Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
814 PM EDT Tuesday Sep 23 2014
high pressure will hold over the region through early Wednesday.
Low pressure will move north along Atlantic coast from late
Wednesday through through Thursday night. More high pressure is on tap
for this weekend.
Near term /tonight/...
Large area of high pressure centered over New York state. High clouds
primarily cover southern Virginia...but scattered cirrus stretch into southern PA.
Tonight cloud cover will begin to spread into southern and eastern
parts of the County Warning Area...but dry weather is expected. Lows range from the low
40s in the Potomac Highlands to the upper 50s near Chesapeake Bay.
Short term /Wednesday and Wednesday night/...
Low pressure becomes gradually more organized as it moves up the
coast. Forecast follows European model (ecmwf) and GFS more closely...as NAM is an
outlier in organizing the low more fully and a more eastward
track. Likely probability of precipitation for rain into southern Maryland...but precipitation shield
may reach further northward towards Washington District of Columbia and
Charlottesville by the end of the day. Highs generally in the
upper 60s and low 70s.
The low continues to push northward Wednesday night...reaching the
Delaware-Maryland-Virginia by early Thursday morning. See Hydro section below about rain. Breezy
easterly winds expected as the low interacts with a high along the
New England coast. Likely probability of precipitation pretty much everywhere east of the
Blue Ridge. Cloud cover and marine moisture will keep temperatures from
dropping much Wednesday night...with lows over most of the area in
the upper 50s and low 60s.
Long term /Thursday through Tuesday/...
As an area of low pressure moves northeast from the Delaware-Maryland-Virginia
peninsula out into the open Atlantic Ocean Thursday...rain chances
will decrease from west to east. High pressure will provide good
subsidence in the western half of the region.
This high will dominate the region Thursday night through Sunday
morning...providing plenty of sunshine which will lead to warm
afternoons and comfortable nights. Highs should reach 80 if not a
few degrees above during each afternoon.
A weak...yet moisture-starved...cold front could drop in across the
region late Sunday into Sunday night. Left probability of precipitation around 10 percent or
less for now...considering the limiting moisture factor ahead of the
A reinforcing area of high pressure will build behind the front
Monday through Tuesday. This will lead to highs reaching the upper
70s to near 80 and beautiful afternoons.
Aviation /00z Wednesday through Sunday/...
VFR conditions expected through Wednesday morning.
Rain expected to move into the Baltimore/Washington terminals
wednesdsay evening and Wednesday night...with MVFR or IFR
MVFR or IFR conditions more probable at the iad...dca...BWI and mountain
terminals Thursday as rain showers and a gusty breeze linger on the
backside of a departing low pressure system. Winds north-northeast 10 to 20 kts
gusting 25 kts Thursday.
VFR conditions at all terminals Thursday night and Friday. Winds
north to northwest 5 to 10 knots gusts 15 knots Thursday night and
Winds continue to increase Wednesday as low pressure approaches
from the south. Small Craft Advisory begins 10 am Wednesday for the southern
portion of the tidal Potomac and Chesapeake Bay south of Sandy
Point. Periods of rain likely Wednesday afternoon through
Wednesday night. Small Craft Advisory has been extended through Wednesday night for
these areas as the low approaches the Tidewater/Delaware-Maryland-Virginia region
and the pressure gradient near the low increases.
The Small Craft Advisory may need to be expanded further northward in future
Small craft advisories may be needed Thursday into Thursday night.
Small craft advisories are possible...once again...Friday as a low
pressure system near the East Coast interacts with building high
Took a look at the potential for freshwater fldg. At this time blv
threat is on the low end. Although for the yr total we have been above
average in precipitation this month has been very dry. Sept totals:
Dca 0.43" iad 0.22" BWI 0.95" cho 0.26" mrb 1.83"
This avgs over 2" below normal for the month.
There will be low level Erly flow Wednesday into Thursday. Rafl will likely begin Wednesday
afternoon in the Northern Neck of Virginia...working into the District of Columbia/balt corridor Wednesday evening.
Hviest rafl expeceted Wednesday night into Thursday morning. The area of hviest rafl looks
again to be in the I-95 corridor. Models project the low pressure as being
fairly transitory...which works against the possiblity of fldg from rain.
In adtn given the low rafl totals of the past month the grnd is
quite dry. If the rafl intensity was going to be at the r+ level the
hardness of the grnd could work to exacerbate the runoff/fld
threat. However suspect rain would fall at more of a MDT rate which
would lead to greater absorption.
Have added mention of possible fldg of streams and crks in the eastern part
of the forecast area. River levels are much too low to be of concern.
Blv hviest rafl will be moving into Delaware/New Jersey Thursday morning.
A coastal low pressure system well to our south will slowly approach
the area Wednesday into Wednesday night. This will lead to higher
than normal water levels particularly over the western shore of
the Chesapeake Bay. Minor tidal inundation will be possible during
the times of high tide. Effects for Thursday will be highly
dependent on the track of this system. Winds will shift to the
north of the low tracks east of the Bay...which would reduce or
eliminate tidal anomalies.
District of Columbia...none.
Marine...Small Craft Advisory from 10 am Wednesday to 6 am EDT Thursday