227
FXUS61 KBTV 291420
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
1020 AM EDT Mon Apr 29 2024

.SYNOPSIS...
Outside some rain in New York and light sprinkles elsewhere,
today is expected to be mostly dry. Our next system will impact
the region late Monday night into Tuesday with showers likely,
followed by another batch of afternoon showers and perhaps a
rumble of thunder. Temperatures will hold in the 40s to lower
50s tonight and warm into the 50s north to near 70 degrees
south through Tuesday. Quieter weather is expected for the
latter half of the week, with a warming trend across the region.

&&

.NEAR TERM /THROUGH TUESDAY/...
As of 1007 AM EDT Monday...Minimal changes were needed with this
update as showers continue across northern New York this
morning, with cloud cover across the entire forecast area.
Temperatures this morning are generally in the low to mid 40s,
except the lower Connecticut River Valley, with temperatures
already near 60.

Previous Discussion...Today, the region will warm towards
seasonal norms in the upper 50s to mid 60s, except in the lower
Connecticut River Valley, which could climb up the 70s. Mainly
north flow will remain today, with some diversions around
terrain features. We`ll be at the eastern periphery of a warm
conveyor belt, and so moisture will arc over the strong ridge to
our south. The exact placement is in question, but there`s also
a very narrow tongue of dry air at 850hPa. The air is very dry
at lower than
-30 C dewpoints, but the layer is so thin that it`s reasonable
to assume some rain will make it past over northern New York at
least. Amounts a few hundredths at most.

On Monday night into early Tuesday morning, a strong warm front
will slide northeastwards. A strong surface high in far
northern Quebec Province will try to maintain dry air across
northern Vermont as deep, tropical moisture overruns the
relatively dense, stable air mass. Strong upper divergence along
the frontal feature will result in an FGEN band at the boundary
of dry, seasonable air and humid, late Spring-type air. A weak
surface low will develop while an upper trough acts to break the
strong upper ridge that`s remained in place resulting in good
surface convergence alongside the FGEN band. Ingredients appear
to come together to produce a narrow strip of moderate to heavy
rain with the warm front just south of the international border.

Then we monitor how far north new low pressure gets across the Mid-
Atlantic and what it means for our instability. The air behind the
warm front is very warm, and could create a gradient of about 50
north to about 70 south. If warm air advects far enough north, we
will weakly destabilize across the region as PWATs climb higher to
about 200 percent of normal. High resolution guidance depicts at
least 2 rounds of precipitation, likely as a result of wind profiles
that would support backbuilding convection. However, an important
caveat, is that if we can`t get the convection, then we don`t get
the backbuilding. The NAM12 forecasts southeast flow that would keep
conditions more stable as well and limit convection. Given how weak
the surface low is expected to be at 1010mb or higher, tracking
where exactly that will be is going to be tough. For now, the
forecast leans heavily on high resolution ensemble data.
Precipitation will likely continue into the overnight hours. For
additional details on hydro, please see the discussion below.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY/...
As of 338 AM EDT Monday...Widespread rain and thunderstorms during
the day will decrease in coverage overnight Tuesday, tapering off
into showers by Wednesday morning. Weak high pressure builds in from
the Great Lakes, resulting in a rather pleasant day with quiet
weather, light winds and partial sunshine on Wednesday. Daytime
highs would likely be cooler across the northern Adirondacks and
east of the Green Mountains, reaching only the mid 50s to near 60.
On the other hand, southern locales in the CWA should reach into the
60s. For perspective, the average high temperatures for the first
day of May across North Country are in the low to mid 60s.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
As of 338 AM EDT Monday...Overall, the second half of the work week
features a gradual warming trend with mostly quiet conditions.
Models depict a weak shortwave trough sliding southeastward across
Vermont on Thursday, so there could be some showers and cooler
temperatures east of the Greens. But overall, the weather pattern
looks quite quiet across North Country as we begin the month of May.
This coming weekend does look potentially unsettled, but there
remains considerable spread in the global guidance. The overall
upper level pattern favors the development of an omega block
somewhere east of the Mississippi River, book ended by a meandering
closed low centered near Manitoba/Ontario and a anomalously deep
trough that is slow to exit the Canadian Maritimes. At this time,
there is just about equal odds of a toasty weekend, especially for
our western zones and an unsettled period with widespread rain and
thunderstorms. So there is low forecast confidence in how the
weekend will transpire at this time so stuck very close to blended
guidance. Additionally, given the lack of confidence in any
significant storms, let`s spend some time to discuss the potential
for heat risk heading into the first weekend of May.

