Area Forecast Discussion
Issued by NWS Burlington, VT

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FXUS61 KBTV 240228

Area Forecast Discussion
National Weather Service Burlington VT
1028 PM EDT MON MAY 23 2016

High pressure will provide mainly clear and quiet weather tonight
with seasonably cool temperatures expected.  Moisture pivoting north
and west around departing offshore low pressure will bring a renewed
threat of scattered showers and a few thunderstorms Tuesday afternoon
and early evening, mainly across Vermont.  Thereafter, the first
prolonged stretch of summerlike weather will build into the region
for the remainder of the week and into the Memorial Day weekend
with warm and increasingly humid conditions. While much of the
period will be dry, there will be a daily threat of scattered
showers and a few thunderstorms, mainly during the afternoon and
early evening hours.


As of 1024 PM EDT Monday...minor update to capture latest trends
in temps/dewpoints and sky cover. ir sat continues to show
mid/upper level clouds across southern vt with a few clouds along
the spine of the green mountains. temperatures continue to fall
back into the 50s and lower 60s...except already 47f at slk. all
covered very well in current forecast.

A few tweaks to capture current trends
in sky temps and dewpoints. Dew points have been running 5 to 10
degrees below any MOS guidance though lamp data is pretty good.
with clear skies KSLK should get into the 30s otherwise running
forecast looks good.

previous discussion....High pressure will provide mainly clear
skies and light winds to the region again tonight. While there is
an outside chance of some patchy mist or fog in favored areas once
again, deep drying that has occurred today should limit the
overall coverage across the area. Minimum temperatures a blend of
of MOS-based and bias-corrected consensus data offering values
generally from the mid 40s to lower 50s with a few spot readings
around 40 in colder northern mountain hollows.

On Tuesday short-term models continue to show good consistency
showing a filling upper low will drift northeasterly along the
northeastern seaboard through the day.  While the system is
essentially equivalent barotropic, weak deformation/moisture
band rotating into our region on the system`s northwestern periphery
should interact with some marginal instability and low level
convergence to spark scattered showers and a few storms, mainly from
the Champlain Valley east.  Here solid chance to low-end likely pops
(40-60%) will be maintained.  Further west, a mainly dry and sunnier
day is expected as this area will be removed from spoke of deeper
moisture and convergence.  High temperatures will be similar to today
from the northern Champlain Valley west into northern New York (upper
70s to lower 80s) with slightly cooler readings (70s) further east
where coverage of afternoon clouds and showers will be greater.


As of 355 PM EDT Monday... tuesday night: showers/isolated
t-storms mainly for vermont will quickly fade by mid evening with
the loss of heating. maybe a touch of patchy fog for late night,
though confidence not high enough to include that in the forecast.

wednesday: hi-res models are all pretty similar with overall
scenario of a shortwave and associated weak surface front pushing
into the region from the northwest. with temperatures well into
the 70s, we`ll have some surface based instability. models suggest
cape values of 500-1000 J/kg. nam also showing 0-6km shear of
roughly 30-40kt developing during the afternoon especially across
northern ny. looks like enough ingredients coming together for
convection to develop during the afternoon -- perhaps with semi-
organization to them. model radar reflectivity output from various
hi-res models suggests a broken line of t-storms will rapidly
develop mid-day across northern new york and push southeast and
then quickly fade by early evening as they reach southern vermont
where less instability will be available. have blended the
reflectivity outputs to form the basis of the PoP forecast for the
day. basically a 30-50% chance of t-storms for the afternoon,
especially across northern ny and extending into northern vermont.

thursday: will be a transition day. for most of us, it will be
dry and fairly sunny. perhaps some showers or isolated t-storm
across northern ny later in the day as a developing southwest flow
sends a surge of moisture our way. stuck with the model blend with
highs well into the 70s for the region.


