923
FXUS63 KDTX 050920
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
420 AM EST Wed Feb 5 2025

.KEY MESSAGES...

- A Winter Weather Advisory is in effect for Lenawee, Monroe,
  Washtenaw, and Wayne Counties this evening through Thursday
  morning.

- A brief period of snow occurs ahead of a rapid transition to
  longer-duration freezing rain for Metro Detroit while snow/sleet
  are more dominant north of I-96.

- Ice accumulations up to a tenth of an inch will be possible in the
  advisory. Up to an inch of snow/sleet accumulation will be
  possible across all of SE Michigan.

- Colder air returns Thursday night with gusty westerly winds, in
  excess of 30 mph at times.

- Another mixed precipitation event is possible this weekend with
  potential for accumulating snowfall and additional icing.

&&

.DISCUSSION...

Sprawling high pressure will track across the area through this
afternoon, ensuring a dry forecast for most of the daytime hours.
NBM solution remains an outlier in producing measurable QPF/snow
this afternoon/evening, likely latching onto the deformation and FGEN
that will be lifting into lower Michigan at that time. Will take a
lot to overcome the 20+ degree dewpoint depressions that forecast
soundings depict at this time though, but cannot rule out a few
flurries.

The main focus of this forecast period however is upstream where
substantial moisture transport will be occurring into the Plains
region. This moisture interacts with a rather low amplitude
shortwave to direct the next weather system into SE Michigan this
evening through Thursday morning. As advertised for the past several
days, mixed precipitation is expected during this event with light
snow and ice accumulations anticipated especially over the southern
tier of SE Michigan counties. A Winter Weather Advisory was issued
with this forecast package given the timing of the wintry mix just
prior to the morning commute.

Starting with the higher certainty items: model data is quite
consistent in bringing the shortwave to lower Michigan after 10 PM
EST, which will introduce a fleeting but sufficient deep layer of
moisture to produce QPF on the order of 0.1 to 0.15" by Thursday
morning. Peak precipitation rates are expected between 05z to 10z
(Midnight to 5 AM EST) amidst the deepest/strongest ascent (omega of
20-25 ubar/s). The highest uncertainty item is still the phase in
which this precipitation falls to the ground (snow vs sleet vs
freezing rain) and how long each of these phases lasts. There is
increasing confidence that precipitation will begin as all snow, as
the aforementioned shortwave brings a fleeting but sufficient
moisture depth into the DGZ. Forecast soundings continue to trend
colder, such that as long as ice nuclei is present favored p-type
remains either snow or sleet even as the warm nose arrives. This is
evident as the warm layer is quite shallow (around 2.0 kft deep and
Tmax of 1 C) compared to the deep cold layer (4.0 kft deep and Tmin
of nearly -7 C). These conditions will be favorable for refreezing of
likely only partially melted ice crystals, if they melt at all.
Snow/sleet accumulations will be subject to very low snow-liquid
ratios (5-7:1) and a large degree of riming, so accumulations should
hold under one inch during this phase of the event.

The transition to freezing rain is expected after the shortwave
departs and strips away ice nuclei from the column, which per model
soundings looks to occur between 07-09z (2am-4am). Overlap with the
higher rates will be minimal, but in general we still look to grind
out around about 0.01-0.02" per hour of liquid through the mid
morning hours which will be enough to produce a light coating of ice
up to a tenth of an inch. Near the Ohio border where there is a bit
more of the warm nose influence and earlier changeover potential,
localized ice accumulations up to 0.15" will be possible. The column
will gradually lose moisture depth to taper off freezing rain to more
of a freezing drizzle before temperatures rise above the 32 degree
mark by late Thursday morning. Daytime highs peak in the mid to upper
30s but drop back into the teens Thursday night as a cold front
drops through the region. This front will be associated with a deep
upper level trough carrying an impressive low level jet presence of
50-60 knots in the lowest 5.0 kft agl. Gusty westerly winds of 30 to
40 mph thus are likely Thursday evening through Friday morning.
Frequent gusts are expected to hold below advisory thresholds per
current data.

The end of the work week will be drier but cooler with temperatures
dropping a few degrees below normal (daytime highs in the mid 20s to
low 30s). The colder airmass may activate Lake Michigan
stratocumulus, but a very dry column aloft keeps conditions dry.

Finally, attention turns to potential for a strong low pressure
system to impact the Ohio Valley/Great Lakes this weekend.
Deterministic and ensemble guidance both suggest accumulating snow
will be in play with this system as well as mixed precipitation,
which is progged to have a much larger degree of synoptic support
than the system we will see tonight. There are still plenty of
scenarios that could play out regarding the track of the system
which will substantially impact precipitation amounts and
precipitation type. This will be one to monitor heading into the
weekend.

&&

.MARINE...

High pressure builds into the Great Lakes this morning, maintaining
light winds and waves through the day. A low pressure system then
tracks through the region overnight tonight through Thursday
morning, bringing light snow and a wintry mix. Strong westerly winds
are forecast to develop Thursday afternoon and evening as the
departing system ushers in an arctic air mass. A Gale Watch remains
in effect for Lake Huron Thursday afternoon through Friday morning
with peak gusts likely to reach 40 knots over parts of the lake
Thursday evening. Snow showers/squalls and freezing spray will
likely accompany the arctic air Thursday night into Friday. An area
of high pressure then briefly slides across the region early
Saturday before the next low pressure arrives Saturday night,
bringing strengthening northeast winds and another round of wintry
precip.

&&

.PREV DISCUSSION...
Issued at 1051 PM EST Tue Feb 4 2025

AVIATION...

High pressure and dry low level air will maintain light winds and
clear skies below 5000 feet through Wednesday morning. Mid and high
level clouds will however remain prevalent. An upper level frontal
boundary will support a chance of light snow late Wed afternoon.
Given the dry low levels, ceilings are likely to remain VFR with any
light snow.

For DTW...An influx of moisture and elevated warm air will support
an 70 percent chance of freezing rain and sleet in the 07Z to 12Z
Thursday time frame.

DTW THRESHOLD PROBABILITIES...

* Moderate in freezing rain overnight Wednesday into early Thursday
  morning.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory from 10 PM this evening to 9 AM EST
     Thursday for MIZ075-076-082-083.

Lake Huron...Gale Watch from Thursday afternoon through Friday morning for
     LHZ361>363-421-422-441>443-462>464.

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

$$

DISCUSSION...MV
MARINE.......TF
AVIATION.....SC


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