881
FXUS61 KBTV 210229
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
1029 PM EDT Sat Jul 20 2024

.SYNOPSIS...
A weakening cold front will bring clouds and a few showers,
especially across northern areas, overnight. Skies will trend
sunny on Sunday with light north winds ushering in drier and
cooler air. After an extended drier stretch, unsettled weather
will begin by early Tuesday associated with a quasi-stationary
front that will set up across New York and New England. Periods
of rain are expected, with increased thunderstorm chances on
Thursday.

&&

.NEAR TERM /THROUGH MONDAY/...
As of 1027 PM EDT Saturday...Cold front currently approaching
the international border has sparked an area of showers, with
embedded localized moderate to even briefly heavier downpour.
The PWATs associated with this area of isentropic lift tops out
at 1.4 inches, or roughly the 75th percentile of SPC sounding
climatology for Albany, NY. There is no lightning associated
with this line of showers, and wind gusts have been mostly in
the 15-20 mph range, except locally up to 25 mph. Given the
narrow swath of higher PWATs, main adjustments with this update
were to nudge the rainfall amounts especially close to the
international border higher. No weather concerns but some
locations like Massena and Highgate could see upwards of 0.25
inches of rain but rainfall amounts over 0.1 inch are not
expected to be widespread for overnight tonight. Otherwise,
forecast remains in good shape. Previous discussion below.

PREVIOUS DISCUSSION...It`s been just about the most seasonable
summer day possible, which makes it unusual given that we
typically deviate from climatological normals. We are in a zone
of weak high pressure with gradual pressure falls ahead of cold
front shifting southward across southern Canada this evening.
For this time of year it is a moderately strong front
thermodynamically, as low level temperatures will drop several
degrees along with lowering dew points. Refreshing dew points in
the low to mid 40s are found on the cool side of the front and
beyond the post- frontal clouds in southern Ontario/western
Quebec this afternoon.

The frontal zone, with regard to cloud cover, is relatively large
and corresponds well with progged 700 millibar relative humidity
exceeding 80%. This will be shifting southward over our region
mainly in the nighttime hours, lingering into perhaps late morning.
Based on satellite imagery today, mostly cloudy skies may linger in
a particular location for upwards of seven hours. Solar heating and
further weakening of the front will tend to reduce the cloudiness in
central and southern Vermont during the morning, and these areas are
most likely not to see any rainfall with the front. Farther north,
while the intensity of the rain will be on a decreasing trend, some
rain showers are likely, especially across the northern tier
counties. Amounts still look to be mainly a few hundreths of an
inch, with perhaps 0.1" in area like Swanton, Vermont.

Behind the front, then the question is how low will afternoon
relative humidity get? The NBM dew points are a little high relative
to the HREF, and it remains to be seen how quickly the clouds
dissipate/shift south during the day. The cool air advection will be
battling strong heating, but overall temperatures have trended a
touch cooler with this forecast with highs mainly in the low to mid
70s. An exception is over the lower Connecticut River Valley and
lower elevations in the Taconic Foothills in Vermont, where weaker
and later arrival of cool air advection will allow temperatures to
reach near or above 80.

Then tomorrow night, a dry air mass with light northwest winds aloft
and climatological fog season should support localized dense fog in
the favored locations mainly in central and southeastern Vermont and
western Adirondacks. At our typical cold spot, Adirondack Regional
Airport/Saranac Lake, MOS guidance suggests a low around 40 degrees,
which would match the observed low on July 2nd when we last had a
cool and dry air mass in the region. That would also suggest our
broad valleys should see lows in the low and mid 50s, with many mid
to upper 40s across central and northeastern Vermont as well as
other portions of the Adirondacks.

&&

.SHORT TERM /MONDAY NIGHT/...
As of 335 PM EDT Saturday...Conditions remain dry Monday with
temperatures generally running around to slightly above seasonal
averages in the upper 70s to mid 80s. Synoptically, major features
will be a large blocking ridge over the inter-mountain western US, a
relative longwave trough across the Central Plains, and the Bermuda
Ridge in the western Atlantic. While upper flow remains fast and
zonal, a lifting migratory low will push a warm front through the
North Country Monday night increasing chances of rain. With the
track of the low south of Vermont, overrunning will favor spreading
rain chances south to north overnight.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 335 PM EDT Saturday...Model consensus highly favors lingering a
quasi-stationary boundary across portions of the Northeast Tuesday
through Thursday night of next week building the Bermuda High
northwestward. The actual placement will be key in determining which
areas will receive heaviest rain, but the conceptual model for this
setup points to potential for periods of moderate to heavy rainfall.
Given the week of drying, flood potential will start lower early
Tuesday across southern Vermont and likely be contingent on multiple
rounds of thunderstorms (5-15% chance of flooding at this time).

Moving forward, a couple of impulses are progged to move along the
boundary Wednesday and Thursday bringing additional chances of
moderate to heavy rainfall with some potential for localized
flooding. Depending on where heaviest rain falls, some locations`
susceptibility to flooding will likely increase from Tuesday to
Thursday while precipitation chances become more widespread to
include all locations to the Canadian border. While thunderstorm
chances will be present Tuesday and Wednesday, the likely, most-
active period for thunderstorms looks to be on Thursday when surface
dew points will be highest and potential for increasing shear
exists.

Models suggest jet energy will be sufficient with the last impulse
Thursday into Friday to push a surface front through the North
Country allowing for a transition to relative ridging. However,
thermal parameters along this proposed boundary will likely be weak,
keeping temperatures in the mid/upper 80s heading into next weekend.

&&

.AVIATION /03Z SUNDAY THROUGH THURSDAY/...
Through 00Z Monday...A line of showers is moving along a cold
front from northwest to southeast this evening. It is currently
north of the international border, but it is expected to bring
some rain and lower ceilings to the sites, starting with MSS,
this evening and overnight tonight. Winds currently out of the
southwest will turn more north/northwesterly following the
frontal passage. Showers are most likely to occur through about
12Z for most sites. Looking at upstream observations,
visibilities are remaining about 6 miles or higher in rain,
though we will be monitoring the line of rain throughout the
evening for any necessary amendments. Ceilings could fall to
MVFR levels around 06Z-12Z at times for some. There remains the
potential for some brief IFR ceilings at SLK and/or MPV, though
it is low enough to leave out of the TAF at this time.

Outlook...

Sunday Night: VFR. Patchy BR.
Monday: VFR. NO SIG WX.
Monday Night: VFR. Slight chance SHRA.
Tuesday: Mainly VFR, with local MVFR possible. Chance SHRA,
Slight chance TSRA.
Tuesday Night: Mainly VFR, with local MVFR possible. Chance SHRA,
Slight chance TSRA.
Wednesday: Mainly MVFR, with areas VFR possible. Chance SHRA,
Slight chance TSRA.
Wednesday Night: MVFR/IFR conditions possible. Chance SHRA.
Thursday: Mainly MVFR, with local IFR possible. Likely SHRA,
Slight chance TSRA.

&&

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

&&

$$
SYNOPSIS...Kutikoff
NEAR TERM...Chai/Kutikoff
SHORT TERM...Boyd
LONG TERM...Boyd
AVIATION...Storm