Special Weather Statement, NWS Burlington, VT

Area Forecast Discussion
National Weather Service Burlington VT
719 PM EDT Sun Aug 2 2020

.SYNOPSIS...
Showers and thunderstorms will develop across northern New York
after 3 PM and spread eastward into Vermont late this afternoon
into this evening. Strong to locally severe storms will be possible
across northern New York and western Vermont through about 8 PM. All
rainfall associated with the convection will exit the region around
midnight. A few showers will be again possible on Monday as a cold
front moves through the region. We will see a brief break in
rainfall Monday afternoon but will see rain chances increase as
Tropical Storm Isaias approaches. We are looking at moderate to
heavy rain moving into southern and eastern Vermont Tuesday evening
and continue through early Wednesday morning before the storm moves
quickly to the northeast. Quieter weather awaits the region through
the remainder of the week once Isaias exits the region.

&&

.NEAR TERM /THROUGH MONDAY NIGHT/...
As of 710 PM EDT Sunday...So far this evening, severe activity
has remained for the most part to the south and west of the CWA.
While there is still potential for a few strong to severe storm
before the end of the evening, the chances for a tornadic
activity, as seen earlier across western MA and eastern Ontario,
look slim for the North Country. Previous discussion follows.

A warm front continues to work through the
North Country this afternoon with the front currently being located
along a line extending from Ogdensburg to Crown Point to
Springfield. Behind this warm front, we have seen dewpoints rise
into the upper 60s to lower 70s as our temperatures begin to warm
near 80 degrees. Visible satellite imagery shows a dry slot
developing behind the front which will allow temperatures to
continue to warm through the afternoon hours with highs in most
locations topping out in the lower to mid 80s. A sharp shortwave
trough in advance of an approaching cold front will eject over the
region between 3 and 5 PM this afternoon and we will likely see
showers and thunderstorms develop across the North Country. Looking
across central and western New York, we are just starting to see a
few storms fire along this feature. Confidence is increasing in the
chances for thunderstorms this afternoon across northern New York
and the ingredients are present to see strong to severe
thunderstorms between 3 and 8 PM today. The latest mesoanalysis
shows around 1000 J/kg of CAPE with 0-1 km shear of 35-40 knots.
This shear and instability coupled with upper level divergence ahead
of the shortwave trough should allow for organized convection to
develop with the potential for a few bowing segments and supercells.
While the areal coverage won't be great, any storms that do develop
will likely be rotating given out low level shear and the threat for
a tornado does exist although it is very low.

By the time the showers and thunderstorms work into western Vermont
this evening, the atmosphere will begin to stabilize and the
convection should shift from surface based to elevated. This will
likely reduce the likelihood of severe weather across much of
Vermont but any supercells will need to be monitored should they
develop. Much of the rainfall associated with this convection will
exit the North Country by midnight as a strong low level jet helps
to push the rainfall out of the region. However, by sunrise on
Monday morning, we will begin to feel the influence of the surface
cold front as additional showers will form along the boundary. These
showers should be generally light in nature as the high PWAT air
mass exits this evening with the convection. Monday afternoon into
Monday evening look to be dry with temperatures residing a few
degrees above seasonal normals.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY/...
As of 341 PM EDT Sunday...The remnants of Isaias will be affecting
our region in the short term. See NHC products for the latest
updates.

We are under a slight risk of excessive rainfall as the remnants
moves rapidly through New England Tuesday night into Wednesday
morning. Consistent with the previous forecast rainfall amounts look
to be 1-3" especially south and east of BTV. Right now with the
rapid movement of Isaias there is a low threat of isolated flash
flood and poor drainage flooding based on these amounts but with dry
antecedent conditions most of the rain looks to be beneficial.

Models are in pretty good agreement with the overall track of the
center of low pressure through NH with the heaviest rain along and
just to the left of the track. However, there are model differences
with the timing with the GFS fastest and ECMWF/UK/NAM slowest with
ICON/CMC/GEFS right in the middle and closest to official NHC track.
With some uncertainty in the speed of the system there will be some
uncertainty in the duration of the expected heavy rainfall.

Low level convergence ahead of the Isaias, the upper level trof to
our west, precipitable water 1.75-2" and the strong upper level jet
over 100 kts to the north brings good forcing for ascent and the
chance of a predecessor rainfall event which is out ahead of when
the main low pressure passes by Tuesday night. The heaviest rain
looks like it will fall Tuesday afternoon and evening. Again a
general 1-3 inches of rain is expected at this time, perhaps an
isolated higher amount, is expected mainly south and east of BTV but
the exact track will determine the final location.

For the wind, there looks to be a period of stronger 15-30kt
southerly winds over the Champlain valley by Tuesday as the pressure
gradient increases well ahead of Isaias. There may also be a period
of higher winds in the vicinity of the southern Greens depending on
the exact track of the low and how fast the system weakens, so
haven't included those details as of yet.

As the system moves quickly northeast and away from the region on
Wed, drier air with with weak cold advection moves in leaving us
with improving weather by Wed afternoon, but will be governed by how
quickly the remnants of Isaias moves away.

Looking for high temps in the lower to mid 70s on Tuesday and then
warming to the mid 70s to lower 80s.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
As of 341 PM EDT Sunday...Things look mainly mild and dry in the long
term as surface high pressure dominates the period. In the upper
levels, some very weak troughiness remains but the airmass is dry so
there is little chance for precipitation. Expecting seasonably warm
conditions with highs in the upper 70s to mid 80s and lows ranging
from the mid 50s to mid 60s.

&&

.AVIATION /23Z SUNDAY THROUGH FRIDAY/...
Through 00Z Tuesday...VFR conditions are expected overall across
the region. Showers and thunderstorms are still firing across
northern New York and could still spread into western Vermont
after 00Z. Some of these storms could be strong to severe with
gusty winds and heavy rainfall possible. Showers and
thunderstorms will weaken as they enter Vermont but could still
produce some moderate to heavy rainfall at times which may
briefly drop visibilities to 3-5 miles. Gusty south winds are
developing behind a warm front but as these winds weaken tonight
we will see LLWS develop at a few sites with a strong southerly
jet of 45 knots right off the surface. This jet will exit
between 04Z and 09Z and any shear thereafter would subside.

Outlook...

Monday Night: VFR. Slight chance SHRA.
Tuesday: Mainly VFR, with areas MVFR possible. Definite SHRA.
Tuesday Night: Mainly MVFR, with local IFR possible. Definite
SHRA.
Wednesday: Mainly VFR, with local IFR possible. Slight chance
SHRA.
Wednesday Night: VFR. NO SIG WX.
Thursday: VFR. NO SIG WX.
Thursday Night: VFR. NO SIG WX.
Friday: VFR. NO SIG WX.

&&

.MARINE...
As of 300 PM EDT Sunday...South winds between 15 and 25 knots
will continue through the overnight period with the possibility
of a few gusts approaching 35 knots this afternoon. Waves will
continue to build to 2 to 4 feet with locally higher waves
possible where the stronger gusts occur. Boaters should
exercise caution on Lake Champlain today as conditions will
continue to be choppy this afternoon and evening. A lake wind
advisory continues until Monday morning.

&&

.BTV WATCHES/WARNINGS/ADVISORIES...
VT...None.
NY...None.

&&

SYNOPSIS...Clay
NEAR TERM...Clay/Verasamy
SHORT TERM...Sisson
LONG TERM...Sisson
AVIATION...Clay/Verasamy
MARINE...Clay

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