St. Clair Shores, Michigan 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

406
FXUS63 KDTX 180459
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1159 PM EST Fri Jan 17 2025

.KEY MESSAGES...

- Widespread rain/snow to snow expected tonight into Saturday
morning. Snow accumulation totals of a half-inch up to 2 inches
likely, with higher-end amounts possible within the Irish Hills.

- The coldest temperatures of the winter thus far arrive early next
week. Dangerous wind chills of -15 to -25 likely for the morning
hours, with little relief for the afternoon, centered Monday through
Wednesday.

&&

.AVIATION...

Plume of deeper moisture will arrive early this morning, resulting
in a steady increase in precipitation potential through the morning
with an accompanying reduction in both ceiling and visibility. The
milder temperatures at onset will support primarily rain initially,
with a transition toward a rain/snow mix and then straight snow from
northwest to southeast as precipitation rates increase. This will
afford a window of IFR conditions, with a brief period of LIFR
possible. Passage of an arctic front will bring a wind shift to
northwest by early afternoon, with a rapid decline in coverage of
snow. Cold northwest flow with some gustiness and lingering MVFR
stratus through the remainder of daylight period.

DTW...Precipitation arrives as rain early this morning. Snow will
begin to mix in late tonight, before turning to all snow during the
latter half of the morning Saturday. Wind shift to northwest occurs
around 14z.

DTW THRESHOLD PROBABILITIES...

*   Low for ceiling aob 5000 feet this evening. High after 06Z
    tonight through Saturday.

*   High for a precipitation type of rain at onset 07z-09z, then
    transitioning to a rain/snow mix before ending as snow 12-17z
    Saturday morning.

*   Low for crosswind threshold exceedence Saturday afternoon.

&&

.PREV DISCUSSION...
Issued at 1148 PM EST Fri Jan 17 2025

DISCUSSION...

Shortwave ridge axis passed to our east this morning opening the
door for gusty southwesterly winds around the broad surface high
pressure centered over the eastern conus. Gusts to 30 knots have
helped usher a fairly warm airmass into the region this afternoon,
and aided by peaks of sun, has resulted in temps into the upper 30s
across southeast MI. This warm air will be short lived as a strong
low tracking through southern Canada tonight will open the door for
long duration cold air advection with multiple surges of arctic air
through the region as the longwave trough stalls and digs down to
the Gulf into the midweek period. This will be one of the coldest
airmasses we`ve experienced in the last few years.

For tonight, the low pressure system will pass through Ontario
tonight, pulling an arctic cold front through SE MI Saturday
morning. As this northern stream trough digs southward through the
MS Valley it will partially phase with the southern stream and a
shortwave tracking through OK/MO. A strong low level jet ahead of
the deepening trough will peak around 60 knots tonight over southern
MI and is already closing in on 40 knots helping to generate the
gusts this afternoon. This will also bring a surge of moisture up
into the area just ahead of the arctic front resulting in several
hours of precipitation tonight into Saturday morning. Models have
been fairly consistent with around 0.25 inches of QPF, but the ptype
will be an issue with this event. Starting off near 40 this evening,
with temps above 32F up through 6kft will offer the initial ptype
issue with too much warm air at onset around midnight. So first few
hours will be rain or a rain snow mix working south to north through
the region. Warm layer gradually cools through the night with
sounding favoring colder profiles after about 5am which would offer
more snow, or melting snow, for much of the area especially the
higher terrain of the Irish Hills. Lower terrain from Monroe County
up through Wayne and into Macomb are expected to hold the warm air
longer. Temps most of the night will reside in the low to mid 30s
also helping to reduce snow accumulation. NAM is definitely one of
the colder models which isn`t surprising with HRRR and RAP coming in
much warmer, keeping rain almost through 12Z Sat. So with such a
fine line between rain and snow in these scenarios, will hold with a
mainly 1-2 inch forecast for a portion of the area with 3 inches not
out of the questions if the cold air can surge in faster and mainly
for the Irish Hills. With warm temperatures holding at the surface,
any accumulation will likely be minimized on paved surfaces that are
wet to start and warm at transition. So higher accumulations
expected on grass or elevated surfaces.

With the arctic front sweeping across Saturday morning, the moisture
and warm air will all get shunted east with cold air advection
kicking in. Some lingering light snow in the morning will be
possible until the front finally passes but drier air will end that
by noon. Warmest temps will be early in the morning with temps then
falling through the day. After increasing to around +4C Friday
evening, 850mb temps will fall to around -4C by Saturday morning and
-10C by evening. After falling further to around -20C by Sunday
afternoon, ECMWF suggests -25C is in play for Monday with the
coldest airmass sweeping through Tuesday close to -30C. Expect a
long duration cold outbreak with temperatures holding below 20F from
Saturday night through Wednesday night with highs on Tuesday and
Wednesday in the single digits. Wind chill values will fall into the
negative range Sunday night and will remain below zero through
Wednesday night. At this time they look to bottom out in the -10 to -
20F range which will need to be watched as we refine things. Looks
likely that we will need a Cold Weather Advisory for a period this
week at a minimum.

MARINE...

A cold front tracks across Lake Huron this morning, bringing a shift
in wind direction to northwest and areas of rain and snow through
the early afternoon. Drier, cold air works into the area through the
day with northwest wind peaking in the 20 to 30 knot range this
afternoon before weakening slightly tonight. Lake effect snow
showers and periods of freezing spray will ensue Sunday through mid
next week as a frigid arctic air mass takes residence over the Great
Lakes. Prevailing wind direction will hold out of the northwest
through this period, but may fluctuate locally at times as a lake
aggregate surface trough develops over Lake Huron. At this time wind
speeds are favored to remain below headline criteria.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Gale Warning until 4 AM EST Saturday for LHZ362-363-421-441-462>464.

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

$$

AVIATION.....MR
DISCUSSION...MR
MARINE.......TF


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