-- Discussion containing changed information from previous version are highlighted. --
756
FXUS61 KBTV 121758
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
158 PM EDT Wed Jun 12 2024

.SYNOPSIS...
Today will feature a mix of sun and clouds with highs in the 70s
and a few widely scattered showers across the higher terrain.
Temperatures rise into the 80s on Thursday along with breezy
conditions, before a cold front brings more widespread showers
and thunderstorms Thursday night into Friday. A spectacular
weekend is on tap with plentiful sunshine and comfortable
temperatures. Summer heat and humidity arrives early next week.

&&

.NEAR TERM /THROUGH THURSDAY/...
-- Changed Discussion --
As of 158 PM EDT Wednesday...Temperatures have been running a
touch cooler than forecast with coverage of clouds tending to be
broken rather than scattered. The stratocumulus is helping to
limit heating, but is is still a pretty nice day out there.
Stable conditions over the broad lake of Lake Champlain is
supporting sunny skies there, and that should continue through
the rest of the day. Showers have still not materialized, even
in far northeastern Vermont where surface-based CAPE has reached
500 J/kg; have further reduced PoPs such that greatest values
are down to 25% later this afternoon coinciding with peak
heating.

Previous discussion...The main theme this morning remains the
vertically stacked upper level low in the vicinity. So despite
broad 1017 mb surface high draped across much of the northeast,
the cyclonic flow aloft means that the 925-750mb level remains
moist enough for a 2000 to 4000 ft stratus deck to hang around
across much of North Country during the overnight hours. As the
568 Dm upper low slowly moves east into Maine, a 572 Dm upper
ridge starts building in, but there is an embedded piece of weak
shortwave energy. Given the overall weak dynamics, isolated
showers should mainly be confined to the terrain across the
Adirondacks as well as along and east of the Greens.
Thunderstorms potential is almost nil given that the instability
is below the hail growth zone.

Today should be the pick of the week with seasonable temperatures in
the low to upper 70s, a mix of sun and clouds along with light
winds, generally under 10 mph. The immediate Champlain Valley should
once again see more sun than clouds owing to downsloping off the
Adirondacks. With 925mb temperatures reaching +15 to +17C east of
the Adirondacks, Champlain Valley locales that enjoy the most amount
of sun should see highs peak in the 76-78 range, or right around
climatological normal. Some of the hi-res guidance does hint at the
potential for lake breeze development, as well as the possibility of
the showers that develop across the Adirondacks to spread into
portions of the Champlain Valley. Nonetheless, any showers that do
develop should be fairly localized and brief. Across the region,
highs generally top out in the low to mid 70s, except 60s across the
high terrain.

Any afternoon showers subside by sunset. A period of high clouds
move from west to east early this evening, but skies should clear
out for most locations by the latter half of the overnight hours.
Winds at the surface stay mostly light, but will be increasing aloft
from the southwest and the south. This means that the typically
sheltered colder hollows should see temperatures fall into the mid
40s but the St Lawrence and Champlain Valleys only drop into the mid
to upper 50s. The warming trend peaks on Thursday. With 925mb
temperatures +19C to +22C and deep boundary layer mixing up to
800mb, daytime highs should reach the upper 70s to the mid 80s. With
a 40-45 kt 925-850mb low level jet nosing into the St Lawrence
valley and portions of norther NY by Thursday afternoon, have bumped
up the winds mainly west of the Adirondacks with southwest winds
possibly gusting 30-35 mph, locally 40 mph possible. The deep
boundary layer mixing should also help mix down some lower dew
points from aloft, so utilized the 10th to 25th percentile of
available modeled dew point guidance. So between the breezy
conditions and dew points in the 50s, temperatures in the low to mid
80s would feel a lot more manageable, unlike the potential summer
heat that comes next week. A shortwave trough will also be
approaching western NY by mid day and northern NY by the afternoon
hours, so have forecasted 15-25 percent chance for showers mainly
west of the Champlain Valley. Chance for thunder is non zero, but
forecast soundings suggest that the instability mainly stays
elevated until after sundown.
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&&

.SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY/...
As of 328 AM EDT Wednesday...Thursday night into Friday, a prefrontal
trough will swing southeast across the region. There still remain
several nuances about the strength of the upper jet and the
placement of better dynamics, but compared to yesterday night,
forecast guidance is in better agreement. Convection will develop
across Ontario Province east of the Great Lakes and meander into the
region. Showers and storms will be sustained by the relative maximum
in moisture in northern New York with about 250-400 J/kg of mid-
level instability as a strong- for-summer 100 kt jet streak develops
over the Great Lakes. Better dynamics will be lifting north, and so
activity should generally weaken as it moves east across northern
New York into Vermont. During the afternoon, model guidance is
trending back towards a more coherent upper shortwave than the sort
of one-two punch with the prefrontal trough and drives the cold
front south while more connected with moisture is still around.
Although, there are still models like the 00z deterministic EC that
keep features more distinctly separate and spread still remains with
how Friday evolves. By late Friday morning, there should be showers
and thunderstorms developing ahead of the frontal boundary with
about 500-1000 J/kg of CAPE and about 40-50 kts of 0-6km shear. This
may bear watching before very dry mid-level air filters in by late
afternoon. Joint probabilities of CAPE greater than 500 J/kg and 30
knots of shear is about 20-30 percent across various ensembles.
Rainfall amounts will be generally 0.20-0.50", but with PWATs 1.50-
1.75" and somewhat favorable upper dynamics, there will likely be a
few spots that observe rainfall amounts around 1.00".

As to the temperature part of the forecast, Thursday night will be
warm and humid, with gradient south to southwest flow keeping
conditions warm in the 60s. Friday will be in the 70s to near 80
with abundant clouds and rain.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
As of 328 AM EDT Wednesday...Weather conditions still look nothing
short of spectacular over the weekend. Rain moves out by Friday
night and Saturday will open to sunny skies beneath a strong surface
high. High temperatures will be in the upper 60s to mid 70s. Then
somewhat warmer on Sunday as temperatures moderate, but still very
nice with mid 70s to lower 80s. Enjoy!

By Monday, a Bermuda high will become established, and that will
drive increased warmth and humidity. It looks like we`re still
forecast to be positioned near the edge of the feature, and that
should allow a few pop up showers and thunderstorms during the
afternoon. It`s possible that activity may prevent us from
consistently hitting 90, but with 925hPa temperatures remaining as
elevated as they are, there`s the potential for BTV to record its
first heat wave of the year, which here is defined as at least 3
days of 90. The probabilistic data from global ensembles suggests a
greater than 30 percent chance across next Tuesday through Thursday,
and the NBM probabilities generated from percentile data is somewhat
more aggressive at around 60 to 70 percent. Given this will be the
warmest and most humid air for this year, there will likely be
increased heat-health impacts, and we`ll continue to monitor
forecast trends for the heat next week. The forecast HeatRisk is
presently at Level 2 of 4 for Monday for the valleys and Tuesday
across almost the whole region.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
-- Changed Discussion --
Through 18Z Thursday...Mainly VFR conditions are expected during
the period. Stratocumulus will remain through the rest of the
day, which will flirt with MVFR ceiling height at the higher
elevation sites. Overnight as skies clear and winds aloft become
light there may be IFR conditions due to dense fog, especially
from 07Z to 12Z. Greater chances (~20%) will be in eastern
Vermont, with 3SM BR currently indicated at EFK and MPV until
confidence increases/lead time decreases. Winds will remain
light and variable or terrain-driven through about 12Z, then
modest south or southwesterly winds will develop. At MSS gusts
could ramp up to about 20 knots towards Thursday afternoon.


Outlook...

Thursday Night: VFR. Chance SHRA, Slight chance TSRA.
Friday: VFR. Chance SHRA, Slight chance TSRA.
Friday Night: VFR. Slight chance SHRA.
Saturday: VFR. NO SIG WX.
Saturday Night: VFR. NO SIG WX.
Sunday: VFR. NO SIG WX.
Sunday Night: VFR. Slight chance SHRA.
Monday: VFR. Slight chance SHRA, Slight chance TSRA.
-- End Changed Discussion --

&&

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

&&

$$
SYNOPSIS...Chai
NEAR TERM...Chai/Kutikoff
SHORT TERM...Haynes
LONG TERM...Haynes
AVIATION...Chai/Kutikoff