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FXUS63 KDTX 182248

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
548 PM EST Mon Jan 18 2021


With westerly flow persisting, the Lake Michigan moist plume will
sustain frequent MVFR based ceilings into the night. There will be
some decrease in the mid level moisture during the night which will
cause the light snow showers/flurries to undergo a gradual decrease
in coverage. The brevity of any higher intensity snow showers this
evening will limit any accumulations to a dusting.

For DTW...With a slightly more southwest flow in the boundary layer,
the higher intensity snow showers will remain largely north of
metro. This flow may also support some more prolonged erosion of the
MVFR cloud deck overnight.


* Moderate in ceilings at or below 5000 feet tonight and Tuesday.

* High in precip type as all snow tonight.


Issued at 328 PM EST Mon Jan 18 2021


Seasonably cold, moist west-northwest flow will continue to govern
conditions through tonight. A diurnal increase in lapse rates under
weak cold air advection yielding a broadening region of light snow
showers within the background of larger scale cyclonic flow.
Shortwave energy noted exiting lake Michigan will effectively
supplement this ascent while temporarily reinvigorating the
downstream moisture flux off lake Michigan under a secondary period
of cold air advection tonight. The net effect will be a tendency for
some degree of light snow shower production to occur over roughly
the next 12 hours. If recent observational trends locally and just
upstream are any indication, then meaningful snowfall rates will
remain transient/brief thereby limiting accumulation potential
/less than an inch/.

Slightly colder thermal profile in residence Tuesday - 850 mb
temperatures down around -13C. Brief period of mid level dry/warm
air advection will temporarily undercut the magnitude of ongoing
lake moisture flux and reduce the downstream moisture depth. This
points to dry conditions, at least early in the day. Additional
shortwave energy will traverse the area during the afternoon period.
This could offer a brief synoptic increase in moisture depth,
affording a window for some inconsequential very light snow showers
or flurries to emerge within the underlying cold westerly flow. A
firm gradient and modest diurnal mixing yields a gusty afternoon
condition - in excess of 25 mph at times. Highs arrive right at
seasonable levels - upper 20s to lower 30s.

Stronger height falls commence Tuesday night as an upper wave of
arctic origin dives into the mean trough. Standard increase in
forced ascent via a combination of dcva and cold air advection will
support an increase in snow shower coverage during this time. The
general brevity of deeper layer ascent again contains accumulation
prospects - less than an inch this period. Lake modified arctic air
then entrenched through the Wednesday period. The existing cold west-
northwest flow again lends to some light snow shower/flurry
production, but a warming/drying profile upstream steadily
deteriorates the lake response with time.

Building upper heights with an ensuing increase in warm air
advection within low level southwest flow nets a solid, albeit brief
moderating trend Wed night-Thursday. Dry conditions maintained this
period, as greater moist isentropic resides well north.


Lake enhanced moisture will continue to bring flurries to the
central Great Lakes this evening while snow hangs on overnight for
northern Huron given the proximity to weak low pressure. Winds turn
more south of west tonight with speeds increasing late. Surface
pressure gradient contraction early Tuesday morning will lead to an
increase in speeds throughout the day. Discrepancies in modeled
upper level winds yield low-confidence for gusts to exceed 30 knots,
but there is enough support for steady 20-25 knot winds along the
Thumb shoreline to produce Small Craft Advisory waves until late
Tuesday evening. A ridge of high pressure then approaches from the
midwest working to maintain higher gradient winds producing moderate
northwesterly flow across the local waters with occasional gusts in
the 25 knot range. The offshore component of the wind is expected to
keep nearshore waves below small craft criteria.


Lake Huron...Small Craft Advisory from 7 AM Tuesday to midnight EST Tuesday
night for LHZ421-441.

Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.



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