226 
fxus61 klwx 211450 
afdlwx 


Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia 
950 am EST Sat Nov 21 2009 


Synopsis... 
high pressure will cross the region and settle over New England 
through the weekend. A low pressure area will move up coastal 
Carolina Sunday night into Tuesday...bringing rain. High pressure 
will return late Tuesday...though a cold frontal passage is 
expected in the middle to late portions of next week. 


&& 


Near term /until 6 PM this evening/... 
current analysis shows a surface high that is draped across the Ohio 
Valley into the mid-Atlantic. The jetstream remains split across the 
central and eastern Continental U.S.. an upper-level low in the northern branch 
is located over the Ohio Valley while another upper-level low is 
located over Texas in the southern branch. 


A southwest flow between these two systems has allowed for high 
clouds to overspread the area this morning. A strato cumulus deck has 
also spread into the area from the northwest. High clouds should 
dissipate from northwest to southeast during the afternoon hours as 
the dry slot wraps around the upper-level low that is located over 
the Ohio Valley. The strato cumulus deck will hang on throughout the 
day...especially across the northern and western County Warning Area. Will continue 
mostly cloudy/partly sunny skies. 


Surface high pressure will keep dry conditions in place. Maximum temperatures 
should be near climatology...in the 50s across most locations...but 40s in 
the higher elevations. 


&& 


Short term /6 PM this evening through 6 am Sunday/... 
cirrus and lower stratus deck in the northwest are expected to thin out a 
bit by the evening...however moisture from the Gulf states system is 
expected to stream northward overnight. Partly cloudy/mostly cloudy 
skies are expected mainly after midnight. Mav numbers continue to 
verify slightly better than the other guidance...and have used for 
the overnight mins. 


&& 


Long term /Sunday through Friday/... 
Sunday...flow becomes northeasterly with high pressure over New England and 
an approaching coastal low off the Carolinas. Clouds in the region 
due to coastal system...so expect mostly sunny skies until cloud 
bank rolls north-Ward in advance of the low. With more sun northern 
zones...maximum temperatures Sunday could be the inverse of normal with warmest 
/around 60f/ locales in Harford/Baltimore and cooler /mid 50s/ 
Nelson/Albemarle. 


Sunday night through Monday night...high pushes off New England and 
low pushes east of Hatteras...bringing Ely flow/cad to the area. 
Having already moistened...expect light rain spreading east across 
the area with east facing slopes having the greatest precipitation 
potential due to topography. Should be quite cloudy with some 
rain...expect low diurnal range...mins middle 40s...maxes middle 50s. 


Tuesday and Wednesday...a closed low over the Central Plains/middle 
west to break cad with southwesterly flow by Tuesday afternoon /did increase 
probability of precipitation for Tuesday morning across eastern half of County Warning Area due to extended 
cad/. Warming trend Tuesday /upper 50s/ to Wednesday /around 60f/ ahead of 
frontal passage. 


Wednesday night/Thanksgiving...short wave lobe/S/ from the low to bring one 
or more cold fronts passages in middle to late week timeframe bringing 
precipitation chances across the County Warning Area. However...moisture availability for 
the middle Atlantic is uncertain. Cold air does look to follow the 
front...bringing a cool down and mountain wintry precipitation. 


Thursday night/Friday...models uncertain of low intensity and 
track...but the potential is there for an early upslope snow event 
in northwesterly flow around the backside of the low feeding Great Lake 
moisture to the Allegheny Front and possibly ridges further east. 
Will have to monitor future models for consistency/greater 
discernment. If anything...cooling trend late next week. 


&& 


Aviation /15z Saturday through Wednesday/... 
VFR conditions this afternoon. High clouds will dissipate from 
northwest to southeast this afternoon...but a broken strato cumulus deck 
will persist through the afternoon. Ceilings will remain above 3kft. The 
strato cumulus deck will dissipate this evening. VFR conditions along 
with light winds are expected most of tonight. MVFR visibilities are 
possible towards morning with patchy br. 


Onshore northeasterly flow sets up Sunday...with moistening/precipitation beginning 
by late Sunday night as Ely flow sets up across the terminals. Low 
ceilings and reduced visibilities in rain/drizzle into Tuesday morning. Southwesterly 
flow ahead of the next cold front later Tuesday/Wednesday with 
improved aviation conditions. Quantity of precipitation associated with front 
looks to be low at this time though with timing later 
Wednesday/early Thursday certainly pay attention to subsequent 
forecasts. 


&& 


Marine... 
north-northwest winds are expected across the marine area through 
tonight. No flags are expected. 


High pressure building over New England and a coastal low moving up 
the Carolinas Sunday/night brings about northeasterly flow. Small Craft 
Advisory winds possible Sunday night through Monday night. Southwesterly flow 
ahead of the next front later Tuesday and Wednesday. One or more 
fropas later Wednesday through Friday to bring some precipitation and 
colder air. 


&& 


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


&& 


$$ 
Listemaa/lasorsa/baj