Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 051140

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
640 AM EST Mon Dec 5 2016


Aviation conditions have been steadily improving this morning as a
substantial area of midlevel dry air builds into the region from the
west. Ceilings have steadied into a solid MVFR stratus deck while
visibilities have improved to VFR for all areas. High ambient
moisture environment continues to exist at the surface with surface
dewpoints running in the low 30s, event above the freezing mark.
Given a well defined inversion, preference is to remain pessimistic
with sky cover and carry MVFR cigs right through the afternoon. An
active area of subsidence is expected to lead to a pocket of dry air
in the lower troposphere. This drier air is expected to develop over
the mid Mississippi valley today before lifting northeastward into
southeastern Michigan tonight. There is moderate to high confidence
the dry air will lead to scattering cloud conditions this evening.
The uncertainty for the tonight period is overall potential for
stratocumulus to fill back in after 06Z tonight with surface wind
directions decidedly turning to the southeast. There is some signal
that Lake Erie moisture may be advected to the NW and lead to
additional MVFR cloud.

For DTW...

MVFR cloud through today with high antecedent near surface moisture.
Strong low level dry air advection and loss of daytime heating
brings high confidence in loss of cloud this evening. Moisture will
eventually stream off of Lake Erie and push toward DTW after 06z
tonight. Confidence is medium in additional MVFR cloud development,
however, confidence is low in how widespread this cloud will be.

//DTW Threshold Probabilities...

* High in ceilings below 5000 feet today. Medium to low this
  evening, medium again after 06Z tonight.


Issued at 342 AM EST Mon Dec 5 2016


The next wave to exit out of the Alaskan region will be a strong one,
carving out a deep trough through the Mountain West and into the
Northern Plains mid week. The will reinforce the the weaker, more
chaotic trough already present near the region. This system will
usher in one of the coldest airmasses we`ve seen in a while with
850mb temps down to -20C spreading across much of Canada and into
the Northern Plains. 850mb temps in the mid teens will dig farther
south into the Central Plains, eastward through the Ohio Valley and
toward the Eastern Seaboard by the end of the week. The Great Lakes
will be engulfed by this airmass beginning Wednesday night and
persisting almost through the weekend. This will result in an
extended period from Thursday to Saturday where high temperatures
struggle to hit 30F and low temperatures will linger in the low 20s
or possibly upper teens. The other issue this airmass presents is
lake effect snow. This cold airmass over the relatively warm lake
water with westerly flow will produce lake effect snow through the
end of the week. At this point any accumulations look to be minor.

First things first though. Today a ridge will slide over the region
in between the exiting trough that brought accumulating snow to much
of MI Sunday evening, and the next lobe of vorticity to rotate
through the aforementioned Canadian trough. Model soundings show
this subsidence aloft will strengthen the inversion thus locking the
low stratus in through most of the day. Some drying after 21Z looks
to start scattering out the low level moisture so will follow this
trend with sky grids. High clouds streaming in ahead of a system
lifting north into Ohio will bring cloudy skies back by Tuesday

As the next northern stream vort lobe swings up through the western
Great Lakes, a southern stream system will race from Louisiana
Tuesday morning to the Carolinas that evening. Question remains as
to how much phasing there will be between the two systems. Models
have been back and forth about this for several runs now and appears
the eastward progress of the southern system will keep enough of a
disconnect to minimize impact over southern MI. There appears to be
a region of height falls advecting across the area with SE MI under
a relative minimum. With the amount of dry air in the lowest 10kft
of the column, it will take some time for the top down moistening of
the column enough to precipitate over the area. Trimmed pops down
from 12-18Z Tuesday to account for this. 18-00Z will likely need
some adjusting but it`s far enough out to allow hires to get a
better grasp of it before jumping all in. With the likely later
starting time of any light precip, ptype should be primarily all
rain through the afternoon and evening as surface temps climb to
around 40. Dewpoints in the mid 30s will not allow for wetbulbing to
cool the column enough for much snow to mix in. High pressure
sliding across the Ohio Valley Tuesday night will work up into the
area ending any light precip.


Surface high pressure will track along the Ohio River bringing
relatively benign marine weather for December to the central Great
Lakes. West winds will develop today with wind speeds in the 15 to
25 knot range, transitioning southeasterly on Tuesday at 15 to 20
knots. Two separate surface low pressure systems are forecasted to
advance into the central sections of the United States for the
middle of the week. At this time, it appears that lower Michigan and
Lake Huron will be positioned in a corridor of weak pressure
gradient as the low pressure systems track eastward. An organized
cold front is shown to push across the area Tuesday opening the door
to an unmodified arctic push and stronger westerlies. West wind may
exceed 30 knots later Tuesday night and on Wednesday. Unstable
conditions over area waters and fresh westerly surface flow is
likely to hang around through the end of the week.


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



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