NWS Forecast Discussion

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FXUS63 KDTX 020453
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1153 PM EST Sun Dec 1 2024

.KEY MESSAGES...

- Scattered to numerous snow showers in the Tri Cities to northern
  Thumb and flurries elsewhere tonight.

- Lake effect snow band over Lake Huron may brush the eastern Thumb
  Monday.

- A storm system will bring a chance of snow Wednesday and Wednesday
  night and the potential for strong winds Wednesday night into
  Thursday along with much colder temperatures.

&&

.AVIATION...

A west to east surface trough, initially enhanced by Lake Superior,
is pulled slowly southward by the large low pressure system in
Quebec late tonight and Monday. Low level wind backed more WNW ahead
of the trough guides northern Lower Mi clouds and snow showers
mainly east of the terminal corridor after grazing MBS in the short
term. Fragmented low end VFR stratocu and altocu is the prevailing
condition until the surface trough reaches central Lower Mi by early
afternoon when it brings greater coverage of VFR ceiling generally
less than 5000 ft. Intervals of MVFR ceiling and a few snow showers
are also possible but with predictability too low to include at this
time range as the boundary slides north to south during the
afternoon into Monday evening.

DTW THRESHOLD PROBABILITIES...

*  Low for ceiling 5000 ft or less late tonight and in the morning,
   then moderate Monday afternoon and evening.

&&

.PREV DISCUSSION...
Issued at 953 PM EST Sun Dec 1 2024

UPDATE...

The northern thumb region is being monitored closely after a couple
of heavier snow showers materialized there this evening. Upstream
preconditioning of NW flow helped with brief flare-ups across outer
Saginaw Bay into the area from about Caseville around to Harbor
Beach. The latest mid evening satellite and radar imagery now also
show some open sky upstream into NE Lower Mi while a band hugs the
Rogers City to Alpena portion of the Lake Huron shoreline feeding
into central Lake Huron. Approach of the next larger scale surface
trough farther upstream over Lake Superior backs the low level wind
field just enough to keep the longer fetch Lake Huron bands offshore
while also possibly directing clusters of northern Lake Mi activity
from NW Lower Mi toward Saginaw Bay where a boost could be had into
Huron and northern Tuscola counties. Given these trends, the
forecast update will extend the more robust scattered to numerous
POPs/sub 1 inch accumulation in that area through the night and into
the early morning.

PREV DISCUSSION...
Issued at 351 PM EST Sun Dec 1 2024

DISCUSSION...

A surface trough is dropping south through the area this afternoon
providing enough convergence forcing to utilize the remaining low
level moisture to produce a few light snow showers. The showers will
be transient as it drifts southward resulting in little to no
accumulations this afternoon. The Lake MI moisture plume is still
reaching ADG and TTF but as the trough passes and introduces more
dry air those showers should come to an end. Heading into tonight
we`ll nee to keep an eye on the lake effect band coming off northern
Lake MI as the northwesterly winds try to push it closer to Saginaw
Valley.

Broad upper level trough will hold over the region through most of
the upcoming week, with only a brief break Tues into Wed as a ridge
sliding to the south noses up into the area. 850mb temps will
largely be in the -10 to -15C range through the week outside of Wed
when warm advection gets us back into the negative single digits.
This should keep highs below average, mainly in the 30s F (maybe
some 20s later in the week) with lows in the upper teens to 20F.

The longwave trough will be fairly active this week with a couple
different shortwaves diving into it. The first one will dive south
of the region through the Ohio Valley Monday and Monday night. The
precipitation will hold to our south as ridging slides through
southern MI. With surface ridging across the Midwest helping veer
the winds more northerly over Lake Huron, the Thumb may get grazed
by the Lake Huron lake effect band.

Much of the attention for the week has been on the Tues/Wed clipper
that will pass over the northern Great Lakes. General setup remains
the same over the last few model runs with a strong 120 knot upper
level jet tracking through the souther Great Lakes with a strong
vort max. Surface low track much further north through northern MI.
Warm advection isentropic ascent north of the warm front is supposed
to touch off some light snowfall during the day Wednesday before the
better elevated forcing and cold front come through Wednesday night.
Still looks like the bulk of the Wednesday activity will be to the
north keeping our focus on the Saginaw Valley and northern Thumb.
More widespread activity fills in overnight. Warm advection will
lead to some questionable soundings in terms of mixed precip as mid
levels warm Wed. Cooler air surging in with the cold front will turn
it back to all snow. Snow amounts should increase from south to
north with general amounts in the 1-4 inch range possible based on
recent QPF and local probabilistic guidance.

Cold advection and a tight gradient will lead to wind concerns
Thursday in the wake of the exiting system. MIxing depths could
reach to around 7kft with a deep layer of winds around 40 knots
within the mixed layer (per GFS) Thursday. Local probs are also
already advertising strong wind gusts so will continue the mention
of near advisory level wind gusts Wednesday night into Thursday with
the current forecast mainly in the 30 to 40 mph range.

MARINE...

A trough is passing southward into southern Lake Huron this
afternoon, shifting wind direction to northwest. Meanwhile, the
gradient is weakening causing wind speed to ease to generally a 10
to 20 knot range. This will allow the remaining Small Craft
Advisories to expire on time this afternoon as wave heights slowly
subside in the Lake Huron nearshore waters. This moderate northwest
flow will hold through Monday and Tuesday with lake effect snow
continuing mainly along the NW-SE axis of Lake Huron. A clipper low
pressure system then tracks across the northern lakes Wednesday and
Thursday, bringing the next round of widespread snow and potential
for marine headlines. This system will usher in a reinforcing shot
of arctic air for the late week with a period of northwest gales and
snow squalls looking increasingly likely on Thursday.

&&

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

$$

AVIATION.....BT
UPDATE.......BT
DISCUSSION...DRK
MARINE.......TF


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NWS DTX Office Area Forecast Discussion