Special Weather Statement, NWS Burlington, VT

Area Forecast Discussion
National Weather Service Burlington VT
335 PM EDT Tue Jul 13 2021

.SYNOPSIS...
Low clouds and humid conditions will prevail across much of the
North Country tonight and Wednesday. A slow-moving upper trough
across the central Great Lakes region will bring scattered
showers and thunderstorms into the St. Lawrence Valley this
evening, with another round of showers and thunderstorms
expected across much of the North Country for Wednesday
afternoon. A few stronger thunderstorms will produce heavy rain
and gusty winds in localized areas. Increasing sunshine will
allow for very warm conditions Thursday and Friday, with some
valley high temperatures approaching 90 degrees. Another frontal
system approaching from the west will interact with the hot and
humid air mass to bring another round of showers and
thunderstorms late Friday into Friday night.

&&

.NEAR TERM /THROUGH WEDNESDAY NIGHT/...
As of 333 PM EDT Tuesday...Tale of two air masses across the
North Country for this evening and tonight. Surface ridge along
the Maine coast continues to bring recycled marine modified air
westward into central/eastern VT and the Champlain Valley.
Anticipate low clouds and perhaps some patchy fog overnight
given humid conditions, but only a 20-40% chance of showers from
the Champlain Valley eastward across VT. Low temperatures
generally in the low-mid 60s tonight east of the Green Mtns, and
in the upper 60s for the Champlain Valley.

Meanwhile, west of the marine modified air mass, seeing surface-
based instability axis across w-central NY (SBCAPE values 2500-3500
J/kg per SPC mesoanalysis) extending nwd into srn St. Lawrence
County this afternoon. Precipitable water values are near 1.9" east
of Lake Ontario with surface dewpoints in the lower 70s. Convective
storms thus far have generally not been associated with elevated
reflectivity cores across St. Lawrence County, but environment
supports heavy rainfall with high PW values and freezing levels near
14 kft. Mid-level lapse rates around 6C/km are not particularly
favorable for severe storms into St. Lawrence county, but can't rule
out locally gusty winds with a stronger core or two thru early this
evening. KMSS has already seen 0.7" of observed rainfall, and
localized radar estimates near 1" exist across swrn St. Lawrence
County. With continued moist S-SW low-level flow, we'll need to
monitor for possible training thunderstorms and additional moderate
to heavy rainfall through this evening. Overall coverage and
intensity of storms should decrease after sunset. The 6hr flash
flood guidance across St. Lawrence and Franklin Counties is
generally 2.5 to 3", so overall likelihood of any flash flooding
remains low. Overnight lows across nrn NY generally in the mid-upper
60s tonight.

For Wednesday, mid-level ridge axis shifts to our east, allowing mid-
level trough and cyclonic flow aloft to move ewd into nrn NY and VT
during the daylight hours. The 12Z HREF members generally show
convective development across the nrn Adirondacks, with a better
chance of thunderstorms moving eastward across the Champlain Valley
and central/ern VT during the mid-late afternoon hours. High PBL
dewpoints in the upper 60s to lower 70s largely drive SBCAPEs of
1000-2000 J/kg, but once again with marginal mid-level lapse rates.
Appears heavy rainfall will be the primary threat with any t-storms
tomorrow, but did include gusty wind wording. We remain in a
Marginal risk of severe storms based on the updated SPC SWODY2. Some
partial sunshine results in highs in the upper 70s to lower 80s
areawide for Wednesday. Appears any lingering showers and thunderstorms
exit east of the CT River valley later Wednesday evening. Not much
change in air mass, and partial clearing should result in favorable
conditions for fog formation in the favored valleys Wednesday night.
Lows mainly in the mid 60s.

&&

.SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/...
As of 333 PM EDT Tuesday...On Thursday a weak ridge of high pressure
and a pocket of drier air will be over the area much of the day, so
expecting sunshine and warm temperatures. With 850 temps getting
close to +17 could see highs in the 80s and pushing 90 at BTV. A
relatively fast WSW-ENE flow aloft will bring more moisture/clouds
gradually late in the day into Thursday night across the north
though timing could be a challenge. This is all south of a quasi-
stationary frontal boundary stretching from the Great Lakes across
southern Canada. With precipitable climbing above 1.50" have an
increasing probability of showers Thursday night. There will also be
a strengthening pressure gradient to keep south winds blowing and
with clouds around we are expecting lows in the mid 60s to lower 70s
Thursday night.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
As of 333 PM EDT Tuesday...The WSW-ENE stream of moisture high
precipitable water continues Friday into the weekend with a front
oscillating through the area. The highest probabilities of showers
and thunderstorms will be in the afternoon and evening, but really
can't be ruled out at any time. There are some model differences in
location of the front and strength of an upper level trof that moves
into the region by Sunday, but any way you slice it, it looks like a
daily threat of showers and thunderstorms through at least Sunday.
The flow aloft turns around more northwesterly then northerly next
week as a large ridge pushes north into central Canada. There will
be a gradual trend toward drier but warm summery weather. Still
can't rule out a shower or thunderstorm but the deep moisture will
be pushed off to our south. Temperatures should start out warm
Friday especially from the Champlain Valley east and south where
highs again in the 80s perhaps pushing 90. Currently going with the
front over the region Sat into Sun with highs mainly in the 70s,
then rising back to our seasonal norms in the upper 70s to lower 80s
next week as the airmass dries out and more sun expected with
slightly lower dewpoints.

