900 
fxus61 kbtv 240219 
afdbtv 


Area forecast discussion 
National Weather Service Burlington Vermont 
1019 PM EDT Wednesday Jul 23 2008 


Synopsis... 
the potential for heavy rain and flooding will continue through 
much of the overnight hours across a good deal of the north 
country. This will be in response to a slow moving upper level 
trough of low pressure over the Ohio Valley interacting with 
tropical moisture flowing northward into New England. The 
potential for more heavy rain will continue on Thursday and 
Thursday afternoon. 


&& 


Near term /until 6 am Thursday morning/... 
as of 1018 PM EDT Wednesday...axis of moderate to heavy rainfall 
has become established over the area tonight...mainly along the 
New York and Vermont borders. This is associated with deep 
southerly fetch with tropical origins flowing up ahead of a 
pronounced upper trough over the Ohio Valley. Synoptic scale 
pattern conducive to heavy precipitation and thus Flood Watch will 
continue through Thursday afternoon as upper trough remains to the 
west and deep moisture flows northward. Already seeing places this 
evening picking up a half to one inch and plenty of convection 
south into New Jersey that will spread northward overnight. 
Should see smaller streams and creeks rising rapidly...ponding on 
roadways...then a trend toward rapid rises on larger mainstem 
rivers on Thursday. Can see a lot of 1 to 3 inch rain amounts from 
this event with an axis of 2 to 4 inches across parts of western 
Vermont with some isolated 5 inch readings. 


&& 


Short term /6 am Thursday morning through Friday night/... 
as of 345 PM EDT Wednesday...axis of heavier rainfall shifts 
slowly east during the day on Thursday as upper trough and surface 
boundary make their way very slowly east. Rainfall amounts of 1 
to 3 inches expected across much of Vermont during Thursday...with lesser 
amounts over northern New York. Rafl then slowly exits east by Thursday night 
as drier air attempts to wrap around the S/southeast side of upper low. 
Some considerable differences in the models for this period...as 
GFS maintains a quicker exit of rafl across our region. Rainfall 
totals with the event expect to average 2 to 4 inches in the watch 
area...with localized amounts of 5+ inches. Lingering showers 
Friday...mainly in the morning...then mainly dry for later Friday/Friday 
night as weak and temporary ridging develop over the area. 


&& 


Long term /Saturday through Wednesday/... 
as of 237 PM Wednesday...for Saturday...surface cold front will begin to 
push east-southeast across the County Warning Area. Strong warm air advection west/ 850 temperatures around 14c-16c 
should provide enough instability to trigger scattered thunderstorm ahead of 
frontal passage. By the evening hours the loss of daytime heating will allow 
for just rain shower overngt. System exits by Sunday morning...allowing 
broad...slow moving upper low to set up over eastern Quebec. A series 
of troughs and weak shortwaves will mv down across the County Warning Area Sunday 
into Monday night. Some minor clring ahead of each system during the 
day/aftnoon may provide enough instability to allow scattered thunderstorm to 
develop...so have mentioned aftnoon thunderstorm sun/Mon...and just rain shower for 
morning/late night hours. By Tuesday morning...remnants of exiting 
upper trough will have exited east of the region...with surface ridge 
building slowly east. West/ north flow setting up over the 
area...expecting ll cloud cover which will limit aftnoon sunshine 
somewhat...so have cut back on guidance highs a few degrees for 
both Tuesday and on Wednesday...which will be just blw normal. 


&& 


Aviation /02z Thursday through Monday/... 
through 00z Friday....expect MVFR conditions through much of the 
period with localized IFR conditions due to widespread rainfall 
over the region. Moisture source is tropical in nature thus expect 
the lower ceilings and the moderate to heavy rainfall at times. 
Areas most likely to see the moderate to heavy rainfall will be 
east of kslk and west of kmpv. The band of steadier precipitation 
will be eventually begin to move east across the area after 18z on 
Thursday and will result in conditions trending toward VFR...especially 
after 21z. 


00z Friday through Sunday...unsettled weather to continue for much of 
the extended aviation. Heavy rain will persist into Thursday 
morning...with widespread MVFR and scattered IFR expected. 
Lingering showers Thursday afternoon should dissipate 
overnight...with Friday dry and VFR. More rain expected for 
Saturday and Sunday especially in the afternoon. VFR conditions 
with occasional MVFR in showers and thunderstorms over the 
weekend. 


&& 


Hydrology... 
corridor of moderate to heavy rainfall has become established over 
eastern New York and western Vermont this evening. This looks to 
be the main area for additional heavy rain overnight as deep 
southerly flow has become established over the area along with a 
connection to the tropics. This is all occurring ahead of dynamic 
forcing associated with a very slow moving upper trough over the 
eastern Great Lakes. This is a favorable synoptic pattern for 
heavy rain and given the already saturated environment...it will 
not take much to cause additional flooding. Look for total 
rainfall amounts across eastern New York and Vermont in the 2 to 4 
inch range with localized amounts to 5 inches. Given tropical 
connection to this event...favorable synoptic scale 
pattern...already wet conditions...and low flash flood guidance 
values it will not take much to have potentially serious flood 
concerns. Thus this situation will continue to be closely monitored. 


&& 


Btv watches/warnings/advisories... 
Vermont...Flood Watch through Thursday afternoon for vtz001>012-016>019. 
New York...Flood Watch through Thursday afternoon for nyz028-030-031-034- 
035. 


&& 


$$ 
Synopsis...evenson 
near term...evenson 
short term...rjs/jmg 
long term...jn 
aviation...evenson/jn 
hydrology...evenson