Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 252011
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
311 PM EST Sat Feb 25 2017

.DISCUSSION...

Strong upper trough axis is exiting the area, and should be to our
east by 21Z. Lower Michigan will become positioned between this wave
and another one upstream tonight, allowing high pressure centered
over the Tennessee Valley to expand up into the area. Light snow
shower/flurries over Southeast Michigan should end this evening, as
inversion heights over Lake Michigan lower and subsidence behind the
trough takes hold. Drier air and flow turning more to the southwest
should allow for partial clearing late tonight before high and mid
clouds blanket the area again towards morning. Breaks in the clouds
and cooler air continuing to filter in the area will drop
temperatures into the low 20s tonight.

Upper shortwave seen on water vapor over Southern Saskatchewan will
drop across the Northern Great Lakes Sunday. Main effect from this
will be a re-strengthening of the surface pressure gradient between
weak surface low pressure to our north and the high over the
Tennessee Valley. Steep lapse rates of 7-9 C/km in the low levels
combined with strong core of 40-45 knot winds above 2000 feet
arriving in the late afternoon and evening should provide for a
windy day. Gusts look to reach to about 40 mph (NAM, as typical,
hints at a little stronger) before a weak nocturnal inversion sets
in during the late evening. Precipitation chances tomorrow look
paltry as surface low pressure passes to our north. Isentropic
ascent along an elevated warm front looks weak as does moisture
advection, and most likely outcome tomorrow is just clouds. The
exception could be over Bay and Midland counties, closer to surface
troughing and better forcing from the upper wave, but lower levels
may stay too dry, and will only retain slight chance pops there.
Thermal profiles from forecast soundings over the Saginaw Valley
support snow showers, with dewpoints in the lowest 5000 feet solidly
below freezing. No accumulation is expected. Max temperatures will
warm under weak advection and clouds, reaching close to 40.

Zonal flow and southwest winds will help temperatures warm further on
Monday, pushing highs well into the 40s for most of the area. Ascent
increasing late Monday night in advance of the next low pressure
system will bring a chance for precipitation late along/south of M-
59. Higher temperatures and dewpoints advecting into the area per
latest NAM/GFS look warm enough to support rain overnight.

A warm front ahead of a weak surface low will bring the increasing
chance for precipitation early Tuesday. WAA will usher above
freezing 850 mb temperatures by 12Z as seen throughout the
GFS/ECMWF/GEM model suites, bringing a rain solution to the CWA
throughout the day. A second surface low is expected to develop over
Kansas/Missouri late Tuesday to early Wednesday, and will push
northeast into the southern half of Michigan by late Wednesday. This
will allow the chance for precipitation to continue through
Wednesday, with PoP values diminishing throughout Thursday. Surface
temperatures are expected to hold well above freezing Tuesday into
Wednesday, which will continue to bring a rain solution throughout
the CWA. This is further confirmed by 850 mb temperatures averaging
6-8 C by 6Z Wed. A swift transition from rain to a wintry mix and
then snow solution will be possible late Wednesday into Thursday as
the surface low pushes east of MI, ushering in cooler Canadian air
into the region. Additionally, a strong pressure gradient on the
back-end of the low will bring breezy conditions and possible gale
force winds over the lakes late Wednesday into Thursday.

Otherwise, the chance for precipitation will taper off Thursday into
Friday, as high pressure settles into the Ohio Valley. Temperatures
will stray away from seasonal norms, peaking into the 40s to 50 for
the first half of the week. Cooler air from the back-end of the low
will return the more seasonal values, as temperatures return into
the 30s for a high by Thursday and Friday.

&&

.MARINE...

Westerly wind gusts to gales over much over Lake Huron this
afternoon will come to an end this evening, as a ridge of high
pressure arrives tomorrow morning over the Central Great Lakes.
However, southwest winds will quickly increase during Sunday ahead
of a cold front, with gales likely over central centions of Lake
Huron. The gale watch for Sunday afternoon has been converted to
Gale Warning, with Inner Saginaw Bay added as well. The weakening
cold front will track through Sunday evening, with high pressure
leading to light winds by Monday morning. Light southerly winds can
then be expected early next week as milder air returns to the
region.

&&

.PREV DISCUSSION...
Issued at 1148 AM EST Sat Feb 25 2017

AVIATION...

Westerly cold advection and deep mixing allowing for wind gusts up
around 30 knots this afternoon, with the low levels slowly drying
out. Cold flow off Lake Michigan will attempt to slow the process
(flurries this afternoon), with good subsidence kicking in early
this evening behind mid level cold pool exiting east. Will maintain
low VFR/possible high MVFR ceilings for much of Tonight underneath
subsidence inversion, but low level warm advection kicking in by
sunrise should allow for a quick dissipation in the low clouds, with
mid/high clouds spreading in during Sunday. Once again, winds look
to be strong tomorrow afternoon ahead of a cold front, with gusts
around 30 knots, but out of the southwest direction.

For DTW... Westerly wind gusts around 30 knots will continue this
afternoon, helping to dry out the low levels, with just flurries
expected as Lake Michigan activity struggles to reach the terminal.
Banking on just enough moisture to become trapped underneath
strengthening low level inversion this evening to support Low
VFR/borderline MVFR ceilings, with clearing taking place sometime in
7-11Z time frame.

//DTW THRESHOLD PROBABILITIES...

* Moderate for ceiling 5000 feet or less through 7Z, then low.

* Low for exceeding westerly cross wind threshold today.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Gale Warning until 10 PM EST this evening for LHZ363-421-441>443-
     462>464.

     Gale Warning from 10 AM to 10 PM EST Sunday for LHZ362-363-421-422-
     441-462.

     Gale Warning until 4 AM EST Sunday for LHZ361-362.

     Small Craft Advisory until 10 PM EST this evening for LHZ422.

Lake St Clair...Small Craft Advisory until 10 PM EST this evening for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 10 PM EST this evening for LEZ444.

&&

$$

DISCUSSION...HLO/AM
MARINE.......SF
AVIATION.....SF


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