Weather

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fxus61 kbtv 071047 
afdbtv 


Area forecast discussion 
National Weather Service Burlington Vermont 
647 am EDT sun Sep 7 2008 


Synopsis... 
the remnants of Tropical Storm Hanna will quickly lift into eastern 
Canada as surface high pressure slowly builds into the north 
country. Leftover moisture will produce plenty of clouds with areas 
of drizzle and fog this morning...but some breaks in the overcast 
will develop this afternoon...as temperatures climb to near normal 
levels. Surface high pressure will continue for Monday...but clouds 
will increase associated with our next weather system by Tuesday. 
This will provide the region with another chance for showers and 
thunderstorms on Tuesday with temperatures slightly above normal and 
breezy conditions developing. 


&& 


Near term /through tonight/... 
as of 615 am EDT Sunday...water vapor this morning shows the 
remnants of Hanna quickly moving NE into eastern Canada 
associated with the fast SW follow aloft. As predicted this system 
had limited impacts on our forecast area...with btv receiving only 0.03" of 
quantitative precipitation forecast yesterday...mpv 0... our southern County Warning Area saw amounts near 
1.50". It should be noted our cxx radar is significantly over 
estimating precipitation amounts across our central/southern County Warning Area by 1 to 3 
inches...based on ASOS observation at leb/vsf. 


Otherwise...big pict shows large middle/upper level trough across 
northern Continental U.S. With fast west to SW follow aloft with embedded vorts 
across the western Great Lakes. This energy and area of enhanced 
moisture will impact our western County Warning Area by 18z today. Meanwhile...large 
area of subsidence/dry air aloft has develop behind Hanna this 
morning across central PA into western New York...which will move into our 
County Warning Area. However...plenty of low level moisture per soundings and observation 
upstream suggest strato cumulus deck will be hard to erode 
today...especially across central/eastern Vermont...where low level moisture 
from recent rain is highest. Also...helping to enhance low level cloud 
development today will be northwest upslope follow through 800mb of 15 to 25 knts. 
BUFKIT soundings show deep moist layer between surface-800mb through 18z at 
btv today...then slow clring after 18z. Will mention mostly skies this 
morning with areas of fog/drizzle in the mountains and slow clring by middle 
afternoon. Interesting to see the btv 4km WRF holds clouds/low level moisture 
through 20z from cpv and points east...and keeps surface temperatures in the 
middle/upper 60s. Will trend toward the slower clring trend based on 
northerly follow and prognosticated moisture profiles...and mention temperatures in 
the m60s slk to around 70 btv. 


Tonight...weak embedded short wave energy near Chicago at this time...will quickly 
move across our County Warning Area. This lift will enhance more middle level clouds/moisture 
from west to east across our County Warning Area. However...best 850-500mb q-vector 
convergence...along with deepest 850-500mb moisture/lift fields will 
pass north and west of forecast area. Will mention increasing clouds and keep 
temperatures several degrees above machine numbers. If more clring occurs 
than anticipated...then temperatures will cool into the l/M 40s slk/nek to 
m50s btv...otherwise thinking u40s to near 50f slk/nek to u50s to 
near 60s btv/pbg. 


&& 


Short term /Monday through Tuesday/... 
as of 615 am EDT Sunday...the short term forecast challenge will be timing 
of fall like cold front on Tuesday and the potential for 
thunderstorm development. First...fast west to east follow aloft 
continues across our County Warning Area...as surface high pressure shift toward the eastern 
Seaboard. Middle/upper level follow indicates some channeled vorticity 
across the central/northern zones on Monday...which will interact with 
some middle level moisture to produce some clouds. However...overall 
dynamics/moisture is limited...therefore not expecting any quantitative precipitation forecast. 
Prognosticated 850mb temperatures between 8-10c support highs in the u60s slk to 
l/M 70s elsewhere. 


Tuesday...potent short wave energy and associated strong cold front will move 
across our County Warning Area. Latest model trends have indicated our forecast area will be in the 
warm sector as surface low pressure tracks to our north and west. Expected 
850 mb temperatures under strong low level jet quickly warm into the 12-14c range by 
18z Tuesday...supporting highs in the middle/u70s mountains to l80s valleys. In 
addition...surface dewpoints are expected to rebound into the u50s to l60s 
ahead of approaching surface cold front. This moisture/heat will create surface 
based cape values around 1000 j/kg...along with lifted indices near -4c...and a 
very strong low to middle level wind field is expected given gradient. GFS 
soundings indicate 40 knts at 900mb...near 50 knts at 850 mb...and 60 
knts at 700mb associated with digging short wave trough. This strong 
unidirectional wind follow supports organized convection...developing 
along the front on Tuesday afternoon. Current Thermo-dynamics and wind 
profiles supports a convective line with bowing line segments. This 
event looks like a classic late season severe weather event for our 
County Warning Area...which will have to be monitored closely in the upcoming days. 


&& 


Long term /Tuesday night through Saturday/... 
as of 620 am EDT Sunday...after frontal passage...strong cold air advection pushes 
into the region as 850hpa temperatures fall to below freezing overnight 
Tuesday. Maximum temperatures will struggle to get out of the middle 50s to 
lower 60s on Wednesday as high pressure builds in. Wednesday night 
high pressure becomes centered directly overhead and even though 
850hpa temperatures increase slightly...clear skies and light winds will 
provide strong radiational cooling and should be the coldest night 
of the season to date. Expect to see lower to middle 40s in the 
valleys with lower to middle 30s elsewhere. Frost is almost a 
certainty across the Adirondacks with spots elsewhere. High 
pressure remains in control through Thursday with moderating 
temperatures as high pressure pushes east and southerly flow 
develops. Forecaster becomes a little more uncertain for Friday 
heading into the weekend as extended models differ on timing and 
intensity of a shortwave trough moving from the upper Great Lakes 
into our region. For now have kept with previous forecast thinking 
and ensembles with low chance probability of precipitation but will need to be monitored 
in later forecasts. 


&& 


Aviation /12z Sunday through Thursday/... 
through 12z Monday...my previous thinking was that drier middle level 
air would mix in a bit today providing a bit of clearing in between 
systems...but looking at upstream satellite it looks as if our 
window of opportunity for any clearing will be slim to maybe none. 
Thus have gone will a little more pessimistic aviation forecast 
for the 12z package in keeping skies broken-overcast across the forecast 
area for today. Ceilings should lift a little though with the dry air 
coming in...but still expect MVFR at kmpv/kslk...otherwise it will 
be a low VFR deck elsewhere. 


After 12z Monday...VFR conditions are expected for Monday as 
surface high pressure builds overhead. A strong cold front will 
track through the forecast area on Tuesday with strong surface 
winds ahead of the front. Expect to see showers and thunderstorms 
develop during the day with MVFR/IFR conditions possible. High 
pressure then builds back into the region with VFR conditions for 
Wednesday through Thursday. 


&& 


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


&& 


$$ 
Synopsis...Taber 
near term...Taber 
short term...Taber 
long term...lahiff 
aviation...lahiff 

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