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Area forecast discussion 
National Weather Service Detroit/Pontiac Michigan
505 am EST sun Dec 28 2014



Aviation...

High pressure building into the region will result in clearing skies
through the afternoon and light northwesterly flow. Clouds will
start off today with some lingering MVFR ceilings but dry air will bring
VFR conditions to all terminals this afternoon and into the
overnight. A cold front dropping in from the north will introduce
some middle clouds late tonight.

For dtw...only issue in the near term is The Pockets of MVFR ceilings in
the area hovering around the 2000ft threshold. They should not last
long into the daylight hours before lifting to VFR.

//Dtw threshold probabilities...

* high for ceiling below 5000 feet through about 16z...and
medium after 12z Monday.

&&

Previous discussion...issued 358 am EST sun Dec 28 2014

Short term...today and tonight

The story for the short term is the influx of cold air resultant of
a pair of cold fronts passing through lower Michigan. The first front
passed through Southeast Michigan between 00-04z early Saturday night.
Temperatures aloft have already been trending down with the warm
bubble at 700mb dropping from about 3c 00z Saturday to -3c Sunday
00z and forecast to be down to -10c by 12z Sunday. Cold air advection will steady
itself through the day before a back door cold front passes through
tonight bringing another surge of cold air into the area. Besides
decreasing temperatures...the airmass will be much drier with little
moisture above 850mb until the back door cold front brings in some
middle level moisture. The dry air should be able to scatter out the
low stratus deck allowing a good deal of sunshine later this
afternoon...especially for southern locations further away from the
approaching backdoor cold front. This will offset some degree of
cooling but not enough to allow temperatures to climb out of the middle 30s.
Some returns on radar early this morning are amounting to nothing
more that a low stratus deck over the area. Some lake enhanced snow
showers drifting across western lower will take a run at our western
counties but with the shallow nature of the moisture and the dry air
it has to work across...will keep the forecast dry. With mostly
clear skies taking US into the overnight...radiational cooling will
allow US to drop into the 20s before clouds start filling back in.

Long term... Monday through Saturday

A gradual expansion of the lower height field associated with the
northern stream central Canadian trough will work into Southeast Michigan
on Monday. This process will help initiate the early and weaker
stages of what becomes roughly a 60 hour period of cold air
advection that will define weather conditions throughout the early
and middle week periods. Lead frontal boundary will exit to the south
by Monday morning...the ensuing cold air advection dropping
temperatures within the 850-925 mb layer 4-5 degrees relative to
today. Low level flow out of the northwest favors a drier low level
moisture profile...the limited depth suggesting at least partial
sunshine with simply a few flurries within any pockets of stratocu
with the cloud layer residing around -12c. Highs upper 20s north to
lower 30s south.

Cold air advection will strengthen into Tuesday as the passage of
weak shortwave energy provides a more sizable southward expansion of
the existing lower height field. This process will continue through
Tuesday night...reinforced by a secondary and stronger elongated
wave of Arctic origin translating through. 850 mb temperatures
remain projected to bottom out in the -18c range by Wednesday.
Highs will arrive in the 20s both days /coldest Wednesday/...the
first time for consecutive days below the 30 degree mark since late
November. Suppressed inversion heights with limited moisture depth
above 850 mb maintains a lackluster profile for greater downstream
penetration of lake moisture and associated snow showers through
this time...despite a general realignment of the flow toward west-
northwest by Wednesday. Void of any tangible forcing at this
stage...looking at nothing more than the occasional flurries.

Upper troughing firmly entrenched through New Years Day...modest
recovery off the cold morning lows /teens/ will again leave highs in
the 20s. Deepening southwest flow immediately downstream of the
southwest Continental U.S. Cutoff low set to eject east initiates a solid
response in warm air advection and moisture transport by Friday.
This will likely introduce a lead corridor of precipitation within
the expanding Wing of isentropic ascent...as early as Friday night.
Too early at this stage to properly delineate ptype...but both the
European model (ecmwf) and GFS point toward a thermal profile still cold enough for
snow at least at the onset. Beyond this...the usual uncertainty
remains at this timescale in terms of timing...strength and track of
the parent upper low/wave projected to open up and work east-
northeast across the Midwest through Saturday. Subsequent model
treatment of the maturation of this synoptic system as it pulls east
of the Mississippi will certainly be Worth monitoring going forward.

Marine...

Recent observations across Northern Lake Huron indicate winds are
diminishing in speed early this morning. This will support allowing
the ongoing Gale Warning and small craft headlines to expire as
scheduled. A modest westerly wind will remain in place today.
Winds will shift to northwesterly as much colder air funnels in
through the early week period. Despite this wind speeds will remain
at moderate levels both Monday and Tuesday. There will be some
increase in winds by Wednesday and Thursday. This will bring the
potential for a period of west or southwest gales over portions of
Lake Huron during this time.

&&

DTX watches/warnings/advisories...
Michigan...none.
Lake Huron...none.
Lake St Clair...none.
Michigan waters of Lake Erie...none.
&&

$$

Aviation.....Drk
short term...drk
long term....mr
marine.......mr



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