NEK Weater

Forecast Discussion for BTV NWS Office
FXUS61 KBTV 241921

Area Forecast Discussion
National Weather Service Burlington VT
321 PM EDT Mon Jul 24 2017

An upper level low pressure will keep showers and clouds around
through Tuesday morning. Drier weather moves in late Tuesday
with high pressure and remains in place for a day or two. A
cold front will bring a renewed threat of showers and storms on
Thursday. Fair weather then returns for Friday into the weekend
with temperatures near seasonal late summer norms.


As of 230 PM EDT Monday...robust shortwave continues to move
eastward toward the region, however the best upper level
diffluence/divergence is beginning to shift east across Vermont,
so not expecting any additional torrential rains for northern
NY. Can`t rule out an isolated t-storm, primarily in northern
NY, but instability is pretty meager, and really better farther
south toward central NY. Also not expecting any problems in
Vermont. Yes, it`s continuing to rain, but given the cool
easterly flow advecting in a cool, stable airmass from the
Atlantic, there is no low level instability to work with for
t-storms or deeper convection to develop. Expect about another
0.15" across south- central VT to near 0.50" across northern
sections where the precipitation will be more concentrated
before the bulk of the steadier precipitation ends by mid-

Overnight, upper trough and associated shortwave move across the
region. Lots of low-mid level moisture will remain, so showers
will continue, though forcing is very weak. No low level jets.
Heck, not much in the way of wind throughout the atmosphere. So
expecting clouds to hang tough, with a considerable amount of
low level stratus and light fog to make for a murky night. All
those clouds won`t allow temperatures to fall much overnight
(maybe 5 degrees), with 50s for the entire area.

Tuesday, troughiness slowly gets pushed out to the southeast as
upper level ridging tries to build to our west. The good news --
we should end the day with a good deal of sun and drier conditions.
However, the bad news is that I really mean the end of the day.
Up until mid/late afternoon, murky conditions with lots of
clouds and a few light showers will be around. The very late day
sun will allow temperatures to top out in the upper 60s,
especially in northern areas where clearing happens first.

Tuesday night, high pressure builds over the region. Calm, clear
and drier airmass will allow for good radiational cooling,
especially outside of the larger valleys. We should see
temperatures drop into the 40s for many colder spots in eastern
VT and the `Dacks. The NAM MET guidance has Saranac Lake going
down to 36F (brrr) degrees. Don`t think it will be quite that
cold, but 39-41F is quite reasonable for that notoriously cold
location. With the wet ground, patchy dense fog is also expected
in the river valleys and sheltered valleys.


As of 320 PM EDT Monday..1025mb high pres directly overhead at
12z Weds morning will provide region with dry conditions and
near normal temps. Have continued with previous forecasters idea
of patchy valley fog thru 13z...before mixing increases and fog
dissipates. Otherwise...progged 850mb temps between 10-11c by
21z weds support highs lower 70s mtn towns to near 80 warmer
valley locations. With plenty of sun have trended toward the
warmer side of guidance. Weds night...mid/upper level clouds
increase as winds turn southerly ahead of our next surface
boundary. Best 1000 to 500mb rh fields and forcing stays west of
our anticipating a mainly dry night. Temps fall
quickly early...but level off or increase slightly after
midnight with clouds and gradient flow increasing. Mainly mid
50s to l/m 60s depending upon location. Have mention schc/chc
pops nw sections by 12z Thursday. Clouds/winds should confine
fog/br to the immediate ct river valley on weds night.

Thursday...Mid/upper level trof digs across the northern Great Lakes
into the NE Conus with associated surface cold front. Still some
uncertainty on timing of system with gfs 3 to 6 hours faster than
the latest 12z NAM solutions. Timing of boundary will play an
important role on amount of instability and magnitude of convection.
Slower arrival would support greater instability with CAPE values
between 1200-1800 j/kg...combined with 0 to 6 km shear of 35 to 45
knots...indicating a pre-storm environment favorable for stronger
storms with some organization. Meanwhile...faster GFS shows less
destabilization with CAPE values of 400 to 800 j/kg...mainly over
northern NY...with plenty of clouds limiting sfc heating over VT.
Both solutions show favorable deep layer shear associated with 700
to 500mb wind max of 35 to 45 fast mid level flow...just
lacking instability with potential 5h energy. Some of the stronger
convective elements would be capable of producing locally heavy
rainfall given pws between 1.75 and 2.0 and the progged forcing
associated with potent 5h energy. Meanwhile...12z ECMWF is
completely different with much slower and deeper trof with 996mb low
pres developing over central NY. This scenario would support a
general widespread rainfall with embedded convective elements. Will
continue with idea of chc to likely pops for showers with isolated
to scattered thunder potential. Too much uncertainty for enhanced
wording...but time frame should be watched for potential stronger
convective elements. Temps on Thurs are tricky with potential for
morning showers followed by some sun...before more aftn
showers/storms arrive with progged 850mb temps climbing to near 14c.
Will mention highs l/m 70s mtns towns to lower 80s warmest valley


As of 320 PM EDT Monday...Mid/upper level trof continues to influence our cwa on Thurs night
into Friday and depending upon timing...showers with embedded storms
could linger into midday Friday. Will continue to mention chc/likely
pops during this time plenty of uncertainty with
timing/magnitude of trof and associated surface low pres/boundary
continues to be advertised in model solutions. Cooler and drier air
eventually returns by the surface high pres builds into
our cwa. Progged 850mb temps between 9-11c Friday support highs
mainly 70s...but if ecmwf surface pres was to verify easterly winds
and much cooler temps would be possible...especially eastern/central
vt. Have played mid of the road with superblend guidance and will
fine tune as event become closer.

For the weekend...eventually 1020 mb high pres builds from the Ohio
Valley/Great Lakes...with building mid/upper level heights. This
will provide a mainly dry weekend with seasonable temps. Highs mainly
in the upper 60s to mid/upper 70s with lows mid 40s to mid 50s and
much lower humidity values. Expect some areas of patchy fog in the
deeper/protected valleys of northern NY and parts of central/eastern


Through 18Z Tuesday...Not an easy forecasting situation.
Conditions range across the entire gamut, IFR to VFR (and
believe it or not, BTV has been IFR, while SLK has been VFR).
The steadier rainfall will be coming to an end by mid-evening,
however scattered light showers will remain through Tuesday
morning. Ceilings are expected to decrease to MVFR, if not IFR
levels, for all TAF locations as stratus clouds develop and
become widespread. Light fog will also develop in many areas,
though visibilities should remain between 2-5sm. Clouds will
begin to break up just prior to 18z Tuesday, though widespread
VFR not expected until just after the TAF period for all sites.


Tuesday Night: VFR. Patchy FG.
Wednesday: VFR. Patchy FG.
Wednesday Night: VFR. Slight Chance SHRA.
Thursday: VFR/MVFR. Likely SHRA...Chance TSRA.
Thursday Night: VFR. Chance SHRA.
Friday: VFR/MVFR. Slight Chance SHRA.
Friday Night: VFR. NO SIG WX.
Saturday: VFR. NO SIG WX.





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