Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 301850 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 250 PM EDT Fri Sep 30 2016 .SYNOPSIS... Upper level low pressure over the Ohio Valley will weaken as it slowly lifts across New England over the upcoming weekend. Mostly cloudy skies and scattered showers will result, though pronounced periods of dry weather are also expected. With the abunance of clouds temperature ranges will be narrower than normal with seasonably cool daytime highs and relatively mild overnight lows through Monday. && .NEAR TERM /THROUGH SATURDAY/... As of 245 PM EDT Friday...A relatively quiet night remains in store for the forecast area. The blocking high pressure across central Quebec which has provided our area with ideal early fall weather will continue to slowly weaken while increasing mid to high level moisture increases in advance of upper level low pressure across the Ohio Valley. There has been some light shower activity associated with this latter feature across southern New England and portions of central/upstate New York this afternoon, though the abundance of dry air in the lower levels has largely inhibited this activity across our area. In regard to pcpn threat tonight I stayed close to inherited guidance with some emphasis on the latest CAM output which suggests the primary threat of light pcpn should occur across our western counties (mainly western Dacks/SLV) this evening, transitioning to areas of central/southern VT later tonight as better moisture plume rides northward. Areas across the northern Champlain Valley and in general the northernmost tier of counties should remain largely dry overnight. Low temperatures should be similar to last night given thickening upper cloud cover will limit raditional processes - mainly 40s to around 50. By tomorrow a mainly persistence forecast will be offered as upper low pressure will remain nearly stationary across the Ohio Valley allowing modest south to southeasterly flow to continue into our area. Deeper moisture and better threat for scattered light showers will be tied to either 1)a weak plume across central/upstate New York on the upper low`s eastern periphery, or 2)across southern/southeastern New England where a maritime airmass with PWATs to 1.5 inches will reside. Further north across the intl border and northern Champlain Valley conditions should again remain largely dry. Only notable larger-scale change was to lower high temperatures by several degrees over prior forecast. This is consistent with over half of the consensus blended output and in closer agreement with latest MOS guidance which show values mainly from the mid 50s to lower 60s (perhaps a few mid-60s in the SLV). && .SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/...
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As of 249 PM EDT Friday... Little substantive change noted in today`s 12z guidance suite pertaining to the forecast for Saturday night through Sunday night. A very slow-evolving upper low over the Ohio Valley begins to pivot north-northeastward through the period, and beginning to deamplify as it does so. The system will continue to advect Atlantic moisture northward, but will run into lingering weak subsidence associated with a weak ridge across our northern counties. Forecast challenge remains timing a period when PoPs may be highest. While PoPs are generally in the Slight Chance to Chance range through this period, overall forecast QPF is kept very low - on the order of a few hundreths. It looks at this point that Saturday night may be a period where a greater coverage of showers may exist, with a break Sunday before ramping up late Sunday night. While temperatures still trend above-normal compared to 30-year normals, blanket of overcast skies through the weekend will lead to narrow diurnal ranges with cooler highs and "milder" lows. Highs Sunday in the 60s, though may struggle to climb much above 60 in eastern VT. Lows Saturday night in the 40s to lower 50s and Sunday night upper 40s to mid 50s.
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As of 249 PM EDT Friday... Continuing a trend with last night`s 00z global guidance, today`s 12z guidance suite continues to indicate that Monday would offer the best chance at widespread, if light, rain. This is as the deamplifying upper-level low from the previous period evolves into an open wave trough and gets entrained in the broader belt of westerlies. While PoPs are the highest in the Monday period - high Chance to low Likely - precipitation is expected to be showery driven mainly by cold pool aloft and any weak instability that can be generated. Temps still in the 60s for highs and lows in the 40s/around 50. A period of generally dry conditions is then anticipated Tuesday through the remainder of the period, as CONUS 500 mb pattern becomes more amplified with a large upper level ridge over the eastern third of CONUS with a digging trough over the central US. Anticipating more sunny skies and larger diurnal temperature ranges (milder than normal highs in the mid 60s to low 70s and cooler but seasonable lows 40s to low 50s). Will be looking at how Matthew evolves over the next several days in the Caribbean/Bahamas, but at this point in time guidance does not suggest any impact to our area. See the latest forecasts at NHC`s website for more details on Matthew`s current and forecast evolution.
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&& .AVIATION /19Z Friday THROUGH Wednesday/... Through 18Z Saturday...Generally BKN/OVC mid to high level VFR cigs over the next 24 hours as upper low pivots to our distant southwest. Cigs mainly above 100 AGL until later tonight into Saturday when some patchy bkn cigs in the 050-090 AGL range may encroach into southern VT/KRUT terminal with a threat of light showers/sprinkles. Remainder of forecast area should remain largely dry/pcpn free through the forecast period. Winds generally light east to southeasterly with occasional gusts to 20 kts possible at KRUT through 00Z due to downsloping effects. Outlook 18Z Saturday through Tuesday... 18z Sat - 12z Tue: Mainly VFR with brief bouts of MVFR/sct showers as upper low drifts into the region while weakening over time. Much of the period will remain dry. 12z Tue onward: Mainly VFR with building high pressure. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...JMG NEAR TERM...JMG SHORT TERM...Loconto LONG TERM...Loconto AVIATION...JMG is the U.S. government's official web portal to all federal, state and local government web resources and services.