404
FXUS61 KBTV 291408
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
1008 AM EDT Sat Jun 29 2024

.SYNOPSIS...
Rainfall associated with a warm front will overspread the region
this morning, with a brief break in rain before several rounds of
showers and thunderstorms develop tonight. Ahead of a cold front,
isolated to scattered thunderstorms are expected Sunday, especially
from the Adirondacks and points east. By Sunday night, drier air
will be ushered in, with seasonable and dry weather on tap to start
off July. Some chances for showers and thunderstorms return
midweek, potentially impacting holiday activities.

&&

.NEAR TERM /THROUGH SUNDAY/...
As of 755 AM EDT Saturday...Made a few adjustments for PoPs
over the next few hours with light rain continuing across much
of the area. A very moist air mass is just beginning to nose
into northern New York and will spread eastward through the
remainder of the day. For perspective, the Buffalo RAOB this
morning measured 2.11" of PWAT which shattered the old daily
record of 1.85". This is an anomalously moist air mass that
will bring moderate to heavy rain to the region this afternoon.
Based on upstream observations, many locations have seen between
0.5" and 0.75 of rain which is likely what we will see from
this warm frontal precipitation. In addition, we still have
multiple rounds of convection expected this evening and again
Sunday morning/afternoon. More on this later.

Previous Discussion...
No big changes to the weekend outlook. There has been a small
downward shift in rainfall amounts, slightly reducing the
confidence in flash flooding. At the same time, severe weather
potential for Sunday has come up a little bit.

In the big picture, a storm system more typical in the cold
season will be impacting us throughout the period. The parent
low pressure area will be tracking far to our northwest, so
forcing for rain today will be driven by isentropic lift and
embedded upper level shortwaves in fast southwesterly flow. The
initial batch of rain will have some brief heavier downpours,
but no thunderstorm chances. This will help moisten a very dry
air mass that is currently in place. Objective analysis shows
strong moisture advection is occurring this morning, with 850
millibar moisture transport directed at northern New York. So
as showers overspread our area and moisten the boundary layer,
dew points currently only near 50 degrees will climb into the
60s this morning west of the Adirondacks. The humid air will
gradually expand eastward as showers work their way through
the region, reaching northeastern Vermont last.

At the same time, a strong pressure gradient is helping to
produce potent low level winds, which are currently around 30
MPH at 925 millibars. A low level jet surge is expected to
arrive from the southwest this afternoon with 850 millibar winds
exceeding 50 knots by this evening. Precipitable water will
surge to near or just above 2", or near climatological maximum
values as a surface warm front pushes through our region.
Combined with a strong southwesterly jet, moist upslope flow
could enhance rainfall rates in portions of the Adirondack
region and Green Mountains. This stronger flow will be
eventually be coincident with some drying in the mid levels
tonight. As such, we do have potential for wet microbursts as
tall skinny CAPE profiles develop from the modifying air mass,
featuring increasingly warm and moist low level air and
cooling/drying aloft. The latest data has trended towards a
break in precipitation after midnight, so PoPs decrease into the
chance range (mainly 30-50%). That being said, instability will
continue to increase so there could be some nocturnal
thunderstorms in the wee hours of the night.

Tomorrow as a cold front approaches from the west, a pre-
frontal trough will trigger scattered showers and thunderstorms.
By this point, the heavy rain potential will be somewhat lower
as warm cloud depths decrease. The convective environment looks
like it will be characterized as high shear, moderate CAPE,
especially in the southern Champlain Valley and southern/eastern
portions of Vermont. The shear will be west-southwesterly, or
partially perpendicular to the cold front. The storm mode,
therefore, will tend to be discrete. Taller storms will be
capable of frequent lightning and damaging winds. Thunderstorm
chances will shift south and east, most likely during the
midday hours. A secondary cold front will follow, with
potentially more showers but a minimal threat for thunderstorms,
late in the day.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/...
As of 345 AM EDT Saturday...Surface cold front should be moving
through the CWA at the start of this period with showers and
t-storms although the strongest activity should have likely
exited the region by 00z Mon. Upper level shortwave rotates
across the area overnight and clears out the humidity and may
ring out any leftover isold/sct showers during the overnight.

