National Weather Service United States Department of Commerce


606
FXUS63 KDTX 112308
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
608 PM EST Tue Feb 11 2025

.KEY MESSAGES...

- Winter Weather Advisories are in effect for the Tri-Cities area,
Shiawassee, and Livingston counties 1PM Wed to 7AM Thurs. These
areas are forecast to see 4-6" of snowfall during that timeframe
with the highest snowfall rates expected Wednesday afternoon.

- Winter Weather Advisories are in effect for Washtenaw, Wayne,
Lenawee, and Monroe counties 1PM Wed to 7AM Thurs. These areas are
expected to start as all snow with a transition to wintry mix
including freezing rain mainly south of I-94. Icing amounts between
up to 0.1" possible over these southern areas with highest totals
towards the Ohio border. 2-4" of snow also forecast.

- Winter Storm Watches remain in effect for the Thumb and remaining
I-69/M-59 counties. Snowfall amounts between 5-8" possible with
highest totals focused towards the Lake Huron shore.

- Reinforcement of below normal temperatures follows this system for
the late week period.

- Another chance for accumulating snow comes Friday night into this
weekend.

&&

.AVIATION...

There are lingering post frontal strato cu across Se Mi with bases
ranging from 2200 to 4000 feet. A veering of the low level flow to
the east tonight will limit the moisture feed off Lake Huron. This
and mid level subsidence and a corresponding lowering of the
inversion base will erode the strato cu during the course of the
evening. A subtle easterly moisture feed late Wed morning will
advect some low level moisture back into Se Mi. Confidence as to
whether this equates to a development of a low end stratus deck is
low at this time. Widespread accumulation snow will overspread Se Mi
Wednesday afternoon (18-21Z time frame) in advance of a low pressure
system. This aspect of the forecast carries high confidence.

For DTW...Lingering clouds below 5000 feet are expected to persist
this evening, possibly completely eroding during the overnight.
Accumulating snow is forecast to overspread metro Wednesday
afternoon. Chances for precipitation to change over the sleet and
freezing rain increase during the evening on Wednesday.

DTW THRESHOLD PROBABILITIES...

* Low for ceiling at or below 5000 feet today and tonight, then high
Wednesday.

* High precipitation type as all snow Wednesday afternoon. Moderate
in precipitation type as sleet and freezing rain Wednesday
evening.

&&

.PREV DISCUSSION...
Issued at 305 PM EST Tue Feb 11 2025

DISCUSSION...

Isolated light snow/flurries taper off through the remainder of the
afternoon-early evening as a weak cold front finally pushes south
and east of the area. Fropa sets up another colder night as the
region resides on the fringe of an arctic airmass centered over
northern Ontario. Lows in the teens can be expected for areas
along/south of I-69 with single digits likely for areas north.

Focus remains on the winter storm system set to arrive over SE MI
starting Wednesday afternoon. Starting off with the mixed precip
side of things, 12Z model runs have largely held with the prior
solution space consensus in a low track between Sandusky-Cleveland
placing the wintry mix-snow line over portions of eastern
Monroe/Wayne counties. There still some variability in the magnitude
of elevated warm advection wrapping around the low center with runs
such as the 12Z NAM being significantly more aggressive and pushing
freezing rain well into Detroit, and others like the 12Z RGEM
showing a weaker warm conveyor keeping mixed precip confined to NW
Ohio. Given the breadth of the both hi-res and coarser model
outcomes, confidence is increasing for at least Monroe and
southeastern Wayne to see a transition to wintry-mix/freezing rain
late Wednesday evening into the first half of the night (~00-08Z) as
the low center lifts through northern Ohio. This wintry mix/freezing
rain could extend into eastern Lenawee, southeastern Washtenaw, and
all of eastern Wayne should the stronger push of warm air develop. A
brief transition back towards snow is possible late night as colder
air pushes back in on the backedge of the low, however QPF is
quickly tapering off as this NW CAA dries the column and deformation
shifts to southern Ontario. For ice accretion over these areas,
totals between 0.02-0.1" are possible with the highest amounts in
the range focused towards eastern Monroe.

Shifting to the snow side of this system, worth starting off with
leaner QPF trends that have been consistently seen across nearly
every deterministic model and ensemble family, with the GEFS and
RGEM being the main hold outs. Total QPF has trended 0.1-0.2" lower
with the 12Z guidance compared to the prior 00Z runs resulting in a
storm total amounts between 0.25-0.5" for the majority of SE MI. The
exception to this is portions of the eastern CWA, east of I-75 and
potentially more narrowly focused east of M-24/53, where QPF amounts
up around 0.6" still look favored. These areas are positioned more
favorably to see a longer duration of moderate snowfall rates
(around 0.5"/hr) and better potential to see periods of enhanced
rates near 1"/hr as low pressure deepens while lifting into southern
Ontario Wednesday night. Lake enhancement for snow over the eastern
Thumb as still very much in play given ~25mph onshore flow.
Confidence remains high for SLR`s to hold around normal (12:1) for
the bulk of the event as soundings still advertise a deep isothermal
layer around -8C. Due to the aforementioned trends, snow totals have
been lowered to 4-6" for areas north of I-94 and west of M-24.
Wintry mix looking more likely to cut into snow totals south of I-94
where 2-4" are now forecast. For areas east of M-24, 5-8" remain
possible, particularly towards the Sanilac/St Clair Lake Huron
shore. In coordination with neighbors and with the consistent leaner
QPF, opted to flip the watch to advisories for the western/southern
counties. Will keep the watch going to those east/northeast counties
given there`s still a decent shot at reaching warning criteria
though not confident to pull the trigger yet with QPF still partly
in flux.

Broad Plains high pressure then follows for Friday bringing a brief
break from the active pattern. Said pattern then looks to make a
return Friday night through the weekend as a amplifying upper
troughing develops across the central CONUS. A lead shortwave
reaches the Great Lakes late Friday night offering a period of
widespread light snow and setting up an active baroclinic zone for
the weekend somewhere over far southern lower MI to northern OH/IN.
Area to watch then is the behavior of the main southern stream
shortwave and its associated surface low developing over ArkLaTex.
Depending where the baroclinic zone sets up and the longitudinal
component of the surface low track, there is a distinct scenario for
a long duration snowfall event for at least a portion of SE MI.

MARINE...

Light north to northeast flow persists under the guise of high
pressure. Flow will veer in anticipation of the next approaching
winter system which will strengthen the pressure gradient, bringing
breezy conditions, while producing widespread snow. Gust potential
will remain sub-gales, with sustained winds peaking over Lake Huron
around 20 knots, gusts to 25 knots, tomorrow afternoon and evening.
Will preclude any issuance of Small Craft Advisories due to ice
cover across the nearshore. Widespread snow will expand across the
Great Lakes starting tomorrow afternoon, the heaviest of which will
be found over southern Lake Huron and locations south. The path of
the low will track from the Ohio Valley into east Ontario, which
will then back wind direction to the northwest on Thursday as the
low departs. Cold air advection increases with the northwest flow,
expanding mixing depths and allowing breezy conditions to continue
into Thursday. While widespread snow will taper off on Thursday, the
boost in over lake cold air will support some lake effect snow
showers.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory from 1 PM Wednesday to 7 AM EST Thursday
for MIZ047-048-053-060-068-075-076-082-083.

Winter Storm Watch from Wednesday afternoon through Thursday
morning for MIZ049-054-055-061>063-069-070.

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

$$

AVIATION.....SC
DISCUSSION...KDK
MARINE.......AM


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