451
FXUS61 KBTV 281109
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
709 AM EDT Fri Jun 28 2024

.SYNOPSIS...
A beautiful day is on tap with plenty of sunshine and mild
temperatures in the upper 60s to mid 70s. Clouds increase tonight
with occasional showers developing on Saturday, along with breezy
south to southwest wind gusts of 30 to 45 mph. Localized heavy
downpours are possible on Saturday afternoon into Sunday, which will
need to be watched closely for the potential for localized flooding.
Drier weather returns by the start of next week.

&&

.NEAR TERM /THROUGH SATURDAY NIGHT/...
As of 700 AM EDT Friday...Temps acrs the North Country this
morning confirm the turn has occurred with SLK down to 32F, Lake
Placid and Gallup Mills 36F, and many locations in the low/mid
40s with 48F here at BTV. Temps wl warm quickly this morning
under sunny skies and light winds. No changes made to the fcst
today, but based on latest 06z guidance I have increase timing
of likely pops associated with initial waa on Saturday morning
acrs northern NY into parts of central/northern VT. We should
see a mid morning to early aftn break in showers, before
additional showers overspread the area btwn 18z-21z on Sat.

Previous discussion follows: The near term concerns wl be gusty
winds and developing precip on Saturday acrs our fa. Today is
very quiet with 1022mb high pres shifting from the northern NY
into the Gulf of Maine by 00z this evening. Plenty of sunshine
expected with comfortable temps in the upper 60s to mid 70s.
Light and variable winds become south by this evening at 4 to 8
mph.

Tonight-Saturday...As sfc high pres shifts to our east, deep
south/southwest flow develops ahead of our next s/w trof with strong
moisture advection. Pw values surge to near 2.0" by 00z Sunday,
which are near daily maximum for the date or 2 to 4 std above normal
for late June. The dynamics associated with approaching
mid/upper lvl trof and orientation of the jet stream aloft wl
help us to maximize qpf amounts, but initially instability is
limited so rainfall rates should be held in check. Helping to
advect this deep layer moisture into our region with be an
anomalously strong 850mb jet of 50 to 60 knots from the
southwest on Sat. Sounding profiles show a sharp inversion
around 2.5kft, with top of the mixed layer winds of 35 to 42
knots on Sat. We should see enhanced southerly flow given
inversion height, especially acrs the central/northern CPV with
localized gusts 40 to 45 mph likely midday Saturday. Also,
secondary enhanced area of gusty winds are likely over the
northern Dacks along the route 11 corridor from near Malone to
Altona, where gusts to 40 mph is likely. A few isolated power
outages are possible in these areas on Saturday.

Timing of rain showers on Saturday acrs our cwa is rather
challenging, especially in the morning into early aftn hours.
Initially airmass is rather dry at all levels and expect some virga
associated with first surge of warm air/moisture advection. However,
secondary s/w energy and another surge of moisture advection
develops btwn 18-21z from sw to ne acrs our region and expect
showers to increase in areal coverage, with developing widespread
wetting rainfall likely acrs most of the region by 21z Saturday. I
have tried to integrate this thinking into the pop grids for Sat. As
we have mentioned multiple times over the past several days, many
ingredients are coming together for localized heavy downpours on Sat
aftn/evening, including warm cloud depths of 12.0 to 13.0 kft, pw
values near 2.0", sw orientation of 850mb jet of 50 to 60 knots, and
rrq of 250mb jet passing to our north acrs central Canada. Given the
orientation of the llvl jet toward the High Peaks, this area wl need
to be watched closely for localized heavy rainfall and potential
flooding, especially overnight as instability aloft increases to
help enhance localized heavier rainfall rates. WPC has upgraded
parts of northern NY in their latest day 2 ERO to slight risk, which
from our perspective looks reasonable given the synoptic scale
setup. Difficult to pin point exact qpf amounts thru 00z Sunday, but
generally 0.25 to 0.75 with highest values over northern NY with a
tenth of an inch or less over eastern/southern VT. Have placed
localized heavy rain wording into the grids btwn 21-00z acrs
northern NY on Sat, as elevated instability increases btwn 150-400
J/kg from west to east. Also, given the increasing elevated
instability parameters off both the NAM 3KM and HRRR have mention
isolated thunder. SPC has expanded their day 2 marginal risk to
cover all of northern NY, but feel the greatest threat maybe aft
00z, when instability increases further. Highs on Sat in the upper
60s to mid 70s, with increasing humidity toward sunset.

&&

.SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/...
As of 354 AM EDT Friday...Continuing from the near term discussion,
expect heavy rain showers and a few rumbles of thunder, especially
towards daybreak as temperatures aloft cool. A strong jet stream to
our north will aid in large scale lift in conjunction with a strong
low level southwesterly jet bringing us very warm and moist air.
Accordingly, an axis of greatest precipitable water in excess of 2
inches, or near the climatological maximum, will slide eastward
overnight. As this happens, rich moisture will continue to stream
northward as the main frontal system trails to the west. Surface dew
points will be steady or slightly rise through the mid and upper
60s, while 1000 to 500 millibar relative humidity stays above 90%
with high freezing levels sitting nearly at the top of this layer.

