118
FXUS61 KBTV 081803
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
203 PM EDT Wed May 8 2024

.SYNOPSIS...
Showers with embedded thunderstorms will move across the region this
morning. Although there will be a brief break in the precipitation,
another round of isolated to scattered showers and thunderstorms are
expected later this afternoon into the evening. The rest of the week
will be cool and damp with rounds of showers.

&&

.NEAR TERM /THROUGH THURSDAY/...
As of 139 PM EDT Wednesday...Dry slot moved in to the forecast
area over the past couple of hours, allowing for the development
of enough surface based instability to see some thunderstorms
already develop over northern NY. However, SPC analysis and RAP
forecast soundings suggesting cap still in place over Vermont,
but it should erode over the next hour or two. Still on track
overall with the messaging of scattered showers with some
isolated thunderstorms embedded this afternoon. Very favorable
shear in place with 0-6 km bulk shear values over 50 knots and
impressive 0-3 km SRH 200 to 300+ m2/s2. Previous discussion
follows...

The first round of precipitation will spread over the area this
morning. SPC mesoanalysis shows elevated instability of 400-700
J/kg along with a 100+ kt 300 mb jet, which have served to keep
thunderstorms going overnight. Have noted some observations of
moderate to even briefly heavy rain with these thunderstorms,
and that trend will continue as the system moves into our
region. Showers will move into the St Lawrence Valley around
daybreak, quickly spreading eastward through NY and across VT by
mid morning. A dry slot, wrapping around the southern side of
the low and readily evident on satellite imagery, will lift into
our area behind this initial batch of showers/thunderstorms,
giving us a brief break in the precipitation. What happens
thereafter remains somewhat uncertain as much depends on just
how dry the incoming airmass is. Even at this time, the hi-res
CAMs are having a hard time agreeing on how much clearing we may
see with this dry slot, which in turn would determine how much
warming we can get. Model soundings still indicate a subtle warm
nose/cap will exist aloft, and more dry air/warming would help
to overcome this convective obstacle. In this scenario,
isolated to widely scattered showers and thunderstorms would
develop mid-late afternoon as SB CAPE values approach 800+ J/kg.
Should the airmass hold more moisture, warming would be less
pronounced and instability would remain elevated, generally
remaining in the 400-750 J/kg range. This would make for more
showers, but less in the way of strong convection. Shear still
looks ample at 40-50 kt, so any thunderstorms that are able to
become a bit more robust will have the potential to become
strong to perhaps locally severe. Main threats would be
strong/damaging winds and small hail. The central/southern
Adirondacks eastward through southern Champlain Valley/southern
VT, particularly central Addison southward through western
Rutland Counties, have the best chances of seeing more clearing,
more warming, and thereby more instability and better chances
for stronger convection. Although it has varied some from run to
run, soundings off the HRRR and to a lesser extent the NAM3
both indicate that SLK and RUT break the cap this afternoon, and
at the least show gusty surface winds, with upwards of 45-50 kt
at the top of the mixed layer. All that being said, SPC`s
latest Day 1 Convective Outlook still has our southern border
included in a Marginal Risk, which seems reasonable at this
point.

