239
FXUS63 KDTX 101058
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
558 AM EST Fri Jan 10 2025

.KEY MESSAGES...

- A Winter Weather Advisory is in effect for all but Midland and Bay
counties this afternoon-evening. Persistent light snowfall supports
accumulations between 2 to 4 inches by early Saturday morning.

- Peak snowfall rates expected during this evening`s commute.

- Another period of light snow possible Sunday afternoon into early
Monday, with below normal temperatures and lake effect snow showers
returning next week.

&&

.AVIATION...

The region of light snow expanding across nrn Illinois preceded a
mid level trough, forecast to lift across Se Mi this afternoon into
tonight. Available hi res model guidance suggests an expansion of
the light snow across Se Mi during the afternoon, reaching MBS and
FNT early in the afternoon. There will be ample low level dry air
across Se Mi as the light snow expands in from the southwest. It
will therefore take a few hours after the start of the snow for
ceilings to lower into the MVFR and/or IFR category. The snow will
peak during the afternoon at MBS and FNT and late afternoon/evening
across metro Detroit. Forecast snowfall amounts are in the 2 to 4
inch range across the terminals. The passage of the upper trough
overnight will end the widespread light snow and transition winds
toward the west-southwest.

For DTW...Light snow will expand into the region from the southwest
between 19Z and 21Z. Snow intensity will increase fairly rapidly
once the snow begins, with peak snow intensity around a quarter inch
per hour at times expected between 21Z and 02Z.

DTW THRESHOLD PROBABILITIES...

* High in ceilings aob 5000 feet this afternoon and tonight.

* High for precipitation type as snow today.

&&

.PREV DISCUSSION...
Issued at 328 AM EST Fri Jan 10 2025

DISCUSSION...

Mid-upper troughing across the southern Plains phases with a
northern stream trough coming out of the upper Midwest early this
morning shunting resident upper ridging toward the Northeastern US.
Said wave interaction results in an elongated trough axis across the
central CONUS creating a favorable setup for moisture tied to the
southern US low to partially advect northeastward into the Great
Lakes combining with attendant northern stream moisture. Result
locally is top-down saturation of columns through the morning hours
as height falls build in from western Great Lakes. Lead arm of
isentropic ascent lifts into central MI and the Tri-Cities around
midday day supporting light snow by early afternoon. Snow chances
lag slightly for the eastern half of the CWA (east of I-75/US-23)
though these areas look to eventually reach column saturation mid to
late afternoon.

Mid-upper trough base pivots into the western/central Great Lakes
this evening shifting from a positive to neutral tilt. This occurs
while a 140+kt jet streak still resides over central OH with SE MI
holding under the fringe of its left exit region. The combination of
these two factors results in a rapid uptick in snowfall intensities
during the evening commute and late evening timeframe with rates
peaking between 0.25-0.4 inch/hr, per local probabilistic guidance.
Bulk of accumulation occurs within this window with most areas
seeing a relatively quick 1-2" of fresh snow. Rates then gradually
lessen through the night as the trough slides directly overhead and
jet support shifts east. Synoptic snow tapers off by the first half
of Saturday morning as the system vacates the central Great Lakes.
In total, from this afternoon to early Saturday morning, widespread
snow between 2-4" is expected. Due to trends creeping up towards
reaching 3" in 6hrs and the higher snowfall rates during evening
rush, erred on the side of issuing a Winter Weather Advisory.
Midland and Bay were left out as these areas have lower potential to
see totals near 3" due to the NE-SW orientation of the
deformation/precip and better upper support holding to their south
and east.

Winds back to the west-northwest on the backside of the trough
Saturday offering a chances for a few flurries or light lake effect
snow showers. That said, overall flow isn`t particularly strong
(winds are sub 25kts below 700mb) keeping a leaner moisture flux off
the lakes limiting the effectiveness of diurnally steepening low
level lapse rates. Lake effect potential quickly wanes by Saturday
afternoon as mid-level ridging expands of the Great Lakes further
weakening winds and eventually veering them back to the west-
southwest. Little to no accumulation is anticipated with this
activity.

Next chances for snow come late Sunday as a clipper lifts out of the
Plains and into the northern Great Lakes. Latest 00Z runs continue
to favor a northerly track keeping the vast majority of QPF to our
north. First window for precip chances comes daytime Sunday tied to
isentropic ascent along the lead edge of the warm conveyor. Forecast
soundings struggle to reach saturation however with some solutions.
like the NAM. being nearly entirely dry for our CWA. Area for `best`
chances are the Tri-Cities owing to closer proximity to the low and
subsequent better lift/saturation potential. Some question as to ice
nuclei quality with soundings (that show sufficient saturation)
having it largely outside the DGZ, so in collaboration with
neighboring offices, added a slight chance (~15%) mention of
freezing rain to p-type forecast. Second, better window for precip
arrives Sunday evening/night in advance of the system`s cold front.
Soundings depict deeper saturation supporting all snow during this
window with minor accumulations possible.

Another arctic airmass is drawn south behind this clipper with 850mb
temps falling from -4C to -18C late Monday into midweek. Highs look
to hold in the teens to low 20s Tuesday and Wednesday with wind
chills near zero. Lake effect snow showers are likely as well given
open water lake temps still in the 40s.

MARINE...

Low pressure influence gains traction this morning with organized
flow now fully out of the southwest. Over-lake sustained winds
approaching 20 knots will elevate wave heights to 6-8 feet over the
open waters, although direct offshore component to the flow will
keep nearshore waves below 4 feet (and thus below Small Craft
Advisory criteria). Widespread snow is expected to expand from SW to
NE across the Great Lakes later today and continues through Saturday
morning, with rates approaching a half inch per hour at times.
Intermittent drops in visibility to 1-2 nm will be possible. High
pressure then returns for Saturday and the early half of Sunday,
with quieter marine conditions ahead of another low pressure system
early next week. Potential for wind/wave headlines with this system
is low, with the main impact being another round of widespread snow.
Arctic air and sustained NW flow will be conducive for lake effect
snow showers to persist through most of next week.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory from 1 PM this afternoon to 1 AM EST
     Saturday for MIZ049-053>055-060>063-068>070-075-076-082-083.

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

$$

AVIATION.....SC
DISCUSSION...KDK
MARINE.......MV


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at www.weather.gov/detroit.