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fxus61 klwx 180130 

Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
830 PM EST sun Dec 17 2017

a weak boundary overhead will lift to the north as a warm front
tonight into Monday. An upper level disturbance will approach
the area from the west Monday afternoon and evening. This
disturbance could bring some light precipitation to the
appalachian front later Monday. High pressure will build in
briefly before the next storm system scoots by to our south
during the middle of the week.


Near term /through Monday/...
a warm front was stationed just north of the Potomac River as
of 8 PM. Removed mention of sleet along the Mason-Dixon line as
dew points have risen to 30+ degrees and air temperatures are
in the lower 40s. Wet bulb 0 c heights are, at best, 2500 feet.
Otherwise, forecast on track with sprinkles or spotty light
rain ending this evening as the warm front lifts north. Skies
are expected to remain mostly cloudy overnight. Low temperatures
will bottom out near or slightly above freezing outside of the
major cities, upper 30s in the downtown areas.

As for the upslope areas west of the Allegheny Front,
moisture/lift appear too shallow/weak for appreciable snowfall
accumulation. Some light rain and drizzle mixed with pellets or
snow grains seems most likely, with perhaps a light coating at
the highest elevations between midnight and daybreak before
temperatures warm.


Short term /Monday night through Tuesday night/...
as a warm front pushes to the north Monday, so do the milder
temperatures will highs about 5 degrees warmer than Sunday. A
light persistent southwest wind will aid in this milder trend.
By Monday afternoon into Monday evening, clouds and precipitation
will return with the bulk of any precipitation remaining light
and mainly confined to the appalachian front in the form of
light rain or drizzle. A leeside trough of low pressure should
set up just to the east of the appalachian spine, thus, allowing
for this precipitation to occur with the help from a weak mid-
level disturbance.

Tuesday should be even milder yet with highs ranging from the
middle 50s to the middle 60s widespread across the region. A
persistent southwest wind and a little added sunshine during the
day should aid in this. Tuesday night will be about the same as
Monday night with low temperatures dropping into the middle to
upper 30s for the most part.


Long term /Wednesday through Sunday/...
southern stream shortwave energy will be approaching the mid-Atlantic
region on Wednesday into Wednesday night. Guidance suggests that the
forcing will stay south of US, but showers associated to this system
could reach the southern counties of our County Warning Area. Still to be determined
in more detail is timing and p-types.

A ridge of high pressure builds over the region on Thursday and into
Thursday night bringing a period of dry weather. Sometime on Friday
a warm front will push through, followed by a cold front on Saturday.
Models suggest that Friday will remain on the drier side while Friday
night we might see showers ahead of the front, but it all depends
on the timing of it. Saturday's pops are higher with the front moving
through the region from the west. Uncertainty exists on sunday's
weather depending on how close to the area the front stalls.


Aviation /00z Monday through Friday/...
winds generally southwest less than 5 knots through Monday. VFR
conditions expected tonight through Tuesday night. Hrrr hinting
at some MVFR visibility 9-12z in vicinity of iad/BWI/mtn tonight. Can't
rule out brief patchy fog in these areas if breaks in clouds
develop given high relative humidity values/calm winds.

Some guidance (namely the met) is hinting at fog development
near the Bay Monday night which makes sense given light winds
and environmental dew points higher than water temperatures.

Mainly VFR conditions expected the second half of the week.


no marine hazards through Monday night. Winds become light and
variable tonight, then southwest 5-10 kts Monday into Tuesday.

Fog is possible over the waters Monday night which makes sense
given light winds and environmental dew points (mid to upper
40s) higher than water temperatures (around 40).

Winds should increase late Tuesday into Wednesday near and behind
a cold front. Small craft advisories may be needed for portions
of the waters during this time. Near shore waters likely see
gusts first since open waters will be much cooler than
environmental airmass. Mixing would presumably be more
difficult over open waters until a cooler airmass arrives later
Tuesday night into Wednesday.


Lwx watches/warnings/advisories...
District of Columbia...none.


near term...klw/dhof

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