855
FXUS61 KBTV 212353
AFDBTV
Area Forecast Discussion
National Weather Service Burlington VT
753 PM EDT Tue Jul 21 2026
.WHAT HAS CHANGED...
As of 249 AM EDT Tuesday...
Thunderstorm chances for Wednesday have been lowered as an
earlier timing of the frontal passage allows for less
destabilization.
&&
.KEY MESSAGES...
As of 209 PM EDT Tuesday...
1. Showers with some embedded thunderstorms this afternoon and
evening, diminishing overnight.
2. Some lingering showers Wednesday as a front moves through,
then becoming drier through Friday.
3. Quiet weather and increasing temperatures are expected this
weekend before another storm system brings showers and thunderstorm
chances to the region early next week.
&&
.DISCUSSION...
As of 209 PM EDT Tuesday...
KEY MESSAGE 1: Scattered showers and thunderstorms will move into the
area this afternoon from the west, driven by shortwave energy
rotating around the base of an upper level trough. A longwave
trough axis will gradually shift eastward today through eastern
Ontario, placing our forecast area in deep southwesterly flow ahead
of the trough. This setup will briefly drive a higher dewpoint
airmass northward into our area this afternoon and evening, when
PWats are forecast to rise to 1.5+ inches in valley locations.
Satellite imagery and observations show ample cloud cover over our
area, which is limiting heating. Have continued to cap temperatures
slightly lower than suggested by the NBM, with highs this afternoon
expected to remain in the mid 70s to low 80s. These temperatures,
along with dewpoints rising to the 60s, will allow for some marginal
destabilization to develop. The latest model guidance suggests
MLCAPE values will rise to 250-750 J/kg later this afternoon. With
no strong boundary moving through and a lack of low-level
convergence, this afternoon`s showers and thunderstorms will be
generally be tied to more disorganized individual shortwaves moving
through the broader flow. This leads to the best shower and
thunderstorm chances this afternoon into this evening, when the
individual shortwaves currently visible on water vapor
satellite imagery over and north of NY will move into our area.
0-6 km bulk shear values between 20 and 40 knots could support
the development of some more organized multicell
clusters...though overall lack of strong instability will remain
the limiting factor. Some storms today may produce gusty winds,
small hail, and locally heavy rainfall. Given the strong
background flow with gusts 20 to 30 mph common in the Champlain
Valley right now, it won`t be difficult to get some gusts to at
least 40 mph or higher within showers or thunderstorms. Coverage
of showers and thunderstorms will diminish after midnight
tonight with the loss of instability and deeper moisture.
Storm total QPF amounts for this afternoon through tonight will
generally range from 0.25 inch near the International Border to
0.75+ inch over the Adirondacks. Noting some swaths of 1.0+ inch
QPF progged in some of the higher res guidance in areas where
heavier showers or thunderstorms track through. This does look
like a reasonable scenario for some isolated locations based on
available moisture profiles. While 1.0+ inch rainfall totals
will be the exception rather than the norm, the most favorable
locations for heavier rainfall tracks will be over the southern
St. Lawrence Valley, the Adirondacks, and potentially into
portions of southwestern VT. Some ponding in poor drainage areas
is possible, but overall flood risk is low.
KEY MESSAGE 2: A cold front will move through on Wednesday from
west to east, with latest guidance favoring a slightly faster
progression of the boundary. Scattered showers and thunderstorms
can be expected morning through early afternoon as the front
moves through, though cloud cover and the earlier timing of the
frontal passage will limit destabilization. Though the overall
severe threat is low, can`t rule out an isolated stronger
thunderstorm capable of briefly heavy rainfall and gusty winds.
The trend towards a lower severe threat tomorrow due to the
earlier timing of the frontal passage is reflected in the latest
Convective Outlook update from the Storm Prediction Center.
This outlook has much of Vermont outlined in the General Thunder
risk, and shifts the Marginal severe risk further east and out
of our forecast area.
High temperatures for Wednesday will be dependent on frontal timing,
with the earlier onset of cold air advection in our western counties
keeping highs in the 60s over the Saint Lawrence Valley and
Adirondacks. Further east, The Champlain Valley along with
eastern Vermont will see highs in the 70s.