As of 355 PM EDT Monday...
looks like a summer pattern for the holiday weekend. that means
warmth, moderately humid and the chance for thunderstorms each
day. GFS and ECMWF are in "okay" agreement with the large scale
synoptics, however there will be a "back-door" front setting up
somewhere probably just to our east thanks to the still quite
chilly atlantic ocean. depending on how far inland this front will
push will greatly affect the weather we see. considerable
differences in this subtle but important detail in the global
models, so there is some bust potential in parts of the forecast.

daily details:

thursday night: southwest flow and associated moisture advection
will lead to scattered showers. clouds and precipitation will keep
it rather mild overnight, with lows in the 50s to lower 60s.

friday: we`ll be solidly into a warmer and slightly more humid
airmass. both GFS and ECMWF indicate a decent amount of surface
based instability, with cape values likely topping out over 750
J/kg by the afternoon. not a lot of dynamic forcing, but the
atmosphere will be fairly moist (precipitable water values over
1.25"). looks like a typical early August weather pattern, so
I`ve gone ahead with a typical forecast for that part of the
summer. 35-50% chance of afternoon thunderstorms looks good. will
probably initially form over the higher terrain and then push east
during the afternoon. with 850mb temperatures rising to around
15C, that would support support highs in the lower to mid 80s for
the region. went a little warmer than the first guess model

saturday: looks a lot like friday, except the surface dewpoints
are a little bit higher. i think this will be the first day that
we`ll really start to notice the humidity. some differences in the
overall temperature fields as denoted by the GFS and ECMWF. ECMWF
wants to slide in slightly cooler air from the north, as it has
the ridge axis suppressed slightly further south than the GFS. the
GFS has 925mb temperatures rising to 20-23C, which would mean we
could approach 90f in some valley areas. ECMWF is cooler (17C
across the Canadian border to 22C in far southern vermont). took
the blend of the models, but that still results in temperatures
solidly into the 80s. based on those temperatures and a little
higher humidity, afternoon thunderstorms will be a good bet once
again. no strong focus other than terrain, so t-storms will be a
hit and miss proposition.

sunday & memorial day (monday): both GFS and ECMWF indicate that
cooler atlantic airmass will pool to our east and try to make a
westward push as a small high pressure develops east of new
england. this "back door" front will be shallow, and just how much
the terrain (white mountains and green mountains) restrict it`s
westward movement is just a little beyond the resolution of the
global models. for sunday, this backdoor front should still be to
our east, so sunday looks to be a repeat of saturday (temperature
wise and t-storm chance-wise). for monday, if anything, the models suggest
a cooler airmass will push into eastern vermont. if this happens,
we could see a pretty significant temperature variation (60s far
east to mid 80s far west) across the forecast area. those specific
details, as mentioned, are tough to pin down this far out. thus
stuck with straight guidance blend for monday, which indicates an
overall cooler day than sunday. still a rather moist airmass
around, so will maintain 30-40% PoPs. given the cooler forecast,
surface instability will be less, so probably not as many t-storms
around for memorial day. still doesn`t look like a total washout
of a day, so i think most outdoor activities/bar-b-ques should
still be okay.


.AVIATION /03Z Tuesday THROUGH Saturday/...
Through 00Z Wednesday...VFR through the forecast period. Winds
variable less than 10 kts. After 15Z Tuesday, increasing moisture
from the east/south will bring sct/bkn VFR cigs in the 050-100 AGL
range with an increasing threat of a shower/isolated storm,
especially at KMPV/KRUT terminals.

NOTE: KMSS ASOS seems to be reporting erroneous visibility/weather
as low as 1/4SM HZ for the past several hours since about 21Z.

Outlook 00Z Wednesday through Saturday...

18z Tue - 00z Thu: VFR with chance of afternoon/early evening
showers and/or isolated thunderstorms each day. Activity generally
scattered in nature with long periods of VFR/dry weather. Brief
gusty winds and/or MVFR visibilities possible with any heavier
Thu: VFR under high pressure.
Thu night-Fri: VFR/Chance MVFR in SHRA/TSRA with a warm front.
Sat: Mainly VFR. SCT pm SHRA/TSRA.




NEAR TERM...JMG/Taber/Sisson
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