates over Southeast Michigan.

Lower confidence does exist with regards to the average of the snow
to liquid ratios for this event. Keep going back to the forecast
soundings that show any great thermal frontal structure and UVVs
occurring above the Dendritic Growth Zone, above 14.0 kft agl.
Interesting that modified Cobb techniques continue to show 12:1
snow ratios will be good for much of the event. The only thought on
these higher values is that southeast flow off of Lake Erie/Lake St
Clair supports a very moist and supersaturated environment with
respect to ice especially in the lowest 5.0 kft agl. It is in this
minus 2C to minus 4C range that we could see the second dendritic
activation zone along with the potential for sticky aggregation of
flakes. Do not want to discount some higher rate potential
particularly in the 01-05z window (LLJ forcing). The last item to
ratchet up the uncertainty for SLRs is the models are adamant in
showing surface dewpoints climbing towards and reaching 32F for far
southeastern cwa after 08Z. Could be a real snow eater dewpoint that
causes a considerable amount of settling and compaction.

Good agreement and continuity amongst hires time-lagged ensemble
that much of the event will observe snowfall rates of up to 0.5 to
0.75"/hr throughout all of Southeast Michigan with the aforementioned
deep lift. Contingent on good low level jet forcing/moisture
eclipsing Southeast Michigan could see snowfall rates approach/reach
1" per hour across the south. Given the strong consensus amongst the
nwp for liquid equivalent amounts of 0.5 to 0.6 inch, total snowfall
amounts of 5 to 8 inches remains reasonable. Less warm Lake Erie
influence supports better thermal structure for accumulating across
the western counties. No changes to the headlines will be made.

Plan views of relative humidity on isentropic surfaces supports a
low level occlusion feature holding on from east to west across
portions of Metro Detroit between 09-14Z Sunday morning. A good near
surface convergence signal exists in addition to a persistence of
1000-850mb UVVs. Expectations are for snow showers to continue
within this forcing with perhaps an additional 1 or 2 inches
grinding out. The cold front is timed out after 14Z with steepening
lapse rates below 3.0 kft agl. With fresh snow, potential to limit
daytime heating and moisture downwind of the Great Lakes, LCL
heights are in question. A forecast of west to northwest wind gusts
to 30 mph is reasonable.

Strong 1000-500mb geopotential height rises and the tendency toward
increasingly anticyclonic trajectories will cause surface high
pressure to build aggressively into Southeast Michigan late Sunday
night and Monday. Downsloping component with northwest flow will be
good to break up low cloud so clearing is expected with some morning
sunshine Monday. Winterlike conditions Monday with fresh snow and
850mb temperatures of -11 to -13C. High Monday are expected to be in
the upper 20s with wind chills in the lower 20s.

A deep tropospheric trough axis and a well organized phasing of the
southern stream will bring favorable upper level jet dyanmics for
lift to the Ohio and Tennessee River Valleys beginning Monday night.
High confidence exists that greatest low deepening rates will occur
well south and east of Lower Michigan due to PV anomaly/trough axis
holding onto a late positive tilt and forward jet streak and
associated dynamics not emerging/taking on anticyclonic curvature
over the Northeast until late Tuesday. Less than 10% of 29.00z EPS
members resolved a system track through Lower Michigan. Most likely
forcing will be an area of 700-500mb system relative isentropic
ascent that is progged by the NAM to be collocated with some
midlevel frontogenesis. Uncertainty does exist with the quality of
moisture and saturation in the lowest atmosphere with control run of
the ECMWF much drier. With weak progged forcing, precipitation
potential of 60% and a snowfall accumulation of up to 2 inches is
reasonable at this time for southern portions of the forecast area.

Complex evolution of the upper level jet is expected over North
America during the middle and end of the weak period as a pseudo
split flow regime holds on to the south of the polar vorticity
reservoir. Net result is that Southeast Michigan will remain
sandwiched in an unfavorable zone for ascent Tuesday. Despite the
anticyclonic shear side of the jet axis remaining in place over the
Great Lakes through approximately Thursday, models do support some
moisture advection across the state ahead of a sharp, cold upper
level trough late Wednesday and Thursday. Light qpf amounts will
support some light snow/flurries potential.

