Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 272359

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
759 PM EDT Thu Oct 27 2016


Some lingering low level cyclonic flow and surface convergence
continues to sustain some light showers, especially along the I-75
corridor from Saginaw to Detroit. The flow will trend anticyclonic
during the course of the night, with the low level flow backing
toward the west. This will result in the lingering showers
weakening as they push off to the east during the latter half of
the evening. A forecast update was issued simply to carry
isolated/sct showers later into the evening hours.


Issued at 701 PM EDT Thu Oct 27 2016


Ongoing cold air advection in the 4-5k ft layer is slowly lifting
inversion bases, a trend that will continue over the next several
hours. This will support a slow rise in ceiling heights above 3k ft.
The approach of a sfc ridge axis will back the low level flow toward
the west tonight before it weakens. This will result in a loss of
flow off Lake Huron and will cause the low level winds across Se Mi
to become strongly anticyclonic. These factors suggest partial if
not complete clearing of the low clouds between roughly 04Z and 06Z.
Warm air advection below the inversion base overnight will also act
to erode/weaken the inversion, making clearing more probable.
Current temp/dewpoint spreads are quite low, so some fog may be of
concern overnight assuming some clearing. There is ongoing weak low
level dry air advection which suggests enough of a limiting factor,
possibly supporting just a brief period of reduced vsby toward

The low clouds across Wisconsin will likely slide into wrn Lower Mi
Fri Morning. The flow will back toward the south by Fri afternoon,
which should keep these clouds well west of the Se Mi terminals.

For DTW...Timing the partial to complete clearing of the clouds
carries with it some degree of uncertainty. Taking into
consideration recent hi res solutions and the current extent of
clouds across lower Mi, a clearing around 06Z seems reasonable attm.

//DTW Threshold Probabilities...

* High in ceilings below 5000 feet this evening. Low overnight
  through Friday morning.

Issued at 335 PM EDT Thu Oct 27 2016


Some lake effect showers may impact the Thumb and Saginaw Valley
through the late evening as flow off Lake Huron turns northeast and
then north. Drier air and falling inversion heights will make
conditions increasingly less favorable as we go through the evening.
Most locations should be dry by 800 PM, with activity expected to
then end by midnight.

Upper ridge axis over the central CONUS will shift east into the
Great Lakes late tonight and Friday. Corresponding area of high
pressure at the surface will slide overhead tonight. Forecast
soundings indicate that moisture trapped under a lowering and
strengthening subsidence inversion will keep plenty of lower clouds
around for the first half of the night, while pronounced mid-level
drying occurs with the subsidence. Low pressure tracking through the
Upper Mississippi Valley will then start to send warmer below 850mb
into the area late tonight. Model forecast soundings suggest this
will weaken the inversion enough to allow the cloud deck to begin
eroding from north to south between 03-09Z. The decrease in clouds
and winds will provide a chilly night, especially over central
Michigan where skies will clear out longer. Min temps are expected
to run in the in the 30s, with coolest readings over the
northern thumb.

High pressure will remain the dominant influence on the weather
tomorrow even as the center shifts into the Eastern Great Lakes.
Lead energy ejecting out of the Pacific Northwest and surface low
pressure riding through Ontario and the northern Great Lakes will
send warmer air into the area, with southerly flow allowing max
temperatures to warm into the 50s. Strong low-level jet and warm
front will keep gusty winds and mild conditions around for Friday
night, with temperatures actually rising overnight behind the warm
front. Temperatures around sunrise Saturday should run in the mid
50s to 60, setting the stage for a warm day as the boundary layer
deepens and we mix into warmer air aloft. Increasing clouds and
gusty winds/good mixing lend some uncertainty to how warm temps will
actually rise. Forecast plays things a little safe given incoming
cloud cover ahead of a cold front, with max temps near Detroit
running around 70 and temps in the thumb reaching the mid 60s. Cold
front dropping through on Saturday night should provide a good chance
of showers with healthy plume of theta-e along the front positioned
under right entrance region forcing. Steepening mid-level lapse
rates will provide a chance for a few thunderstorms south of Saginaw.

A shortwave trough crossing through Michigan on Saturday night will
bring a chance for precipitation early Sunday. High pressure moves
over the region late Sunday into Monday. Calm, milder conditions
will develop as a ridge builds on Monday. Low pressure passing to
the north of Michigan on Tuesday will bring increased southwesterly
flow maintaining mild conditions. Another chance of precipitation is
possible midweek as a weak low pressure system passes through
the southern Great Lakes region.


Onshore northeast winds in the wake of low pressure now tracking
over Lake Erie will maintain large wave action over Lake Huron into
this evening. Small Craft Advisories will remain in effect for these

While winds and waves will diminish this evening into tonight as
high pressure works across the region, southerly flow will quickly
ramp up on Friday, peaking Friday evening into Friday night. The
potential exists for gusts to reach gale force over portions of the
Lake Huron open waters during this time frame. A Gale Watch will
remain in effect for this possibility.


Lake Huron...Small Craft Advisory until 10 PM EDT this evening FOR LHZ421-422-

     Gale Watch from Friday evening through late Friday night FOR LHZ362-

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



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