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fxus61 klwx 090853 
afdlwx 


Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia 
353 am EST Friday Jan 9 2009 


Synopsis... 
high pressure over the middle Atlantic moves off the coast tonight. 
Low pressure will move through the area on Saturday. High pressure 
returns Sunday into Monday. Another low pressure system moves 
through on Tuesday...ushering in a much colder air mass for the 
middle and end of next week. 


&& 


Near term /until 10 am this morning/... 
WV loop early this morning shows upper trough axis pushing east of the 
region. Surface hipres currently over the Tennessee Valley will continue to 
build east across the middle Atlantic region this morning. Some 
locations in Maryland and north Virginia have been gusting 15 to 20 kts early this 
morning while winds have been mainly calm across the rest of the 
area. Orographic induced scattered to broken skies over the mts while mostly 
clear skies will continue east of the mts this morning. 


Going to cancel the winter weather advection for the western slopes. Chances 
for accumulating snows are quickly diminishing as bl inversion 
lowers below 1000 feet....although an additional dusting cannot be 
ruled out. 


&& 


Short term /10 am this morning through 6 am Saturday/... 
kept scattered shsn and flurries across western slopes today as northwest 
flow exists. Hipres over the middle Atlantic today will quickly move 
offshore tonight as a low pressure system tracks over the central 
U.S. 


Cloud cover should gradually be increasing this afternoon and tonight 
as lower level warm air advection occurs out ahead of this system. Light snow is 
expected to develop tonight across far northwest zones as a warm front 
approaches the area. The warm front will push north across the County Warning Area 
later tonight...allowing for snow to mix or change over to freezing rain over 
the mts while warmer air at lower levels is advected northward. 
Light snow may develop after midnight just north of the warm 
front...across extreme northern Maryland along the PA border. Latest sref 
guidance is also indicating this. 


&& 


Long term /Saturday through Thursday/... 
precipitation is still expected to develop ahead of low pressure on 
Saturday...then low pressure moves across the middle Atlantic Saturday 
evening. Continue to prefer the timing from the GFS compared to the 
NAM...although the GFS has slowed down a tick. Forecast leans toward 
the GFS and sref. 


Current track of low is not favorable for a warning caliber winter 
event for our County Warning Area. This looks more likely just to our north in 
Pennsylvania. Of course...if the track shifts a little further 
south...this could paint a different story. Right now...this looks 
to be an advisory caliber winter event that will be most apparent 
across our northern County Warning Area. 


Our northern County Warning Area is also the first area to see precipitation early 
Saturday morning which will be in the form of warm advection 
produced snow. Precipitation spreads across the rest of the County Warning Area 
later in the morning and early afternoon. Precipitation may begin as 
a wintry mix...but will more than likely change to plain rain in the 
afternoon except across northern areas where a wintry mix may 
persist. Near the PA border...a couple of inches of snow and some 
light ice accumulations may be possible. Further south...any 
freezing rain would be brief and only result in possibly a light 
glaze before the changeover to rain. Models and ensembles are not in 
total agreement yet...so there is some margin for error...so stay 
tuned. 


As low pressure departs Saturday evening...cold air wraps back 
around making areas in plain rain possibly changing back to snow 
before ending. 


High pressure builds in Sunday through Monday...then a clipper 
system moves through with a chance of snow showers on Tuesday. 
Additional clippers are possible through the rest of the week 
/although gauging their timing and strength this far out is a 
challenge/...and they will tend to pull in colder air during the middle 
to late week. 


&& 


Aviation /09z Friday through Tuesday/... 
VFR conditions expected today and tonight. West-northwest flow will 
continue today with gusts 15-20 kts expected during the daytime. 
Ceilings will increase in coverage later this afternoon...becoming broken at 
midlevels tonight as an area of low pressure approaches the area 
from the central U.S. 


Low pressure approaches on Saturday and moves across the area 
Saturday evening. A period of wintry precipitation is possible 
Saturday morning before rain in the afternoon. IFR conditions are 
possible. Cold high pressure returns for Sunday with gusty northwest 
winds. High pressure lasts into Monday then a clipper moves through 
on Tuesday. 


&& 


Marine... 
hipres will build towards the waters today...before an 
area of lopres approaches from the central U.S. Tonight. Small Craft Advisory 
conditions will continue today over the Bay into early this 
evening with gusts 20 to 25 kts. 


Small Craft Advisory conditions could return across the Middle Bay by 
Saturday evening on southerly winds ahead of low pressure...and then 
more likely overnight Saturday and Sunday on the northwest winds 
behind it. Tuesday may also feature Small Craft Advisory winds. 


&& 


Lwx watches/warnings/advisories... 
District of Columbia...none. 
Maryland...none. 
Virginia...none. 
WV...none. 
Marine...Small Craft Advisory until 6 PM EST this afternoon for 
anz530>534-537. 


&& 


$$ 
Synopsis...peloquin 
near term...Klein 
short term...Klein 
long term...peloquin 
aviation...Klein/peloquin 
marine...Klein/peloquin