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Area forecast discussion 
National Weather Service Burlington Vermont 
337 PM EDT Sat Sep 6 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 Sunday morning/... 
as of 330 PM EDT Saturday...rain in advance of Hanna has 
overspread portions of the forecast area rather quickly this PM. 
Precipitation convective in nature over western zones due proximity 
with cold front over St Lower Valley...even some lightning strikes just south 
of our County Warning Area in northern New York. Precipitation more tropical in nature from chmpln valley 
eastward across Vermont. Heaviest precipitation remins to the south...closer 
to Hanna...which is now moving into Delaware-Maryland-Virginia region. Have gone 
rather close to GFS in its solution regarding Hanna and its quantitative precipitation forecast. 
While precipitation is being drawn north into much of btv County Warning Area this PM as 
moisture from Hanna interacts with frontal system over western New York...still 
expect most of the heavier precipitation to be located just south and east 
of our County Warning Area...where best low level moisture convergence...dynamics and lift 
will be located. However...some locally heavy rain are now expected to 
affect our southern Vermont zones. Amounts of 2 to 3 inches are possible 
across southern Windsor city...with a sharp gradient in expected quantitative precipitation forecast as you 
head north and west. Most northern areas still expected to see amounts of 
a half inch or less. While some locally heavy rainfall amounts possible 
over southern zones...not enough to warrant Flood Watch at this time as 3 hour ffg 
values in this area around 4 inches. As remnants of Hanna move into 
the Gulf of Maine by Sunday morning and cold front traverses forecast area 
overnight...expect precipitation to come to an from west to east...ending in 
most locations by 12z Sunday. 


&& 


Short term /6 am Sunday 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 /20z Saturday through Thursday/... 
through 18z Sunday...aviation forecast concerns over the next 
12-18 hours will be affects of Tropical Storm Hanna moving up the 
coast. Steadiest rain looks to impact krut and possibly kmpv...yet 
MVFR-IFR conds possible everywhere with light cold air advection/low clouds/inversion 
tonight into Erly sun. Gradual prtl clearing from west to east across New York into Vermont on 
Sunday. 


After 18z Sunday...conditions should gradually improve on Sunday. 
VFR for Monday with surface high pressure in control. Strong cold front 
slated to come through Tuesday. Surface winds will be on the increase 
ahead of front and continue Tuesday night behind the front. Should 
be some showers and thunderstorms with front for MVFR/IFR conditions. Hi 
pressure and VFR conditions build in for Wednesday. 


&& 


Hydrology... 
as of 330 PM Saturday...given the expect track of Tropical Storm 
Hanna along the eastern Seaboard from TPC...the greatest threat 
for heavy rainfall will be across southern New England...extending north into extreme 
southern portion of btv County Warning Area. Total quantitative precipitation forecast amounts will be 1 to 2 inches 
across southern Vermont with isolated 3 inch totals extreme south. 0.25" to 
1" expected across central Vermont...and less than a 0.50" across most of 
northern Vermont/northern New York zones. Overall...only slight rises are 
anticipated on most local streams and rivers...except southern 
Rutland/Windsor where larger rises expected. 


&& 


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


&& 


$$ 
Synopsis...rjs 
near term...rjs 
short term...rjs 
long term...slw 
aviation...lahiff/slw 
hydrology... 

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