Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 150240
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
940 PM EST Tue Feb 14 2017

.UPDATE...

The earlier update bumped POPs higher into the likely category and
over a wider area of SE Michigan for the evening as rain and snow
showers increase coverage along and ahead of the cold front. An
impressive upper level circulation surging southward over the
Great Lakes is interacting with the western fringes of better low
level moisture and the front itself to generate the pattern of
rain and snow showers. Strong dynamic forcing/DCVA and cold
advection around the 500 mb level is easily eroding the cap shown
on the 00Z DTX sounding. This is releasing convective instability
in a steep lapse rate environment approaching 8 C/km in the
850-500 mb layer and producing the bursts of heavier snow and
gusty wind within a larger area of rain/snow mix focused along
and ahead of the front.

The upper circulation will sweep the pattern out of the region by
midnight followed by gusty northwest wind and falling temperatures
through the night. Paved surfaces should remain warm enough for
some drying to occur before temperatures drop below freezing for a
long enough period to produce icing, other than perhaps some
spotty icing on bridges and overpasses. Areas in the Thumb region
will also have potential for a second round of snow as the
trailing deformation pattern brushes across that area overnight
through about mid Wednesday morning.

&&

.PREV DISCUSSION...
Issued at 638 PM EST Tue Feb 14 2017

AVIATION...

Warm and dry westerly flow is in place over SE Michigan preceding
the cold front. Early evening temperatures in the lower to mid 40s
are accompanied by dewpoint mostly in the upper 20s, so there is
some cooling potential with sunset and with precipitation onset
during the evening. That being said, the expectation is for rain
outside of some bursts of higher rates producing snow or a rain/snow
mix and brief borderline IFR/MVFR conditions. There will be a
tendency for all snow just as the pattern exits the region toward
midnight. NW wind gusting 25-30 knots will develop post front which
will be the main concern over pockets of MVFR ceiling that will
linger for a few hours overnight through Wednesday morning. The
gusty conditions are projected to last through Wednesday afternoon
with low end VFR ceiling and possibly some flurries during peak
heating.

For DTW... Wind remains the primary concern tonight as direction
shifts toward northwest behind the cold front and gusts increase to
around 25 knots. The front is expected to bring mostly rain with a
rain/snow mix possible in bursts of heavier rates. Temps near 50
preceding the front have warmed pave surfaces enough to prevent
accumulation considering the short duration of the event.

//DTW THRESHOLD PROBABILITIES...

* High for ceiling 5000 ft or less tonight through Wednesday
  morning.

* Moderate for exceeding NW cross wind threshold tonight through
  Wednesday.

* Moderate for rain/snow mix precip type this evening.

PREV DISCUSSION...
Issued at 307 PM EST Tue Feb 14 2017

DISCUSSION...

Mild afternoon within moderate west southwest flow in advance of
approaching cold front. Temperatures have reached the 40s over the
whole forecast area and would not be surprised to see a few 50
degree readings over the southern portion of the region before
heating top out. Aforementioned cold front will bring a quick end to
this though as it sweeps south through lower Michigan between 8 pm
and midnight.

Scattered rain and snow showers will accompany this frontal boundary
with the best concentration most likely over the Thumb where best
forcing/convergence along the front will exist (nearer the low as it
drops southeast along Georgian Bay). While these showers will change
to snow pretty quickly, especially over the northern forecast area,
do not expect anything more than a dusting in some spots. Winds will
also be a bit breezy, but not nearly as much as the previous cold
front a few days ago. Wind gusts will peak more in the 25 to 30 mph
range within cold air advection in the wake of the front.

Much colder weather will settle into the area behind this cold front
for the next several days as the low pressure continues on to the
New England area where it rapidly deepens and leads to a very
amplified upper trough over the northeast CONUS. Expect highs to
range in the upper 20s/lower 30s Wednesday and Thursday with lows in
the teens and 20s. Scattered snow showers/flurries from lake effect
activity can be expected on Wednesday. A moderating airmass from the
west will then squelch this activity by Thursday, even as
temperatures at the surface remain similar to Wednesday.

Warming trend will begin on Friday as a broad upper level ridge sets
up over the Great Lakes through the weekend. Under the ridge dry,
mild conditions will stay in place through Monday. With 850 mb temps
approaching 10 C on Saturday high temperatures will surge well into
the 50s and possibly near 60. Above normal temperatures look to
remain in place into early next week before the next storm system
brings a chance for rain to SE Michigan.

MARINE...

Models continue to highlight a sharp thermal trough feature crossing
northern Lake Huron as low pressure drops southeast along the shores
of Georgian Bay and drags a strong cold front through the area. This
should lead to local compaction of the pressure gradient field. This
will be enhanced further by the interaction with coastal convergence
effects over Lake Huron. These factors are expected to compensate
for a rather lackluster environmental wind profile and allow for a
period of gale force gusts over parts of the open waters of Lake
Huron overnight into Wednesday morning. Hence, the Gale Watch will
be upgraded to a warning with this forecast package.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...NONE.

Lake Huron...Gale Warning from 1 AM to 11 AM EST Wednesday for LHZ362-363-462.

Lake St Clair...NONE.

Michigan waters of Lake Erie...NONE.

&&

$$

UPDATE.......BT
AVIATION.....BT
DISCUSSION...DG/JD
MARINE.......DG


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