Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
1016 am EDT Tuesday may 21 2013
Synopsis...
high pressure over the Atlantic will continue to aid a southerly
flow through Thursday...bringing warm and humid conditions.
Afternoon and evening thunderstorms are possible each day. A
cold front will pass through the region Thursday night into
Friday. Cooler conditions are expected over the weekend.
&&
Near term /through tonight/...
weak upper-level low pressure remains over southern Virginia into
the Carolinas this morning while surface high pressure remains
centered over the Atlantic Ocean. Plenty of clouds banked up along
and east of the blurdg...while mosun skies prevail to the west. 12z
lwx radiosonde observation indicates an inversion associated west/ the low clouds up to about
h9. Above that sndg unstable...W/ approx 1850 j/kg cape. However cnvctv
temperatures /89f/ will be hard to reach under the cloud cover.
Lamp temperatures running lower than forecast maxt. While lamp has had a good
feel for eroding low clouds past cpl days and like its handling today
/sct out low level moisture between 15-18z/...temperature have been running a little on
the cool side. Indeed...our obsvd sndg could warm up in a hurry.
Therefore...will be holding onto going temperature forecast.
That leads to the precipitation forecast. The warm and humid air will lead to
high amounts of instability. NAM/GFS BUFKIT are indicating around
2000-2500 j/kg of MLCAPE this afternoon. Got simlr rslts in SBCAPE
modifying obsvd sndg to 85/65. However...there was also about 50 j/kg
cinh. This inhibition will make it difficult for convection to
develop. Like prvs forecast...which concentrated on terrain
circulations...a surface trough and the upper-level low acting as
lifting mechanisms. Main premise of probability of precipitation remain unchgd. Will also
have to monitor convection over the Midwest. This may survive off
its cold pool and bring a threat for more widespread convection
along the Allegheny and Potomac Highlands this evening. The
highest probability of precipitation are located across these areas for that reason.
The threat for severe T-storms this afternoon and evening should be
low due to the strong capping inversion. However...if the lifting
mechanisms end up being strong enough to erode the inversion...then
gusty winds and hail are possible.
Any leftover convection will dissipate overnight due to the loss of
daytime heating. Low clouds and areas of fog may develop as moisture
gets trapped underneath the nocturnal inversion. However...low
clouds/fog should not be as widespread as recent nights due to a
higher temperature/dewpoint depression and a stronger gradient. Min temperatures
will be in the 60s across most areas to the lower 70s in downtown
Washington/Baltimore.
&&
Short term /Wednesday through Thursday/...
central middle-Atlantic in warm sector of Midwest low until a cold front
in the Thursday night timeframe. Surface high well off eastern Seaboard aids
southerly flow/moisture advection. Temperatures about 10 degrees above normal
with upper 60s to near 70f dewpoints. Expect a diurnal trend in precipitation
coverage with prefrontal forcing entering the area Thursday. Slight
risk for Wednesday due to potential for straight line winds from
ongoing mesoscale convective system activity over the Ohio Valley pushing east.
&&
Long term /Thursday night through Monday/...
12z European model (ecmwf) forecasts the cold frontal passage as Thursday night (there has been
fluctuation from late Thursday to Friday morning). Canadian high
pressure builds in with a Crystal clear and cool with temperatures 5-10
degrees below normal. Shortwave over the Tennessee Valley on Sunday should
remain west of the lwx County Warning Area...will have to monitor for increased
probability of precipitation. As of now expect some high clouds Sunday with a warming trend
starting that continues into middle next week.
&&
Aviation /14z Tuesday through Saturday/...
low-level moisture is trapped underneath the still present
nocturnal inversion. Low clouds and fog just beginning to erode...and
will improve to VFR by/around noon. Isolated showers and T-storms are
possible this afternoon and evening. Threat too slim for taf
inclusion. Areas of low clouds/fog may impact the terminals late
tonight.
Diurnal thunderstorm activity Wednesday/Thursday with IFR conds possible in
the heaviest ones. Southerly flow until a cold frontal passage Thursday night. Northwesterly
flow with clear conds Saturday. Just some high clouds on Sunday.
&&
Marine...
southerly winds are expected over the waters through tonight. Wind
gusts will be close to Small Craft Advisory criteria this afternoon and tonight. Have
capped gusts around 15 knots for now due to the relatively cooler
waters. Scattered showers and thunderstorms are possible this
afternoon and evening.
Southerly flow with high pressure offshore ahead of a cold front that
comes through Thursday night. Southerly channeling to 20 knots possible Wednesday
evening...and Thursday. Northwesterly flow to 20 knots possible Friday. Light
and variable flow this weekend.
&&
Tides/coastal flooding...
tidal anomalies have increased to around one quarter foot above
normal. Anomalies may increase a bit more due to the southerly
flow...but water levels should remain below thresholds for minor
flooding through tonight. Will have to watch southerly flow
Wednesday and Thursday as it may support an increase in departures
again.
&&
Lwx watches/warnings/advisories...
District of Columbia...none.
Maryland...none.
Virginia...none.
WV...none.
Marine...none.
&&
$$
Synopsis...bjl
near term...hts/bjl
short term...baj
long term...baj
aviation...hts/bjl/baj
marine...baj/bjl
tides/coastal flooding...bjl
