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fxus61 kbtv 201719 
afdbtv 


Area forecast discussion 
National Weather Service Burlington Vermont 
119 PM EDT Wednesday Aug 20 2008 


Synopsis... 
high pressure over the Great Lake states will supply a northwest 
flow of cool dry Canadian air along with some fair weather clouds 
to the north country today. High pressure will move over the area 
with a warming trend through Saturday with fair and dry weather 
expected. 


&& 


Near term /until 6 PM this evening/... 
as of 11 am EDT Wednesday... 
freshen up the forecast grids with GFS lamp forecast and for a 
bit more clouds (30-50%) with some cirrus/ac with warm advection and 
some mountain cumulus developing in decent north-northwest flow of 10 to 20 kts. Cwmw 
sounding indicates some low level moisture still lingering and visible 
Sat confirms. 4km WRF output shows a sprinkle possible far NE Vermont 
but may be more like some virga with dew points in the 40s and relative humidity in 
the 30-40 percent range this PM. 


&& 


Short term /6 PM this evening through Friday/... 
as of 448 am EDT Wednesday...mainly clear skies expected tonight 
through Friday as a strong ridge of high pressure at the surface 
and aloft will be over the region. Expecting areas of patchy 
dense fog to form after midnight in the sheltered valleys of 
eastern and northeast Vermont...as well as in the valleys in the 
Adirondacks tonight and Thursday night...as a combination of 
clear skies and nearly calm winds will lead to excellent 
conditions for radiation fog to form. Also...expecting a warming 
trend in temperatures Thursday and Friday...with maximum temperatures 
on Friday climbing to the upper 80s in some valley locations...as 
850 mb temperatures forecast to climb to around 16 celsius on 
Friday. 


&& 


Long term /Friday night through Tuesday/... 
as of 448 am EDT Wednesday...the ridge of high pressure will 
continue over the region Friday night and Saturday with mainly 
clear skies expected. Maximum temperatures are again expected to 
climb into the 80s on Saturday. Previously issued zone forecast 
had a mention of rain showers Saturday night...but look at 00z 
GFS and 00z European model (ecmwf) models show any shower activity will remain 
west of the region Saturday night...as upper ridge over the 
region will slow down the eastward progression of a cold front 
over the western Great Lakes...so will keep forecast for Saturday 
night dry. 


00z GFS and 00z European model (ecmwf) models showing some significant differences 
in the forecast from Sunday Onward...with the GFS model bringing 
a cold front into the region Sunday and Sunday night...with a 
chance of showers and thunderstorms...while the European model (ecmwf) model is 
even slower with this cold front and wants to keep it dry across 
the region during the day on Sunday...and holds off bringing a 
chance of showers and thunderstorms into the region until Sunday 
night and Monday. European model (ecmwf) model may have the right idea in slowing 
down the arrival of this cold front...especially given the strong 
upper ridge that initially will be over the region. 
However...given the uncertainty this far out...have opted to 
stay with previous forecast continuity and will keep in a chance 
of showers and thunderstorms Sunday and Sunday night...and then 
go with a dry forecast for Monday and Tuesday. Given these 
differences in the models forecaster confidence is low in the 
forecast from Sunday through Tuesday. Later shifts will need to 
reexamine the forecast from Sunday Onward. 


&& 


Aviation /18z Wednesday through Sunday/... 
through 18z Thursday...water vapor shows middle/upper level trough 
lifting NE away from our County Warning Area this afternoon...as weak elongated 500 mb vorticity 
and associated jet couplet continues to produce a middle level cloud 
deck across southern Canada. In addition...visible satellite pic shows some weak 
vertical cumulus clouds across our taf sites this afternoon...which 
should dissipate around sunset. However...weak 500 mb vorticity upstream 
has plenty of clouds...per latest satellite trends...therefore expect a 
broken to overcast deck to develop between 21-23z across our taf sites this 
evening. Will mention a broken deck between 050-080kft through 06z...then 
clring. Feel enough clring will develop late tonight...along with 
light winds to form some fog at mpv/slk between 08z-12z. Will mention 
tempo with vlifr conditions in fog at mpv/slk through 12z 
Thursday...before fog dissipates between 12-14z Thursday. Surface high pressure 
overhead tonight...expect light and variable winds to becoming 
southerly on Thursday as high pressure slowly shifts into eastern New 
England. 


18z Thursday through Sunday...the combination of surface high pressure and 
building hghts aloft will provide taf sites with VFR conditions 
through Saturday. However...areas of fog at mpv/slk each morning 
between 08-12z will cause vlifr conditions. Middle/upper level trough and 
associated surface cold front will produce showers/storms on Sunday. 
Given...the small ribbon of 850-500mb moisture/uvv's and best ulvl 
dynamics staying closer to the middle/upper level circulation across 
central Canada...feel only a 1 to 3 hour window of IFR conditions will 
accompany the front. 


&& 


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


&& 


$$ 
Synopsis...wgh 
near term...Sisson 
short term...wgh 
long term...wgh 
aviation...Taber