Late Wednesday through Friday will be dry with high pressure in
control. Humidity levels will be comfortable with highs in the 70s
Thursday and mid 70s to mid 80s Friday.
KEY MESSAGE 3: High pressure will begin to drift east this weekend with
more southerly to southwesterly flow, helping to advect warmer air
into the region. Temperatures will warm into the low to mid 80s in
general, with perhaps a few spot upper 80s in the Champlain Valley.
Given an unfavorable moisture advection pattern, dewpoints should
remain on the drier side for the weekend, remaining in the 50s. Warm
air advection will keep overnight temperatures on the mild side in
the low to mid 60s. Subsidence under the high should keep any
precipitation at bay through most of the weekend with mainly clear
skies. Our next system is expected to swing through the area late
Sunday into early next week. A cyclonic gyre over northern Quebec
will bring troughiness to the East Coast, with a few shortwaves
riding along the southern periphery of the gyre through the Great
Lakes into our region. There is still quite the spread in the timing
and phasing of any of these shortwaves, but trends have denoted best
chances for precipitation to be Monday and Tuesday afternoons, which
is in line with the current WPC forecast. As these waves pass
through they will take with them small chunks of heat and moisture,
gradually knocking our temperatures and humidity levels down into
mid next week.
&&
.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
Through 00Z Thursday...Changeable and variable conditions will
continue through the next 12 hours for most sites as a series of
boundaries moves through the entire area. Current radar shows
two areas of thunderstorms around both MSS and PBG. Have a
PROB30 with VCTS for both terminals for an hour at PBG, and
until 03Z at MSS with training thunderstorms along the US 11
corridor (Best chance of a terminal impacting thunderstorm is at
MSS). The MSS boundary will continue to drift east across SLK
and into PBG/BTV between 04-07Z. Thunderstorm chances will
decrease in time, but a few strikes in the vicinity of the
terminals cannot be ruled out; thunderstorm chances will be
about 20-40%. As the showers and thunderstorms move through
between 04-07Z, LLWS associated with a 40knot jet at 2000ft agl
will be present at RUT/MPV/EFK. The difficult part of this
forecast will be how low ceilings get. With a combination of
ongoing rain, and a developing inversion tonight, ceilings will
likely bounce between IFR and low MVFR beyond 04-06Z,
particularly at SLK/MPV/EFK. BTV/PBG should have enough flow
under the inversion to keep cigs above IFR. With added moisture,
some low lying fog will be possible due to more sheltering at
SLK/MPV with IFR vsbys possible, mainly after 07Z. GLAMP
probabilities show 40-60% chance of IFR ceilings between 06-11Z
at SLK/MPV. Towards sunrise, conditions should gradually
improve towards VFR. A few light showers will be possible at
MSS/MPV/EFK, but terminal impacts are not expected. A boundary
will cross the region tomorrow morning turning winds to the west
southwest.
Outlook...
Wednesday Night: VFR. NO SIG WX.
Thursday: VFR. NO SIG WX.
Thursday Night: VFR. NO SIG WX.
Friday: VFR. NO SIG WX.
Friday Night: VFR. NO SIG WX.
Saturday: VFR. NO SIG WX.
Saturday Night: VFR. NO SIG WX.
Sunday: VFR. Chance SHRA, Slight chance TSRA.
&&
.MARINE...
As of 209 PM EDT Tuesday...
A Lake Wind Advisory remains in effect with sustained
south/southeast winds 20 to 35 knots and waves in the 2-4 foot
range. Winds will peak late this afternoon/early this evening, then
diminish to 15 to 25 knots overnight with waves 1 to 3 feet.
Wednesday, winds will decrease to under 20 knots and the Lake
Wind Advisory will likely be able to be dropped early in the
day.
In addition to the strong background winds, showers with some
embedded thunderstorms are expected late this afternoon into this
evening. Within these showers and thunderstorms, gusty winds may
briefly change directions and intensify. Some cloud to ground
lightning is also possible.
&&
.BTV WATCHES/WARNINGS/ADVISORIES...
VT...None.
NY...None.
&&
$$
WHAT HAS CHANGED...Duell
DISCUSSION...Duell/Danzig
AVIATION...Danzig
MARINE...NWS BTV
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