Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
401 am EDT Wednesday may 22 2013
Synopsis...
high pressure persisting over the Atlantic with warm and humid
conditions until a cold front Thursday night. An upper trough
will linger over the area Friday with high pressure building
through Saturday. A frontal boundary stalls out across the middle-
Atlantic Sunday night through early next week.
&&
Near term /through tonight/...
high pressure both at the upper-levels and the surface will remain
over the Atlantic Ocean through tonight. An upper-level trough will
slowly shift from the central Continental U.S. Into the Great Lakes. A
southerly flow around the high will continue to usher in warm and
humid conditions across our area.
Low-level moisture trapped underneath the nocturnal inversion will
result in patchy fog along with areas of low clouds. The best chance
for low clouds and fog will be east of the Blue Ridge mountains and
in sheltered valleys west of the Blue Ridge mountains. Any low
clouds and fog should burn off by mid-morning. Sunshine and a
southerly flow will cause maximum temperatures to reach the middle and upper 80s
across most locations.
The warm and humid airmass will lead to high amounts of instability.
NAM/GFS BUFKIT indicate around 2000-2500 j/kg of MLCAPE this
afternoon...similar to Tuesday. Terrain circulation and a surface
trough will act as lifting mechanisms for convection this afternoon.
This is also similar to Tuesday. However...the capping inversion
will be weaker than Tuesday due to height falls as the upper-level
trough to our west slowly shifts eastward. Therefore...a better
chance for thunderstorms exists this afternoon and
evening...especially near and west of the I-95 corridor. Although
widespread severe weather will likely hold off to our west for
locations closer to the upper-level trough...there is a threat for
locally damaging wind gusts and large hail in any thunderstorms that
do develop due to the high instability.
Convection will likely dissipate later this evening due to the loss
of daytime heating. However...an upper-level disturbance is expected
to pass through the region late tonight as the upper-level trough
continues to slide closer to our area. Plenty of moisture and
forcing from the upper-level disturbance may result in scattered
showers/T-storms toward morning. Min temperatures tonight will range from
the 50s in the mountains to the lower and middle 70s in downtown
Washington/Baltimore.
&&
Short term /Thursday through Friday/...
Thursday looks to be the last above normal temperature day for
awhile ahead of the cold front that crosses Thursday night
timeframe. Prefrontal lines/clusters of showers/thunderstorms
progress east across the area Thursday into Thursday night. GFS bufr
sndg for kiad forecasts a 1.6 inch precipitable water which is certainly high...but
just shy of the 2 stdev indicator of flash flooding. With
progressive nature of the activity...any flash flooding would be
localized. Damaging wind threat...particularly with heating on
Thursday is able to peak before organized activity moves through.
Friday...upper trough drifts east over the area with back edge of
clouds slow to come in the afternoon. Gusty northwesterly flow Friday
continues as high pressure builds through Saturday.
&&
Long term /Friday night through Tuesday/...
shortwave from Tennessee Valley on Sunday now looks to expand east across the
southern-central mid-Atlantic. Convergence along this boundary would
set off showers. Pattern is stalled into middle next week...so a
prolonged cloudy/rainy period is possible. This would result in
below normal temperatures.
&&
Aviation /08z Wednesday through Sunday/...
low-level moisture will be trapped underneath the nocturnal
inversion early this morning. This may result in low clouds and
areas of fog...especially across the eastern terminals. IFR
conditions are possible.
Any low clouds will burn off by middle-morning and VFR conditions are
expected through this evening. However...scattered showers and
thunderstorms will develop. Some of the thunderstorms will be
capable of producing gusty winds and large hail. Areas of low clouds
are possible late tonight along with scattered showers/T-storms.
Thunderstorms Thursday into Thursday evening ahead of a cold front.
IFR conds possible in the heaviest activity. Southerly flow until a cold
frontal passage Thursday night. Northwesterly flow with gusts 25 to possibly 30 knots with
middle level ceilings Friday. Northwesterly flow continues through Saturday as high
pressure builds.
&&
Marine...
high pressure will remain over the Atlantic Ocean through tonight. A
southerly flow will continue over the waters during this time. A
Small Craft Advisory is in effect for portions of the waters through
tonight. Scattered showers and thunderstorms are possible later this
afternoon and evening. Any thunderstorms that do develop will be
capable of producing gusty winds and hail.
Southerly flow ahead of a late Thursday night cold front. Small Craft Advisory expanded
through Thursday. Expect an extension Thursday night for prefrontal
southerly flow...then northwesterly flow around 25 knots Friday through Saturday as
high pressure builds.
&&
Tides/coastal flooding...
a southerly flow will continue over the waters through Thursday
night...but the flow may remain just west of south. Tidal anomalies
will likely increase a little...but with the flow remaining west of
south the water levels should remain below thresholds for minor
coastal flooding. The closest water levels will come to minor
flooding thresholds will be during the high tide cycle late Wednesday
night and late Thursday night...the higher of the two high tides.
Tidal anomalies will decrease Friday behind a cold front.
&&
Lwx watches/warnings/advisories...
District of Columbia...none.
Maryland...none.
Virginia...none.
WV...none.
Marine...Small Craft Advisory from 9 PM this evening to 6 PM EDT
Thursday for anz530-531-539.
Small Craft Advisory from 9 am to 6 PM EDT Thursday for anz535-
538.
Small Craft Advisory from 2 PM this afternoon to 6 PM EDT
Thursday for anz532-536-540-542.
Small Craft Advisory until 6 PM EDT Thursday for anz533-534-
537-541-543.
&&
$$
Synopsis...bjl/baj
near term...bjl
short term...baj
long term...baj
aviation...baj/bjl
marine...baj/bjl
tides/coastal flooding...bjl
