Area Forecast Discussion
Issued by NWS Burlington, VT

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FXUS61 KBTV 162316

Area Forecast Discussion
National Weather Service Burlington VT
716 PM EDT Fri Aug 16 2019

A warm front draped across the region will continue to provide a
focus for scattered showers and a few thunderstorms this evening
into tonight. A stronger upper level disturbance moving in from
the west will result in the potential for stronger thunderstorms
late Saturday afternoon into Saturday evening, with stronger
storms containing gusty winds and brief heavy downpours. Valley
high temperatures near 80 are expected on Saturday, followed by
highs in the mid to upper 80s to begin next week.


As of 710 PM EDT Friday...Showers and thunderstorms have had a
tough time getting going this afternoon with the only forcing
mechanism available today being the terrain of the Adirondack
and Green Mountains. We have yet to see a lightning strike in
our forecast area as narrow updrafts have really choked off the
afternoon convection with CAPE values between 500 and 1000 J/kg
just not enough to support stronger storms. That being said,
there is a strong thunderstorm in northern Hamilton County that
could move into Essex County New York by the top of the hour. It
seems the most robust convection should begin to taper off with
the loss of heating as the sun begins to set. However, continued
showers activity looks likely based on broad cyclonic flow
aloft. All of the CAMs are showing spotty showers across the
forecast area through the overnight hours so have kept the
mentioned of scattered showers in the forecast. A rumble of
thunder is possible but unlikely with CAPE values less than 500
J/kg expected tonight.

Previous Discussion...Primary forecast problem over the next
24-36 hours will be coverage and strength of convective storms
across the North Country. Surface warm front extending from
WSW-ENE across nrn NY and nrn VT has become ill-defined this
afternoon, but is associated with rich moisture with dewpoints
about 10deg higher than yesterday (in the low-mid 60s at 18Z).
Absence of mid-upper level forcing is a limiting factor this
afternoon and evening. However, just enough heating (highs upper
70s to around 80F) combined with orographic ascent should
result in convective initiation across the nrn Adirondacks, and
possibly across the Greens through early this evening. Any
storms that do develop should track enewd at 20-25 mph. Surface-
based instability is highest across nrn NY, up to 1000-1500
J/kg, and stronger cells should generally be across nrn NY
through this evening. Maintained PoPs near 35-40 percent through

Can`t rule out some continued isold/scattered rain showers
overnight with weak, cyclonically curved flow aloft and weak
forcing. PoPs generally 20-30 percent overnight, with a slight
chance of thunder with minimal CAPE present in NAM/RAP forecast
soundings. Overnight lows will remain warm with humid air mass
and variable low cloudiness expected. Lows generally in the 60s,
and locally 68F near BTV with continued south winds 5-10 mph in
the Champlain Valley overnight.

On Saturday, the 12Z GFS and ECMWF indicate a stronger
700-500mb shortwave trough tracking enewd from sern Ontario into
the North Country, coincident with peak daytime heating. While
low-level gradient flow is light with modest low-level shear,
sfc-6km shear values increase to 35-40kt with approach of
shortwave trough. Though mid-level lapse rates are only near
6C/km, noting 2-m dewpoints increasing to 66-68F range and PBL
temps into the low 80s...should be sufficient for CAPE values of
1000-2000 J/kg per 12Z HREF mean values. Combination of factors
suggest somewhat better potential for robust convective
updrafts and greater areal coverage of storms. Consistent with
consensus of CAM output, should see scattered thunderstorms
develop by mid- afternoon across nrn NY before spreading ewd
into the Champlain Valley and central VT late in the
afternoon/evening. Increased PoPs to 55-65 percent during peak
heating hours with mention of gusty winds with stronger cells.
Also, updated the Hazardous Weather Outlook to highlight
potential for a few stronger storms based on present
indications. High temps in the mid 70s to lower 80s on Saturday.
Should see convective activity wane after 00-03Z Sunday as best
synoptic forcing departs ewd and with onset of diurnal cooling
cycle. Lows Saturday night generally 62-67F, warmest in the
Champlain Valley.


As of 305 PM EDT Friday...A shortwave ridge will move overhead
Sunday morning bringing a brief reprieve from shower activity
to the area. As the day progresses however, a warm front will
push through the area from southwest to northeast, increasing
temperatures, humidity, and precipitation chances as it moves
through. Increasing southwesterly flow will allow 925 mb temps
to climb to over 20C by Sunday evening and precipitable water
values to increase to around 1.75 inches. As a result,
conditions will feel increasingly warm and muggy as we close out
the weekend. Highs Sunday will be in the low to mid 80s and
lows Sunday night will be in the mid 60s to around 70. Showers
and thunderstorms will increase in coverage through Sunday
evening as instability increases. Given 1000+ J/kg progged
MLCAPE and 0-6 km shear values 30+ kts, some storms could become
strong with gusty winds being the main storm threat. Any
thunderstorms that do develop look to be isolated to scattered
in nature however given the lack of upper-level support along
with the absence of much low-level convergence. Any showers and
thunderstorms that do develop will weaken after sunset Sunday,
but additional showers will develop in the early morning hours
on Monday as another frontal boundary moves through.


As of 305 PM EDT Friday...The long term forecast continues to look
warm and unsettled as ridging over the western Atlantic directs
warm, moist air toward New England. At the same time, a series
of upper-level waves will quickly move through the progressive
zonal flow aloft, interacting with the unstable air mass to
create showers and thunderstorms Monday through Wednesday.
Daytime high temperatures during this time frame will be in the
mid to upper 80s, with muggy overnights with lows in the mid to
upper 60s. At this point, the highest chances for precipitation
looks to be on Wednesday as a cold front pushes through. Once
this front exits the area, models are continuing to indicate
high pressure building in towards the end of the week which
would bring drier conditions and a return to slightly below
normal temperatures.


Through 00z Sunday...Expect a mix of VFR and MVFR conditions
through the overnight period with the MVFR conditions most
likely east of the Green Mountains. A marine layer will work
westward overnight and may impact KMPV with some of the guidance
bringing them down to IFR ceilings. With the marine layer barely
ashore it`s tough to be so aggressive bringing the ceilings
down but will need to monitor overnight. Otherwise, scattered
showers will continue through the evening and overnight periods
but should be very spotty. More widespread and stronger
thunderstorms are expected Saturday afternoon which will have
the potential to bring some gusty winds and MVFR to IFR
visibilities with the strongest of storms.


Saturday Night: Mainly VFR, with local MVFR possible. Chance
SHRA, Slight chance TSRA.
Sunday: VFR. Chance SHRA, Chance TSRA.
Sunday Night: Mainly VFR, with local IFR possible. Chance SHRA,
Slight chance TSRA.
Monday: Mainly VFR, with local IFR possible. Chance SHRA, Chance
Monday Night: VFR. Slight chance SHRA.
Tuesday: VFR. Chance SHRA, Slight chance TSRA.
Tuesday Night: VFR. Chance SHRA, Slight chance TSRA.
Wednesday: Mainly VFR, with local MVFR possible. Chance SHRA,
Chance TSRA.




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