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fxus61 klwx 210213 aaa 
afdlwx 


Area forecast discussion...updated 
National Weather Service Baltimore Maryland/Washington District of Columbia 
913 PM EST Friday Nov 20 2009 


Synopsis... 
high pressure will remain over the region through Saturday. High 
pressure will retreat to the north Sunday and low pressure will move 
up the eastern Seaboard Sunday night through Monday night...bringing 
another round of rain. High pressure will return Tuesday...but a 
cold front will pass through during the middle of next week. 


&& 


Near term /until 7 am Saturday morning/... 
a residual upper wave remains back to the northwest...sliding down through 
the upper Midwest tonight west/ little-no precipitation but a large mass of 
low clouds streaming from the shores of Lake Erie down into the 
central Appalachians. This will be about the only weather activity for the 
region into the early part of the weekend. Portions of this cloud 
bank will break-up and slide down across the northern Shenandoah Valley 
and Potomac Highlands through the overnight hours. Winds decreasing 
and after a long period of northwesterly winds this afternoon...conditions are 
relatively dry...so widespread fog development not expected 
/outside of sheltered valleys and other typical fog-prone areas 
toward the pre-dawn hrs/. The relatively dry conditions will also 
allow temperatures to slide down into M/u30s /l40s in the metropolitan areas and 
closer to the Bay/. 


&& 


Short term /7 am Saturday morning through 6 PM Saturday/... 
surface high will remain over the region Saturday bringing dry and 
seasonable conditions. Maximum temperatures will be in the middle to upper 50s 
across most locations. Mostly/partly sunny skies are expected with a 
scattered cumulus deck due to diurnal heating and some high clouds due to 
a southwest flow aloft. 


&& 


Long term /Saturday night through Friday/... 
large hipres hanging out across the NE/Great Lakes region Sat ngt-sun. Diff this 
cycle is the combo of surface high and 500 mb ridging...making it harder to 
dislodge. Thrfr..gdnc this cycle sloer than prvs cycles. GFS seems 
to be quicker...but it also seems to be affected by gridscale 
feedback...owing to shortwave phasing. Ggem/NAM in concert...suggesting 
precipitation will be centered on sun ngt-Mon. A weak low will then emerge off middle 
Atlantic CST Monday night. Will make appro changes to grids. One thing of note is 
that there/S no cold air around. Aftr making appro MOS temperature 
adjustments /neglecting the cooler maxt of wet GFS and siding warmer 
Sun night as clouds advect nwd/...maxt will be near normal but min-T warmer 
than normal. 


Should get a respite Tuesday before anthr storm affects County warning forecast area in the 
Wednesday-Thursday timeframe. Will need to monitor due to travel impacts. At this time... 
the warm trend continues as a cutoff 500 mb low develops west of the Mississippi. 


&& 


Aviation /01z Saturday through Wednesday/... 
high pressure will bring VFR conditions through Saturday. A 
scattered stratus deck /3-4 kft/ will continue to drift in from 
the northwest /but only in smaller portions from its larger mass - back 
across Ohio/western PA. This area of clouds will continue to move into 
the area toward Saturday morning and into the afternoon...drifting 
through and dissipating by later in the evening. Wind speeds will remain 
below 10 knots through this time. 


VFR through sun. Flgt restriction due to lopres Sun night-Monday night. 


&& 


Marine... 
northerly winds will continue to move over the waters overnight...and 
high pressure begins to move in from the west...though winds will 
be light west/ a minimal pressure gradient...so no weather concerns into the 
weekend. 


No flags expeceted through the weekend. Lopres affecting waters Monday. Winds may 
pick up in advc of low...W/ a east-northeasterly fetch. 


&& 


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


&& 


$$ 
Update...gms 
previous discussion...bjl/hts