Area Forecast Discussion
Issued by NWS Burlington, VT

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FXUS61 KBTV 222350
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
750 PM EDT Thu Jun 22 2017

.SYNOPSIS...
Showers and thunderstorms return to the region tonight and
tomorrow. Locally heavy rainfall is possible with stronger
showers and storms during the day Friday. A brief return to dry
weather is expected on Saturday before more showers return for
the early portions of next week.

&&

.NEAR TERM /THROUGH FRIDAY NIGHT/...
As of 719 PM EDT Thursday...Main change to the forecast for this
evening`s update was to hold back precip chances a few hours
based on latest radar and hi-res model trends. Still looking
like around midnight for arrival time in the St. Lawrence
Valley, but not until closer to 3-4AM for the Champlain Valley
and points eastward. Ahead of that, quiet conditions will
prevail with increasing mid clouds and light winds leading to
low temps mainly in the 60s.

Previous Discussion...Retreating warm front brings shower
and thunderstorm activity back to the region this evening and
overnight. Carrying pretty high pops later this evening and the
remainder of the overnight. Strong warm advection bringing
moisture rich air back into the region very quickly. PW values
rapidly increase back into the 1.75-2.00" range with deep warm
cloud depths suggests heavy rainfall a possibility. Overall
progressive nature of the system with a big convective component
in the afternoon hours suggests areal risk of flash flooding
remains low in any given location so no watches at the moment.
Isolated flooding remains possible given very moist soil
conditions.

Very challenging forecast for the daytime and evening hours
Friday. Kinematically speaking wind fields are favorable for
severe convection tomorrow. Deep layer shear in the 30-40 kt
range along with large sweeping low-level hodographs suggest
organized convection, including supercells. However, this is a
highly conditional risk given sufficient instability is able to
be realized. Morning shower activity, lots of low and mid-
level moisture would suggest that the sun will have a tough time
tomorrow developing any big CAPE. Despite good kinematic fields,
if there`s no instability, organized convection will be limited,
and pulse marginal severe at best would be the result, along
with the heavy rainfall threat. If we see a lot of sun tomorrow
and develop any meaningful amounts of instability a higher end
severe threat would be expected. Will have to continue to
evaluate the stability parameters in the forecast through
tomorrow evening. Best shot at getting warm will be in the
Champlain Valley where downslope southwesterly flow off the
Adirondacks may help to clear out low level cloud cover. Have
mentioned gusty winds and heavy rainfall in the forecast and
hazardous weather outlook.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY/...
As of 300 PM EDT Thursday...Mid/upper level trof will
deepen across the ne conus for the weekend with several embedded
vorts. Atmosphere will have much better dynamics to work with...but
moisture and stability profiles will be weaker than friday...so
expecting less areal coverage of showers and embedded rumbles of
thunder. Neither Sat or Sun will be a wash out...but will continue
to mention low chc pops between 18z-03z each aftn. Instability
ranges from 400 to 800 j/kg...with axis of highest values near the
international border each afternoon/evening with strong
mid/upper level westerly flow. Soundings show slightly better
instability with steeper lapse rates on Sunday aftn with the
potential for some localized gusty winds...but threat is limited
based on available energy. Progged 850mb temps btwn 10-12c
Saturday support mainly 70s with values falling btwn 7-9c on
Sunday supporting highs mid 60s to l/m 70s warmer valleys. Lows
mainly in the upper 40s to mid/upper 50s over the weekend.
Depending upon areal coverage of precip...some patchy fog is
possible in the deeper protected valleys. Mid level moisture
associated with remnants of Cindy may produce a light shower
early Sat morning across extreme southern Rutland/Windsor
Counties and have continued to mention low chc to cover this
potential.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
As of 300 PM EDT Thursday...Large scale synoptic pattern shows
mid/upper level trof persisting across the Great Lakes into the
ne conus. This general setup will support at or below normal
temps with chances for showers...as unsettled weather is
expected. Thermal profiles show limited instability with some
afternoon heating producing daily cape values between 300-600
j/kg. A rumble or two of thunder is possible...especially when
the strong dynamics arrive during peak heating hours...but
overall severe threat is limited. Have tried to focus higher
pops during the aftn/evening hours...except on Tues when better
dynamics and deeper moisture is present associated with
mid/upper level trof. Progged 850mb temps btwn 6-8c
Monday/Tuesday support highs in the mid 60s to lower 70s. These
low level thermal profiles slow warm back into the 9-11c by late
next week...supporting highs back into the mid 70s to lower
80s. Overnight lows range mainly in the mid 40s mountain valleys
to mid/upper 50s in the warmer urban areas of the Champlain
Valley.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
Through 00Z Saturday...Mainly VFR except becoming MVFR toward
12z mainly KMSS/KSLK. Clouds are moving in this evening as a
warm front now just past KBUF approaches from the southwest. The
front will bring rain showers to the TAF sites in NY shortly
after midnight reaching BTV in the pre-dawn hours Fri. There
is a chance of thunder as instability is advected in aloft, but
the risk is hard to pin down any one time or location to
include thunder at this time. The main warm front moves
northeast of the region 12-15z so expecting any showers and
thunder to become scattered and shown as VCSH in the TAFs as
surface based instability increases ahead of a cold front. The
frontal passage is expected tomorrow night.

Some chance of LLWS tonight at SLK/MSS for a few hours as
surface winds go light with increasing low- level jet aloft.
Surface winds will be generally light then increase from the
south and southwest at 10-20 knots with some higher gusts
possible during midday at BTV.

Outlook...

Friday Night: VFR. Chance MVFR SHRA...Slight Chance TSRA.
Saturday: VFR. Chance SHRA.
Saturday Night: VFR. Slight Chance SHRA.
Sunday: VFR. Chance SHRA.
Sunday Night: VFR. Chance SHRA.
Monday: VFR. Chance SHRA.
Monday Night: VFR. Slight Chance SHRA.
Tuesday: VFR. Chance SHRA.

&&

.HYDROLOGY...
An isolated flood threat on Friday. Last rainfall event
recharged streamflow across the region, and storms Friday will
be very efficient rainers given very high PW values and some
possibility of training given the wind field. In addition some
heavy rainfall overnight tonight may saturate surface conditions
for Friday afternoon convection. Can`t really pin down any one
location, and overall the system is pretty progressive so
widespread flash flooding is not expected at this time. Storm
total QPF of around an 1"-1.25" expected over central and
northern VT and northern NY...with lesser amounts to the south.
Don`t anticipate any mainstem river flooding at this time.

&&

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

&&

$$
SYNOPSIS...Manning
NEAR TERM...Lahiff/Manning
SHORT TERM...Taber
LONG TERM...Taber
AVIATION...Sisson
HYDROLOGY...Manning


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