693 
fxus61 kbtv 030213 
afdbtv 


Area forecast discussion 
National Weather Service Burlington Vermont 
913 PM EST Tuesday Dec 2 2008 


Synopsis... 
weak high pressure will build into the north country tonight with 
temperatures cooling into the 20s. A few light mountain snow 
showers will be possible...but little snow accumulation is 
expected. Meanwhile...a warm front will lift across the region on 
Wednesday...with more clouds and slightly warmer temperatures. 
The next chance for rain and snow showers will be associated with 
a strong surface cold front on Thursday...which will bring much 
cooler temperatures for the weekend. 


&& 


Near term /through Wednesday/... 
as of 913 PM EST Tuesday...update to going forecast tonight mainly 
to increase probability of precipitation in southern Saint Lawrence County of New York due 
to lake effect Snows. Lake effect snow band off Lake Ontario has 
shifted north this evening as surface winds have become southwesterly. 
Spotter reports in Edwards New York indicate snow has been falling since 
before 7 PM though accumulations only a dusting at this time. 
Local mesoscale models handling this feature very well and 
indicate lake effect snows to continue through midnight before 
surface winds become more southerly and shut off any lake effect 
processes. Thus...have update the forecast to include likely probability of precipitation 
for southern Saint Lawrence County and also put some scattered 
snow showers across the northern Adirondacks as Adirondack Airport 
reporting 6sm -sn at this time. Snowfall accumulations with lake 
band should remain light with a dusting to up to 2 inches possible. 
Remainder of the forecast in good shape for tonight with no 
additional changes. Previous forecast from this afternoon below... 


The forecast challenge through Wednesday will be temperatures...followed by schc probability of precipitation 
across the mountain locations. Visible satellite pic shows mostly cloudy skies 
across our forecast area...but some breaks have developed upstream across 
southern Ontario into the northern Great Lakes. This region last 
night had temperatures in the single digits to l10s...but feel clouds 
associated with lake moisture/upslope follow...will prevent temperatures from 
dropping this far. Based on clouds/winds will mention temperatures in the 
l20s slk/mountains to M/u 20s elsewhere. BUFKIT soundings at slk show 
plenty of moisture between surface- 800mb...which combined with 240 to 
260 follow will produce plenty of clouds overnight. 
Furthermore...expect enough low level lift from mountains to produce a few 
-SW. Also...surface observation show winds veering to the SW across the Ohio 
Valley...which will help to Shift Lake moisture/band back across the 
dacks this evening. Therefore will continue to mention chance probability of precipitation across nny 
zones...but no accumulations are expected. 


Wednesday...mid/upper level hghts increase as strong low level warm air advection continues for 
Wednesday across our forecast area. Prognosticated 850 mb temperatures warm between 1-3c by 00z 
Thursday...but soundings support mixing levels to only 925mb on 
Wednesday...which combined with 925mb temperatures around 0c support highs 
m30s nek/mountains to l40s mss. Best 850-700mb warm air advection lift...along with 
best 850-500mb moisture is prognosticated to stay north and west of forecast area 
on Wednesday. Therefore...will keep forecast dry at this time. 


&& 


Short term /Wednesday night through Thursday night/... 
as of 330 PM EST Tuesday...surface high pressure will shift into eastern 
New England...as potent short wave energy and associated surface cold front 
approach our western County Warning Area by 12z Thursday. Forecast area will continue to experience 
SW follow ahead of this system...which will result in a large temperature 
spread across our forecast area. Coolest temperatures will be east of the Green 
Mountains...where low level temperature inversion will develop and limit mixing. 
However...across cpv/slv southerly winds will continue overnight and 
temperatures will remain steady or rise slightly overnight. Based on 
prognosticated low level thermal profiles...early evening lows could 
happen...with temperatures rising overnight...especially across the 
wider/deeper valley locations. Will mention l/M 30s cpv/slv to 
l/m20s eastern/central VT/slk. 


