Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 202357
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
657 PM EST Mon Feb 20 2017

.AVIATION...

Thin coverage of high clouds will continue during the evening and
then begin to thicken overnight ahead of the next frontal system.
This will be accompanied by southeast surface wind holding in the 5
to 10 knot range which is expected to keep LLWS on the marginal side
tonight through Tuesday morning.

Low pressure parent to the cold front will be well north over Hudson
Bay during Tuesday and moving away from the Great Lakes. The
trailing cold front that is left behind continues to exhibit signs
of weakening in model data as it approaches SE Michigan. MBS has the
best chance of MVFR rain showers from about mid morning through
early afternoon although MVFR ceiling is expected to hang on through
the day over the rest of the area. The frontal wind shift will
likely dissipate and leave light southwest flow over the region by
Tuesday evening.

For DTW... Easterly flow lingering around the 100 degree direction
during the evening will veer toward the south overnight with speed
10 knots or less. The veering trend will at least help switch
runways back to southwest traffic operations by morning. VFR will
otherwise persist until the remains of the cold front arrive during
Tuesday afternoon.

//DTW THRESHOLD PROBABILITIES...

* None

&&

.PREV DISCUSSION...
Issued at 315 PM EST Mon Feb 20 2017

DISCUSSION...

Record setting upper level ridge (574 DAM at 500 MB per 12z DTX
sounding) in place over Southeast Michigan Today, but backed surface
flow out of the southeast holding temps in the 50s this afternoon.
Upper level ridge axis will continue to slide East, reaching the
East Coast Tomorrow. Rather narrow upper level trough over Central
North America, to break off into two pieces, as 500 mb cutoff low
develops over southern Mississippi River Valley, with northern
stream energy lifting through western Great Lakes Tonight into
Ontario Tomorrow. Narrowing moisture Axis and weakening nature of
the front draws into question the rain chances over southeast
Michigan, as bulk of upper level forcing and low level jet lifts
north of the CWA. Still, it appears there will be enough low level
convergence for some light showers (likely) to hold together on
Tuesday as the front moves across the area, as Local SREF weighted
probabilistic guidance suggest pops around 70 percent are justified
across most areas. However, 12Z HRRR gives one pause, as front comes
through mainly dry with lack of instability. Regardless, does look
like bulk of shower activity arrives after 12z, and will be trimming
pops for Tonight, and a bit for tomorrow. Clouds and showers working
through during peak heating will limit maxes, but still expecting
temps around 60 degrees.

Another surge of warm air on Wednesday with increasing southwest low
level flow as low tracks through Lake Superior. 850 mb temps progged
to rise back to around 10 C over southeast Michigan, with lower
teens at 925 mb level, supporting highs well into the 60s to
potentially 70 degrees at the high end. However, there is some
concern in the development of low clouds Tuesday night into
Wednesday morning behind tomorrow`s frontal passage, but suspect
models over doing the low level moisture just a bit, especially if
rain is very light tomorrow or does not materialize, and planning on
skewing the forecast on higher end of guidance, mid to upper 60s.
With the higher chance of low clouds in the south, along with the
surface flow potentially more southerly vs southwest, would subsequently
favor Flint Vicinity to be the warmest location during the day.

Well above normal temperatures will continue through the end of the
week before cooler air works in bringing temps back down closer to
seasonal for this time of year.  The main issue in the extended is
the strong storm system that models are showing coming up from the
plains for Friday and into the beginning of the weekend.  Chances
for precipitation are expected to increase by later in the day on
Thursday as the warm front approaches.  Currently, the low is
advertised to move northeast over the central Great Lakes area
keeping Southeast Michigan in the warm sector.  A chance for
thunderstorms will be possible as well as gusty winds as the cold
front slides across the area this weekend.   Conditions then look to
dry out for a brief time to round out the weekend as high pressure
settles in to the south.

MARINE...

East-southeast winds will continue to increase this afternoon and
persist into Tuesday morning as strong high pressure retreats to the
eastern Great Lakes. A frontal boundary will approach the western
Great Lakes. Warm air above the cold lake surface will keep fairly
stable conditions. Nonetheless, the gradient will increase with a
long trajectory over the lakes. This suggest winds will become
rather gusty tonight. Gusts in the 25 to 30 knot range knots are
forecasted across much of Lake Huron tonight. A cold front will
slowly move across Lower Mi and Lake Huron on Tuesday. There will be
substantial weakening in the winds as the broad frontal boundary
moves into the region. Further weakening of the post frontal
gradient will support light and variable winds Tues night. Modest
southwest winds are then forecast to develop on Wednesday.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...NONE.

Lake Huron...Small Craft Advisory from 10 PM this evening to noon EST Tuesday
     for LHZ441.

Lake St Clair...NONE.

Michigan waters of Lake Erie...NONE.

&&

$$

AVIATION.....BT
DISCUSSION...SF/SS
MARINE.......CB


You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.



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