Area Forecast Discussion
Issued by NWS Burlington, VT-- Highlight Changed Discussion --
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FXUS61 KBTV 211903
Area Forecast Discussion
National Weather Service Burlington VT
303 PM EDT Thu Jul 21 2016
Ridge of surface high pressure will remain over the North Country
today, providing the region with warm, sunny, and dry weather.
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
.NEAR TERM /THROUGH FRIDAY NIGHT/...
As of 106 PM EDT Thursday...Forecast going to plan...noticed some
convective streaks across ontario well ahead of MCS thus
suggesting some instability which just lends to greater confidence
of nocturnal event tonight.
Previous discussion...Any early morning fog will burn off
in the next hour, then it will be a very nice, warm, and sunny
late July day with high temps 85 to 90.
Large ridge of surface high pressure will remain over the region
right through Thursday with dry weather. Some high level cirrus
clouds are possible from time to time with NW flow aloft from
thunderstorms up near James Bay early this morning.
Highs today will be warmer than normal with ample sunshine and
warming aloft as 850 temps rise to 16 to 18C. Expecting highs 85
to 90. Winds will become south to southwest and some gusts to 20
knots in the St. Lawrence Valley.
Late Thursday night into early Friday morning A surface front in
Ontario/Northern Great Lakes will be slowly approaching with
increasing chance of showers and thunderstorms, mainly after
Deep low-level layer moisture with PWATS >1.5 inches advecting
ahead of front. There will be elevated instability with CAPE over
1000 J/kg in the St. Lawrence valley by 09-12Z Friday. The boundary
layer should be stable with instability resulting from lifting
parcels from the 900 mb level. There is also the remnants of an
elevated mixed layer with 700-500mb lapse rates around 7C/km. Lift
to be provided by a shortwave trough and associated QG forcing and
divergence ahead of exit region of 300mb jet. They may be a
mesoscale convective complex in northern Great Lakes/Ontario
moving into the area during late Thursday night/early Friday
morning as a result. Not really looking for much of a severe
threat tonight but can`t rule out the possibility of a few
stronger thunderstorm cells toward Friday morning.
South to southwest winds will continue all night tonight and as a
result low temps will only be in the mid 60s to lower 70s.
.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 humdid.
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.
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.LONG TERM /SUNDAY THROUGH THURSDAY/...
-- Changed Discussion --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.
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.AVIATION /19Z 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.