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  Thursday September 20, 2018

 

NWS Area Forecast Discussion


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470
FXUS61 KBTV 180721
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
321 AM EDT Tue Sep 18 2018

.SYNOPSIS...
Steady rains come to an end across southern Vermont this
morning, followed by a few showers this afternoon and early
evening as a strong cold front pushes south through the area.
Behind this front, variable clouds and cooler, more seasonable
weather is expected by tonight onward into Thursday. A brief
warmup is expected by Friday before another strong front brings
more cool weather for the upcoming weekend.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
As of 321 AM EDT Tuesday...Changeable weather is on tap for
today and is not without its challenges, especially in terms of
temperatures and cloud cover. Current analysis places steady
light to moderate rainfall across eastern NY state into MA and
the southern portions of VT/NH associated with remnant moisture
from once Hurricane Florence. Expect this rainfall to continue
across these areas through mid- morning before tapering off by
late morning. Little to no precipitation is expected along and
north of a Ticonderoga, NY to Newberry, VT line this morning,
with just high clouds the rule. Total rainfall in
Rutland/Windsor counties from this event to generally range from
0.25 to 0.75 inches with localized totals near 1 inch.

We`re also watching a strong cold front across southern ON/QE this
morning, which will drop southward into northern counties by early
this afternoon, and into southern VT by late afternoon/early
evening. In actuality there are two fronts - one in ON approaching
from the northwest, and another backdoor-type boundary surging
southwest from QE. This morning`s hi-res CAM output show these
features and their associated wind shifts quite nicely. In terms of
sensible weather the low to mid level flow will actually trend
northwesterly later this morning behind Florence`s remnants and in
advance of the front(s). This will allow an overall weakening of
boundary layer convergence and with limited instability only
scattered light showers are expected as these fronts pass. A number
of spots across the north may miss these showers altogether and
remain dry. High temperatures are a bit tricky as well given morning
rainfall and clouds south, and the frontal passage in the north by
early afternoon. Felt a blended solution of available bias-corrected
guidance and our running forecast was a best approach showing highs
ranging through the 70s to around 80.

Lingering showers then end over time this evening as cooler air
filters south/southwest into the area and variable clouds prevail
under a fairly sharp frontal inversion. Some patchy drizzle may be
possible in the higher terrain as low level moisture will be
abundant. Did lean away from the NAM MOS guidance in regard to
temperatures as it continues to suffer from a pronounced cold bias.
Overall, lows tonight should range from the upper 40s to mid 50s
north and mid to upper 50s south.

Variable cloudy skies then continue into Wednesday, though will tend
to erode by afternoon as mixing processes deepen and the
aforementioned inversion weakens. Some patchy morning drizzle may
linger along the eastern slopes of the Greens. Once again have
discounted cool NAM MOS guidance for temperatures, opting instead
for a blended solution incorporating at least some bias-corrected
data which offeres readings from the mid 60s to lower 70s.

&&

.SHORT TERM /WEDNESDAY NIGHT/...
As of 350 PM EDT Monday...Wednesday should see gradual
improvement throughout the day as high pressure nudges south out
of Canada. Morning clouds will hold on across much of the area
with an inversion in place preventing the mixing of drier air
aloft. As temperatures warm slowly, the inversion should begin
to break down allowing us to eventually mix out some to possibly
most of the clouds, with far southern and eastern VT likely
holding on to clouds the longest. Overall, precipitation chances
are close to nil Wednesday but a few hi-res models are hinting
at some subtle surface convergence, and subsequently some light
drizzle, for far eastern Northeast Kingdom (along the NH-VT
border) Wednesday afternoon. Have kept a slight chance in across
these areas at this time.

With cooler air moving in, 925mb temperatures Wednesday will be
around 11C, supporting temperatures in the mid to upper 60s across
much of the area. Temperatures spreads on Wednesday are highly
dependent on cloud coverage, and since thinking is at this time that
clouds could be lingering into the afternoon have trended away from
some of the warmer guidance for Wednesday...but didn`t want to take
it as cold as NAM is suggesting. Currently have high of 68 in for
BTV.

With plenty of dry air aloft, and most of the clouds dissipating by
sunset, anticipating a good night of radiational cooling across much
of the area. Have nudged temperatures down a bit, mainly across the
Northeast Kingdom and Adirondacks. Biggest challenge for Wednesday
night, aside from temps, will be the fog potential across the area.
Difficult to tell at this time whether or not fog or low status deck
will develop. As with temperatures, if areas hold onto any residual
clouds this would affect their ability to radiate efficiently.
Overall, still quite a bit of uncertainty on exact details of the
forecast at this time...a lot of moving parts at play here.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
As of 350 PM EDT Monday...Thursday should see similar
conditions to Wednesday. Temperatures will moderate slightly as
winds gradually turn southerly throughout the day Thursday. High
clouds will increase Thursday night ahead of the next system
which should keep temperatures slightly warmer compared to
Wednesday night. Model consensus is becoming better aligned for
the system Thursday/Friday with ECMWF beginning to catch on to
the idea of a deepening low tracking well north out of the Great
Lakes. The greatest forcing, and bulk of the precip, will be
considerably north of the CWA, but portions St. Lawrence and
Franklin counties, NY, could see a chance for rain Thursday
night as the warm front pushes north into Quebec. A chance for
rain remains during the day on Friday into Friday night with the
cold front expected to cross our area quickly Friday
evening/night. CAPE values as this front pass are pretty meager,
~200 J/kg (GFS) ~500 K/kg (ECMWF), but wouldn`t rule out the
possibility of an isolated strong storm and a few rumbles of
thunder. Additionally, winds ahead of this cold front will
likely be pretty breezy, with SW winds between 40-50 knots at
850mb. With differences still in the strength of this low, the
strength of these winds could change as things become better
resolved.

Aside from the brief warm up ahead of the low on Friday,
temperatures through the weekend should be seasonable with highs in
the mid to upper 60s Saturday, Sunday and Monday. Low temperatures
will certainly feel fall-like with the coldest temperatures likely
Sunday night (mid 30s to mid 40s across the area) as Canadian high
pressure settles over the region. The system that the ECMWF was
picking up on during the Sunday timeframe looks to pass just south
of our far southern zones. However, the GFS has some piece of energy
streaming north of the area...with uncertainty in the forecast at
this time have kept a 20-30% of rain in the forecast for
Sunday/Sunday night.

&&

.AVIATION /08Z TUESDAY THROUGH SATURDAY/...
Through 06Z Wednesday...Changeable conditions over the next 24
hours with a mix of VFR/MVFR. Mainly VFR/light winds through 15Z
with only restrictions at KRUT where a period of steadier light
rains and occnl MVFR will prevail in the 06-12Z time frame.
Thereafter, two separate cold fronts drop south into the area by
this afternoon/evening with scattered light shower activity
expected. Scattered nature of activity warrants only VCSH in the
forecast at this point. Winds shift from light
south/southwesterly to northerly behind the boundaries with cigs
likely lowering to MVFR at northern terminals by later this
afternoon and this evening.

Outlook...

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

&&

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

&&

$$
SYNOPSIS...JMG
NEAR TERM...JMG
SHORT TERM...LaRocca
LONG TERM...LaRocca
AVIATION...JMG



 
 
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