The forecast challenge for late Wednesday night into Thursday will be timing of 
precipitation associated with potent short wave energy and cold front now 
located over the northern plains. This system will have good 
850-500mb q-vector convergence...along with a brief ribbon of 
good 850-700mb convergence/moisture...and some enhanced lift between 
850-500mb. The best lift/moisture approaches our western forecast area by 
12z Thursday...is located across the cpv by 18z Thursday and through County Warning Area by 
00z Friday. Will continue to mention likely to Cat probability of precipitation for extreme 
western forecast area late Wednesday night...with chance probability of precipitation for dacks and schc 
probability of precipitation for cpv. On Thursday...will increase probability of precipitation to likely/Cat across 
entire County Warning Area...based on above parameters...along with good surface 
convergence and some low level lake moisture interaction. Soundings at 
btv show plenty of moisture between 925mb and 700mb...but very dry 
llvls blw 925mb. This combined with SW downsloping low level jet of 40 
to 50 knts...will make pop fcsting tricky. Latest pop guidance at 
btv shows 40% off the metbtv to 70% pop off the mav...therefore 
will stick very close to mav given my recent struggles with pop 
fcsting. Strong low level cold air advection develops from west to east across our County Warning Area on 
Thursday...with temperatures falling into the 20s across nny by 00z Friday. 
Prognosticated 850 mb temperatures start near 2-4c...but quickly drop between -10 and 
-12c by 00z Friday...with 925mb temperatures starting near 1c...but 
drops to near -8c by 00z Friday across our nny zones. Will mention 
temperatures l/M 40s btv/vsf/mpv...with M/u30s nny falling into the 20s 
by late afternoon. 


Thursday night...strong low level cold air advection continues as northwest follow develops behind surface 
cold front. This upslope follow combined with secondary 500 mb vorticity 
moving across our County Warning Area...will produce some light mountain snow showers. In 
addition...very cold air mass will hold less moisture...therefore 
as air rises against the mountains...the moisture will be forced from 
the atmosphere. Best Lake moisture will be south of dacks...but 
southern Vermont mountains near Killington will have the potential for a 
couple of inches late Thursday night into Friday. Based on 
clouds/gradient will stick close to machine numbers. 


&& 


Long term /Friday through Tuesday/... 
as of 335 PM EST Tuesday...chance of snow showers in the higher 
elevations across northern New York and Vermont during the day 
Friday. Surface high pressure will then build into the area for 
Friday night and Saturday. Next clipper type system approaches 
the region from the Great Lakes region on Saturday night. System 
is very slow moving across the area...but having limited moisture 
have only included chance probability of precipitation for Sunday and Sunday night. Upper 
level trough crosses the region Sunday night and pushes clipper off 
the coast of New England. Surface nigh pressure will build into 
the area Monday and Monday night. Another clipper approaches the 
area for chance of precipitation on Tuesday...although this is very far 
out in the forecast...therefore low confidence. Through the 
weekend will have temperatures well below normal with Arctic 
Canadian air streaming over the region. 


&& 


Aviation /02z Wednesday through Sunday/... 
through 00z Thursday...broken to overcast VFR ceilings across Vermont terminals 
tonight (cigs 3500-4500 ft). Ceilings lowering to MVFR at kslk and 
kmss this evening. Southwest flow will allow weak lake snow band 
off of Lake Ontario to affect kslk with snow showers and MVFR visibilities 
overnight...with a slight chance that snow showers may affect kmss. Flow 
becomes more southerly during Wednesday. Expect a decrease in low 
clouds with only scattered stratocu...with a broken deck of middle clouds at 
about 10 kft. Winds south-southwest 10 kts with gusts around 20 kts at 
kbtv/kmss/kslk. 


From 00z Thursday through Sunday...MVFR to occnl IFR late Wednesday 
night into Thursday in rain/snow showers as cold front moves across the 
region. VFR to occasional MVFR Friday and Saturday...except possible IFR at 
kslk in lake effect snow/weak clipper system. MVFR to occasional IFR in 
snow on Sunday. 


&& 


Equipment... 
the AWOS (automated weather observing system) at krut (rutland- 
southern Vermont regional airport) continues to report erroneous 
dew point data...and thus the relative humidity data for this 
site is also erroneous. The FAA has maintenance responsibility 
for the AWOS at krut. It will likely be sometime this week at the 
earliest before the dew point sensor at krut can be repaired. 


In addition...the temperature sensor at kmvl ASOS (morrisville- 
Stowe airport) is reporting erroneous temperatures due to an 
inoperative fan. Ets have been notified and a part is on order. 
The problem will be fixed within the next couple of days. 


&& 


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


&& 


$$ 
Synopsis...Taber 
near term...Taber/lahiff 
short term...Taber 
long term...neiles 
aviation...rjs/neiles 
equipment... 

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