831 
fxus61 kgyx 211915 
afdgyx 


Area forecast discussion 
National Weather Service Gray ME 
215 PM EST Sat Nov 21 2009 


Synopsis... 
high pressure over the Ohio Valley will build east across the 
region through Sunday. High pressure will crest over northern 
New England Sunday night...then move east into the Maritimes 
Monday and Monday night. Low pressure will approach from the 
southwest Tuesday and Tuesday night...before moving out to sea. 
Low pressure over the Great Lakes will track through eastern 
Canada Wednesday into Thursday... dragging a front across northern 
New England Wednesday into and Thursday morning. Another low 
pressure system developing on the front will affect the area late 
next week. 


&& 


Near term /through tonight/... 
surface wind has shifted into the northwest with the passage of a 
weak surface trough. Consequently...low clouds continue to diminish in 
coverage to the Lee of the higher terrain in downslope flow. The question 
tonight is how much low cloud will linger across the mountains...and 
hence low temperature forecast as well as potential for valley stratus 
and fog development in the predawn hours. Elsewhere...only a few stray 
low clouds and high clouds expected tonight as the 1024 millibar high 
centered over Ohio at 19z builds eastward. A blend of met/mav 
temperatures used to initialize min temperature forecast tonight. 


&& 


Short term /Sunday/... 
outside of scattered fair weather clouds...a sunny day with highs 
a few degrees either side of 50...nearly a full 10 degrees above 
average for the date. Winds shift into northeast by afternoon with 
onshore flow adding a bit of a chill along the immediate coast. 


&& 


Long term /Sunday night through Friday/... 
high pressure at the surface and middle level ridging should keep 
cloudiness to a minimum Sunday night. With clear skies and light 
winds...would expect good radiational cooling conditions for the 
normally colder locations. With dew points dropping into the 20s 
in all areas...favored a cooler GFS MOS solution in just about all 
areas. 


The middle level ridge breaks down in advance of short wave energy 
in the southern stream Monday afternoon. Surface high pressure 
will be exiting through the Maritimes...so the airmass should be 
dry to start. The low to middle level warm air advection is not that 
impressive...so would expect that increasing moisture will go into 
moistening the column. As such...will keep the day dry during 
Monday. After a cold start...would think a blend of MOS numbers 
should be OK for highs. 


The short wave will spin up a surface low across the low level 
baroclinic zone across the northern Middle Atlantic States. Based on 
the track of the surface system...and the orientation of the low 
level warm air advection...the best chance of precipitation with 
this system should be across southern zones. The column warms in 
response to the warm air advection...so only liquid precipitation 
is expected. 


Further north...the airmass appears to be too dry for much in the 
way of precipitation. Even here the warm air advection warms the 
column...but it should remain too dry for much beside middle level 
clouds. A blend of MOS numbers was used as a basis for lows Monday 
night...then bumped up a bit due to clouds...especially north. 


The surface low looks to affect southern zones Tuesday. Not a lot 
of confidence in the northern extent of the rain shield...as the 
baroclinic zone and the track of the slow suggest most places away 
from the immediate coast could stay dry. Maintained a mention of 
rain near the coast. 


After this...the forecast confidence GOES down for Wednesday and 
Wednesday night. While models are relatively close with respect to 
the mass fields...the placement of precipitation is not. With broad 
warm air advection ahead of the closed low over the Great Lakes.... 
would expect clouds...but not much in the way of precipitation. 
The 1200 UTC GFS swings a short wave out ahead of the closed system... 
but not sure about this. 


The best chance of precipitation should be ahead of the occluded 
front late Wednesday into Wednesday night. Based on the timing at 
this point...Thanksgiving itself could be dry...but not completely 
sold on the timing since it is tied to a closed middle level system. 


After this...expect to see a much more robust system for Friday 
into Friday night as the closed system passes across northern New 
England. Right now...the column looks warm enough for rain for 
most of the event...but cooling with lower height could introduce 
the potential for snow Friday night in the higher terrain. 


&& 


Aviation /19z Saturday through Thursday/... 
short term /through 23z Sunday/...VFR expected through Sunday...with 
areas of MVFR in valley stratus and fog between 08 and 14z with local 
IFR conditions possible at /kleb/ between 10 and 13z. 


Long term...with high pressure exiting northern New England Sunday 
night and Monday...would expect VFR conditions for much of the 
period. The return flow around the high will start to bring low 
level moisture to southern sections Monday night...and kpsm...kpwm 
and perhaps kaug may see conditions drop to IFR by late Monday 
night. 


Low pressure passing south of the area Tuesday will brush southern 
sections will level level moisture in an east to northeast flow. 
This would suggest IFR conditions for most terminals Tuesday into 
Tuesday night. As a complex system affects the region during the 
middle of next week...it would appear MVFR/IFR conditions will 
continue into at least early Thursday. 


&& 


Marine... 
short term /through Sunday/...winds and seas remain below small craft 
threshold as surface high builds eastward across the waters. 


Long term...as surface high reorients itself west to east...the 
gradient flow becomes northeast then east. The gradient remains 
constant Sunday night into Monday...as winds remains below 20 
knots. 


As the gradient produces a more favorable east to northeast 
fetch...seas will start coming up over the coastal waters. 
Would expect seas to reach near 5 feet across the southern 
waters...where the fetch should be most effective. 


The gradient increases Monday night into Tuesday...as the 
gradient tightens between the high exiting over the Maritimes and 
the surface low moving off the New Jersey coast. Model consensus 
suggests the best chance for small craft winds will be late Monday 
night into Tuesday. Based on the fetch...would expect to seas 
reach small craft levels over all of the ocean waters...and 
perhaps even the bays. 


There has been a shift in the model consensus for Wednesday and 
Wednesday night. Not sure if the southeast flow ahead of an 
occluded front will have enough time to reach near gale. The 
gradient may be close...but mixing in the low levels should be 
limited. Because of this...winds were capped below gale through 
late Wednesday night. 


Winds may drop off quickly Wednesday night as the surface gradient 
relaxes. However...the swell that develops in the southeast flow 
should maintain seas well above 5 feet into Thursday. 


&& 


Gyx watches/warnings/advisories... 
ME...none. 
New Hampshire...none. 
Marine...none. 


&& 


$$ 

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