Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 211903 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 303 PM EDT Thu Jul 21 2016 .SYNOPSIS... 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 Monday. && .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 midnight. 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/...
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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/...
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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 this point. 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 hail. Sun...Mainly VFR under weak high pressure. Mon/Monday night...VFR with scattered brief MVFR/IFR in showers and thunderstorms with frontal passage. Tuesday...VFR/high pressure. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Sisson NEAR TERM...Sisson/SLW SHORT TERM...JMG LONG TERM...JMG AVIATION...JMG

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