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Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia
400 am EDT Sat Apr 18 2015

high pressure across the region today will be replaced by a back
door cold front tonight as low pressure moves from Quebec to the
Gulf of Maine. Weak high pressure will build back into the region
briefly Saturday low pressure approaches the area from
the Carolinas Sunday and Sunday night. A cold front will pass
through late Monday before high pressure brings cooler than
normal temperatures for the middle portion of next week.

Near term /through Sunday/...
a weak boundary bisects the area early this morning...marked most
notably in the dew point field. In central Virginia/southern Maryland where the
dew points are higher...and rain fell earlier...patchy fog has
developed. There have been a few fleeting observations of 1/4
sm...but for the most part the fog has been light. As long as the
lower dew points continue to advect in...the chance of widespread
dense fog is low...but will monitor.

High pressure over southern Canada will spread into the region
today. Mostly sunny skies...a drier airmass and sufficient mixing
will allow temperatures to once again rise above normal...with highs
in the 70s to near 80. Cannot totally rule out a sprinkle in the
southern Highlands due to low level easterly flow and a little more
moisture in place...but have left the forecast dry for now.

As the high slips east this effective back door cold
front will push down east of the Appalachians. Cooler and drier air
will settle in with lows dropping into the 40s...with 50s in the
metros and near the Bay.

The next system of note will approach from the SW on Sunday. Energy
digging into the central Continental U.S. Will turn the middle/upper flow to the
SW. Expect increasing clouds and rain to begin to spread in from the
SW due to isentropic processes. The timing may be a little
faster...but the highest rain chances remain in central Virginia...and
areas NE of District of Columbia may remain dry until evening. While it will take some
time for the airmass to saturate...moisture return will be strong
from Gulf and Atlantic trajectories. Temperatures will be cooler
with highs ranging from the middle 50s in the SW to middle 60s east.

Short term /Sunday night through Monday night/...
active 24 hour period of weather starting Sunday night through
Monday night. The first round of precipitation will be steady rain moving
into the region from the SW in response to an area of low
pressure. This is depicted well on both the 00z GFS and 00z European model (ecmwf).
Then a cold front will cross the region late Monday
afternoon...brining showers and thunderstorms to the area. Potential for
severe will be limited by the cloud cover...but despite this the
00z GFS is still giving about 1000 j/kg of cape for Monday
afternoon and evening with the frontal passage.

Long term /Tuesday through Friday/...
an upper low over Great Lakes will dominate the weather for the
long term as several vorticity maxes around the low will impact the
middle-Atlantic and NE unsettled weather for middle to late
week. Daytime highs will be about 10 degree below average starting
on Thursday and continuing into the weekend.

Aviation /08z Saturday through Wednesday/...
patchy fog has developed in central Virginia early this morning...with
variable visibility at cho. Am not sure if they will settle into one
category...but IFR or lower will be possible at times until after
sunrise. Otherwise expecting VFR conditions through the taf
period. Wind will be have a northerly component at less than 10
knots...becoming easterly on Sunday and increasing slightly.

MVFR ceilings late Sunday afternoon followed by IFR conditions for
both ceilings and visibilities expected at all terminals from 00z Monday through
12 Monday...improving Monday morning.

expect light northerly winds to continue today and tonight over the
waters as high pressure passes to the north. Do not see evidence of
increasing winds for tonight in the latest have
canceled the Small Craft Advisory for tonight. However winds will increase out of the
east for Sunday...and have raised an Small Craft Advisory for all waters beginning at
6 am as low pressure approaches from the Carolinas. Expecting to see
Small Craft Advisory winds from early Sunday through midnight Monday as shown by
both the 00z GFS and NAM BUFKIT profiles.

audio degradation at the National oceanic and atmospheric administration weather radio Charlottesville
transmitter is expected to continue through this weekend.
Technicians are scheduled to perform maintenance at the
transmitter site Monday.

Lwx watches/warnings/advisories...
District of Columbia...none.
Marine...Small Craft Advisory from 6 am Sunday to 2 am EDT Monday for

short term...Lee
long term...Lee

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