Area Forecast Discussion
Issued by NWS Burlington, VT-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KBTV 212319
Area Forecast Discussion
National Weather Service Burlington VT
719 PM EDT Thu Jul 21 2016
Periods of showers and thunderstorms are expected after midnight
tonight through Saturday as a frontal system moves slowly through
the region. Some of the storms will have the potential to become
strong or severe. Another round of thunderstorms is possible on
Monday. Meanwhile Sunday looks dry and seasonable.
.NEAR TERM /THROUGH FRIDAY NIGHT/...
-- Changed Discussion --As of 718 PM EDT Thursday...Overall forecast in good shape with
just some minor tweaks to the convective potential for the next
few hours as upstream convection weakening and it now looks like
if anything moves into the region it will be after midnight.
Given the general consistency and thinking of the larger features
discussion is largely borrowed from previous shifts with slight
editing for current model runs and thinking.
.This Evening...Generally fair skies with high clouds from
gradually weakening MCS upstream across Great Lakes. Light south-
southwest winds but they will be increasing well ahead of surface
cold front and approaching shortwave along with increasing humidity
and thus will will result in low temps only dropping into the mid
60s to lower 70s.
.Tonight...Ring of Fire activity (last night/this morning) that
is typical in these synoptic patterns was largely missed by models
and was on the leading edge of strong elevated mixed layer...
moisture pooling along boundary and shortwave. The shortwave and
EML associated with that feature moves into eastern Great Lakes
overnight and eventually North Country early Friday morning. This
activity has continued across the Great Lakes today and could see
some of it holding together and moving into our area after
Friday: The initial shortwave and likely decaying MCS will shift
east across area for temporary stabilization along with some
shortwave ridging. Sounding data brings in decent dry air advection
that should allow for plenty of sun to develop and thus heat up for
high levels of surface instability (GFS has CAPE around 2000
J/kg, and still some remnants of elevated mixed layer and waiting
on a trigger..perhaps a pre-frontal trof in the early-mid aftn
Very dry mid-levels and strong CAPES...surface and aloft support
some downward momentum for winds and large hail given wet bulb
zero levels drop below 10K.
Otherwise the main trigger should be toward evening hours. Low level
instability still prevalent early and area in closer proximity to
approaching stronger nrn stream shortwave...surface front as well as
nose of 300mb and 500mb jets moving into area by 00z Sat enhancing
any lift. The elevated mixed layer is in question again...it`s been
back and forth with models if we had it I`d feel more confident
about this period but even without it still should be enough support.
Any shower/thunderstorm activity wanes after midnight but still
influenced by northwest cyclonic flow which will keep shower threat
especially across NC-NE Vermont.
-- End Changed Discussion --
.SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/...
-- Changed Discussion --As of 303 PM EDT Thursday...By Saturday another potentially
active weather day is in store as secondary and fairly robust
northern stream shortwave drops southeast through the region.
Reasonably steep mid-level lapse rates and boundary layer
instability along with 35 to 50 kts of deep-layer shear all
support this idea. Thus prior forecast of scattered to numerous
showers/storms, a few strong to perhaps severe, still appears
reasonable and have leaned toward a blend of consensus and WPC
progs for timing of pops/weather. High temperatures in the 78 to
86 range and rather humid.
Evening convection then wanes fairly quickly from midnight onward if
not sooner Saturday night as shortwave energy pulls across the area
and is replaced by building heights and surface high pressure by
Sunday morning. Again, a few of the storms could be on the strong
side early. Low temperatures in the 50s to around 60. There could be
some patchy fog here and there but given lingering wind fields aloft
confidence is on the lower side at this point.
-- End Changed Discussion --
.LONG TERM /SUNDAY THROUGH THURSDAY/...
As of 303 PM EDT Thursday...High pressure then builds atop the
region on Sunday providing for an ideal mid-summer day with plenty
of sun and moderate humidity levels. After a partly cloudy and
seasonably mild night on Sunday focus then turns to the next
shortwave and attendant surface front approaching from the Great
Lakes and southern Canada. Global models suggest another
potentially active weather day with several favorable factors
coming into play. Time will tell but the idea of another round of
scattered to numerous showers/storms still appears reasonable at
Behind this system dry and seasonable mid-summer weather is expected
from Tuesday onward into next Thursday as surface high pressure is
bridged aloft by zonal/westerly flow. Temperatures should
average within a few degrees of seasonal norms with daily highs
in the upper 70s to mid 80s and overnight lows generally in the upper
50s to mid 60s.
.AVIATION /23Z Thursday THROUGH Tuesday/...
Through 18z Friday...VFR through 08Z with a few clouds around 060
AGL at KMSS/KSLK but otherwise above 200 AGL. After 06Z moderate
confidence of showers/storms and/or a convective complex to
approach from the northwest with some possibly stronger cores in
the 08-12Z time frame at northern terminals, though overall trend
should be for activity to be weakening over time. MVFR
visibilities possible with this activity with cigs remaining
generally VFR. Again, confidence remains moderate as CAM output
is not handling current convective complexes across the northern
Great Lakes into central Ontario/western Quebec that well. Some
minor southwesterly LLWS concerns to 40 kts in the pre-dawn hours
ahead of the potential convection otherwise mean southerly flow to
12 kts with terrain/lake-driven variations. After 12-15Z
lingering showers/isolated storms should weaken/exit south and
east with VFR continuing. Winds mainly south to southwesterly 6 to
12 kts and trending moderately gusty.
Outlook 18z Friday through Tuesday...
Fri-Sat...VFR, with scattered brief MVFR/IFR in showers and
thunderstorms. Some thunderstorms may contain strong winds and
Sun...Mainly VFR under weak high pressure.
Mon/Monday night...VFR with scattered brief MVFR/IFR in showers
and thunderstorms with frontal passage.