Weather

424 
fxus61 kbtv 062338 
afdbtv 


Area forecast discussion 
National Weather Service Burlington Vermont 
738 PM EDT Monday Oct 6 2008 


Synopsis... 
a cold upper level trough will shift southeast off the New England 
coast tonight resulting in diminishing cloud cover across the 
north country this evening. A strong area of high pressure will 
build in behind this system...from north of Lake Huron to 
southeast Ontario into central New York state by early Tuesday 
morning. This will result in ideal radiational cooling conditions 
tonight with much of the north country at or below freezing for 
early morning lows on Tuesday...with areas of frost expected. 
The region of high pressure will bring fair weather conditions 
through Wednesday. 


&& 


Near term /until 6 am Tuesday morning/... 
as of 343 PM EDT Monday...steep low-level lapse rates and shallow 
instability resulted in widespread daytime cumulus clouds 
today...and isolated rain shower activity across central Vermont. Per 
latest RUC analysis...the core of coldest 500mb temperatures /-28 
to -30c/ is already shifting eastward across New Hampshire and southern ME. This 
combined with the loss of insolational heating will result in a 
rapid decrease in cumulus clouds this evening...with skies become 
mostly clear areawide by 1-2z. With surface high pressure centered 
between Lake Huron and James Bay this afternoon...a northerly gradient 
flow will continue into this evening...until planetary boundary layer fully decouples. 
In the forecast...have maintained mention of northwest winds around 10 
miles per hour through this evening. The wider valleys and higher elevations 
will see these winds diminish later in the evening...while the 
sheltered valleys will see winds become nearly calm shortly after 
sunset tonight. 


With the diminishing cloud cover...surface dewpoints already in the 
lower 30s...and high pressure building toward the 
region...conditions will become favorable for radiational cooling 
from late this evening Onward through the remainder of the 
overnight hours. We continue to expect widespread frost 
formation...except very near the Lake Champlain shoreline. Most 
sections will fall below freezing tonight...with lows very near 
32f at btv tonight. The Saranac Lake Airport will likely see a low 
temperature near 20f tonight...with readings in the low to middle 20s in far 
northestern Vermont where winds will stay in the 5-10 miles per hour through most of the 
evening /owing to stronger low-level gradient flow/. 


Have maintained previous frost/freeze headlines /please see latest 
statement...albnpwbtv/...except decided to upgrade Windsor County Vermont 
from a frost advisory to a freeze warning...based on expected low 
temperatures 29-32f across much of the County. The only areas 
excluded from the advisory/warning areas are across the northern 
Adirondacks and Caledonia/Essex counties in northestern Vermont where a 
widespread freeze occurred on the morning of September 19th. 


&& 


Short term /6 am Tuesday morning through Wednesday night/... 
as of 350 PM EDT Monday...a deep-tropospheric ridge axis in place 
across the north country will bring a tranquil stretch of weather 
Tuesday through early Wednesday night...with no precipitation 
expected. Another cold night is expected Tuesday night...with low 
temperatures in a similar range to those expected tonight /most of 
the forecast area will see min temperatures at or below 32f/. Skies will 
be mostly clear through much of the period...except for increasing 
clouds from west to east during Wednesday night. A weakening 
frontal system approaches late Wednesday night and have included a 
chance of showers for this feature. At this point...most 
precipitation amounts through 12z Thursday should be at or below a tenth 
of an inch. 


&& 


Long term /Thursday through Monday/... 
as of 300 PM EDT Monday...above normal temperatures to affect the 
area from Thursday through Sunday. Warm air advection will stream into the area 
ahead of approaching weak cold front on Thursday. Limited 
moisture with this feature...and best dynamics will remain well 
to our north...so have only included chance for showers during 
Thursday. A surface ridge will build in behind the front on 
Friday...and another low pressure system will form over the 
Carolinas. Formation of this low has actually been pretty 
persistent in the GFS model runs over the past two days. There is 
a possibility for the moisture associated with this low to get 
caught up in the flow and stream across the northeast for 
Saturday through Sunday. At this time have just included chance 
probability of precipitation because of a lack of model to model consistency. Hopefully 
soon the models will come together a bit more for days 4 through 
8 because the last few days have been low confidence 
forecasts...as is today. Another low pressure system will pass 
well to our north on Sunday...bringing weak cold front across the 
region. Have again mentioned very low chance probability of precipitation. 


&& 


Aviation /00z Tuesday through Saturday/... 
through 00z Wednesday...mainly VFR through the first 24 hours with 
scattered IFR or below in patchy fog after midnight. Clear skies and 
light winds will prevail tonight and Tuesday. This will allow fog to 
develop at the usual sites. Kmpv will drop to vlifr after 03z and 
remain so through 14z. Opted to leave out mention of freezing fog at 
kmpv as temperatures will be borderline. If it does drop below 
freezing at kmpv...it should only be for a few hours. Krut will see 
visibility around 4sm after 06z...with off and on vlifr 08z-12z. 
Kslk should remain VFR with occasional IFR possible 07z-11z. Both 
the WRF and GFS hint at possible east winds late tonight at 
kbtv...which is usually favorable for advection fog. 
However...airmass will be very dry and met MOS keeps winds 
northwest. This would preclude any visibility obstructions due to 
fog at kbtv. Given the uncertainty...this will bear watching 
tonight. 


00z Wednesday through Saturday...VFR to continue through Wednesday 
night as high pressure at the surface and aloft remain the dominant 
feature across the north country. IFR can be expected early 
Wednesday morning at the usual sites due to fog. A weakening cold 
front will slip across the forecast area Thursday bringing the 
chance for light rain showers to all taf sites. Given the lack of 
moisture with this system...conditions should remain VFR/MVFR. High 
pressure and fair weather will return by Friday morning...then more 
rain Saturday as low pressure slides by to the south. MVFR with 
perhaps scattered IFR for the weekend system. 




Notice to users of terminal Aerodrome forecasts (taf)...beginning 
at 0000 UTC on November 5...2008...the format for tafs will 
change. The National Weather Service will begin to issue tafs 
using a valid date and time group in the forecast. All 
meteorological agencies worldwide will also issue their taf 
forecasts in this new format. This is being done to accommodate 
30 hour taf forecasts that will be done for select major 
international airports worldwide. There will be 32 major U.S. 
International airports for which tafs forecasts will be valid for 
30 hours. This format change is being mandated by the 
international civil aviation organization (icao). The 6 taf 
forecasts being done by the National Weather Service in 
Burlington will continue to be valid for 24 hours. To see 
examples of this new format...please go to the internet web site 
listed below. 


Www.Aviationweather.Gov/notice/taf30.Php (all lower case) 


&& 


Btv watches/warnings/advisories... 
Vermont...freeze warning from 1 am to 8 am EDT Tuesday for vtz003-006- 
008-010-012-016>019. 
Frost advisory from 1 am to 8 am EDT Tuesday for vtz001-002- 
005-009-011. 
New York...freeze warning from 1 am to 8 am EDT Tuesday for nyz026-027- 
087. 
Frost advisory from 1 am to 8 am EDT Tuesday for nyz028-035. 


&& 


$$ 
Synopsis...banacos 
near term...banacos 
short term...banacos 
long term...neiles 
aviation...mb 

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