850
FXUS61 KBTV 012333
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
733 PM EDT Wed May 1 2024

.SYNOPSIS...
A potent upper level disturbance and weak surface low pressure
system will bring a period of scattered to numerous showers to much
of the forecast area late tonight through Thursday before high
pressure and drier conditions return for Thursday night and Friday.
Saturday will be mainly dry with a low chance for showers across
northern New York, with periods of showers likely for the latter
half of the weekend.

&&

.NEAR TERM /THROUGH THURSDAY NIGHT/...
As of 657 PM EDT Wednesday...
Watching upstream shortwave currently moving eastward over
Ontario on satellite. As this shortwave moves into northern
NY/VT overnight tonight, will see 50-200 J/kg elevated CAPE
develop. This instability, coupled with observed lightning
strikes upstream, is enough to warrant adding in a slight
chance of thunder to the overnight forecast tonight, especially
northern NY around and shortly after midnight. Given the
elevated nature of the instability, no concerns for severe
weather. Otherwise, just watching some light radar returns this
evening move through. Enough dry air is present in the low
levels to prevent much if any of this initial wave of showers
from reaching the surface, so expect a quiet evening until the
shortwave arrives closer to midnight.

Previous discussion...Quiet weather over the forecast area
this afternoon will once again turn unsettled tonight as a potent
shortwave trough currently moving east from Lake Superior will
continue eastward through southern Ontario and Quebec tonight before
diving southeastward across the North Country and Vermont on
Thursday. A warm front currently draped across southern New York
will be the focus for showers to develop on as it lifts northward
into northern New York around midnight or shortly thereafter, with
precipitation spreading eastward through central/northern Vermont
through sunrise. Thereafter for Thursday, a cold pool aloft and
steepening low level lapse rates will support scattered showers to
continue across the region with perhaps some small hail or graupel
as well until an upper level ridge begins to build in Thursday
evening. Overall basin-averaged QPF will be light across southern
zones with only a few hundreths to a tenth of an inch expected, but
northward a light wetting rain of a quarter to third of an inch is
likely. Clouds and low level moisture will keep temps mild overnight
with lows mainly mid 40s to around 50, and highs will generally
range through the 60s on Thursday. Cooler temperatures and dry
conditions follow for Thursday night with lows in the lows and areas
of fog possible.

&&

.SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/...
As of 345 PM EDT Wednesday...An anomalously strong, but narrow, upper
level ridge will slide eastward into the region during this period.
In the low levels, there will be less impressive low level warmth
due to the position of high pressure to our northeast rather than
east or southeast. As a result, while this pattern supports dry
weather, we don`t see anything unusually warm at the surface. Expect
warmer spots such as the central/southern Champlain Valleys
currently have about 50-60% chance of seeing 70 degree highs. As
normal highs are now in the low to mid 60s, these temperatures could
be considered seasonably warm. While southern St. Lawrence County
sees the most favorable conditions under the ridge - with gentle
downsloping easterly low level winds to warm well into the 70s, they
also will likely see thickening high clouds arrive. Similar to the
day of the solar eclipse last month, there may be a sharp north-
south oriented line between thicker and thinner cloud cover.
Generally have mostly cloudy skies for much of the day in northern
New York and partly cloudy in Vermont, but certainly not clear cut
on the degree of cloud cover with some minor impact on high
temperatures possible. Expect there will be enough mixing to
overcome any lingering morning low clouds/fog, but that is another
possible way to underachieve on temperatures. Lowering clouds will
continue to be the gradual trend ahead of a shortwave trough that
looks to slide northeastward across the Great Lakes Friday night,
and have a slight chance of showers after midnight in the far
western areas of northern New York. Precipitation chances and
amounts will be limited by continued mid- level ridging and related
lack of instability and forcing for ascent. It will be a mild night
even where winds remain light. Overnight temperatures will be
moderated by cloud cover and increasing, modest southeasterly
gradient flow, as a ridge of high pressure in eastern New England
strengthens while weak low pressure approaches from Ohio.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
As of 345 PM EDT Wednesday...Aside from a bit more southerly wind,
the pattern on Saturday is not too different from Friday. Ridging
will slowly break down, setting up increasing shower chances through
the day with greater chances west and lower chances as you go
eastward. Especially across Vermont, even the wettest model
solutions suggest if it does rain it will be very light and brief. A
more significant shortwave will probably move through Saturday
night, leading to much greater chances of showers. Have continued to
leave out mention of thunder as elevated instability associated with
this system looks meager and better southwest of our region.

Sunday looks like the coolest/cloudiest day of the long term period
despite southerly winds and continued mild air aloft. Why? Thick
cloud cover will likely be present as mid-level southwesterly flow
increases with advection of moisture from upstream showers. A window
of clearing ahead of a cold front seems to hold off until after
sunset with the front passing through with nothing more than some
scattered showers Sunday night. Weak high pressure will then build
in for Monday, with seasonably warm and frankly beautiful weather in
store for the beginning of the week. Model agreement in quiet
weather is fairly high for the Monday-Tuesday period. The low level
temperatures have modest spread, so how warm we get on Tuesday is a
question. Widespread highs in the 70s look reasonable at this time.

Looking at the 12Z global model ensemble data, the joint probability
of surface-based CAPE exceeding 500 J/kg and deep layer shear
exceeding 30 knots suggests our next chance for notable convective
weather returns on Wednesday. Although the signal for strong
thunderstorms is greater to our southwest, one of the four global
model clusters provides a plausible scenario with deep southwesterly
flow bringing modest heat and humidity into our region, especially
northern New York. In general, more active weather looks favored
Wednesday and beyond.

&&

.AVIATION /00Z THURSDAY THROUGH MONDAY/...
Through 00Z Friday...Crntly VFR conditions prevail at all taf
sites with a bkn to ovc cloud layer between 3500 and 10000 feet.
The trend will be for a line of showers with a few embedded
rumbles of thunder to approach the SLV by 04z and spread into
the CPV by 06z. Brief heavy rainfall along with cigs trending
toward MVFR are likely, while a 10 to 15 min window of IFR vis
is possible in the heaviest convective showers. As moisture
continues to increase and winds shift to the west/northwest
expect MVFR cigs to locally IFR conditions to develop toward 10z
on Thursday. Greatest potential for IFR conditions will be
MSS/SLK and MPV with mostly MVFR elsewhere. Additional showers
are possible on Thursday aftn, but given the limited moisture
only isolated activity is anticipated. Winds are south/southeast
4 to 8 knots this evening, become southwest/west by morning,
before shifting to the west/northwest by late Thursday morning.
A few localized higher gusts are possible at BTV/RUT at times.

Outlook...

Thursday Night: Mainly VFR, with areas MVFR possible. NO SIG WX.
Friday: Mainly VFR, with local MVFR possible. NO SIG WX.
Friday Night: VFR. NO SIG WX.
Saturday: VFR. Chance SHRA.
Saturday Night: Mainly VFR, with local MVFR possible. Chance
SHRA.
Sunday: Mainly MVFR, with local VFR possible. Chance SHRA.
Sunday Night: Mainly MVFR, with areas IFR possible. Chance SHRA.
Monday: VFR/MVFR conditions possible. Slight chance SHRA.

&&

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

&&

$$
SYNOPSIS...Lahiff
NEAR TERM...Duell/Lahiff
SHORT TERM...Kutikoff
LONG TERM...Kutikoff
AVIATION...Taber