024
FXUS63 KDTX 121655
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1155 AM EST Sun Jan 12 2025

.KEY MESSAGES...

- Light snow is expected today, with minor accumulations expected.
There is a chance of freezing drizzle this evening.

- Another surge of arctic air is expected late Monday into mid week.

- Lake effect snow showers redevelop with the arctic airmass.
  Greatest coverage looking to be Monday night through daytime
  Tuesday.

&&

.UPDATE...

For this afternoon... Positive theta-e advection downstream of a
prefrontal trough will continue to fill in and produce widespread
light snow across SE MI through the early evening. Moisture content
will be relatively uniform across SE MI with enhanced mid-level
forcing aligning over the Tri-Cities and Thumb. Elevated DGZ heights
to and above 10kft with surface temperatures ranging between 28-32F
will keep snow ratios in check, around normal values of 10:1 - 12:1.
Snowfall totals around a half-inch... Up to an inch... are expected
across the Metro region. Snow total potential gradually increases
the farther north one goes, tied to the better forcing. This will
result in totals around an inch...up to two inches... across the
Tri-Cities to Thumb by late tonight.

&&

.PREV DISCUSSION...
Issued at 1145 AM EST Sun Jan 12 2025

AVIATION...

Snow showers will increase in coverage again during the afternoon as
an upper level disturbance tracks through SE lower MI. Snow will be
most concentrated from KMBS to KFNT and to a lesser degree into KPTK
but will still impact KYIP/KDTW/KDET from mid/late afternoon into
evening. IFR cigs/vsbys will be more likely KPTK north at times with
1-2" of snow possible. MVFR conditions will be the rule further to
the south where accumulations will remain under an inch. As the deep
moisture associated with the snow shifts east, there may still be a
brief period of light freezing drizzle/mist this evening although
the probability for this is shifting lower (10-15%). MVFR moisture
plume off of Lake Michigan will then set up overnight into Monday as
flow veers to the west and ushers in the next batch of arctic air.
Lake effect snow showers will become more prevalent beyond this
forecast period into Monday night.

For DTW... A period of 5000+ ft ceilings will be possible early this
afternoon before MVFR cigs return with snow showers by the middle of
the afternoon. MVFR/IFR vsbys can be expected with this activity
into early evening. Total accumulations less than an inch still most
favored outcome. Period of light freezing drizzle possible (10-15%
chance) this evening.

DTW THRESHOLD PROBABILITIES...

* Moderate for ceiling 5000 feet or less by mid afternoon, high this
  evening into the overnight, medium to high through Monday.

* High for snow as precipitation type this afternoon/evening. Low
  for patchy freezing drizzle this evening.

PREV DISCUSSION...
Issued at 315 AM EST Sun Jan 12 2025

DISCUSSION...

It will be a dry albeit cloudy start to the day as upstream
observations indicate ceilings are still quite high. A fast moving
mid level short wave will advance across Iowa this morning, before
quickly translating across Se Mi late this afternoon/evening. Mid
level positive PV advection and divergence within the left exit of a
150 kt upper jet streak will result in a period of respectable
dyanmics this afternoon.

Per model soundings, deep layer moisture will not be entirely
present through the duration of better dynamics. Deep layer system
relative ascent is shown to be relatively brief, focused during the
mid to late afternoon hours. This will be the time period when
moisture depth will be most favorable for ice nucleation and a
precip type of entirely snow. Per upstream observations, the degree
of low level moistening later this morning within low level theta e
advection may be a bit overdone on latest model solutions,
suggesting precip chances will be better after noon. Ensemble mean
QPF ranges from just under a tenth of an inch in the south to around
15 inches across the Tri Cities where moisture quality will be a
little better. Considering cloud microphysics may not entirely be
ideal for good dendrites through the afternoon, accumulations of an
inch or two north to less than an inch south remains reasonable. Low
level southerly flow will push afternoon temps into the 30s. So even
with some periods where ice nucleation may be lacking, air temps may
be warm enough to mitigate icing concerns. The passage of the mid
level moisture to the east with the departure of the short wave
around 00Z may however strip ice nuclei from the clouds. Given ample
low level moisture and good shear atop the moist layer, a chance for
some freezing drizzle during the evening hours seems warranted.

Inversion heights will lift during the day Monday as a result of
cold air advection under westerly flow. There will be limited
moisture across Se Mi. However, model soundings suggest enough
supersaturation near the dendrite layer Mon afternoon to warrant
scattered flurries and/or light snow showers. The cold air advection
(which will result in steady or slowly falling temps in the 20s) is
associated with the circulation around an upper low forecast to drop
south into Minnesota/Wisconsin on Monday. This upper low is forecast
to transition to an open wave as it crosses Lower Michigan late Mon
night/Tuesday. The resulting large scale ascent and increasing depth
of the cold air will support an increase in the response off Lake
Michigan. West-northwest flow will drive the snow showers across Se
Mi. The potential for much if any accumulations looks low due to the
very dry ambient airmass and the fact the airmass will be so cold
that the ascent will be above the dendrite layer, keep flake size
small. The passage of the wave will support a reinforcing shot of
arctic air through the mid week period. The next chance for snow
will be Wed night into Thursday with model solutions in relative
agreement in showing a short wave feature along the nose of the
upper jet supporting an increase in mid level frontal forcing across
Lower Michigan.

MARINE...

Low pressure tracks toward Lake Superior this afternoon, with
widespread snow filling in across the local waters throughout the
day. Dry air initially will limit snowfall rates, but rates pick up
this afternoon and evening and may drop visibility below 2 miles at
times. Light southerly flow persists today and tonight, but shifts
to the southwest by early Monday morning as the low`s cold front
drags across the region. Arctic air fills in behind this front,
generating over-lake instability that will be conducive for gusty
winds and lake effect snow showers Monday and Tuesday. SW winds
gusting around 25-30 knots are anticipated early week, with
funneling along/downwind of Saginaw Bay possibly producing a few
gale force gusts. Flow veers to the northwest Tuesday as the low
finally releases into Ontario and drives a secondary trough axis
down Lake Huron. A burst of heavier lake effect snow showers
accompanies this trough axis. A brief axis of high pressure builds
in on Wednesday before the active period continues to end the week.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...None.
Lake St Clair...None.
Michigan waters of Lake Erie...None.
&&

$$

UPDATE.......AM
AVIATION.....DG
DISCUSSION...SC
MARINE.......MV


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