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Area forecast discussion 
National Weather Service Detroit/Pontiac Michigan
314 am EST Friday Dec 19 2014

Short and tonight

The 00z DTX showed a saturated 850 mb layer...with a temperature/dew pt of
-10 c. Farther north...a dramatic apx revealed an
850 mb dew pt depression of 31 c. An upper wave seen over eastern
Ontario tracking into the eastern Great Lakes today will continue to
help with the dry push to the south...but confidence in clearing
diminishes as one heads south of the M-59 00z NAM
still indicating enough 950-925 mb moisture/relative humidity the
low level flow will be calm to very light. Surface
trough/convergence seen sinking south and exiting Lenawee and Monroe
counties shortly after 12z...and thus should end the freezing
drizzle threat as the drier air takes hold. NAM soundings showing
shallow moisture layer within the 1-2 kft layer through tonight (i-
94 corridor and points south) the low level inversion
increases/sharpens up. Current trends/clearing line are matched up
fairly well with the NAM...and will thus maintain a good deal of
clouds toward the Ohio border. Even with sunshine farther north
today...surface high in place will limit the mixing
middle December insolation will probably be only good for low/middle line with 925 mb forecasted temperatures of -4 to -6 c. Guidance
temperatures for tonight call for upper teens north to lower 20s south
due to the lingering clouds.


Long term...Saturday through Thursday

Upper level pattern will remain quasi-zonal through the weekend as
upper troughing over New England shift northeast and the beginnings
of the next upper trough over The Rockies/plains just get underway.
While precipitation chances will remain minimal through the weekend
as high pressure east through the Ohio Valley and Great Lakes...the
cloud forecast will remain tricky as a series of weak upper level
disturbances races through the relatively flat upper level flow.
This should maintain a general partly to mostly cloudy forecast.
Temperatures really won't change too much...perhaps moderating a few
degrees with highs ranging in the Lower/Middle 30s and lows in the middle

Aforementioned plains troughing begins to amplify significantly
early next week as a steady stream of northern Pacific jet energy
works east/southeast from the Pacific northwest/British Columbian
coast into the middle of the Continental U.S.. initially...this will lead to an
expanding shortwave ridge into the eastern Continental U.S....which will bring
a more notable moderation in temperatures Monday and Tuesday as
highs climb back to 40 degrees or better. Precipitation chances will
steadily increase during this time frame as moisture streams into
area within expanding southwest flow regime in advance of the
developing storm system over the plains. Other than an initial mix
of light rain/snow Monday as cold air is dislodged...expect mainly
rain Monday night into Tuesday as precipitation
general...markedly increase.

From that point forward...the forecast becomes ever more difficult
to pin down as the upper trough to the west pivots into area as a
negatively tilted feature. This should lead to a gradual transition
back to a rain/snow mix and then snow as colder air works east into
area with this expanding trough. Precipitation chances will remain
rather high as this trough works into the area. To complicate
matters further...medium range models remain somewhat split as to
how significant a southern stream shortwave will be as it lifts into
the developing upper trough over the area. However...given fact that
00z European model (ecmwf)/Canadian Gem noam both develop a rather robust storm over
or near the area by Wednesday as this southern energy phases into
northern stream trough...confidence is perhaps increasing slightly
that a noteworthy storm will work into/near the area by midweek.
While GFS does not share this solution at this least half of the
ensemble members do to a significant degree.

Such a solution would bring an expanding precipitation shield into
the area on Wednesday with a mixture of rain/snow changing to snow
with time as the system intensifies and lifts north/northeast into
the eastern Great Lakes/northeast Continental U.S. Into Wednesday night. While
the European model (ecmwf)/noam CMC do have rather ominous representations of this
potential winter storm...a number of scenarios still remain quite
plausible...ranging for minimal southern development of this
trough to the southern energy shifting east of the Appalachians and
then lifting up/near the eastern Seaboard. Given the uncertainty
of a day 6 forecast...will not adjust forecast too any great degree
with this forecast package. Suffice it to say that the midweek
period next week does appear to be rather active for the area as
compared to the current weather regime.



Surface high pressure is forecasted to build into the area during
the day today and then drift east across the central and eastern
Great Lakes over the weekend. This will lead to exceedingly calm
conditions for this time of least into much of Sunday.
Southerly winds will then begin to increase on the backside of this
high Sunday into Monday. Even so...rather agreeable marine
conditions are expected into early next week as winds/waves only
increase marginally within this developing south/southeast flow.


Aviation...issued 1154 PM EST Thursday Dec 18 2014


Weak surface troughing sustaining a light mix of freezing drizzle
with some snowflakes early this morning. This precipitation is
expected to diminish in coverage through the early morning hours.
The existing deep plume of low level moisture and associated MVFR
ceiling will be slower to decrease. Upstream satellite trends
would bring the edge of the clearing line now moving through
northern lower into mbs by daybreak. Moisture may be slower to
erode toward the south and will maintain a more gradual clearing
into the remainder of Southeast Michigan on Friday. A light wind field
through the period.

For dtw...there will continue to be the potential for a light
mixture of freezing drizzle and snow through 09-10z.

//Dtw threshold threats...

* high confidence ceilings remain below 5000 feet through Friday
morning...low confidence into the afternoon.

* High confidence that precipitation type will be a mixture of light
freezing drizzle and snow early this morning.


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


Short term...sf
long term....dg

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