Weather

654 
fxus61 kbtv 070555 
afdbtv 


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


Synopsis... 
Tropical Storm Hanna will move along the New England coast 
tonight...while a surface cold front moves across New York and 
Vermont. These two features will produce areas of rain tonight. 
The remnants of Tropical Storm Hanna will move quickly northeast and 
be located across eastern Canada by Sunday afternoon. This will 
provide our region with drier weather for Sunday afternoon through 
Monday. A strong cold front will bring a return of showers and 
thunderstorms to the area on Tuesday. 


&& 


Near term /until 6 am this morning/... 
as of 854 PM EDT Saturday...several additional hours of heavy 
rainfall are expected across S-central Vermont...and Windsor County in 
particular. Maximum rainfall accumulations have been in Windsor 
County to this point...with 1.92" at the Springfield mesonet 
site...and 1.48" at the Springfield Airport /vsf ASOS/. We think 
additional rainfall up to 1 inch is possible across Windsor 
County and are continuing to monitor for possible flooding 
concerns. Owing to dry antecedent conditions...flash flood 
guidance is running high at 4"/3 hours and 4.9"/6 hours. Current 
trends suggest we/ll remain under those thresholds and will 
continue with short term public forecast to highlight ponding on 
roadways and any minor poor drainage flooding. 


Surface analysis is complex at 1z with the tropical cyclone over 
S-central New Jersey and a stalled frontal boundary remaining across the 
Adirondacks into the far northern Champlain Valley. As the tropical 
cyclone shifts northeastward across southern New England overnight per NHC track... 
surface winds will rapidly shift into the north around 10 miles per hour and lead 
to a southeastward progression and ultimate frontolysis to our frontal 
boundary. Thus...Don/T foresee much additional precipitation development 
west and north of a line from gfl-rut-1v4. Have updated the 
forecast to reduce probability of precipitation and sharpen the gradient west of the 
current periphery of heavy rainfall across southern/central Vermont. Skies 
will partial clear across western sections during the pre-dawn hours 
with lows generally in the 50s. In Vermont...overnight lows will 
generally remain in the lower 60s. 


&& 


Short term /6 am this morning through Monday night/... 
as of 330 PM EDT Saturday...the remnants of Hanna will lift quickly 
into eastern Canada during Sunday and cyclonic flow on backside will 
enhance low level cold air advection. Have continued with mention of chance probability of precipitation associated 
with upslope...mainly during morning hours over northern zones. Moisture rather 
limited to llvls...and it decreases during the PM...so expect skies 
to become prtly sunny. Weak embedded 500 mb vorticity will bring some clouds 
to the area Sunday night. High pressure will then prevail across the 
area on Monday...allowing for at least partly sunny skies. Some 
increase in clouds Monday night with onset of warm air advection as high moves 
offshore. Temperatures close to normal during the period. 


&& 


Long term /Tuesday through Saturday/... 
as of 330 PM EDT Saturday...Bermuda-sub tropical ridge in control 
of southeast Continental U.S. With largely zonal west-southwest flow across NE Continental U.S.. a few northern 
stream short wave moving within zonal flow will be the weather makers for forecast area on Tuesday 
and then perhaps late Friday/Sat with surface waves and cold fronts. In 
between...some weak middle/ulvl ridging with high prs and seasonable 
temperatures for middle to late week. 


First northern stream delivers previously advertised cold front through 
the forecast area Tuesday. Models continue to indicate that this 
will be a fairly strong cold front with the GFS showing a strong 
850hpa jet of 50+ knots developing Tuesday from the Saint Lawrence 
valley to northern Vermont...60+ knots at 700 mb and 90+ knots at 
500hpa. Additionally there is a strong emperature gradient with the 
front...where 850mb temperatures go from 15c to 5c in a 12 hour period. 
Timing of the front appears to have been delayed from erlr model runs 
due to strong short wave and deepening trough...thus timing of frontal passage shld allow 
more warm sector and convective development. 


Normally...SW flow does not bring much severe but the very strong 
developing jet structure warrants close monitoring for Tuesday. 


After the front...strong cold air advection pushes into the region as 850hpa temperatures 
fall to around +5c by 12z Wednesday as high pressure drifts overhead. Maximum 
temperatures on Wednesday will be unseasonably cool 60s with high prs building/ 
cresting across forecast area Wednesday night for a cold night and pockets of frost 
psbl/lkly. 


High pressure remains in control through Thursday night and moves offshore 
Friday for return...warm flow ahead of next northern stream short wave...surface low 
and cold fnt Friday ngt/Sat. 


Ike??? it/S way too Erly to speculate but any/if any effects would 
likely not be until late next weekend or the following Monday. 


&& 


Aviation /06z Sunday through Thursday/... 
through 06z Monday...widespread MVFR/IFR conditions will continue 
overnight as Tropical Storm Hanna pushes east off the Atlantic 
coast and light northerly flow develops behind a cold front 
pushing across the region. Exceptions will be at kmss and kslk 
where at kmss front already pushed through here and clearing skies 
already visible on infrared Sat. Still expect to see some scattered-broken VFR 
clouds here overnight which is also indicated on upstream Sat. For 
kslk northerly flow will downslope into the area and help dry out 
the lowest levels though ceilings should still remain MVFR. By 
tomorrow...clouds will slowly lift and erode through the course of 
the day as drier air filters into the region on light northwest 
flow. 


After 06z 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...rjs 
near term...banacos 
short term...rjs 
long term...slw 
aviation...lahiff 

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