613
FXUS61 KBTV 211825
AFDBTV
Area Forecast Discussion
National Weather Service Burlington VT
225 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 vapour 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 /18Z TUESDAY THROUGH SUNDAY/...
Through 18Z Wednesday...Changeable and variable conditions are
expected at all terminals through the next 18 hours as a frontal
system continues to move through the area. Widespread sct to bkn
2500-4000ft agl ceilings are across majority of the region, and will
continue to bounce before more prevailing MVFR cigs are expected to
develop between 02-04Z for most terminals. Winds will be the main
near term terminal impact with gusty southerly channeled flow at
BTV/PBG with gusts around 30- 35 kts likely. Elsewhere southerly
gusts between 25-30kts can be expected through the next 6-10 hours
before an inversion sets up tonight. In terms of precipitation,
current radar shows little to no shower activity, however, showers
with embedded thunderstorms will begin to move into MSS within the
next hour or two, and spread eastward into SLK/PBG and the Vermont
terminals after 00Z. Trends have denoted a few target areas of IFR
thunderstorms at MSS around 21Z and 02Z, and between 00-04Z for all
other terminals (highest confidence of a terminal thunderstorm
passage exists at MSS). Current trends show a 30-50% chance of
thunder for terminals outside of MSS, with PROB30 groups denoting
terminal best timings, and a TEMPO for BTV with some higher
confidence of IFR showers with VCTS at BTV. Beyond 06Z, with an
inversion expected to setup, ceilings will trend towards IFR at
SLK/MPV/EFK between 07-09Z, and continue until 11-12Z. Intermittent
BR and possible BCFG will exists between the aforementioned times as
well with trapped low level moisture. A boundary will then slide
across the area switching winds from the south to the west/southwest
tomorrow morning with breezy conditions developing into the early
afternoon.
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. Slight 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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