Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 212319 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 719 PM EDT Thu Jul 21 2016 .SYNOPSIS... 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/...
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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. Previous Discussion... 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 midnight. 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 hours. 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`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. .Friday night... Any shower/thunderstorm activity wanes after midnight but still influenced by northwest cyclonic flow which will keep shower threat especially across NC-NE Vermont.
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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 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.
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&& .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 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. && .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 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...SLW NEAR TERM...Evenson/SLW SHORT TERM...JMG LONG TERM...JMG AVIATION...JMG is the U.S. government's official web portal to all federal, state and local government web resources and services.