Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
400 am EDT Sat Mar 28 2015
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/...
water vapor imagery shows a deepening trough over the eastern Continental U.S.
This morning with connections to Greenland. A front with developing
low pressure is offshore...while a secondary Arctic front is pushing
into the area ahead of the upper trough axis...notable in the dew
point gradient over the region. Some lift has brought very light
precipitation to central Virginia...which should continue to drift southeast. Based on
regional radar and observation in WV/PA...the Potomac Highlands have the
best chance at accumulating snowfall through daybreak...although the
best returns have likely already occurred. Areas near the PA border
may also see a flurry.
Based on the latest trends in hi-res guidance and projected forcing
mechanisms...made some minor adjustments to the probability of precipitation through today.
While rogue flurries are possible just about anywhere at
anytime...main chances will take place once convective mixing
occurs. Even then...think a compact vorticity maximum within the trough axis
may be the main player in producing showers. This is forecast to
skirt into northern Maryland during the midday/afternoon hours. Coverage
is still expected to be scattered at best so have maintained the
chance probability of precipitation...but tapered them off later in the afternoon. Depending
on near-surface temperatures and the intensity of the
showers...rain...snow...and graupel could occur (more likely the
latter two in the favored area).
Despite good mixing...downslope flow and at least some breaks of
sun...highs will be limited by 850 mb temperatures below -10c. Only minor
tweaks to going forecast...with 40s in Piedmont/coastal area...30s
west...and below freezing at higher elevations. Wind gusts up to 30
miles per hour will add a bite to the air.
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
Aviation /08z Saturday through Wednesday/...
VFR conditions will 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 will be sustained greater than 10 knots.
Sporadic gusts through daybreak...becoming common 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
occasional to frequent gust of 20 knots or greater this morning on all
waters as secondary Arctic front surges into the area. Expect these
gust to become even more commonplace after the sun rises. Mixed
layer winds remain below 30 knots...so that should represent an upper
limit to gusts. Scattered rain/snow showers possible over the
Northern Bay toward the midday hours. 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.
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
Site...3/29 record min T...
District of Columbia...none.
Marine...Small Craft Advisory until 6 am EDT Sunday for anz530>543.