Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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346
FXUS63 KDTX 212252
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
652 PM EDT Mon Oct 21 2019


.AVIATION...

A plume of low level moisture now streaming across western Lower Mi
will advance into Se Mi this evening. This moist plume has been
responsible for ceilings upstream around or just under 2k ft, which
should prevail across Se Mi this evening. The more widespread
showers ongoing will decrease in coverage with scattered to
numerous showers then affecting the area within the prefrontal
environment. The rain cooled boundary layer should suppress the wind
speeds to a degree tonight. Model soundings indicate this will
diminish the low level turbulent mixing, with low level wind shear
becoming more probable until the axis of the strongest low level
winds exit east overnight. Improved conditions with respect to
ceilings are expected overnight as the mid level dry slot moves
overhead.

The passage of the sfc cold front between 06 to 09Z will usher in
colder low level air during the course of the day Tuesday. This will
result in a deepening mixed layer into the stronger south-southwest
winds aloft, leading to a moderate probability of wind gusts around
30 knots Tues afternoon.

For DTW... There will be gradual veering of the southeast winds to
the south between 01Z and 03Z this evening, with speeds expected to
weaken as the rain cooled boundary layer stabilizes. A few higher
intensity rain showers, capable of producing a quick burst of gusty
winds, will traverse the airport between 02Z and 04Z.

DTW THRESHOLD PROBABILITIES...

* Moderate in ceilings at or below 5000 feet.

&&

.PREV DISCUSSION...
Issued at 259 PM EDT Mon Oct 21 2019

DISCUSSION...

Area of rain showers will continue to overspread the region late
this afternoon within theta-e plume surging north in advance of
deepening low pressure over the Mississippi Valley. To this point,
the only pocket of thunder is well south of the area along lead edge
of the cloud shield. So, expect thunder chance to remain very low as
this activity, if it persisting, should shift east/northeast through
Ohio into perhaps parts of Lake Erie.

Shower activity will continue into the evening with an increasing
coverage of convective elements as forcing along strong cold front
works east into the region. Current satellite/radar representation
of this feature shows an increasingly well defined fine line of
vigorous (but shallow) convection. This features will pivot through
the area within the broader area of showers during the evening.
Isolated thunder cannot be ruled out along/behind the cold front as
it sweeps through the area. The back edge of this activity will
begin to work into the area by midnight and then clear the forecast
area completely by 4am or so.

During this time frame, southeasterly winds will steadily increase
as boundary layer mixing increases with an ever strong pressure
gradient in advance of the front. Gusts on the order of 30 mph can
be expected for several hours in the early/mid evening with higher
gusts along the Lake Huron shoreline and also be some degree over
the Saginaw Valley where mixing depth is forecast to maximize.

Winds will then shift to the southwest with the passage of the front
and decrease overnight. Strong boundary layer mixing will lead to
windy conditions by midday as the low pressure center pivots into
the northern Great Lakes and the pressure gradient tightens notably.
Gusts in excess of 30 mph should be common by late morning/early
afternoon with a few higher gusts topping 35 mph during the
afternoon.

Shower chances will return as vorticity lobe rotates through the
area around the storm system. Best coverage would focus over the
north/northwest forecast area where moisture quality associated with
this lobe will be best with just isolated/scattered activity further
south given the amount of dry air that will infiltrate the area
overnight into Tuesday. Another chance of rain showers will come
Wednesday night as a fast moving shortwave lifts into the region
around the base of leftover upper trough. By this time, upper flow
will be pseudo-zonal and quite strong so system will progress thru
the area very quickly.

A few rain showers might still be lingering around across the
eastern portions of the area Thursday morning as the overnight cold
front continues pushing southeast.  This cold front will stall out
across central Ohio as a secondary mid level wave over the Midwest
approaches the Great Lakes drawing it back slightly Thursday night.
This will keep a good deal of clouds around Thursday with a small
chance for showers clipping the southeast portions of the forecast
area late night through Friday morning as models hint at a weak
surface wave riding up along the front.  After high pressure will
move across the region over the weekend bringing mostly clear skies
and seasonable temperatures.  A cold front is expected to sweep
through early Monday bringing a slight chance for showers.

MARINE...

Strong low pressure over the Upper Mississippi River valley will
wobble through the Western Great Lakes tomorrow. Confidence remains
high in southeast-south gales over the open waters of Lake Huron
this evening and tonight. Gale warnings remain in effect and will
likely have to be reissued for parts of Lake Huron on Tuesday as
colder air filters in from the south-southwest behind cold frontal
passage tonight. Best chance for Gales will be across central
portions of Lake Huron, which includes Saginaw Bay, otherwise small
craft advisories will likely be needed for the rest of the area.
Wind and waves will be slow to diminish on Wednesday as
cold axis tracks through, promoting deep mixing. Lighter
winds for the end of the work week, as westerly winds
expected to be below 20 knots on Thursday, and below 15 knots on
Friday as a ridge of high pressure builds through the northern Ohio
Valley.

HYDROLOGY...

Mainly light rain around this afternoon, with moderate showers this
evening as a cold front tracks through. An embedded thunderstorm can
not be ruled out. Even so, basin-average rainfall expected to reside
in the quarter to half an inch rain, thus no flooding anticipated.
Outside of a few light showers tomorrow, the rest of the work week
looks dry.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Lakeshore Flood Advisory until midnight EDT tonight for MIZ049-055-
     063.

     Lakeshore Flood Warning from 10 AM Tuesday to midnight EDT Tuesday
     night for MIZ063-070.

Lake Huron...Gale Warning until 4 AM EDT Tuesday for LHZ361>363-421-422-441>443-
     462>464.

Lake St Clair...Small Craft Advisory until 4 AM EDT Tuesday for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 4 AM EDT Tuesday for LEZ444.

&&

$$

AVIATION.....SC
DISCUSSION...DG/drc
MARINE.......SF
HYDROLOGY....SF


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at www.weather.gov/detroit.



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