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  Monday August 21, 2017

 

NWS Area Forecast Discussion


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000
FXUS61 KBTV 200549
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
149 AM EDT Sun Aug 20 2017

.SYNOPSIS...
A trough of low pressure will move through northern New
York and New England tonight. The threat for isolated showers will
continue tonight but come to an end toward sunrise on Sunday.
High pressure will build in for Sunday and Monday, with
favorable conditions to view the eclipse on Monday. Temperatures
will be seasonably warm, with highs Sunday in the mid 70s to
lower 80s, and into the 80s for Monday. Overnight lows will be
in the upper 50s and 60s. Another low pressure system will renew
chances for showers and thunderstorms Tuesday and Wednesday.

&&

.NEAR TERM /UNTIL 7 AM THIS MORNING/...
As of 111 AM EDT Sunday...Overall forecast in good shape with
no big changes needed. Only tweak was to the current
temperatures otherwise plenty of clouds early this morning and
some isolated showers with the upper trough moving across the
area.

Previous Discussion...
Mid-level thermal trough continues to make its way ewd across
sern Ontario and wrn NY at 0230Z, and remains on track to
translate ewd across the North Country during the overnight
period. May see a few isold showers/sprinkles with this feature,
mainly across the nrn mtns and near the intl border. In most
locations, will just see an increase in cloud cover for a time
(06-12Z) associated with trough passage, and have adjusted skies
to mostly cloudy during the pre-dawn hrs across roughly the nrn
half of the forecast area. Appears there will be enough
westerly gradient flow to maintain PBL mixing and preclude much
in the way of fog development overnight.

Surface dewpoints will gradually fall from mid 60s into the 50s
from west to east overnight. Combination of variable cloud cover
and some continued wind will limit cooling overnight, with early
AM lows 55-65F.

&&

.SHORT TERM /7 AM THIS MORNING THROUGH 6 PM MONDAY/...
As of 340 PM EDT Saturday...Brief 500 mb shortwave ridging
Sunday night, otherwise upper flow is predominately zonal
westerly. A surface high centered over PA on Sunday will move to
off the Delmarva coast by Monday, with surface ridging nosing
north into New England. Quiet weather will result, although
building heights and more sunshine will warm temperatures a few
degrees each day. Highs Sunday 75 to 85, while Monday will be
solidly in the 80s. 850 mb and 925 mb temps support 87 at KBTV
on Monday. Increase in humidity Monday as the surface ridge
shifts east and return flow brings surface dewpoints well into
the 60s especially in the St. Lawrence valley.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
As of 340 PM EDT Saturday...pretty decent agreement with the
12z suite of models for the week. Generally letting the model
blend ride, especially for Wednesday onward. No big changes to
the overall scenario expected, though some of the details -
especially for Tuesday -- appear to becoming a bit more clear.
The models have shifting back a little faster such that we have
better timing with the combo of strong dynamics and instability
with peak afternoon heating, suggesting an increased chance of
organized strong convection and locally heavy rains late
Tuesday. Still rather far out in time to lock down any specific
details, but some of the model guidance did catch my attention.
For the daily details, keep on reading.

Monday night: For most of the region, it will be quiet --
however can`t rule out an isolated shower out across the St
Lawrence Valley and close to the Canadian border. This is from
the initial surge of moisture that will be moving across the
region in a deepening southwest flow. Dewpoints will also start
to increase overnight, so a little muggy feeling.

Tuesday/Tuesday Night: This is the time period the latest model
runs are now focusing in. Potentially a very active 12-18
hours. Upper trough will be moving into the Great Lakes, and
promote the development of a fairly deep surface low for this
time of the year (sub 1000mb). Potent system will also have a
pretty strong low/mid level jet, with 850mb winds 40-50 knots,
which will be spreading into northern NY by afternoon. All the
models show pretty solid amount of instability, with the NAM the
most unstable (probably too high with dewpoints). There is some
question as to how much sun we`ll see, which will also have an
impact on high temperatures and instability, but bottom line
we`ll have instability and strong dynamics in place. Noted that
SPC had shown a day 4 slight risk just southwest of our region,
but that was based on the 00z models, which were a little slower
in timing. Also noted a good slug of moisture with this system,
with precipitable water values nearing 2.0". That suggests
locally heavy rainfall is a good bet as well, and based on some
model signals, rainfall totals over 1 inch will probably occur.
Bottom line, we`ll have to keep watch for how later model runs
trend. Could be a busy weather day/evening with strong/severe
t-storms and locally heavy rain. As they say on TV, "Stay Tuned
for later updates".

Wednesday: Based on the 12z guidance timing, looks like residual
showers will be around in the morning and diminishing by
afternoon as the surface front moves through. Given some
uncertainty in model trends, have kept in a fairly wide
timeframe for the chance of showers, though in reality we might
be sunny and dry for the afternoon.

Thursday/Friday/Saturday: large scale broad upper trough will be
settling in across the eastern half of the US. For sensible
weather in our region, it looks like an extended period of
slightly below normal temperatures but relatively dry/comfy
weather. Have a very small chance for a brief light shower
across the higher terrain of northern VT and northern NY for
Thursday, but otherwise chances for rain are less than 10%
Friday and Saturday. Highs will range from the upper 60s in
higher elevations to lower 70s in the valleys.

&&

.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
Through 06Z Monday...An upper level trough is moving across the
area early this morning and will be east of our area by 12z.
Expect VFR to MVFR ceilings through 12z before VFR conditions
are expected for the remainder of the period as little in the
way of cloud cover is expected. Winds will pick up from the west
and northwest this morning at speeds in the 5 to 15 knot range
before tapering off after 00z tonight.

Outlook...

Monday: VFR. Breezy. NO SIG WX.
Monday Night: VFR. Slight Chance SHRA.
Tuesday: VFR. Breezy. Chance SHRA...Slight Chance TSRA.
Tuesday Night: VFR/MVFR. Occasional SHRA...Slight Chance TSRA.
Wednesday: VFR. Chance SHRA.
Wednesday Night: VFR. Slight Chance SHRA.
Thursday: VFR. Slight Chance SHRA.

&&

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

&&

$$
SYNOPSIS...Hanson
NEAR TERM...Evenson/Hanson
SHORT TERM...Hanson
LONG TERM...Nash
AVIATION...Evenson


 
 
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