748
FXUS61 KBTV 211117
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
717 AM EDT Tue May 21 2024

.SYNOPSIS...
A few showers and scattered storms are possible across northern
New York this morning. More widespread thunderstorms are
expected this afternoon into early evening, some of which could
be strong to locally severe. Temperatures also warm well into
the 80s today and again on Wednesday before cooler temperatures
and drier weather return on Friday into Memorial Day weekend.

&&

.NEAR TERM /THROUGH WEDNESDAY/...

As of 700 AM EDT Tuesday...Forecast remains on track. KTYX radar
shows a thunderstorm just west of Hammond, NY on the Ontario
side. Dew points are a tad lower than modeled, mainly in the
53-57 range this morning so made some minor adjustments. Main
message remains on track, i.e. expect isolated to scattered
thunderstorms to develop mainly after 1 PM. The stronger storms
are capable of producing locally damaging wind gusts and small
hail. Highs top out in the mid 80s with similar apparent
temperatures by late morning before the initiation of the
storms. As we have messaged extensively, despite heat index
values falling shy of Heat Advisory criteria, the lack of
acclimatization means that sensitive groups and those without
access to cooling means could be vulnerable to heat risk
impacts.

PREVIOUS DISCUSSION...A wide range of temperatures currently
exists across the region, depending on the areas that have been
able to decouple. Sheltered hollows are in the upper 40s and low
50s while the broad valleys are generally in the 60s.
Temperatures should not lower much farther as boundary layer
winds will increase a bit. Fog has developed in a few of the
sheltered valleys, but it should be more limited in coverage
compared to previous nights. The first round of convection will
move into northern New York this morning as part of a warm front
type feature. It will bring a few scattered storms as it moves
across, but without much diurnal heating, the severe potential
is low.

A shortwave will pass through the region later in the day, and by
that point, diurnal heating should allow for more vigorous
convection to develop. Overall, there have not been many changes
from the previous forecast. The biggest change is that the highest
CAPE values may no longer reach all the way to the international
border, likely due to cloud cover from the morning convection
causing more interference with diurnal heating up there. This could
cause the area with the highest probability of seeing severe storms
to be farther south. However, shear looks to be lower in southern
areas so the best overlap between higher CAPE and shear looks to be
in between, probably around the latitudes of the central and
southern Champlain Valley. Generally, CAPE values should range
between 1000-2000J/KG. Guidance like the NAM and NAM 3KM that bring
2000+ J/KG are likely outliers because their forecasted dew points
between 65-70 degrees are probably too high, especially since the
they have initialized too high dew points upstream. 0-6KM shear will
generally be between 25-35 KTS, so combined with the CAPE, there
should just be enough ingredients for a marginal risk for severe
storms. The storms should mostly be pulse-type though there could be
just enough organization for a few bowing features to form. DCAPE
values are expected to reach around 1000 J/KG, enhancing the wind
threat due to possible downbursts. Overall, the main threat is
severe winds with the possibility of some small hail. Convection
should dissipate overnight.

Another round of convection is possible on Wednesday, though there
is less synoptic scale lifting and shear. Currently, an area of
convection should develop over Ontario where there looks to just be
enough lift from another weak shortwave. As the storms reach the
region, they will outrun this forcing and encounter less favorable
conditions. There is a chance of seeing severe storms over northern
New York. The SPC put these areas in a marginal risk again. However,
the conditions looks less favorable than Tuesday. These storms will
weaken as they travel east and they should lose any severe
characteristics as they reach Vermont. Wednesday will likely be the
hottest day of the year so far, with highs generally ranging between
85-90.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY/...
As of 300 AM EDT Tuesday...Showers and thunderstorms continue into
the evening hours on Wednesday. Models depict a pre-frontal trough
crossing the area Wednesday evening into the early overnight hours,
with a few hundred J/kg of surface-based CAPE helping to fuel the
forward motion of any storms that form earlier in the afternoon.
0-6km shear is quite marginal between 15 and 20 kt, so while a
stronger storm or two cannot be ruled out, at this time, they are
less likely to reach severe criteria. The current Day 2 SPC
convective outlook has marginal risk (level 1 of 5) across our far
western zones, which seem reasonable given the overall weak shear
and unimpressive forcing. PWATs are in the 1.2 to 1.4 inches range,
which is in the 90th percentile according to the SPC sounding
climatology for the Albany, NY upper air site. While locally heavy
downpours are possible with any storm that develop, flooding threat
is low given the overall fast moving nature. Temperatures wise,
southerly flow means overnight lows will generally be in the mid to
upper 60s, with similar dew points making for a rather muggy night.
Winds gusting 15 to 25 mph at times would help it feel more
tolerable.

Surface cold front comes through on Thursday with height falls and
temperatures aloft falling during the day from west to east. Dew
points should fall rather quickly into the 40s and 50s by the
morning hours across northern NY, but could stay near 60 across
Vermont. As such, the best chance for decent shear to overlap with
surface-based instability is across Vermont on Thursday afternoon.
And this is where the forecast indicates better chances for
thunderstorms. At this time, while a few stronger storms are
possible, they should stay mainly below severe criteria.
Temperatures wise, best probability of low to mid 80s would be
across Vermont, with cooler temperatures in the low to mid 70s
across northern NY.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
As of 300 AM EDT Tuesday...Behind the cold front on Thursday, we get
a reprieve from the recent early season heat, with much more
seasonable highs in the upper 60s to mid 70s expected on Friday into
much of the weekend. While a few showers cannot be ruled out, our
region should see mainly dry weather and rather refreshing
conditions with dew points in the 40s and 50s. The next chance for
more widespread showers and thunderstorms does not arrive until
Memorial Day itself but forecast confidence is low this far out.

&&

.AVIATION /11Z TUESDAY THROUGH SATURDAY/...
Through 12Z Wednesday...All terminals are currently VFR. Any
marginal LLWS is expected to diminish this morning due to better
boundary layer mixing. Scattered showers and thunderstorms will
develop by mid day and impact terminals between 17-23z. The
strongest storms will bring frequent lightning, brief strong
wind gusts as well as heavy downpour. Visibilities could
briefly lower to MVFR or even IFR. However, for most of the TAF
period, flight categories are expected to stay VFR. Winds are
mainly from the south between 5 to 10 kt, except locally higher
gusts in thunderstorms.

Outlook...

Wednesday: VFR. Scattered SHRA, Isolated TSRA.
Wednesday Night: VFR. Chance SHRA, Slight chance TSRA.
Thursday: VFR. Chance SHRA, Slight chance TSRA.
Thursday Night: VFR. Slight chance SHRA.
Friday: VFR. NO SIG WX.
Friday Night: VFR. NO SIG WX.
Saturday: VFR. NO SIG WX.

&&

.CLIMATE...
Record High Temperatures:

May 22:
KBTV: 93/1977
KMPV: 90/1994
KMSS: 89/1977
KSLK: 91/1911


Record High Minimum Temperatures:

May 22:
KBTV: 70/1911
KPBG: 65/1975
KSLK: 63/1921

May 23:
KPBG: 65/1964

&&

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

&&

$$
SYNOPSIS...Chai
NEAR TERM...Chai/Myskowski
SHORT TERM...Chai
LONG TERM...Chai
AVIATION...Myskowski
CLIMATE...Team BTV