Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
354 am EDT Thursday may 23 2013
Synopsis...
a cold front will approach area today before crossing tonight. An
upper-level low persists over the region Friday and Saturday.
Canadian high pressure will build overhead for the Memorial Day
weekend. A warm front will pass through the area during the
middle portion of next week.
&&
Near term /through tonight/...
surface high pressure remains over the Atlantic Ocean early this
morning while a cold front tracks through the Great Lakes. An
upper-level trough also remains over the Great Lakes.
A southerly flow around the high will allow for more warm and
humid conditions today. However...temperatures will not be quite as warm
as recent days due to more cloud cover. Maximum temperatures will range from
the upper 60s in the mountains to the upper 70s and lower 80s
across most other locations. The warm and humid airmass will lead
to moderate amounts of instability. The instability will combine
with forcing from several upper-level disturbances in the
southwest flow aloft and a surface trough to trigger showers and
thunderstorms. The best chance for showers and thunderstorms will
be during the afternoon and evening hours. Increased deep layer
shear along with moderate instability suggests that some
thunderstorms will be capable of producing damaging wind gusts and
large hail.
The cold front will pass through the area late tonight. More
showers are possible...but precipitation will not be as widespread
due to the loss of daytime heating. Temperatures behind the front will be
noticeably cooler across western portions of the County Warning Area.
However...the cooler air may not arrive until Friday for locations
east of the Blue Ridge mountains. Min temperatures will range from the
40s in the Allegheny Highlands to the middle 60s in
Washington/Baltimore.
&&
Short term /Friday through Saturday/...
closed upper low now prognosticated to drift east over the central middle
Atlantic Friday before drifting up to New England through the
weekend. Confidence is low on exact placement of this low. Will
probably update the forecast with the 00z European model (ecmwf) which is
forthcoming. This cold core will bring instability showers to the
area Friday into (uncertain how far into) Saturday with gusty northwesterly
flow (gusts around 30 mph)...cloudy skies...and much below normal
temperatures. Should be pretty similar to last Saturday it dropped
to around 60f once the intermittent showers got going.
Low/trough takes on a negative tilt Saturday which should shunt the
low off the middle-Atlantic coast. Northwesterly flow continues to gust 25 to 30
miles per hour. Our grids do not indicate a wind chill...but if it is pretty
cloudy and that windy there would certainly be a chill.
&&
Long term /Saturday night through Wednesday/...
with the upper low merely drifting to New England through Sunday...the
shortwave over the Tennessee Valley looks contained/away from the central
middle-Atlantic until perhaps Tuesday. With Canadian airmass in
place...expect a steady warming trend due to modification by the
strong late may sun.
Warm front lifts north across the region middle next week with
thunderstorm chances and a return of seasonably warm conditions.
&&
Aviation /07z Thursday through Monday/...
low-level moisture trapped underneath the nocturnal inversion may
result in a brief period of low clouds early this morning. Have
low end MVFR ceilings in the forecast now...but IFR conditions are
possible during this time.
Ceilings will improve later this morning...but perhaps remaining at
MVFR levels. Showers and thunderstorms will increase in
coverage...with the best chance for thunderstorms expected this
afternoon and evening. Thunderstorms will be capable of producing
gusty winds and hail. Subvfr conditions are also expected in
heavier showers and T-storms. A cold front will pass through the
terminals late tonight. More showers are possible along with areas
of br.
Northwesterly flow with gusts 25 to possibly 30 knots with possible MVFR ceilings and
occasional showers Friday under and upper low. Strong northwesterly flow
continues through Saturday as the upper low remains in the region and
surface high pressure builds. VFR early next week in a Canadian airmass
before a midweek warm front.
&&
Marine...
a southerly flow will continue around high pressure today. A Small
Craft Advisory is in effect for the waters. Showers and
thunderstorms will increase in coverage this afternoon and
evening. Some thunderstorms will be capable of producing gusty
winds and hail. Special marine warnings may be warranted.
A cold front will approach the waters tonight. A lull in the
pressure gradient suggests that wind speeds may be below Small Craft Advisory
criteria.
Northwesterly flow with gusts 25 to 30 knots Friday through Saturday as an upper
low persist over the region and surface high pressure builds. Small Craft Advisory in
effect for Friday...expect it to be extended into Saturday night.
More tranquil weather early next week under a Canadian airmass.
&&
Tides/coastal flooding...
tidal anomalies will increase a bit due to the southerly
flow...but with the wind direction being just west of south water
levels will likely be below thresholds for minor coastal flooding.
The closest water levels will come to minor flooding thresholds
will be late tonight during the higher of the two high tides.
&&
Lwx watches/warnings/advisories...
District of Columbia...none.
Maryland...none.
Virginia...none.
WV...none.
Marine...Small Craft Advisory until 6 PM EDT this evening for
anz530>534-536-537-539>543.
Small Craft Advisory from 9 am this morning to 6 PM EDT this
evening for anz535-538.
&&
$$
Synopsis...bjl
near term...bjl
short term...baj
long term...baj
aviation...baj/bjl
marine...baj/bjl
tides/coastal flooding...bjl
