Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia
929 PM EDT Wednesday Apr 16 2014

Synopsis...
high pressure over New England will ridge southward toward the
middle-Atlantic coast through the remainder of the week. An area of
low pressure and cold front may affect the area Saturday.

&&

Near term /through Thursday/...
a 1036 mb surface high that is centered over northern New England at 00z
ridges southward into our region. Winds had already decoupled at the surface
in most locations after sunset and mainly clear skies are
present...setting the stage for temperatures to drop quickly tonight under a
good radiational cooling setup. Except for some locations along
the waters and in the cities...temperatures will fall at or below freezing overnight.
For the second straight night...freeze warnings are in effect for
all counties east of the Blue Ridge where the growing season is
active. A hard freeze is possible in the more rural areas west of
I-95.

North-northeasterly winds around the high will gradually veer out of the east
late tonight and Thursday as the ridge axis shifts toward the middle-Atlantic
coast. Marine layer is expected to advect inland under onshore
flow in the llvls. Models show moisture trapped below subsidence
inversion to the east of the Blue Ridge. Have increased cloud
cover accordingly across the eastern County Warning Area during the late morning and
afternoon. Maximum temperatures will be below normal and in the 50s. Some
spots in the central Shenandoah Valley and valleys of the Potomac
Highlands may reach 60f with more sunshine.

&&

Short term /Thursday night through Saturday/...
a wedge of high pressure from New England to the Carolinas will
interact with an inverted trough of low pressure between the East
Coast and Bermuda to produce a moderate northeast to east flow.
Winds will be gusty Thursday evening but then diminish overnight.
Low temperatures will be about 5 to 10 degrees below normal.

As the high pressure pulls away to the northeast...the pressure
gradient will relax. An upper level system will pivot across
east-central Canada Friday and Friday night. A surface cold front
will push across the region late Friday night but should be a dry
front as there will be very little low level moisture. High and low
temperatures will be about 5 to 10 degrees below normal once again.

As the surface front moves south and east Saturday morning...high
pressure will build across the eastern Great Lakes into the middle
Atlantic region. Winds will become gusty out of the northwest
Saturday but should diminish Saturday night when high pressure
ridges southward along the eastern slopes of the mountains.

&&

Long term /Saturday night through Wednesday/...
high pressure will bring dry weather with near normal temperatures
to the area for the second half of the weekend into early next week.
Ridging erodes by Monday night with low pressure approaching from
the Mississippi Valley by Tuesday. This low will bring a chance of
showers to the area late Monday night through Tuesday. Ridging then
re-establishes itself across the area during the middle of next week
leading to a return to dry weather.

&&

Aviation /01z Thursday through Monday/...
high pressure builds down through the middle-Atlantic through Thursday.
VFR conditions expected during the valid taf period...with winds
veering from northeast to east late tonight and Thursday. Stratocu deck
associated with marine layer may become broken after 15z Thursday over eastern
terminals. Ceilings would likely be around 4 kft.

Marine stratocu hovering near VFR-MVFR levels Thursday night.

VFR Friday through Saturday. Northeast winds may gust 15 to 20 knots
Thursday night near mountain...BWI and dca with a pressure gradient
along the coastal areas. Light and variable winds Friday and
Friday night. With the passage of a cold front Saturday...winds
will become northwest and gust 20 to 30 knots. VFR conditions are
expected Sunday with easterly winds 5 to 10 knots.

&&

Marine...
winds have shifted out of the east-NE this evening and subsided to 10-15
knots. Winds may increase a bit later tonight as winds veer to the
east as the pressure gradient strengthens ever so slightly. Small Craft Advisory
is expected to expand across the waters on Thursday.

No marine hazards expected Thursday night through Saturday morning.
Small Craft Advisory conditions may be possible Saturday afternoon
with northwest winds expected to gust 20 to 30 knots. Sub-Small
Craft Advisory conditions are forecast Sunday into early
next week.

&&

Tides/coastal flooding...
water levels remain 1 to 2 feet above normal but as winds have
diminished and then veer to the east negative departures will
decrease through Thursday.

&&

Climate...
near record cold temperatures this morning...

Two of the three major metropolitan area airports...BWI and iad...got close
to their daily record low temperatures this morning.

At Reagan National Airport...dca...a morning low of 34f was well
above the record of 29f set on this date in 1928.

At Baltimore-Washington international...BWI...a morning low today of
31f was just one degree off the record low for the date set in 1962.

At Dulles...iad...the min of 30f this morning was two degrees shy of
the daily record low of 28f set on this date in 1981.

Regarding record low daily maximum temperatures for April 16...as of 3pm
today...Dulles is still tied with its daily record low-maximum of 46f
but with several hours left of sun will likely rise above 46f. Both
BWI and dca have risen above their respective daily record low-maximum
temperatures for April 16.

Record lows for April 17...

BWI...26f in 1962
dca...26f in 1875
iad...27f in 1983

&&

Lwx watches/warnings/advisories...
District of Columbia...freeze warning from 2 am to 9 am EDT Thursday for dcz001.
Maryland...freeze warning from 2 am to 9 am EDT Thursday for mdz004>007-
009>011-013-014-016>018.
Virginia...freeze warning from 2 am to 9 am EDT Thursday for vaz036>040-
042-050>057-501-502.
WV...none.
Marine...Small Craft Advisory from 3 am to 6 PM EDT Thursday for
anz530>533-538>541.
Small Craft Advisory from 6 am to 6 PM EDT Thursday for anz536-
542.
Small Craft Advisory until 6 PM EDT Thursday for anz534-537-
543.

&&

$$
Synopsis...jrk/bpp
near term...jrk
short term...klw
long term...dfh
aviation...jrk/klw/dfh
marine...jrk/bpp/klw/dfh
tides/coastal flooding...bpp/jrk
climate...smz