Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
159 PM EDT Friday Sep 19 2014
high pressure will remain overhead through Saturday. The high will
move off the coast Sunday and a cold front will pass through the
area Sunday night into Monday. High pressure will return for the
middle portion of next week.
Near term /through Saturday/...
high pressure will continue to move off the New England coast
through tonight. A surface ridge axis will extend southwest from
this high into the middle-Atlantic during this time. The low-level
flow will continue to turn toward the southeast during this time.
The onshore flow will cause moisture to get trapped underneath the
subisdince inversion...resulting in more clouds across central
Virginia into the Potomac Highlands. However...for locations
farther north and east there will be some sunshine late this
afternoon. A couple sprinkles cannot be ruled out...mainly across
central Virginia into this evening. However...most areas will be
The onshore flow will continue tonight...causing low clouds and
patchy fog to develop. Min temperatures will range from the 50s in the
Potomac Highlands and Shenandoah Valley to the lower 60s in
downtown Washington and Baltimore.
The surface ridge will remain in place for Saturday...and an
onshore flow will continue. However...the subsidence inversion
should lower due to rising pressures overhead between a cold front
over the Midwest and low pressure developing off the South
Carolina coast. With a strengthening subsidence inversion...this
means that any low clouds and fog Saturday morning should give way
to sunshine. Maximum temperatures will range from the 70s in the mountains to
near 80 across the Washington and Baltimore metropolitan areas.
Short term /Saturday night through Monday/...
a cold front will approach from the Great Lakes/Ohio Valley during
the second half of the weekend. Above average temperatures will
precede the cold front...but moisture return from the south will be
meager. Still...the upper-level trough forcing the cold front is
forecast to be pretty strong by the models and that should in turn
force narrow bands of showers and thunderstorms. Gusty or perhaps
spotty damaging winds are possible mainly across western areas where
added terrain forcing could result in briefly more robust updrafts.
Showers and thunderstorms will gradually wane as they push east of
the Blue Ridge and towards the Chesapeake Bay during the evening.
The cold front will move offshore as high pressure rebuilds from
Canada resulting in dry and cooler than normal temperatures to start
the beginning of next week.
Long term /Monday night through Friday/...
a dry and fall-like week is forecast for most of next week as a
large area of Canadian high pressure slowly pushes across the
northern/eastern Continental U.S. And ridging persists aloft. With light winds
and mostly clear skies and shallow moisture in light easterly
flow...the setup could be ideal on more than one occasion for late
night/early morning fog or stratus next week.
Aviation /18z Friday through Wednesday/...
an onshore flow will continue through Saturday. Low clouds across
central Virginia may spread north and east tonight. Certainty is
low as to how widespread the low clouds will be. For now...MVFR
conditions are forecast over the terminals tonight into Saturday
morning...but IFR conditions are possible. IFR conditions are
likely at kcho during this time. Any low clouds and fog will burn
off later Saturday morning and VFR conditions are expected in the
Sub-VFR possible sun in sparse coverage showers/thunderstorms in aftn/eve. Winds
SW 10 kts sun. VFR likely Sunday night through Tuesday night behind
front west/ west winds 10-15 kts west/ gusts to 20 kts possible Sun
night-Mon...then north less 10 kts or less Monday night-Tuesday night.
Moderately high confidence forecast in overall setup as models are
in agreement with typical timing differences revolving around the
wind shift immediately following the front and the timing of higher
an onshore flow will continue through Saturday as high pressure
remains near the middle-Atlantic coast. A pressure surge will cause
winds to increase a bit over the waters tonight. A Small Craft
Advisory is in effect for the Maryland Chesapeake Bay and lower
tidal Potomac River...but it will be marginal. Winds should be a
bit weaker Saturday as the gradient subsides a bit.
S flow around 10 kts or so ahead of cold front Sat night-sun along
west/ chance of showers/thunderstorms which could be accompanied by gusty winds sun
evening. Front and precipitation clears the coast Sun night and winds become west
or northwest 10-15 kts gusts 20 kts. Winds become north 10 kts Monday night-Wednesday
before veering around to the east later in the week as high pressure
slowly migrates to the north of the region.
tidal anomalies are around one-half foot above normal this
afternoon. The surface flow will continue to turn toward the
southeast this afternoon and a southeasterly flow will continue
through Saturday. Low pressure will move up the middle-Atlantic coast
Saturday night into Sunday...and this may enhance the threat for
elevated water levels.
Minor tidal flooding cannot be ruled out with the high tide cycle
late tonight into early Saturday morning...but confidence is not
high enough to issue a coastal Flood Advisory at this time. There
is a better chance for minor tidal flooding with the high tide
cycles later Saturday into Sunday.
District of Columbia...none.