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