&&

.AVIATION /20Z TUESDAY THROUGH SUNDAY/...
Through 18Z Wednesday...Thunderstorm potential exists through
this evening at MSS/SLK closer to instability axis across
w-central NY. May see brief heavy rainfall and brief IFR
conditions with any thunderstorms. Further east, seeing
abundant ceilings between 2500-4000 ft associated with maritime
modified air mass with HIR TRRN OBSCD. Will see VFR conditions
trending MVFR overnight for most of the TAF sites. An approaching
trough on Wednesday will bring developing showers and thunderstorms,
with better potential for scattered t-storms to cross into the
Champlain Valley and central/eastern VT during the mid-late
afternoon hours. Winds will generally remain south at 10-15kt,
except locally SE at KRUT with localized gap flow through the
Green Mtns.

Outlook...

Wednesday Night: VFR. Slight chance SHRA.
Thursday: VFR. NO SIG WX.
Thursday Night: VFR. Chance SHRA.
Friday: VFR. Chance SHRA, Chance TSRA.
Friday Night: Mainly VFR, with areas IFR possible. Likely TSRA,
Chance SHRA.
Saturday: Mainly MVFR, with areas IFR possible. Chance SHRA.
Saturday Night: Mainly VFR, with local IFR possible. Chance SHRA.
Sunday: MVFR. Chance SHRA.

&&

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

&&

SYNOPSIS...Banacos
NEAR TERM...Banacos
SHORT TERM...Sisson
LONG TERM...Sisson
AVIATION...Banacos

Hazardous Weather Outlook
National Weather Service Burlington VT
339 AM EDT Tue Jul 13 2021

NYZ026>031-034-035-087-VTZ001>012-016>019-140745-
Northern St. Lawrence-Northern Franklin-Eastern Clinton-
Southeastern St. Lawrence-Southern Franklin-Western Clinton-
Western Essex-Eastern Essex-Southwestern St. Lawrence-Grand Isle-
Western Franklin-Orleans-Essex-Western Chittenden-Lamoille-Caledonia-
Washington-Western Addison-Orange-Western Rutland-Windsor-
Eastern Franklin-Eastern Chittenden-Eastern Addison-Eastern Rutland-
339 AM EDT Tue Jul 13 2021

This Hazardous Weather Outlook is for northern New York, central
Vermont, northeast Vermont, northwest Vermont and southern Vermont.

.DAY ONE...Today and tonight.

There will be the potential for strong to locally severe storms this
afternoon. Gusty winds and heavy rain will be the main threats with
any of the thunderstorms. The most likely area for any stronger
storms will be from the northern Adirondacks westward through the St
Lawrence Valley.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

On Wednesday there will be the potential for strong to severe
storms, especially during the afternoon and evening hours. Gusty
winds and heavy downpours will be the main threats with any of the
thunderstorms. At this time the most likely area for any stronger
storms will be from the northern Adirondacks eastward across the
Champlain Valley and remainder of Vermont.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

Special Weather Statement
National Weather Service Burlington VT
506 PM EDT Tue Jul 13 2021

NYZ087-132200-
Southwestern St. Lawrence-
506 PM EDT Tue Jul 13 2021

...A STRONG THUNDERSTORM WILL AFFECT SOUTHWESTERN ST. LAWRENCE
COUNTY...

At 505 PM EDT, a strong thunderstorm was located near Gouverneur,
moving northeast at 25 mph.

Winds in excess of 40 mph are possible with this storm.

Locations impacted include...
Gouverneur, Canton, De Kalb, Rensselaer Falls, Heuvelton, Richville,
Hermon, De Peyster, Rossie, Pyrites, North Russell, De Kalb Junction,
North Gouverneur, West Fowler and East De Kalb.

Torrential rainfall is also occurring with this storm, and may cause
localized flooding. Do not drive your vehicle through flooded
roadways.

This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

LAT...LON 4475 7541 4453 7501 4423 7547 4433 7570
TIME...MOT...LOC 2105Z 221DEG 20KT 4431 7555

SLW

Special Weather Statement
National Weather Service Burlington VT
603 PM EDT Tue Jul 13 2021

NYZ026-029-087-132330-
Northern St. Lawrence-Southeastern St. Lawrence-
Southwestern St. Lawrence-
Including the cities of Massena, Star Lake, Ogdensburg, Potsdam,
and Gouverneur
603 PM EDT Tue Jul 13 2021

...POTENTIALLY STRONG TO SEVERE THUNDERSTORMS WILL SOUTHERN SAINT
LAWRECE COUNTY AROUND 7 PM...

At 600 PM EDT, a cluster of strong to severe thunderstorms was
located in the southern Tug Hill Plateau was moving north at 35
mph.

These storm should approach Southern Saint Lawrence county around
7 pm.

These storms may have winds in excess of 40 to 50 mph along with
lightning and very torrential rains.

Please plan on the possibility of strong storms this evening and
closely monitor local radio stations and available television
stations for additional information and possible warnings from the
National Weather Service.

LAT...LON 4475 7541 4453 7501 4423 7547 4433 7570
TIME...MOT...LOC 2105Z 221DEG 20KT 4431 7555

slw