Area Forecast Discussion
Issued by NWS Burlington, VT

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788 FXUS61 KBTV 302356 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 756 PM EDT Thu Jun 30 2016 .SYNOPSIS... High pressure remains in control across the North Country this evening and overnight with mainly clear skies and light winds. A frontal system approaching from the Great Lakes region will bring widespread showers with embedded thunderstorm activity Friday afternoon into Friday evening. A few strong to severe storms are possible with hail, gusty winds, and locally heavy rainfall. The frontal system ushers in cooler air for Saturday, with high temperatures only in the upper 60s to lower 70s. A few showers are also possible across the Northern Mountains on Saturday. Increasing sunshine and dry conditions are forecast for Sunday and the Independence Day holiday. && .NEAR TERM /THROUGH FRIDAY NIGHT/... As of 756 PM EDT Thursday...Beautiful early summer weather expected for tonight with clear skies, light winds and seasonable temperatures. Other than some nominal tweaks to winds with latest LAMP output the forecast remains largely unchanged. Held onto some patchy fog in favored locales, though this should be fairly limited in duration and areal coverage given the nocturnal period is near its yearly minimum. Have a great evening. Prior discussion from 224 PM EDT Thursday... Main focus during the near-term period is potential strong to severe thunderstorms and localized heavy rainfall for Friday afternoon into Friday evening. Tonight: Conditions will remain tranquil in the meantime with ridge surface and aloft in place this evening and through much of the overnight. Some flat fair weather cumulus clouds dotting the higher terrain will dissipate with onset of diurnal cooling cycle this evening, setting up clear skies and good radiational cooling overnight. Winds are generally light through the overnight, but will see light S-SE flow develop from the Champlain Valley wwd toward daybreak as surface low moves ewd across lower Michigan, and high pressure shifts east of New England. With generally light winds, should see some patchy fog develop after 04-05Z in the deeper valleys within the northern Adirondack region and central/ern VT. That said, increase in 925mb flow to near 15kts toward daybreak may cause some increased low-level mixing and preclude fog from becoming dense or very widespread. Overnight lows generally in the low-mid 50s, except locally in the upr 50s near Lake Champlain with developing south winds...and also in the mid-upr 40s in the nrn Adirondacks given current dewpoint readings. Friday: Vigorous mid-level trough across lower Michigan at 12Z will shift enewd with increasingly cyclonic flow and height falls across nrn NY into VT during the afternoon and early evening hours. Low-mid level wind fields become moderately strong with sfc to 6km bulk shear reaching 30kts by 18Z and around 35kts at 21Z. Strong differential PVA moving into nrn NY coincides with best insolational heating, which should aid in low-level lapse rates and convective initiation. Given strength of forcing for ascent, not much question on development of showers and embedded tstms across nrn NY and s-central VT beginning around 18Z, and then spreading ENEWD across the Champlain valley mid-late afternoon, and central/ern VT late afternoon into the evening hours. Have included PoPs 80-90% during the peak heating hrs. Primary limiting factor for widespread severe wx will be limited moisture return. Current 2-m dewpoints generally upr 40s to lower 50s across the region, and expected to rise into the upr 50s by early after Friday. These moisture values combined with high temps in the upper 70s to lower 80s will contribute to fairly modest SBCAPE peaking around 1000 J/kg. That said, believe incipient updrafts can make use of excellent low-level hodograph structure (0-1km SRH around 200 m2/s2 at BTV per NAM-12km) and favorable deep- layer shear for a few rotating storms, which can augment relatively low CAPE profiles. As such, will carry enhanced wording at this time with hail and gusty winds mentioned in the forecast. Depending on overall convective evolution, will need to watch for any training cells across the nrn Adirondacks and n-central/nern VT where soils remain moist from rainfall past 48-72 hrs (see hydro section below for additional details). Overall QPF amts generally 0.50 to 0.75", but could see some locally higher footprints with any training thunderstorms. 