Low confidence exists for the evolution of the upper level pattern
for next weekend as it pertains to precipitation timing. The lower
confidence stems from the questionable timing and amplitude of a
closed low that will dig through portions of California and the
Southwest at midweek. GFS is much more progressive than the
deterministic ECMWF which undoubtedly has an impact on ridging
potential over the Pacific Northwest. Higher confidence in below
normal temperatures continuing with daytime readings in the 20s next
weekend.

&&

.MARINE...

Slowly deepening (sub 1010 MB) low pressure entering western Ohio
Valley this evening, moves into southern Lower Michigan tonight.
Snow and increasing southerly winds can be expected, reaching 25 to
30 knots across most marine waters. Strong low level jet will even
support some gusts to gales over western Lake Erie, but bulk of the
stronger winds should be over the open waters as winds also veer to
the southwest toward sunrise Sunday. In addition, there will be some
precipitation drag to weaken surface wind speeds as well.
Regardless, the strong offshore flow will lead to a big water level
drop over western Lake Erie, and a low water advisory has been
issued for tonight through Sunday evening.

The low pressure center of this winter storm looks to be passing
through central Lake Huron around noon Sunday. As the low exits the
Central Great Lakes during the afternoon hours, there looks to be a
good surge of low level cold advection from northwest to southeast,
and confidence is high in a period of gales for much of Lake Huron
late Sunday afternoon into the evening. Duration will be longer over
southern Lake Huron with the longer fetch. The 12z HRRR came in
aggressive with the 10 M winds (35-40 knots), adding confidence to
add the Port Austin to Harbor Beach nearshore zone to the gale
warning. Otherwise, the other nearshore zones will also likely
experience brief gusts to gales as well. With Inner Saginaw Bay
gusting to 30+ knots on Sunday, included them in a small craft
advisory as well.

Sprawling ridge of high pressure arrives Monday morning, assuring
light winds, right into Tuesday. Next strong cold front is on track
to arrive late Wednesday. Arctic shot of cold air behind it, with
strong high pressure over the Central Plains will bring the
potential for short lived gales once again.

&&

.PREV DISCUSSION...
Issued at 1259 PM EST Sat Nov 29 2025

AVIATION...

Light intensity snow to spread across the terminal corridor within
the 19 to 21Z window with an increase in snowfall intensity this
evening into tonight. Greatest impact window to ceilings and
visibility will be during the 23Z to 05Z window where snow rates will
be the highest. Expect ceiling heights to fall mostly in the
MVFR/IFR category with brief intervals of LIFR under the more intense
bursts of snowfall. VSBYs fall below 2SM with potential for 1/2SM
under the heavy bursts of snowfall. Predominately IFR ceilings look
to prevail by 06Z tonight and through about 12Z tomorrow morning. Lighter
snowfall expected to persist until around 15Z. Winds out of the S-SE
to around 10-15 knots into tomorrow morning with a veering wind to
the W-WNW mid morning Sunday into the afternoon with gusts picking up
to 20-25 knots.

For DTW... More impactful snow expected this evening bringing
conditions MVFR to IFR in the 23Z to 05Z window. Potential exists for
LIFR conditions and visibilities AOB 1/2 SM during the peak of the
event, most likely between 01Z and 04Z this evening.

DTW THRESHOLD PROBABILITIES...

* High for ceiling at or below 5000 ft by around 20Z and through
  tonight.

* Medium for visibility at or below 1/2 SM late this evening.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Winter Storm Warning until 10 AM EST Sunday for MIZ047-048-053-060-
     068-075-082.

     Winter Weather Advisory until 10 AM EST Sunday for MIZ049-054-055-
     061>063-069-070-076-083.

Lake Huron...Gale Warning from 2 PM to 10 PM EST Sunday for LHZ362-363-441-
     462>464.

     Small Craft Advisory from 10 PM this evening to 7 AM EST Monday for
     LHZ421-442-443.

     Small Craft Advisory from 10 AM to 10 PM EST Sunday for LHZ422.

     Small Craft Advisory from 10 PM this evening to 2 PM EST Sunday for
     LHZ441.

Lake St Clair...Small Craft Advisory from 7 PM this evening to 10 PM EST Sunday for
     LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory from 7 PM this evening to 10 PM EST Sunday for
     LEZ444.

     Low Water Advisory from 3 AM to 10 PM EST Sunday for LEZ444.

&&

$$

DISCUSSION...CB
MARINE.......SF
AVIATION.....AA


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