081 
fxus61 klwx 200706 
afdlwx 


Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia 
306 am EDT Sat Mar 20 2010 


Synopsis... 
high pressure dominates...with tranquil and mild weather across 
the region through Sunday. A strong upper level disturbance and 
its associated cold front are expected to impact the region 
Sunday night through Monday night. High pressure will then build 
in for middle week. 


&& 


Near term /through tonight/... 
hipres gradually slides of the Atlantic Seaboard tonight...but it remains 
the dominant weather feature through tonight. With center of high east of 
region...light northwest winds this morning will gradually transition to SW 
this afternoon. This will bring modest dewpoint rises to the region... 
though skies should be generally sunny expect for some high clouds 
streaming over from the west. Kept maxima within a couple degrees of 
yesterday...as increasing moisture and some cirrus should counteract effects of 
weak warm air advection. Weakening cold front approaches from the northwest this afternoon...but 
should have no impact on County Warning Area. Hi temperatures expected to reach l/m70s most 
locations... with 60s across higher terrain along and west of Blue 
Ridge. 


Increasing southerly flow and moisture expected tonight. Middle/high clouds will also 
increase overnight as southwesterly flow aloft brings over debris from strengthening 
storm system across Southern Plains. Temperatures should be warmer than previous 
ngts...minima in the 40s...with l50s across urban centers. 
&& 


Short term /Sunday through Monday night/... 
a weak cold front will be stalled either across County warning forecast area or just north of it on sun. 
But...W/o much low level moisture or middle level forcing to work off of...think 
it/ll just mark a swath of cldcvr. The zn in qstn clearly contains a 
thermal gradient on crrnt surface analy...but guidance still suggests 
anafrontal structure. Coupled west/ a persistent southeastern Continental U.S. Ridging and 
cutoff upper low over the lower Maryland valley...which should support a sloer 
system evolution...its hard to see much precipitation lclly during the day on 
Sunday. Have consequently backed off on probability of precipitation and bumped maxt up in 
spite of clouds. 


Southerly h10-8 winds increase Sun night...marking incrsd dewpt advection/higher thte 
air. The upwd tick in moisture/upglide will support precipitation...especially toward dawn 
in the mountains and shen valley as closed low wobbles closer. These areas west/ 
feature likely/Cat probability of precipitation. Outside of areas west/ higher precipitation chances...min-T 
may not drop below 50f...not too far rmvd from normal maxt. 


Monday will feature best forcing...and perhaps a pinch of instability as well. 
Any thunder should be elevated and limited...but cannot discount it in 
light of srefs and indices off model soundings. Plus...precipitable water near an inch 
will make some heavy rainers a possiblity. Actions at this time include placing MDT 
rain showers /def probability of precipitation/ in grids during the morning /coincident west/ thte ridge 
axis...then keep chance thunderstorms and rain during afternoon supported by lapse rates in vicinity of 
closed low. 


Surface features appear to be occluded...but 500 mb low will gradually migrate S 
of Virginia Monday ngt-Tue. Will keep prvs forecast of decreasing probability of precipitation through Monday night. 
&& 


Long term /Tuesday through Friday/... 
after a cloudy-cool Tuesday - since the upper low will take all-day to 
completely exit off the coast...high pressure will again build 
across the southeast and up the eastern Seaboard. Another complex 
scenario will then take shape back to the west. A fairly similar 
upper low feature will cross the same areas of The Rockies/Southern 
Plains Wednesday/Thursday of next week...but not west/ the same upper support at 
the beginning - which would likely mean not as far of a trek to the 
south as the current system. 


Rain chances will begin to increase toward the end of the work 
week...though a more accurate depiction for next weekend still 
uncertain and will depend of the effects a strong upper wave that 
will swinging around the southern Hudson Bay/northern Great Lakes region at 
the time. 
&& 


Aviation /07z Saturday through Wednesday/... 
mostly clear skies and light winds expected through tonight...with no visibility/ceiling 
restrictions. Cirrus at or above 20kft expected...gradually increasing lt this afternoon 
and evening. Middle level stratus begins to push in from the west tmrw. West-northwest 
winds at or below 10 knots early today become southerly late afternoon and tonight. 


No flgt restrictions expeceted sun...but conds will deteriorate Sun 
night-Monday as storm system approaches. MVFR should be wdspd and occasional IFR 
possible into Monday night. Worst conds Monday night as Ely winds may bring in low level 
stratus. Will need to burn this off Tuesday in northwest flow. Once we do...fair 
weather into midweek. 
&& 


Marine... 
dry conds with southerly winds increasing to near 10 knots this afternoon as hipres 
slides east of waters. Southerly winds maintain similar speeds tonight...as 
storm system begins to approach from the SW. 


Southerly flow around 10 knots sun...but then winds pick up a little Sun night... 
and more notably on Monday. Small Craft Advisory possible Monday in advc of lopres...and again 
Tuesday in northwest flow on back side of same system. 
&& 


Lwx watches/warnings/advisories... 
District of Columbia...none. 
Maryland...none. 
Virginia...none. 
WV...none. 
Marine...none. 


&& 


$$ 
Synopsis...sbk/hts 
near term...sbk 
short term...heights 
long term...gms 
aviation...sbk/hts 
marine...sbk/hts