3-hr FFG generally 2-3" attm. Friday night: 700-500mb shortwave trough acquires negative tilt across VT Friday evening, with going strong convective activity exiting across ern half of VT between 00-03Z. Thereafter, surface frontal passage brings westerly wind shift and lingering clouds/isold showers overnight. Low temperatures generally in the low-mid 50s. && .SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/... As of 328 PM EDT Thursday...Saturday and Saturday night we`ll see our typical post frontal regime with the aforementioned upper low settling up over the area post frontal passage. The morning should begin dry with a mid-level dry slot pushing through, but by the afternoon additional shortwave energy moving through the flow aloft combined with residual low level moisture and west/northwest upslope flow will allow for some scattered showers to develop, mainly across northern portions of the area. With this loss of insolational heating, any showers should dissipate though by the late evening with clearing skies developing Saturday night as high pressure edges into the region. Under the influence of the upper low, temps through the period will be on the cool side of normal for early July, with highs ranging only from the mid 60s to low 70s, and lows in the mid 40s to mid 50s. && .LONG TERM /SUNDAY THROUGH THURSDAY/... As of 328 PM EDT Thursday...Long term period highlight will feature another prolonged dry stretch along with temperatures moderating back towards seasonal normals. Behind the departing trough for the early part of the weekend, surface high pressure will build into the region for Sunday with building heights aloft going into the early to middle part of next week. The result will be mainly dry conditions, partly sunny/clear skies and pleasant humidity. Highs will generally range from the mid 70s to low 80s, and lows mainly in the 50s mountains to low 60s valleys. && .AVIATION /00Z Friday THROUGH Tuesday/... Through 00Z Saturday...VFR/high pressure with light terrain- driven winds less than 10 knots expected through 15Z Friday. After 15Z advancing cold front will trigger scattered to numerous showers and thunderstorms across the region as winds trend southerly 6-12 kts and occasionally gusty with sct/bkn VFR cigs from 050-100 AGL developing. Some of the thunderstorms may become strong to locally severe with turbulence, gusty winds and hail possible along with brief MVFR/IFR. Timing of storms generally from 18-00Z from west to east after which activity should wane/exit east. Outlook 00Z Saturday through Tuesday... 00Z Saturday through 03Z Saturday...lingering showers/storms, a few strong to locally severe early will wane and exit east. 03Z Saturday through 12z Saturday...Areas of MVFR ceilings possible (mainly SLK/MPV) with westerly wind shift following frontal passage late Friday evening. Isold rain showers possible during Friday night, diminishing toward daybreak Saturday. 12Z Saturday through Tuesday...Mainly VFR through the period. Broad upper trough brings a chance of light rain showers across the northern mountains and International border area during the daylight hours Saturday. LIFR possible in fog MPV/SLK early Monday and Tuesday A.M., mainly 06-11Z. && .HYDROLOGY... As of 140 PM Thursday...Will be monitoring the potential for heavy downpours Friday afternoon and evening associated with the anticipated widespread showers and embedded thunderstorms. Strong QG dynamics (700-500mb vort axis moving SW to NE across the region) and associated surface front will move into environment across the North Country with MLCAPE values generally 500-1000 J/kg, and moderate PW axis of 1.3 to 1.5" during the mid afternoon through early evening hours. The mid-level trough is progressive in moderately strong swly flow, which may limit duration of heavier downpours in most locations. However, some indication of backbuilding potential of storms with MBE vectors NE at 5-10kts per NAM model soundings across central/nrn VT. So, will need to monitor for training cells as convective evolution occurs. Areas such as Franklin and western parts of Clinton County in NY as well as the northern VT counties of Orleans, Caledonia and Essex Counties would be slightly more vulnerable to flash flooding, given antecedent saturated soil conditions from rainfall past 2-3 days. Main stem river flooding is not currently expected. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Banacos NEAR TERM...JMG/Banacos SHORT TERM...Lahiff LONG TERM...Lahiff AVIATION...JMG/Banacos HYDROLOGY...Banacos/Loconto

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