Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
358 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 early this morning while surface high pressure remains
centered over the Atlantic Ocean.
A southerly flow around the surface high has caused warm and humid
conditions early this morning. Plenty of moisture is trapped
underneath the nocturnal inversion and this will cause low clouds
along with areas of fog early. Fog may be locally dense in valleys
and rural areas.
Low clouds and fog will mix out by middle-morning and a southerly flow
will continue to usher in warm and humid conditions. Maximum temperatures today
should be several degrees warmer than Monday...ranging from the 70s
in the mountains to the middle and upper 80s across most other
locations. Leaned closer to the mav guidance for maximum temperatures which is
a bit warmer than other guidance. The mav has been performing well
and there should be enough sunshine and mixing for higher temperatures.
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. A capping inversion around 5kft will make it difficult
for convection to develop. Did allow for a chance for
showers/T-storms anyway due to terrain circulation...a surface
trough and the upper-level low acting as lifting mechanisms. 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 /08z Tuesday through Saturday/...
low-level moisture is trapped underneath the nocturnal inversion.
Low clouds and fog are expected with IFR/subifr conditions early
this morning. Ceilings/visibilities will improve by middle morning and southerly
winds are expected this afternoon with gusts around 15 knots
expected. Scattered showers and T-storms are possible this afternoon
and evening. 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...bjl
short term...baj
long term...baj
aviation...baj/bjl
marine...baj/bjl
tides/coastal flooding...bjl
