Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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798
FXUS63 KDTX 180028
AFDDTX

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


.AVIATION...

Uncommon warm advection pattern is now setting up over the Northern
and Central Great Lakes region as Pacific moisture plume advects
directly into southeastern Michigan from the northwest.  Developing
fast zonal gradient flow is setting the initial stage, with warm
advection getting accentuated Thursday in advance of the vigorous
shortwave that will dig directly down through the U.P. into Lower
Michigan. High cloud now filling in over Lower Michigan is occuring
on the initial warm air advection aloft. The main item in the
forecast period is the overall likelihood of widespread MVFR cloud
development that is forecasted to occur between 1.5 and 4.0 kft agl
Thursday morning. RAP and NAM are extremely bullish on low cloud
development. There remains some uncertainty yet, namely the lack of
cloud development thus far upstream. However, there has been some
activity on Lake Superior and model data points to Lake Michigan
being a major contributor to the cloud development. Relatively
higher westerly gradient flow will persist through the taf period
with winds in the 15 to 25 knot range throughout the taf forecast.

/DTW THRESHOLD PROBABILITIES...

* Moderate for cigs aob 5kft after 14Z Thursday morning.

&&

.PREV DISCUSSION...
Issued at 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.

&&

.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.
&&

$$

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


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