Area Forecast Discussion
Issued by NWS Burlington, VT-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KBTV 011119
Area Forecast Discussion
National Weather Service Burlington VT
719 AM EDT Fri Jul 1 2016
Increasingly unsettled weather today as a upper level disturbance
and cold front spark heavy showers and strong to severe
thunderstorms this afternoon and tonight. Storms will be capable
of gusty winds, small hailstones and localized heavy rainfall.
Showers and thunderstorms move eastward by midnight tonight.
Breezy conditions, cooler temperatures and chances for showers start
the Independence Day Weekend Saturday. Mostly sunny skies and dry
conditions should lead to good conditions for outdoor holiday
plans Sunday and on Independence Day.
.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --As of 718 AM EDT Friday...No significant changes made to the
forecast. With this update, I`ve just accounted for current
observations in the forecast grids. Strong sunshine underway this
morning, but watching deck of mid-level cloudiness across western
PA/NY move pretty quickly eastward and will begin to overspread
our western zones arond noon. Steadier showers and embedded
thunder associated with cold front extends from near Toronto ON
southward to Cleveland OH. Prospects for strong to severe
thunderstorms today remains on track after reviewing some of the
more recent HRRR output. Highs should top out in the 70s to low
Previous near-term discussion issued at 429 AM follows...
Forecast remains on track toward an active Friday afternoon and
evening featuring strong to severe thunderstorms capable of gusty
winds, small hail and localized heavy rainfall posing some
hydrologic concerns as well.
Generally clear skies continue this morning under weakening
surface ridge, with 2-m temps running in the 50s to low 60s and
dewpoints in the upper 40s to mid 50s. However starting to see
mid-level height falls ahead of a neutrally-tilted 500 mb
shortwave trough with axis extending along the eastern shore of
Lake MI, with an associated cold front from the northern corner
of IN/OH into the lower Ohio Valley. Expect to see at least
mostly clear to partly sunny skies this morning, gradually filling
in by this afternoon from the southwest. Stage will then be set
for developing thunderstorms.
Overall, no significant changes noted from earlier thinking in
terms of instability/shear parameter space and setup. While we
should see steeper low-level lapse rates set up with the sunshine,
instabiilty will be limited to 1000 to 1300 J/kg of SBCAPE at best
due to surface dewpoints in the upper 50s to lower 60s. Dewpoints
only start to climb in the few hours ahead of developing storms,
as southeast low-level winds help tap into reservoir of mid/upper
60s dewpoints over the mid-Atlantic states. In terms of wind
fields and vertical shear, 500mb trough axis becomes negatively
tilted and we should then start to see an increase in mid-level
winds by mid afternoon into the evening, leading to southwesterly
0-6km shear vectors increasing into the 30-35 knot range by early
evening. Also noting that the sfc-1km shear is around 20 knots. So
CAPE and shear at least support stronger storms but will be aided
by forcing for ascent owing to the negative-tilt mid-level trough
and diffluent nature to the mid/upper flow. Nearly all convection-
allowing models (HRRR, BTV-4/6 and the ARW/NMM) show initial
storms developing in the central Adirondacks/Mohawk Valley region
of NY by around 17-18z and move northeast and merge into
clusters/small- scale bowing lines late this aftn into the evening
across the North Country. Think we end up seeing several strong to
a few severe storms late afternoon and evening, capable of gusty
winds (given DCAPEs of 1000 J/kg) and small hail (WBZ heights are
around 10 kft). See the Hydrology section for more details on the
hydro aspects, which will need to be carefully monitored even
though storms should be moving along. Have maintained enhanced
wording for gusty winds, heavy rain and small hail in the Wx
grids, with highest PoPs in the 20-03z period. Storms should pass
into NH by midnight, with residual slight chance PoPs west to
Looking at highs today in the 70s to lower 80s, with lows in the
50s with lowest low temps in NY and on the warmer end of that
range across VT.
-- End Changed Discussion --
.SHORT TERM /SATURDAY THROUGH SUNDAY/...
As of 429 AM EDT Friday...Saturday becomes our typical post
frontal regime with the upper low settling in over the area with
lowering heights, residual low level moisture and west to
northwest upslope flow allowing for showers, mainly across the
northern portion of the area closer to the upper low centered over
Quebec. It will be cool and breezy as well with highs only around
70 and northwest winds 15-25 mph.
.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
As of 429 AM EDT Friday...Daytime showers end and turning dry for
any firework displays sunday night.
Monday(4th) will be dry and seasonably warm. Late morning
temperatures in the 60s/70s will be ideal for any parades.
Broad ridge over the central US sets up for the rest of the week
with westerly flow and building heights thus warming trend through
the week and dry. Late week there are slight differences in the
models on a potential disturbance in the wnw flow but for now...warm
and dry. Dewpoints/moisture seem manageable until late week when
surface high slides east allowing southwest flow and greater
humidity with perhaps another northern stream upper low and trough
for stormy next weekend.
.AVIATION /11Z Friday THROUGH Tuesday/...
-- Changed Discussion --Through 12Z Saturday...VFR through the morning hours, though
focus shifts the afternoon and evening with strong to potential
severe thunderstorms. Showers and strong storms starting around
18-21z as a cold front nears and eventually sweeps across the
area. Frequent lightning, gusty winds capable of localized
turbulence, at least small hail and heavy downpours capable of
brief IFR visiblility restrictions are all possibilities in the
strongest cells. Maintained MVFR +SHRA group in the TAFs to
reflect when the period of greatest strong thunderstorm threat
would be. Later TAFs issuances can better define specific
timing/impact. Cold front exits into NH by 06z with dissipating
showers and a west wind shift. Will need to watch for possible
MVFR ceilings after 06z, particularly for the NY TAF sites.
Outlook 12Z Saturday through Tuesday...
12Z Saturday through 12z Sunday...Generally VFR, though daytime
VFR/MVFR visibility showers as an upper level disturbance passes
to our north. Gusty northwest winds of 25-30 knots likely to be
biggest impact on aviation, strongest during the afternoon hours.
12Z Sunday through Tuesday...VFR under high pressure during the
day. Possible overnight IFR to VLIFR fog at SLK and MPV each
-- End Changed Discussion --
As of 429 AM Friday...We continue to monitor potential for
localized heavy rainfall in strong to severe thunderstorms this
afternoon and evening. Strong QG forcing should help produce a
widespread rain for the area. Precipitable water values increase
during the afternoon and evening to around 1.3 to 1.5", moderately
high but again not excessive. The progressive nature of the mid-
level trough and storm motions should keep cells/lines moving, but
NEly Corfidi vectors of 10-15 kts supports potential for some
backbuilding. Will need to monitor convective evolution today for
this potential. Flash flood guidance still is rather high, but
areas that will need to monitor for heavy rainfall capable of
small areas of flash flooding are in Franklin and western Clinton
Counties in NY and Orleans, Caledonia and Essex Counties in VT
given the flash flooding that occurred in these areas early in the
week. Urbanized areas and mountainous terrain are common trouble
spots as well. Main-stem river flooding is not anticipated.
As of 429 AM Friday...Those boating on Lake Champlain today
should be aware of the potential for strong to severe
thunderstorms near the Lake during the afternoon and evening
hours. Storms will be capable of lightning, small hail and gusty
winds creating choppy waves. A Lake Thunderstorm Advisory may
become necessary today as storms potentially develop/move toward
Lake Champlain. Be prepared to seek safe harbor if threatening
weather approaches today.
Saturday will feature gusty northwest winds, likely in the 15 to
25 knot range.