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Area forecast discussion 
National Weather Service Burlington Vermont 
915 PM EST Friday Nov 21 2008 


Synopsis... 
below normal temperatures will continue across the north country 
through next week. An upper air disturbance will bring snow 
showers or flurries to the region through Saturday. Gusty 
northwest winds are also expected across the region on Saturday 
as an intensifying low pressure area moves into the Canadian 
Maritimes on Saturday. A weak ridge of high pressure will build 
into the region on Sunday. A low pressure area moving southeast 
across the Great Lakes on Monday will bring more precipitation to 
the north country next week. 


&& 


Near term /until 6 am Saturday morning/... 
as of 915 PM EST Friday...quick update to this evenings 
forecast...mainly to reflect current and expected coverage of shsn 
activity across the area this evening...and to tweak sky cover per 
latest satellite/surface observations. Latest synoptic map showing 
coastal cyclogenesis well underway south of the 40n/-70w benchmark 
this evening...with moist cyclonic flow persisting across northern New 
England/SC Canada. As this system pushes quickly northward later 
tonight...digging upper trough and associated middle/upper level height falls 
should build southward into northern New York/New England. This combined with a 
general increase in middle level moisture advection should allow scattered to 
occnly numerous shsn activity to increase in areal coverage after 
midnight...especially in the northern mountains where some minor/light accumulate likely. 
Have tweaked pop/weather grids based off latest radar/surface observation and 
new model guidance...showing highest coverage this evening across 
the northern greens...with activity then building into the northern dacks and 
southward into the southern greens by later tonight. Other than these 
changes and some small sky cover adjustments inherited forecast in good 
shape and no other changes needed at this time. Enjoy the evening. 


&& 


Short term /6 am Saturday morning through Sunday night/... 
as of 355 PM EST Friday...gusty winds during the day Saturday as 
pressure gradient increases and surface low pressure which passed 
off the coast of New England overnight will move north into the 
Canadian Maritimes. Cold air advection continues across the region and gusty northwest 
winds will affect the region. Upslope snow showers 
continue...especially the western slopes of the Green Mountains. 
Have continued to use the NAM 12 bias corrected numbers for 
temperatures...which has done a better job with maximum and min temperatures 
the past couple days as the other models are much too high. A 
weak ridge of high pressure will build into the region Saturday 
night. Have gone warmer than guidance for min temperatures Sunday night 
as warm air advection begins to edge into the area ahead of approaching low 
pressure system...thicknesses will increase and 850 temperatures respond 
as well. 


&& 


Long term /Monday through Friday/... 
as of 355 PM EST Friday...a strong middle-upper level trough digging into the 
Great Lakes/Ohio Valley region at 12z Monday is expected to deepen 
significantly and become a closed low vicinity Lake Erie at 00z Tuesday. 
There is a chance for light snow...or a mix of light rain/snow in 
the central/southern Champlain Valley during the day Monday associated 
with a northward moving band of warm air advection. However...the 
strong qg-forcing and associated potential vorticity advection 
appears to hold off until Monday night. Thus...any precipitation will 
generally be light during the day Monday /less than a tenth of an 
inch liquid equiv/. 


Forcing for ascent increases Monday night as deep-layer cyclone 
shifts eastward across the southern tier of New York. Low-level wind field shifts 
into the east/southeast across the forecast area with very strong 
isentropic lift and moisture advection from the Gulf of ME nwwd 
into our area. Mixing ratio values around 850mb increase to 
4-5g/kg by 12z Tuesday. Wind direction suggests some shadowing 
across northestern Vermont...but also upslope enhancement across western Windsor 
and Orange counties. Precipitation will begin as snow but a mix with sleet 
is likely across especially eastern Vermont toward sunrise Tuesday...based 
on 12z GFS and European model (ecmwf). 


Deep-layer cyclone cuts off to our south on Tuesday...and 
position of the low will determine p-type and potential for 
locally high winds. Based on present indications...it appears 
that mixed precipitation or rain will move east to west across Vermont into the 
eastern Adirondacks with surface temperatures increasing to the middle-upper 30s. 
Other concern is for a downslope wind event along the western slopes 
of the Green Mountains the 12z GFS indicated 80kt winds at 5kft at 
15z Tuesday. This could result in a potentially damaging wind 
event along portions of the western slopes...but it/S too early 
to have high confidence in this until the intensity and position 
of the easterly jet can be better determined. Have indicated surface 
winds of 20-25 kts across the western slopes of The Greens during the 
day Tuesday for now. Stay tuned for further details on potential 
impacts from this system. 


Deep-layer low eventually lifts northeastward away from the region during 
the middle-late week period. Continued cyclonic flow regime will 
bring abundant cloud cover and periods of snow showers to the 
north country - especially in the mountains temperatures will 
generally be slightly below normal Wednesday through Friday. 


&& 


Aviation /02z Saturday through Wednesday/... 
through 00z Sunday...overnight conditions will vary from Vermont 
to northern New York through midnight. Skies have scattered out 
across northern New York except for some MVFR ceilings in the mountain 
locales...with generally cloudy VFR skies continuing over northern 
Vermont. Upstream satellite indicates that with approaching short wave 
that skies will fill back in across northern New York after 
midnight though. After midnight...ceilings areawide will be overcast VFR 
through 12z. Thereafter...ceilings will lower to MVFR with visibility 
briefly MVFR in scattered snow showers. Winds will also be 
increasing after 12z with gusts of 20-30kts expected...especially 
in the valleys. 


00z Sunday through Wednesday...ridge of high pressure brings 
mainly VFR weather conditions for Sunday with middle-upper level clouds 
only. Should see a break in snow shower activity on Sunday. A warm 
front lifts across the area Sunday night...which may bring some 
light snow along the international border...with periods of MVFR conditions. 
Significant storm possible Tuesday with widespread mixed wintry 
precipitation and IFR conditions. May also have to contend with a 
downslope wind event along the west slopes of the Green Mountains with 
strong gusty east-southeasterly winds. Details are yet to be determined at this 
time range and will ultimately depend on the track and intensity 
of the low pressure system. Will continue to monitor this 
potential. 


&& 


Equipment... 
computer specialists have rectified the local server problem that 
had limited data flow to specific web-based and phone recorded 
products over the past 48 hours. All data flow problems appear to 
have been corrected at this time. We apologize for any inconvenience 
this has caused. 


&& 


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


&& 


$$ 
Synopsis...neiles 
near term...jmg 
short term...neiles 
long term...banacos 
aviation...lahiff 
equipment...National Weather Service btv 

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