Upper level trof and shortwave will pass east of CWA by mid-late Mon
morning with SFC ridge slowly pushing into the area. Northerly flow
will bring in cooler, drier, comfortable air with temperatures in
the 70s and dewpoints in the 40s-50s.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 345 AM EDT Saturday...SFC and Upper level ridge building
into the area Monday night for a clear, crisp cool night with
temperatures in the 40s-50s across the area.

High pressure still in control on Tuesday with moderating
temperatures to near or slightly above seasonable levels with highs
in the U70s-L80s.Tuesday night will feature upper ridge axis across
the NE and dampening with the approach of a northern stream
shortwave with the surface high shifting SE for the development
of a return SSW flow and temperatures back into the M50s-L/M60s.

Northern stream shortwave shifts east across southern Canada which
will dampen further the heat ridge across the southern CONUS. A warm
front traverses the area Wed with increased heat/humidity but likely
decent amount of clouds which may limit instability. However, pre-
frontal trof may try to move during or shortly after peak heating so
can`t rule out showers and t-storms late Wed-Wed eve but stay tuned
as there are some firework celebrations Wed eve. Highs in the 80s.

There are still some timing/model discrepancies about cold front
passage overnight Wed or Thu or perhaps the front just washes across
the area. Attm, I will go with front still across the region in the
morning for some clouds and perhaps a sprinkle or shower with front
east of the area by afternoon. Seasonable temperatures U70s-L80s.

Again, some inconsistency about next upstream shortwave/trof,
similar to the first, with GFS more progressive than ECMWF/Canadian
so will lean toward a latter solution with threat of showers
possible late Friday or Friday night.

&&

.AVIATION /14Z SATURDAY THROUGH WEDNESDAY/...
Through 12Z Sunday...VFR conditions with light rain showers
around this morning will give way to a round of heavier showers
which will be capable of brief IFR conditions, especially after
18Z and in northern New York sites. Prevailing visibilities
should be MVFR for most if not all sites. Ceilings will begin
to lower with heavier rain as well, but generally down to
1500-3500 ft agl.

Southerly winds at BTV will be gusting near 25 knots for much of
the next several hours before diminishing gradually tonight,
while most other sites see few gusts but 10 to 15 knot sustained
winds. At 2000 ft agl, increasing south to southwest winds of
45 to 50 knots necessitates LLWS through most of the period.

Outlook...

Sunday: Mainly VFR, with local MVFR possible. Chance SHRA, Chance
TSRA.
Sunday Night: Mainly VFR, with local MVFR possible. Slight chance
SHRA.
Monday: VFR. NO SIG WX.
Monday Night: VFR. NO SIG WX.
Tuesday: VFR. NO SIG WX.
Tuesday Night: VFR. NO SIG WX.
Wednesday: VFR. Slight chance SHRA, Slight chance TSRA.

&&

.HYDROLOGY...
The threat for localized heavy downpours and isolated flash flooding
remains across our region, with greatest risk in the vicinity of
the High Peaks of northern New York. The Weather Prediction
Center Day 1 Excessive Rainfall Outlook maintains northern NY
in a slight risk, or at least 15% chance of rainfall exceeding
flash flood guidance within 25 miles of a given point. Current
forecasts indicate between 0.50 and 1.50 inches of rainfall is
expected with localized amounts of 1.75 to 2.5 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 today. South winds will
be in the 15 to 25 knot range, with 25 to 30 knot winds at times
over the broad lake. Rough waves are expected to develop in
response to the strong winds. Wave heights on the broad lake and
inland sea are forecast to reach the 3 to 5 feet range later
this morning. Winds and waves will decrease slightly by this
evening but remain significant overnight tonight.

&&

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

&&

$$
SYNOPSIS...Kutikoff
NEAR TERM...Clay/Kutikoff
SHORT TERM...SLW
LONG TERM...SLW
AVIATION...Kutikoff
HYDROLOGY...Clay/Kutikoff
MARINE...Clay/Kutikoff