Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 172048
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
348 PM EST Wed Jan 17 2018

.DISCUSSION...

Cloud trends will be the primary subject of the forecast for tonight
with the main question being how active Lake Michigan will be in
producing stratus/stratocu. Observations show the mid and high
clouds overhead associated with the exit region of the upper jet
over northern Ontario and a broad region of mid level isentropic
ascent. These will exit eastward during the evening and allow a
broad short wave ridge to force a subsidence inversion over Lower
Michigan later in the night. Observations also show very dry
conditions in place over the upper Midwest and northern Plains.
Warmer air is moving into this region on increasing southwest flow
but satellite indicates no low clouds anywhere to our west. This
does not mean that Lake Michigan will not activate, only that the
forecast sides with model solutions that offer more limited coverage
of low clouds until observational trends support a more aggressive
approach. Expect temperatures to continue an upward response to the
increasing southwest wind, gusting near 30 mph during the evening,
however wind chill will end up around zero for much of the night as
overnight lows settle in the teens.

The expectation of scattered to broken lake clouds to start Thursday
will be directed farther north under gradually backing low level
flow during the afternoon. Mid and high clouds associated with the
compact upper level circulation will also pass mostly through the
northern Great Lakes. This moisture starved feature will barely be
capable of precipitation and then only on the northeast flank over
northern Lake Huron where dynamic forcing will be maximized. The
passage of the circulation will mark the beginning of broad upper
level height rises associated with continued low level warm
advection to finish the week. The pattern will be dry but steadily
warmer with highs pushing 40 Friday afternoon.

Significant increase in upper mass gradient is anticipated over the
next few days as east Pac jet energy releases into the northern tier
of the US against the southern periphery of the tropospheric polar
vortex Hudson Bay/northern Quebec. Trailing energy will dig into the
southwest United States Saturday through Sunday, prompting a lee
cyclogenesis episode as strong right entrance support steadily
matures through the weekend and becomes increasingly focused over
the Great Lakes region. Light warm advection/overrunning type precip
will be possible as early as Sunday morning as the low-level jet
responds and moves up the developing frontal slope. Surface cyclone
is then progged to lift from the Lower Missouri River Valley to The
Straits by Monday into early Tuesday. Strong model support that SE
Michigan will remain on the warm side of this system, supporting
temps on the milder side for late January. There is potential for
pre-fropa temps on Monday to make a run toward 50 before showers and
possibly t-storms along the front shift through the area. Cold lake
temps/ice on Lake Erie suggest usual caveats with northward
progression of the surface portion of the warm front. Will leave out
t-storms and remain more conservative, low to possibly mid 40s, with
temps for now. Overall extended period characterized by temps on the
warm side of average, high pops early next week, and mainly liquid
precip. Per the norm, a brief snow-fzra-rain transition is possible
as the warm front lifts through Sunday.

&&

.MARINE...

A Gale Warning will remain in effect through Wednesday night as
strong, unstable southwest flow peaks this evening. A tight pressure
gradient between Arctic high pressure over the Tennessee Valley and
low pressure near James Bay will continue driving southwest gusts
approaching 40 knots across Saginaw Bay and the nearshore waters
with gusts reaching 40 knots over the open waters of Lake Huron
through late Wednesday night. The pressure gradient will then weaken
slightly early Thursday as the low pressure near James Bay departs
to the east allowing winds to gradually decrease Thursday morning.
Southwest flow will then continue through the remainder of the week
with diminishing gust potential due to an increasingly warm, stable
fetch.

&&

.PREV DISCUSSION...
Issued at 1228 PM EST Wed Jan 17 2018

AVIATION...

Drier low level air has scoured out much of the morning stratus as
increasingly anticyclonic gradient flow moves into the region
courtesy of high pressure moving eastward across the Tennessee
Valley. The increasing pressure gradient will cause southwest winds
to increase through the afternoon into the evening with 20+ knot
gusts expected by early evening before dissipating gradually late
tonight.

/DTW THRESHOLD PROBABILITIES...

* Medium for cigs aob 5kft this afternoon and low on Thursday
  morning.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...NONE.

Lake Huron...Gale Warning until 4 AM EST Thursday for LHZ363-441-462.

     Gale Warning until 10 PM EST this evening for LHZ362-421.

Lake St Clair...NONE.

Michigan waters of Lake Erie...NONE.

&&

$$

DISCUSSION...BT/JVC
MARINE.......JD
AVIATION.....JD


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