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Area forecast discussion 
National Weather Service Burlington Vermont 
345 PM EST Sat Nov 21 2009 


Synopsis... 
high pressure across the Great Lakes and Ohio Valley states will 
build slowly east tonight and settle across the northeast on Sunday 
into Monday. Therefore...outside any lingering clouds across the 
area this evening...expect generally fair and dry weather during 
the period as temperatures remain on the mild side. The next chance 
of significant precipitation will occur by the middle to later 
portions of next week as low pressure tracks east from the Central 
Plains. 


&& 


Near term /until 6 am Sunday morning/... 
as of 217 PM EST Saturday...quiet conds on tap for tonight as broad 
high pressure builds slowly eastward into the area along with dry 
weather. Only problematical question in the forecast for tonight will be how 
long pesky ll stratocumulus deck persists across portions of the 
area. Current acars data out of Montreal (cyul) continues to show 
very sharp subsidence inversion near 900 mb this afternoon...and 
along with orographically favorable though weak northwesterly flow 
clouds have hung tough across many areas today. Given these factors 
have trended toward idea of some brief clearing early this 
evening...then more clouds later tonight along with some patchy 
br/fg. With the clouds...light winds and overall lack of advective 
processes...min temperatures will hold fairly mild overnight by late 
November standards ... out generally in the upper 20s to 
lower 30s most locales. 


&& 


Short term /6 am Sunday morning through Monday night/... 
as of 217 PM EST Saturday...tranquil and mild late Fall weather then 
continues through the remainder of the short term as aforementioned 
high pressure builds atop the northeast during Sunday/Monday time 
frame. Therefore expect fair and dry conds through the period along 
with a fairly wide diurnal range in temperatures. With shallow nature of 
planetary boundary layer this time of year daytime temperatures will be rather uniform... 
slightly milder perhaps at the higher elevations where shallow planetary boundary layer 
mixing may be able to tap into warmer 925 mb temperatures aloft. Nighttime 
lows will be near seasonal norms...though with at least some 
radiative effects expected...have undercut MOS mins temperatures slightly 
during overnight periods. 


By Monday night...some disagreement begins to creep into the models 
as deeper moisture across the southeast/western Atlantic attempts to 
creep northward beneath western extension of departing ridge axis. 
At this time believe any deeper moisture will have a tough time 
reaching this far north given placement of ll ridge axis...and with 
broad support from this mornings op European model (ecmwf) run and GFS mean 
ensembles have kept sensible conds essentially dry through 12z 
Tuesday. Middle to upper level clouds will likely be on the increase 
however in upper anticyclonic flow...thus have kept overnight min 
temperatures slightly milder than prior counterparts. 


&& 


Long term /Tuesday through Saturday/... 
as of 345 PM EST Saturday...the forecast area will be between two 
low pressure systems on Tuesday...with one system southeast of 
Cape Cod and another system approaching the western Great Lakes. 
Models show area will have a weak ridge of high pressure over the 
region Tuesday and Tuesday night...extending into midday on 
Wednesday. Will go with a mainly dry forecast Tuesday through 
midday on Wednesday. However...will have slight chance probability of precipitation for 
Tuesday for rain showers across south central Vermont. Have gone 
below gmos pop guidance for Tuesday and Tuesday night...as well as 
for Wednesday. An upper low over the Great Lakes will move across 
the area late Wednesday and Wednesday night...bringing a chance 
for some rain showers. 


Thanksgiving day...models show a digging upper trough and closed 
upper low over the western Great Lakes on Thursday. Looks like the 
forecast area will remain dry...but with mostly cloudy skies expected. 
Have put in slight chance probability of precipitation for rain showers on Thanksgiving day... 
but generally feel the daytime will be mainly dry. Have gone below 
gmos probability of precipitation for Thanksgiving day. GFS model is faster than the European model (ecmwf) 
model in bringing the digging upper trough and closed upper low eastward. 
Given the fact that the upper trough is digging southward and 
building the upper ridge east of it...would tend to favor the 
slower European model (ecmwf)...as feel the GFS looke a tad too fast. Will mention 
a chance of showers Thursday night. Will mention rain or snow on Friday... 
as both the GFS and European model (ecmwf) suggest it will be warm enough aloft for 
some rain on Friday...but changing to snow later in the day on Friday. 
The European model (ecmwf) shows a closed 500 mb low will move across the region 
Friday night which will result in dynamic cooling aloft. European model (ecmwf) suggests 
some significant wrap around precipitation is possible Friday 
night. This will have to be watched closely. However...given model 
differences in timing...confidence level is fair at this time. 


&& 


Aviation /20z Saturday through Thursday/... 
through 18z Sunday...low clouds have been hanging in across most 
of the region today...especially over the higher terrain...as a 
low level inversion has trapped this moisture in the lower levels. 
Conditions range from VFR conditions in valley locations to MVFR 
over the higher elevation. Expecting some of this cloud cover to 
become scattered after 00z Sunday...except over the Adirondacks 
and portions of the Green Mountains. Expecting some fog and mist 
to develop tonight...mainly after 05z Sunday...with some MVFR 
ceilings as a high pressure area builds into the region from the 
Ohio Valley. Any fog or MVFR ceilings will dissipate by 14z 
Sunday...with skies becoming mainly clear. 


Outlook 18z Sunday through Thursday...mainly VFR conditions 
expected from 18z Sunday through 12z Tuesday as a ridge of high 
pressure will be over the region. 


Mainly VFR conditions expected from 12z Tuesday through 18z 
Wednesday...as a weak ridge of high pressure will be over the region. 


18z Wednesday through 12z Thursday...areas of MVFR in showers. 
12z Thursday through 00z Friday...mainly VFR. 


&& 


Btv watches/warnings/advisories... 
Vermont...none. 
New York...none. 


&& 


$$ 
Synopsis...jmg 
near term...jmg 
short term...jmg 
long term...wgh 
aviation...wgh 

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