The experimental NWS heat risk website does indicate the potential
for minor heat risk for individuals particularly sensitive to heat
across the St Lawrence Valley on Friday on Saturday. The URL is
https:/www.wpc.ncep.noaa.gov/heatrisk. Global ensemble guidance
indicates the potential for anomalous H5 ridging, with 850mb
temperatures potentially as much as 10C above climatological normal
across portions of far western NY. This would put our far western
zones, i.e. St Lawrence county in the closest proximity to this
anomalous ridge. At this time, the potential of apparent
temperatures or heat indices reaching the mid 80s remain low but non
zero. The in-house Dynamic Ensemble-based Scenario for IDSS (DESI)
tool that aggregates deterministic and ensemble guidance currently
gives a 3 percent chance for heat index values to reach or exceed 85
degrees for Massena on Friday and Saturday, which puts the NWS heat
risk tool output into context. A word of caution against jumping
onto the early season heat bandwagon is the potential for much
cooler maritime influence from the New England coast, as a
anomalously 850mb cool regime associated with a closed off low
across the Canadian Maritimes could pivot further westward and shunt
the heat risk concerns west of our CWA. Nonetheless, those with
outdoor plans for the first weekend of May should keep abreast of
the latest forecast. After all, summer is knocking on our doorsteps.
Forecast wise, have stuck rather close to blended guidance given the
amount of uncertainty at this time frame. But we will monitor the
trends through the week if any upward adjustments to the
temperatures need to be made and message it on various platforms
given the overall lack of acclimatization to early summer heat at
this point in the shoulder season.

&&

.AVIATION /14Z MONDAY THROUGH FRIDAY/...
Through 12Z Tuesday...The frontal boundary bringing abundant
clouds has been slow to exit south of the region, and so we
still have a few locations dealing with IFR ceilings. KMPV and
KSLK have had the most persistent, and KRUT has been more in and
out. Light rain is shifting west to east near KMSS and KSLK,
and may reinforce the 600-800 ft ceilings there, but this should
lift about 15z. Other terminals are mainly MVFR, except VFR at
KMSS, and will gradually improve as ceilings rise to 6000-9000
ft agl and clouds scatter across Vermont. Winds northeast over
New York and north to northwest over Vermont at 6 to 12 kts.
Wind speeds decrease after 22z and become more variable or
terrain driven. Approaching 06z Tuesday, precipitation will
spread over the region from southwest to northeast. Rainfall
rates may be moderate, but for now have only indicated 6SM in
prevailing rain. Ceilings fall back to 2500 to 4000 ft agl are
expected behind this precipitation.

Outlook...

Tuesday: Mainly VFR, with local MVFR possible. Chance SHRA.
Tuesday Night: MVFR/IFR conditions possible. Chance SHRA.
Wednesday: Mainly MVFR, with areas IFR possible. Slight chance
SHRA.
Wednesday Night: Mainly VFR, with areas MVFR possible. Slight
chance SHRA.
Thursday: Mainly VFR, with areas MVFR possible. Slight chance
SHRA.
Thursday Night: Mainly VFR, with local MVFR possible. NO SIG WX.
Friday: Mainly VFR, with local MVFR possible. Slight chance SHRA.

&&

.HYDROLOGY...
There is a marginal risk for excessive rainfall for Tuesday
into Wednesday over the Adirondacks and much of Vermont. The
northern half of our forecast area received a respectable amount
of rain Sunday, with widespread 0.50" to 1.00" across the
northern Champlain Valley and the northern half of Vermont. The
southern half and St. Lawrence Valley mainly saw variable
readings between a few hundredths and 0.25".

Beginning overnight Monday into Tuesday night, multiple rounds
of precipitation will be possible. A warm front will lift north
during the predawn hours Tuesday. Along the front, moderate to
locally heavy rain is possible, producing 0.2 to 0.5 inch of
rain. After some clearing, afternoon showers and a few thunderstorms
are likely to develop. Multiple rounds of moderate to heavy
showers could produce an additional third to two thirds of an
inch. Locally higher rainfall amounts will be possible. With
some trees still dormant and lingering summit level snow, there
could be some areal flooding on low lying farm fields, poor
urban drainage basins, and across ditches. Dry conditions over
the last couple weeks has allowed river levels to fall. At this
time, it does not appear that there will be enough precipitation
and snowmelt for river flooding, but we will closely monitor.

&&

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

&&

$$
SYNOPSIS...Haynes
NEAR TERM...Haynes/Kremer
SHORT TERM...Chai
LONG TERM...Chai
AVIATION...Haynes
HYDROLOGY...WFO BTV