Low pressure will drift over the region tonight, and any showers
will come to an end from west to east. Moisture will become confined
to mainly the lower levels, so showers may actually transition to
patchy drizzle or fog, keeping the overnight cloudy and damp. This
moisture will lift a bit on Thursday, keeping clouds around, but
should remain shallow enough to preclude widespread showers.
However, a few spotty showers could develop east of the
Adirondacks and Greens as flow turns more easterly through the
day. After lows in the 40s tonight, tomorrow will be cool, with
highs remaining in the 50s in most spots, with perhaps a few
locations hitting 60F.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY/...
As of 353 AM EDT Wednesday...The main story is a marked trend towards
less rain. That being said, it remains a low predictability forecast
with regards to rainfall amounts and timing. Generally, the latest
model guidance shows a later arrival of rain with low pressure
tracking farther south, which results in potentially a sharp
north/northeastern gradient. Portions of northeastern Vermont may
see only a short period of light rain while southwestern areas get a
soaking rain for the entire period. The latest GFS ensemble
probabilities of 0.01" in 24 hours continue to support the idea that
it will rain across the region. However, changing the threshold to
0.1" tells a different story with much higher chances just south and
west of our region, and sharply lower chances in northeastern
Vermont. The NBM 6 hour precipitation QMD technique shows large
spread in rainfall amounts for this entire period, especially in
western Vermont into the Adirondacks, suggesting that the fairly
steady chances of rain throughout this period will need to be fine
tuned. Given the trends towards a later and lesser rain event, have
cut back precipitation chances further to indicate more of a 30-50%
chance of rain in hourly PoPs. Again, on a 24 hour basis it looks
like it will rain areawide, but the extent of the rain remains
uncertain. The type of rain will be a stratiform/stable rain with
deep marine influence, so rainfall intensity will be limited even if
duration is long. Temperatures will be highly dependent on how far
north/east the shield of precipitation and thick clouds makes it; a
drier day would support partial sunshine such that temperatures
could end up in the 60s in northern areas and several degrees cooler
to the south. It could be quite uncomfortable in the mountains if
the steady rain materializes with low freezing levels; a cold rain
with temperatures in the upper 30s and lower 40s is possible.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
As of 353 AM EDT Wednesday...Chances of showers then continue through
Sunday night. Nothing really to write home about with the weekend
conditions as an open wave crosses the region without a surface
feature to organize precipitation around. Like last weekend, Sunday
may be the wetter day of the weekend as the upper level low moves
overhead. However, the details are pretty murky with how different
pieces of vorticity rotate around the longwave trough over the
northeastern CONUS. Most of the latest global model clusters do show
the cold pool aloft sufficient to eke out an average of around 100
J/kg of surface based CAPE Sunday afternoon, with greater
instability values in northern New York into the Champlain Valley.
With light cloud layer winds, this environment would support
numerous slow moving showers but unlikely to produce any downpours
let alone thunder.

The upper level pattern looks to evolve such that the cool and
unsettled pattern ends on Monday, although chances of showers do
continue. Upper level data in the global model clusters show good
agreement on northwesterly flow aloft and west/southwest low level
flow, indicative of warmer conditions. Would not be surprised if
high temperatures on Monday and Tuesday trend warmer. At this point
seasonable highs and lows are reasonable, as temperatures could be
tempered by cloudier weather associated with any surface boundaries
that may move through the region.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
Through 18Z Thursday...Isolated to scattered showers with some
embedded thunderstorms are expected over the next few hours,
initially forming over northern NY and progressing eastward into
Vermont. With regards to ceiling heights, expect highly variable
conditions across the forecast area, with a general
downward/deteriorating trend as we head into the overnight
hours. Many sites will see a mix of MVFR/VFR conditions this
afternoon, then see MVFR ceilings become more predominant into
the evening. Overnight, forecasting some IFR ceilings with some
reduced visibilities due to patchy fog and drizzle that will
persist towards the morning hours.

Winds are initially SSE at the beginning of the TAF period for
most sites, with some afternoon gusts expected 15 to 25 kt.
Winds will quickly trend to the NW by 00Z, diminishing to under
10 knots overnight.

Outlook...

Thursday Night: VFR. Chance RA.
Friday: VFR. Chance RA, Chance SHRA.
Friday Night: VFR. Slight chance SHRA.
Saturday: VFR. Chance SHRA.
Saturday Night: Mainly VFR, with local MVFR possible. Chance
SHRA.
Sunday: Mainly MVFR, with areas VFR possible. Chance SHRA.
Sunday Night: Mainly VFR, with areas MVFR possible. Slight chance
SHRA.
Monday: Mainly VFR, with areas MVFR possible. Chance SHRA.

&&

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

&&

$$
SYNOPSIS...Hastings
NEAR TERM...Duell/Hastings
SHORT TERM...Kutikoff
LONG TERM...Kutikoff
AVIATION...Duell