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Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia
1022 am EDT Sat Mar 28 2015

Synopsis...
an upper-level trough will move across the eastern United States
today and tonight. High pressure will build overhead on Sunday. A
series of weak systems will affect the area throughout the
upcoming work week.

&&

Near term /until 6 PM this evening/...
surface analy and water vapor imagery depicts a steep trough axis across
the Great Lakes/upper ohvly. There are several zones of convergence embedded west/in
this trough. The first of these was a dewpt gradient that slid across
the eastern County warning forecast area this morning. The end result was scattered flurries across County warning forecast area
with a more concentrated area of light-MDT snow across NE Maryland. Radr
activity has gnrly diminshed...although rtns in ME Maryland suggest that
flurries linger. Have scaled back on enhanced probability of precipitation for the midday
hours.

Latest model guidance continue a trend first identified overnight-- a 2nd fairly
vigorous vorticity will pinwheel across PA taftn near a nearly cutoff 500 mb
low. This feature will have the advantage of making use of decent
low-middle level lapse rates /5c/km/...supporting another batch of
showers. Surface temperatures should be warmer...and may prompt some melting.
However...800 mb temperatures will be in vicinity of -12c at that time...so some snow and
even some graupel may fall as well. Will pad middle-late afternoon probability of precipitation across
northestern Maryland /again/ to acct for the 2nd round.

Temperatures running colder than guidance...and isnt helped by the now patchy
snowcover in Maryland. Have trimmed maxt by several degf.

&&

Short term /6 PM this evening through 6 PM Sunday/...
middle/upper trough axis begins to slide east tonight as surface high
pressure builds into the Ohio Valley...allowing skies to clear.
Gradient will prevent winds from diminishing...but the air will be
dry and anomalously cold. All locations expected to drop below
30f...with teens west of the Blue Ridge and perhaps some single
digits on the ridgetops. See climate section below for records.

The surface high will quickly drift southeast across the area Sunday as the
next upper trough pushes into the upper MS valley. Skies will be
mainly sunny but return flow will be modest and temperatures will remain
below normal. Expect highs in the upper 40s to lower 50s.

&&

Long term /Sunday night through Friday/...
an upper trough...not nearly as amplified or strong as the current
one...will clip across the region Sunday night into Monday...sending
an associated cold front through the region. Moisture return is
limited and 800 mb/h9 flow quickly shifts to westerly even ahead of the
front. The operational suite of models is quite dry east of the
Allegheny Front...but ensemble data hints at a brief window of light
precipitation overnight further east. Kept mention in generally
along/west of the Blue Ridge...and some light snow is possible in
the cold pockets.

Despite frontal passage...the westerly winds will promote quick warming on
Monday...with highs soaring into the 60s east of the Blue Ridge and
perhaps close to 70 in the Piedmont.

A second shortwave will pass mainly to the north on Tuesday. Most
likely the precipitation stays north of the Mason-Dixon line but I
did keep slight chances in almost the entire forecast area on
Tuesday and roughly north of US 48/50 on Tuesday night.

High pressure quickly shifts offshore by Wednesday afternoon with
return flow commencing and warm moist air quickly spreading north
for the end of the work week. A weak southern stream impulse is
expected to pass across the Carolinas and middle-Atlantic on
Thursday...with scattered showers and perhaps a thunderstorm. Highs
near 70 are likely in valleys west and south of District of Columbia.

Model solutions diverge beyond Thursday...with the 00z GFS pushing a
cold front through on Friday. The European model (ecmwf) is slower...and in these
scenarios I tend to favor a slower solution rather than barreling a
front through. So Friday was kept seasonably warm with rain
chances.

&&

Aviation /14z Saturday through Wednesday/...
VFR conditions will mainly prevail through the taf period. The
only exception could be a chance of showers today. These could
contain a mixture of rain/snow and graupel. However due to
isolated/scattered nature...probability of reduced conditions at a
terminal is low. The most favored locations may be BWI/mountain from
the midday into early afternoon hours. Can/T rule out stray
flurries at other times...but little to no impacts. Northwest winds near
15 knots with gusts commonly up to 25 knots during the daylight hours.
Winds only gradually diminish tonight.

VFR Sunday with winds becoming light and southerly by late afternoon.

Low ceilings possible Sunday night ahead of a cold front. Once that
front passes...gusty west winds up to 30 kts are possible Monday
afternoon. Rain showers are possible on Tuesday and Tuesday night...but
should remain light so restrictions to visibility/low ceilings are not
likely.

&&

Marine...
Small Craft Advisory winds prevail across all waters at this time. Mixed layer winds remain
below 30 knots...so that should represent an upper limit to gusts...
although current observation suggest we/re making use of full mixing for the
morning. Scattered rain/snow showers possible over the Northern Bay.

High pressure begins to build in tonight but will remain to the
west...allowing Small Craft Advisory conditions to continue. Winds will diminish
some on Sunday...but last vestiges of northerly winds will allow
Small Craft Advisory level gusts to continue on the main Stem of the Bay through
the morning.

Southerly channeling ahead of a cold front will raise the potential
for gusts above Small Craft Advisory criteria Sunday night...mainly
after midnight. Once the front passes...winds turn out of the west
but become stronger and gustier with winds/gusts solidly above Small Craft Advisory
levels. Carrying some gusts in the Upper Bay over 30 kts...so will
need to watch for gale potential on Monday. Winds begin to settle by
Tuesday morning as high pressure briefly builds in.

&&

Tides/coastal flooding...
water levels up to a half-foot below astro predictions at this time. This
negative departure should only be enhanced through the day as
strong northwest winds result in blow-out conds.
&&

Climate...
temperatures Sunday morning may approach the record lows for the
date. Currently the forecast lows are above these records.
However...if the low drops to 21 or less at Dulles it would be the
coldest so late in the season since 1987...and if the low drops to
24 or less at BWI it would be the coldest so late in the season
since 1985.

Site...3/29 record min T...
dca......18 (1923).........
BWI......18 (1923).........
Iad......20 (1982).........

&&

Equipment...
Pikesville NWR will experience sporadic outages today as
maintenance is performed on the tower.
&&

Lwx watches/warnings/advisories...
District of Columbia...none.
Maryland...none.
Virginia...none.
WV...none.
Marine...Small Craft Advisory until noon EDT Sunday for anz530>534-
537>543.
Small Craft Advisory until 6 am EDT Sunday for anz535-536.

&&

$$
Synopsis...je
near term...heights
short term...ads
long term...je
aviation...hts/ads/je
marine...hts/ads/je
tides/coastal flooding...heights
climate...dfh/je
equipment...heights

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