Expert Forecast Opinion

649
FXUS63 KDTX 231203
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
703 AM EST Thu Jan 23 2025

.KEY MESSAGES...

- Light snow continues through the morning. Expected totals to range
from a half-inch up to two inches across SE MI.

- A cold front brings a brief return of arctic air with highs
tomorrow around 20 degrees. Wind chills near zero Friday and
Saturday morning.

- Renewed lake effect snow showers possible this afternoon and
evening.

- A gradual warming trend begins this weekend.

&&

.AVIATION...

Low pressure entering northern Lake Huron pulls a cold front across
Lower Mi today passing MBS toward late morning and DTW early
afternoon. MVFR ceiling is in place ahead of the front and is
expected for a few hours post front while the associated pattern of
snow evolves from IFR to MVFR and then becomes scattered snow
showers. The inbound air mass is cold enough to reactivate lake
effect with cloud layer wind NW enough to keep snow showers west of
the terminal corridor. Wind trends back westward tonight which
guides the MVFR plume off Lake Michigan toward the PTK to DTW
corridor late tonight into Friday morning.

For DTW... Greater coverage of IFR snow shifts east of the terminal
during early morning followed by pockets of MVFR until passage of
the cold front during early afternoon. Scattered snow showers follow
into early evening.

DTW THRESHOLD PROBABILITIES...

* High for ceiling 5000 ft or less today and tonight.

&&

.PREV DISCUSSION...
Issued at 339 AM EST Thu Jan 23 2025

DISCUSSION...

Moist system relative isentropic ascent through h750 has maintained
widespread, light snow across SE MI. Light snow will continue
through the morning hours, but the already light snowfall rates will
decrease leading into the late morning ahead of the arrival of a
cold front as the better upslope flow wanes. A lull in snow
production is making its way through the I-94 corridor, but
progression of the cold front, which will traverse from northwest to
southeast between 13Z-19Z, can help reinvigorate snow later this
morning until passage of the front. Snow totals look largely on track
given overnight observations and model output -- Generally 1-2
inches through the Irish hills into the Thumb and Flint to Tri-
Cities, with the higher amounts favored within the Thumb. Weaker
forcing for locations south, later start time to snow production, and
the mid morning lull holds lower amounts south of I-94 to a half-
inch or less.

For this afternoon and evening, caa in the wake of the front will
reinvigorate lake effect snow chances several hours after the
passage of the front as the cooler low-level flow enhance lapse
rates. Flurries to light snow showers will be capable of griding out
an additional dusting of accumulation through the evening. There does
appear to be a secondary frontal feature that sweeps through between
20Z-03Z Fri that will be capable of briefly enhancing convective
depths up through 8kft - 10kft and can drop a quick half-inch to
inch in a 1-2 hour window. Any totals of this magnitude are expected
to be highly localized and highly sensitive to the degree of forcing
and magnitude of surface destabilization. Loss of diurnal heating and
neutral thermal advection will end accumulating lake effect snow
chances late tonight. Flurries remain possible overnight with low-
level flow maintaining a western component. Overnight lows return
into the single digits, wind chills near zero.

Flow backs southwest through the day on Friday in response to a
diffuse high pressure system washing out over the Appalachia.
Flurries remain possible as flow trajectories still pivot Lake
Michigan moisture over SE MI while a shortwave pivots overhead, but
a strengthening low-level inversion will keep cloud depths shallow,
inhibiting accumulating snow potential. Western periphery of a
thermal trough will maintain well below normal temperatures for
daytime high with temperatures peaking to about 20 degrees. Backed
flow will advect dry air late Friday into Saturday morning, cutting
off lake moisture.

For this weekend...Midlevel flow turns more zonal with several
shortwave passing over the Great Lakes over the weekend. This will
inhibit large day-to-day temperature swings and prevent MI from
being subjected to polar air as was observed for the first half of
the week. Temperatures warm up but will still be below normal with
highs in the mid to upper 20s. One large changed noted from the
previous 24 hours... An upper-level trough is expected to amplify
across the central and eastern Canadian Provinces and possibly into
the Great Lakes through the middle of next week, but medium-range
models exhibit high uncertainty regarding the degree of
amplification which will in turn have very large impacts on
temperature and precipitation trends.

A more progressive solution will keep flow zonal, filtering in a
modified warmer air mass from the western Canadian Provinces which
would be capable of produce daytime highs above freezing Tues-Wed.
Deeper amplification of the trough hold highs in the teens to 20s,
and there are some solutions that hold the baroclinic zone right
over the state. There is no clear winner in the trends as hi/low is
multi-model at this time, so note at this point that the outgoing
NBM blended forecast will be susceptible to large changes. The more
amplified solutions will also bring higher chances for snow showers,
moving any storm track closer to the Great Lakes and/or lake effect
chances.

MARINE...

Southwest wind shifts to northwest today as a cold front tracks
across the central Great Lakes. Wind speeds will be in the 10 to 20
knot range. Widespread light to moderate snowfall accompanies the
front then diminishes in coverage this afternoon, though scattered
lake effect snow showers will continue into tonight. Wind weakens
tonight into Friday as a ridge of high pressure builds in from the
south. Southwest wind then increases on Saturday as the next low
pressure system tracks into the northern Lakes. At this time wind
speeds look to remain below gales but may reach 25 to 30 knots for
parts of Lake Huron. An active west to southwest flow pattern will
set up over the region to finish the weekend and begin next week.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

AVIATION.....BT
DISCUSSION...AM
MARINE.......TF


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