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Area forecast discussion...updated 
National Weather Service Baltimore Maryland/Washington District of Columbia
1025 am EST sun Dec 28 2014

Synopsis...
a cold front over Ohio will move into the area today. Low
pressure will move along the stalled front this afternoon and
evening... pushing the front south of the area. Another low
pressure system will move across the Carolinas Monday and Monday
night. Strong high pressure will build over much of the country by
Tuesday...and gradually push eastward during the rest of the work
week.

&&

Near term /until 6 PM this evening/...
a cold front being dragged along by an exiting low pressure system
north of New England has yet to enter the northwestern County Warning Area. Still sliding
from central PA to the windward side of the Appalachians...the surface
boundary - even appearing on regional radar scans - inching its
way east-southeast. Plenty of middle-level moisture has been streaming across
the middle-Atlantic from the upper Midwest - but the westerly component to the
flow has allowed the Appalachians to do their typical moisture
robbing...preventing much more than dense middle clouds to move east.

A minor kink in the upper flow will arrive from the lower tenn
valley in the coming hours...developing a locally more enhanced area of
precipitation from the Blue Ridge eastward. Hi-res derivatives like the hrrr
and various WRF runs show this well...but still only a light and
scattered nature to the incoming rain showers. Total quantitative precipitation forecast values
from this activity through the end of the day only in the trace-few
hundredths of an inch...locally near 0.1-0.2" on the high- end.

&&

Short term /6 PM this evening through 6 PM Monday/...
periodic light rain will drift south with the frontal boundary into
Monday. Perhaps an additional tenth inch rain...particularly south
of District of Columbia. Northwest winds increase to around 10 miles per hour tonight with cold
air advection resulting in min temperatures of low 30s for northern and western
fringes...middle to upper 30s elsewhere. Rain ends as snow for these
fringe areas near the Mason-Dixon line and for ridges. No snow
amounts were added as of yet with low probability of precipitation...but there is the
possibility of a dusting...particularly at high elevations.

21z sref was eager to have high probability of precipitation in for most of the County Warning Area through
Monday. However...went with consensus of NAM/GFS/ECMWF with having
likely probability of precipitation for rain limited to southern Maryland Monday morning. Low level
flow is more northeasterly Monday afternoon...which would promote chance probability of precipitation
for rain/snow mix over terrain the southwestern part of the County Warning Area. No wintry
accumulation there either with just chance probability of precipitation.

&&

Long term /Monday night through Saturday/...
basically the extended boils down to two precipitation systems at the
start and end of the long term with cold high pressure sandwiched
in between.

Monday and Monday night...still some uncertainty based on model spread
of precipitation for Monday. 00z/NAM and GFS solutions show most of the
precipitation slipping south and east of the County Warning Area early Monday am. But
00z/European model (ecmwf) lingers some moisture across southern tier of zones. Kept
slight to chance probability of precipitation in for Monday over the County Warning Area...and with temperatures
cold aloft but boundary temperatures above freezing...mentioned
rain/snow mix possible. By Monday night...lingering moisture across
southern tier of zones warrant chance probability of precipitation...with likely probability of precipitation in
far SW portion of County Warning Area across Highland County and southern Pendleton
counties...and cold enough there for accumulating snow around an
inch in upslope areas.

Tuesday...cold air loft is a certainty as the large polar air mass
settles over much of the Continental U.S. East of The Rockies. The 00z/NAM
and 03z/sref are again show being aggressive with a weak
disturbance that the 00z/GFS/ECMWF/ukmo solutions show a much weaker
and flatter system that stays south. At this point any precipitation
amounts Tuesday will be light but could be in form of snow.

Wed-Fri...high pressure dominates with seasonably cold weather and
dry conditions.

Late Fri-Sat...next system will approach from the southwest as
models show a large low pressure system moving from the Central
Plains late Friday moving into the upper Great Lakes on Sat. This
system looks like it could bring a wintry mix initially Friday
night with the expected track of the low northwest of the County Warning Area...
lots of warm air will be advected into the area...changing precipitation
to liquid by Sat morning. Of course...timing and position and
track of the low is low confidence at this point.

&&

Aviation /14z Sunday through Thursday/...
VFR conds through into the early afternoon...as rain associated with a
cold front approaches from the Ohio Valley today. MVFR conds this
afternoon in mainly light rain. Front stalls/drifts south
tonight...so conds continue to lower with IFR possible...but kept
06z tafs with MVFR ceilings. Light westerly flow today...northwesterly flow up to 10
knots tonight...northerly flow 10 knots Monday.

MVFR to IFR ceilings/visibilities Monday and Monday evening. VFR conditions Tuesday
through Thursday...with possible MVFR ceilings in snsh- activity Tuesday.

&&

Marine...
light southwesterly flow veers northwesterly today as a cold front crosses the waters
this afternoon and evening. Could be a northerly surge with gusts around
18 knots late tonight. Did not raise an Small Craft Advisory due to uncertainty...but
one out of Sandy Point is possible into Monday.

Mon-Wed...expect winds to remain below Small Craft Advisory levels. Precipitation on Monday
pushes south and east late Monday. High pressure builds in Tuesday and
continues through end of the week.

&&

Lwx watches/warnings/advisories...
District of Columbia...none.
Maryland...none.
Virginia...none.
WV...none.
Marine...none.

&&

$$
Update...gms
previous discussion...baj/smz

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