Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 232323 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 723 PM EDT Tue May 23 2017 .SYNOPSIS... Weak high pressure across the northeastern United States brings tranquil weather conditions across the North Country through tonight. There may be patchy fog development in some of the favored river valleys overnight, especially east of the Green Mountains. A weak upper level disturbance may bring isolated rain showers or a thunderstorm Wednesday afternoon, mainly across the higher terrain areas. Temperatures will continue to moderate Wednesday, with afternoon highs into the mid 70s in most sections. A more significant low pressure system evolving across the Ohio Valley and mid-Atlantic region will bring potential for a more widespread rainfall to the North Country Thursday afternoon through Friday. && .NEAR TERM /THROUGH WEDNESDAY NIGHT/... As of 623 PM EDT Tuesday...Minor update this evening to introduce somewhat more clouds across the northwestern counties per latest satellite imagery and sfc observations. A very weak surface trough draped across the SLV is also producing widely scattered light showers or sprinkles as of 22Z and have introduced just an outside shot of a shower along the intl border from the Green Mtn spine west through 8-9 pm or so. Some higher res output, most notably the BTV 4 km WRF also suggesting a brief sprinkle/light shower may affect the northern Champlain Valley in this time frame as well, but given lack of returns currently have downplayed this scenario. The rest of the forecast remains in great shape. Have a great evening. Prior discussion... Tranquil weather expected tonight with dry conditions and light winds. Weak high pressure across the mid-Atlantic coast remains the controlling weather feature overnight. Seeing a mix of sct fair weather cumulus clouds and some thin cirrus this afternoon. The cumulus clouds will dissipate with onset of diurnal cooling this evening. It appears we`ll be within a relatively cloud free axis tonight extending from wrn PA newd across nrn NY/VT. As such, could see enough radiative cooling to reach crossover temps, leading to patchy fog development 06-11Z in the favored river valleys east of the Green Mtn spine, as well as within the nrn Adirondack region. Overnight lows generally expected mid- upr 40s across the ern half of VT, and within the nrn Adirondacks. Should see lows around 50F in the immediate Champlain and St. Lawrence valleys. Low pressure develops east of NJ Wednesday morning, with mid- level vort axis lifting nwd across NY and New England. Meanwhile, at low levels, surface heating should generate some sfc-based CAPE (100-300 J/kg), especially across the higher terrain. Combination of subtle mid-level forcing and surface based instability should result in isold showers and perhaps a thunderstorm across the higher terrain of the Adirondacks and Green Mtns Wednesday aftn. Mentioned a slight chance across valley locations (20 PoPs) with PoPs closer to 30% across the higher terrain. Overall low-mid level flow fields are weak, so any convective activity that does develop should be relatively slow moving. A few mountain locations may see 0.10-0.20" precipitation with this activity. Highs Wednesday generally in the low-mid 70s. Any diurnal SHRA/TSRA activity should dissipate toward evening. Large closed mid-upr level low across the OH/TN valleys will slowly shift ewd Wednesday night, bringing increasing clouds, and a slight chance of rain toward daybreak across nrn NY. The increased clouds will mitigate radiative cooling with lows 50-55F in most sections. && .SHORT TERM /THURSDAY THROUGH FRIDAY/... As of 326 PM EDT Tuesday...Brief period of quiet weather ends on Thursday as the pattern becomes active again to end the work week. The morning will begin dry with high pressure holding strong, but as low pressure over the Ohio Valley begins to shift northeast into the eastern Great Lakes, deep layer moisture along an approaching warm front will spread showers from southwest to northeast across the North Country. Rainfall should be relatively light with daytime amounts only in the 0.10-0.25" range and temps topping out in the 60s to perhaps low 70s. Late Thursday afternoon into early Friday night the forecast becomes a bit more uncertain in regards to precip potential as models are trending towards a weak mid-level dry slot building over southern/central portions of the area as the low transfers energy to the southern New England coastal waters and the deeper warm frontal moisture shifts northward. During this time a strong low/mid level east/southeasterly jet of 35-45kts develops and while the window for mixing these winds to the surface is narrow, the potential exists for wind gusts of 30-45 mph along the downslope communities of the western slopes of the Green Mountains in Chittenden, Addison and Rutland counties. That window closes quickly towards midnight though and through the remainder of the night as the upper level and surface low consolidate and strengthen over Cap Cod advecting a moist stable marine layer into the region with rainfall becoming prevailing across the majority of the region right through Friday afternoon. Additional rainfall amounts of 0.25-0.75" are expected with mild lows in the 50s Thursday night, and cooler highs in the 50s for Friday. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... As of 326 PM EDT Tuesday...Coastal low pressure exits east Friday night and in its wake surface high pressure and a somewhat flat upper ridge build into the Northeast for Saturday and Saturday night offering dry conditions and seasonal temperatures. Sunday looks to be mostly dry as well as deepening upper level low pressure over the northern Plains amplifies the ridge over the Northeast Sunday morning, but increasing moisture advection on southwesterly flow combined with bits of shortwave energy ejecting out of the upper low will renew chance as for showers and possibly thunderstorms Sunday afternoon. Best chance for widespread rain during the period comes Sunday night through Monday as the upper low shifts over the Great Lakes, with continued chances Tuesday as the low barely moves east and the region remains unsettled. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/... Through 00Z Thursday...Generally VFR conditions with light winds expected throughout the TAF period. SCT/BKN cigs in the 060-090 AGL range expected this evening into tonight with thickening higher deck above 200 AGL pushing in from the southwest later tonight. An isolated light shower or sprinkle will be possible at KMSS/KPBG/KBTV through 01Z, but paucity of coverage warrants ommision from the forecast at this point. After 14Z Wednesday SCT/BKN VFR cigs continue with persistent BKN higher overcast under light wind regime. Isolated to widely scattered showers and a possible thunderstorm will be possible after 18Z, but mainly focused across higher terrain. Again, lack of areal coverage warrants omission from the current terminal forecasts at this point. Outlook... Wednesday Night: VFR. SCHC -SHRA. Thursday: VFR. Breezy. Chance SHRA. Thursday Night: VFR/MVFR. Definite RA. Friday: MVFR. Definite RA. Friday Night: VFR. Slight Chance SHRA. Saturday: VFR. Slight Chance SHRA. && .EQUIPMENT... The WSR-88D at Burlington, VT (KCXX) will be unavailable from Tuesday May 23, 2017 through Friday May 26, 2017. During the outage, radar coverage is available from adjacent radar sites including Montague, Albany, and Buffalo, NY and Gray ME. A new signal processor will be installed, which replaces obsolete technology, improves processing speed and data quality, provides added functionality, and supports IT security. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Banacos NEAR TERM...JMG/Banacos SHORT TERM...Lahiff LONG TERM...Lahiff AVIATION...JMG EQUIPMENT...Team BTV is the U.S. government's official web portal to all federal, state and local government web resources and services.