Hazardous weather potential is primarily related to torrential rain,
supported by CAPE with a tall and skinny profile. The heaviest rain
will be in thunderstorms, with chances generally expanding eastward
and increase overnight. Rainfall rates will not be overly intense
outside of any thunderstorms, but even so, a long duration of
moderate rainfall should provide a large swath of 0.75" to possibly
1.5" of rain through Sunday morning. Some sharp river rises are
possible. Area streams and rivers will largely be near normal volume
ahead of this rainfall, which helps lower the flood risk. However,
the Lamoille and Passumpsic basins in Vermont are running a little
high, so those may be more susceptible to seeing small stream
flooding. The footprint of heaviest rain Saturday night may be
important ahead of potential organized convection on Sunday that
develops along a strong cold front.

As typical, said cold front does appear to come through piecemeal,
with showers and a few thunderstorms poised to move through our
region during the morning hours and then more showers could develop
towards evening. The very warm and humid low level air ahead of the
first boundary suggests development of potentially moderately high
CAPE Sunday morning with even modest diurnal heating. If this type
of instability can be realized, the deep layer shear could support
development of a squall line. Otherwise, the risk for organized
convection generally will have to be watched. Winds should tend to
become more westerly with mid-level drying during the afternoon, and
only after a secondary front moves through do we see cold air
advection at the surface usher in refreshing air by Sunday night.
The incoming air mass does not look as unseasonably cool as the one
currently in place, but will still be noticeably cooler.
Temperatures will fall back into the 40s and 50s following a night
with temperatures largely in the mid and upper 60s. Highs on Sunday
will mainly be in the 75 to 80 range, although sensitive to the
amount of partial sunshine that can develop ahead of the morning
frontal passage.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 354 AM EDT Friday...Much quieter weather is anticipated during
the long term period. Low humidity air will be in place early in the
week. After some northerly flow on Monday, there is good model
agreement on strong ridging and light winds for Tuesday. Then we
will see the air mass modify to become more seasonably warm and
gradually more humid. There are low chances of thunderstorms
Wednesday afternoon/evening, mainly in western areas where more
instability is expected. With outdoor activities associated with the
July 4th holiday, the more humid conditions may set the stage for
scattered showers and thunderstorms. At this time frame, chances
look low but have included isolated thunderstorms for Thursday
afternoon. Broad southwesterly flow combined with any shortwave
troughs could trigger thunderstorms, especially if timing coincides
with peak heating. This type of thing cannot be predicted with skill
a week out, so stay tuned.

&&

.AVIATION /11Z FRIDAY THROUGH TUESDAY/...
Through 12z Saturday...Sfc high pres will result in plenty of
sunshine and VFR conditions today with light north winds 3 to 6
knots. Winds shift to the south/southeast by this evening and
increase 5 to 10 knots with gusts up to 15 knots by Sat morning.
Clouds will thicken overnight with some light rain showers
developing btwn 09-12z acrs the northern NY taf sites. VFR
conditions will be associated with these showers as they spread
into VT sites toward 12z.

Outlook...

Saturday: Mainly VFR, with local MVFR possible. Chance SHRA.
Saturday Night: MVFR/IFR conditions possible. Definite SHRA.
Sunday: MVFR/IFR conditions possible. Chance SHRA, Slight chance
TSRA.
Sunday Night: Mainly VFR, with local MVFR possible. Slight chance
SHRA, Slight chance TSRA.
Monday: VFR. NO SIG WX.
Monday Night: VFR. NO SIG WX.
Tuesday: VFR. NO SIG WX.

&&

.HYDROLOGY...
The threat for localized heavy downpours and isolated flash flooding
is possible this weekend across our region. The Weather Prediction
Center Day 2 Excessive Rainfall Outlook has northern NY in slight
risk or at least 15% chance of rainfall exceeding flash flood
guidance within 25 miles of a given point. The area of greatest
concern based on anticipated precipitation amounts would be across
the High Peaks of northern NY, with a secondary area of concern over
central VT, given recent rainfall amounts. Current forecasts
indicate between 0.60 and 1.50 inches of rainfall is expected with
localized amounts of 2.0 to 3.0 inches possible in the heavier
thunderstorm activity late Saturday into Sunday. Please continue to
monitor the latest forecast for additional details over this
upcoming weekend.

&&

.MARINE...
Unseasonably strong winds are expected on Saturday when a Lake
Wind Advisory will be needed for Lake Champlain. South winds
may exceed 25 knots by daybreak and may be be above 30 knots on
the broad lake at times during the day. Rough waves could
develop quickly. Wave heights on the broad lake and inland sea
may build into the 3 to 5 feet range briefly Saturday.

&&

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

&&

$$
SYNOPSIS...Taber
NEAR TERM...Taber
SHORT TERM...Kutikoff
LONG TERM...Kutikoff
AVIATION...Taber
HYDROLOGY...Taber
MARINE...Kutikoff