Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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832
FXUS63 KDTX 211957
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
257 PM EST Tue Nov 21 2017

.Discussion...

Cold front will surge through area late this afternoon/early this
evening. Lift from upper trough forcing this front aided to some
degree by right entrance region of H25 jet streak lifting up east
side of the trough will maintain a band of rain showers along and
immediately behind this front. Cold air advection will be strong
enough to allow for some of this precipitation to chance to snow,
either mixed with the rain or becoming snow showers outright. With
generally light precipitation rates and boundary layer temperatures
in the mid to upper 30s, do not expect any accumulations before the
precipitation ends abruptly in the 22z-02z time frame from north to
south across the forecast area.

Colder air will settle into the area behind this front, with lows in
the low/mid 20s tonight and highs no better than the middle 30s on
Wednesday as the core of this cold airmass settles over the central
Great Lakes. That said, winds will decrease notably as compared to
the past few days, so the "chill" factor will not be as persistent.

A moderation in temperatures will ensue from Wednesday night into
Thursday night as main upper troughing progresses off to the east.T
This process will initially be rather slow as another (weaker)
shortwave pivots into the area and maintains some degree of upper
troughing. This should lead to a progression of temperatures from
the middle 20s once again Wednesday night, rebounding to upper 30s
to around 40 Thursday afternoon, but falling back into the mid/upper
20s Thursday night.

Precipitation, after early this evening, will be basically nil with
perhaps a small chance of snow showers again for at least portions
of the area late Thursday night as a stronger warm air advection
pattern begins to set up in advance of the next strong shortwave
that will be dropping out of the Gulf/Alaska region mid/late week.

&&

.MARINE...

A cold front sweeping across the region will bring gusty northwest
winds across the eastern lakes in it`s wake this evening through
tonight. The switch from southwest flow to northwest flow has
already begun as the front currently resides over central Lake Huron
and Saginaw Bay. The front will pass south of Lake Erie later this
evening with a secondary trough and cold surge lagging a few hours
behind. Cold air funneling into the region with a tight pressure
gradient will lead to a period of northwest gales across northern
Lake Huron through most of the overnight period. Slightly weaker
winds across southern Huron will not necessitate gales, but small
craft advisories are in effect for a portion of the nearshore waters
around the Thumb mainly due to elevated wave heights. Lake-effect
snow showers will be common in the cold air behind the front. Winds
will relax early Wednesday morning as high pressure builds into the
region.

&&

.PREV DISCUSSION...
Issued at 1229 PM EST Tue Nov 21 2017

AVIATION...

A cold front will sweep through SE MI this afternoon bringing with
it increasing cloud cover and a brief window of light precipitation.
The front is current dropping into Mid MI with a surge of moisture
ahead of it now nosing into MBS. Better frontal forcing will be
further south likely keeping MBS dry, but the rest of the sites will
have about a 2 hour window where showers will be possible. Rain will
be the dominate precip type, but as colder air begins moving in,
some wet snowflakes may be possible as well. Front will exit the
area around 00Z. Winds will veer from southwesterly to westerly for
a few hours before veering further to northwesterly. Gusts will
relax in the wake of the front with winds overall decreasing below
10 knots Wednesday. How fast clouds clear out in the wake of the
front will be one of the main forecast decisions.

For DTW...Gusts to 25 knots from the southwest will continue into
the evening until the cold front passes. The cold frontal wind shift
to westerly is expected around 21z and a full shift to northwesterly
around 00z - which may flirt with traffic flow considerations before
gusts relax. Window of rain showers still expected this afternoon for
a couple hours with some wet snowflakes mixing in toward the tail
end. Ground temperatures will remain above freezing.

//DTW THRESHOLD PROBABILITIES...

* High confidence in cigs aob 5000 feet after 20z today...low
  after 03Z.

* Moderate confidence in precip type falling as a rain transitioning
  to melting snow late this afternoon into this evening.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Gale Warning until 10 PM EST this evening for LHZ361.

     Gale Warning until 4 AM EST Wednesday for LHZ362.

     Small Craft Advisory until 1 PM EST Wednesday for LHZ441.

     Small Craft Advisory until 5 AM EST Wednesday for LHZ421.

Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&

$$

DISCUSSION...DG
MARINE.......DRK
AVIATION.....DRK


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