Scientific Forecaster Discussion
fxus61 kbtv 192327
Area forecast discussion
National Weather Service Burlington Vermont
727 PM EDT Mon Aug 19 2019
a weak cold front crossing the north country this afternoon and
evening will lead to clearing skies overnight and a reduction
in humidity levels for Tuesday. High pressure and the drier air
mass will lead to sunny conditions Tuesday with highs in the low
to mid 80s across the region. The next frontal system brings
scattered daytime showers and thunderstorms to the region on
Wednesday, followed by drier and noticeably cooler conditions
for late in the week.
Near term /through Tuesday night/...
as of 722 PM EDT Monday...you can see the dry air just on the
other side of the St. Lawrence River on satellite imagery this
evening. Looking at surface observations, Massena still has a 63
dewpoint while the dewpoint just across the river is sitting at
46. This dry air will advect across the forecast area quickly
overnight which will lead to many sites surpassing their cross
over temperatures prior to midnight. Patchy to areas of dense
fog are expected tonight across much of northern New York and
the favorable locations east of the Green Mountains later on.
Based on the drier air, have reduced pops down to 0 for the next
36 hours as we should see clear skies (other than fog)
persisting through Tuesday. Any gusty winds brought on by deep
mixing this afternoon will diminish shortly after sunset.
Previous discussion...modest low to mid-level forcing
associated with Mobile mid-level trough crossing nrn New York and Vermont
this afternoon is resulting in just isold shower/tstm
development over eastern portions of Vermont. This activity will
quickly move east of the forecast area through 20z. Surface cold
front across the St. Lawrence Valley will follow this evening,
and generally move through with just a westerly wind shift. The
thermal gradient is rather weak in the sfc-850mb layer.
However, upstream 2-M dewpoints are in the 40s to lower 50s
across southeastern Ontario, and this will be our air mass for
For the overnight hours, westerly winds 5-10 mph gradually
become light and variable toward midnight as weak surface high
pressure builds ewd from the Great Lakes. Strong drying and
clearing should lead to patchy dense fog development for the
climatologically favored river valleys of central/ern Vermont and the
valleys of the northern Adirondack region between midnight and
7am. Overnight lows will be somewhat cooler than recent nights.
Looking for lows generally in the 50s, except locally in the
upper 40s across the normally cooler spots within the northern
Tuesday will be a virtually cloudless day with sfc dewpoints
falling into the low-mid 50s. Daytime highs generally 80-85f
with pops none. Tuesday night will begin quiet. However,
combination of weak 850mb warm air advection and increasingly cyclonic flow
aloft should result in increasing mid-level clouds, and just a
slight chance of a shower or sprinkles toward daybreak Wednesday
across nrn New York into S-central Vermont. The higher precipitation
chances should hold off until later in the day Wednesday. With
increasing clouds, lows Tuesday night will remain a bit warmer,
Short term /Wednesday through Wednesday night/...
as of 351 am EDT Monday...the atmosphere will become more moist
and unstable Wednesday as deep southwesterly flow increases
ahead of an upstream upper-level trough and developing surface
low. The btv forecast area will remain within the warm sector of
the cyclone during the day Wednesday, so another warm and muggy
day on tap for midweek. Precipitable water values increase to
1.5-1.75 inches Wednesday night and surface temperatures will be
in the low 80s. Amid the rising instability as the day GOES on
(pockets of 1500+ j/kg MLCAPE per model forecast soundings),
models indicating a compact upper-level wave moving through
during peak heating hours. This wave, along with a pre-frontal
surface trough, will support the development of afternoon
showers and thunderstorms. Thunderstorm threat will be somewhat
conditional, based on the evolution of clouds after a warm
frontal passage earlier in the morning...but if we get enough
clearing the potential is certainly there for some embedded
thunderstorms. Best 0-6 km shear will be removed to the
northwest, but progged values 20 to 30 kts would support some
organized convection. Locally heavy rainers and gusty winds
would be the primary threat associated with any storms.
Long term /Thursday through Monday/...
as of 351 am EDT Monday...a cold front will sweep through the
region Thursday, leading to a cooling trend for much of the long
term. The frontal passage itself looks to be fairly uneventful
given the lack of moisture as the boundary moves through, but do
expect some scattered light showers during the day Thursday.
High temperatures Thursday will depend on frontal timing, with
cooler highs expected in the northern forecast area and warmer
high expected further south. After the front clears the area, a
period of mainly dry weather is forecast through the weekend
with high pressure building in. Temperatures will be noticeably
cooler than the first part of the week, with highs generally in
the 70s and low humidity expected.
Aviation /00z Tuesday through Saturday/...
through 00z Wednesday...gusty winds continue from the Champlain
Valley westward into northern New York but these should diminish
by 01z as the surface and boundary layer decouple. Drier air
filtering in across the region should yield quickly dropping
temperatures this evening and pretty expansive fog across the
forecast area. Locations including kslk, kmss and kmpv will
likely see 1/4sm LIFR fog while other sites will likely flirt
with MVFR patchy fog. Kbtv is a little tricky as we could see
some northeast drainage flow set up which could fog in the
Airport closer to the morning hours. For now have just included
a 1200 ft scattered deck with 4sm visibility for the time being.
Fog should lift by 14z with sky clear and light winds expected
throughout the day on Tuesday.
Tuesday night: VFR. No sig weather.
Wednesday: VFR. Likely shra, chance thunderstorms and rain.
Wednesday night: mainly VFR, with local MVFR possible. Chance
shra, slight chance thunderstorms and rain.
Thursday: mainly VFR, with local MVFR possible. Chance rain showers.
Thursday night: VFR. Slight chance rain showers.
Friday: mainly VFR, with areas MVFR possible. Slight chance rain showers.
Friday night: VFR. No sig weather.
Saturday: mainly VFR, with local MVFR possible. No sig weather.