Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 272347
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
647 PM EST Sun Nov 27 2016


.AVIATION...

Quiet aviation weather will continue tonight with the sharp
downstream 500mb midlevel ridge in place directly over Wisconsin and
Michigan. The main forecast question outstanding for tonight is what
sort of fog potential exists. Been watching reduced vsbys holding in
the Saginaw Valley and northern Thumb where MVFR stratus was very
slow to relinquish. Feeling is this is a precursor that vsbys could
tank and fog may set in over northern areas tonight. Farther south,
expecting more southeasterly gradient flow to hold which should
discourage thicker fog. Undoubtedly expecting some hz/br given
current dewpoint depressions, but expecting just MVFR vsby
restrictions at this time.

There is a model consensus that brings a theta e discontinuity and
convergence corridor that results from a nocturnal low level jet
cycle. This precipitation is forecasted to weaken as it arrives but
will bring the potential for a 2 hour duration for rainfall between
14-16Z Monday.

Quiet weather will then develop for much of Monday with
southeasterly wind increasing between 12-15 knots.

Main area of widespread precipitation is expected to develop and
lift northward into southeastern Michigan during the late afternoon
on Monday. This area of precipitation is of high confidence as fresh
height falls and secondary cyclogenesis event develops from the mid
Mississippi River Valley northward under strong left exit region
dynamics aloft. Expecting widespread rainfall Monday evening with
IFR to possibly LIFR conditions Monday night.

For DTW...Will be watching for fog potential this evening in
regional observations. Right now thinking that MVFR visibility
reductions will exist throughout much of the night. Brief window for
weakening rain showers mid Monday morning. Rain widespread by late
Monday afternoon.

//DTW Threshold Probabilities...

* Moderate for ceiling 5000 feet briefly Monday morning. High for
  prevailing cig less than 5000 ft by late Monday afternoon and
  night.

* Low for visibilities to drop to 1/2sm tonight.

&&

.PREV DISCUSSION...
Issued at 332 PM EST Sun Nov 27 2016

DISCUSSION...

Negatively tilted ridge over the Great Lakes will get forced north
and east away from the area overnight by the approaching upper level
trough currently digging into the Central Plains while it tracks
eastward. This expansive trough will stall over the region through
the coming week presenting several opportunities for precipitation.

The ridge axis traversed the area this afternoon opening the door
for weak southwesterly flow and moisture advection aloft into the
region. Afternoon drying trend in the boundary layer will continue
with increased diurnal mixing, but cirrus will start to spread into
the region tonight on the elevated warm front extending east from
the low. The southwesterly flow will keep low temperatures tonight
above freezing for most locations.

The rest of the forecast focuses on the aforementioned upper trough
which will settle over the Central Plains and Midwest by Monday
evening. The orientation of the jet and strong shortwave surging
around the base of the trough will cause the mid level vort max to
retrograde and get cut off from the main flow positioning it over
the Northern Plains. The initial warm front will lift through
southern MI early Monday morning but will be weakening over the area
being a fair distance from the parent low and best height falls
wrapping into the low to our west. Secondary area of height falls
will be to our south coincident with the surging shortwave lifting
into the Ohio Valley Monday night. With amount of dry air in the low
levels and weakening forcing aloft, think precip should hold off til
after 12Z Monday morning. Monday will feature increasing chances of
rain as a surge of mid level moisture ahead of the shortwave spreads
into the region. Lead edge of the stronger isentropic ascent will
spread north between 12-18Z. The jet will then reorient itself with
the left exit region becoming positioned over southeast MI
overnight. This as the southwesterly 850mb jet flairs up with speeds
approaching 60 knots with good feed of moisture advection
originating from the western Gulf of Mexico. Highest pops will occur
00-12Z Tuesday with around 0.5 to 0.75 inches of rain falling. Ptype
looks to be all rain through the event as temperature profile
remains above 0C from the surface up to around 750mb. One last thing
regarding the strong low level jet Monday night. Will need to watch
mixing depths overnight as models mostly agree in 30 knots winds
down to around 1500 ft AGL. Momentum transfer advertises gusts to
around 20 to 25 knots.

Impressive dry slot with then surge through lower MI on Tuesday
bringing an abrupt end to the rainfall in the morning. The trough,
still holding to our west, will allow ridging to lift into southern
MI. Warm advection will increase 850mb/925mb temps to near 5C/9C by
Tuesday evening. This should allow max temps to make a run into the
upper 50s (maybe a few 60s).

Mild temperatures will be felt for one more day on Wednesday as
strong southwesterly flow continues as the area resides in the warm
sector ahead of the cold front.  The low pressure system over the
Northern Great Lakes region slowly rotates up towards the northeast
through the end of the week.  This system will bring a cold front
across the area late Wednesday, bringing an end of the warmer temps
as colder air filters in behind the front on Thursday.  Slight
chances for showers will remain through the week before conditions
dry out the first weekend of December as ridging builds in over the
region.  Temps will drop back into the 40s for highs to round out
the week, with temps even dropping a little more this weekend.

MARINE...

Favorable marine conditions will continue tonight as high pressure
drifts east of the Great Lakes. Light south wind will become
moderate late tonight through Monday as a large low pressure system
organizes and increases intensity over the Plains states. This
system will support a fresh southeast breeze from Lake Huron through
western Lake Erie Monday likely reaching gale force Monday night
over the open waters of Lake Huron. The central and northern
portions of the lake are expected to experience mid 30 knot to near
40 knot gales and waves near 20 feet as a long SE fetch combines
with a strong occlusion of the low pressure system. There will also
be a few hours of overlapping strong gradient flow with a deeper
unstable layer just prior to passage of the occlusion. Small craft
advisories are in effect Monday for outer Saginaw Bay and southern
Lake Huron as the system ramps up. Gale watches remain in effect
Monday night through Tuesday morning for these areas along with the
open waters of Lake Huron. Wind conditions are projected to improve
Tuesday night into Wednesday as direction shifts to the southwest
bringing milder air and more stable conditions over the region.

HYDROLOGY...

A large low pressure system organizing over the Plains states
tonight will strengthen considerably during Monday. The system will
pull an abundant supply of moisture northward from the Gulf of
Mexico and bring a high probability of rain to SE Michigan Monday
night. Total rainfall amounts around a half inch are expected across
the region during this time. This is an above normal amount of
rainfall for this time of year but it is not expected to result in
any flooding hazards.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Gale Watch from Monday evening through Tuesday afternoon FOR
     LHZ361>363-421-441>443-462>464.

     Small Craft Advisory from 7 AM to 7 PM EST Monday FOR LHZ421-
     441>443.

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

$$

AVIATION.....CB
DISCUSSION...DRK/SS
MARINE.......BT
HYDROLOGY....BT


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