Area Forecast Discussion
Issued by NWS Burlington, VT

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385 FXUS61 KBTV 171221 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 721 AM EST Sat Feb 17 2018 .SYNOPSIS... High pressure building into the Northeast this morning will provide the North Country with tranquil weather conditions for the first half of the weekend with plentiful sunshine and highs in the low to mid 30s. Tonight, an area of low pressure moving from the Delmarva peninsula and southeast of New England will bring light snow to mainly eastern portions of Vermont with light accumulations likely. A significant warming trend is expected Monday through Wednesday of next week, along with increasing chances for rain. Near record high temperatures are possible Tuesday into Wednesday, with highs well into the 50s and possibly lower 60s. && .NEAR TERM /THROUGH SUNDAY/... As of 330 AM EST Saturday...Overall very little change from the previous forecast thinking for the weekend which is largely dominated by high pressure both Saturday and Sunday with some light snow for portions of the region expected tonight. Today: Surface high pressure building into the Northeast this morning will provide clear skies to start the day, temps warming back above seasonal normals in the low to mid 30s this afternoon, and high clouds increasing from west to east from mid-day onward. Tonight: The combination of a passing weak upper trough and some increased low/mid level moisture associated with low pressure passing southeast of the benchmark will spread some light snow into much of eastern Vermont. A very progressive mid- level flow will track these features out to sea quickly by sunrise Sunday, so it`ll be hard to get much accumulation, but a solid 1-3" can be expected from the spine of the Green Mountains eastward with the highest amounts across Rutland and Windsor counties. Clouds and snow will keep overnight temps mild, ranging through the 20s. Sunday: Aforementioned low pressure and shortwave trough exit quickly offshore and are replaced by upper ridging and surface high pressure building in over the mid-Atlantic states. Lingering low level moisture combined with blocked NW flow will keep some scattered mountain snow showers going through the first half of the day, but by the afternoon expect to see coverage diminishing and some breaks of sun developing. Highs will once again rise above normal ranging through the 30s, but a brisk NW wind gusting up towards 20 mph at times will make it feel a little colder, at least through early afternoon before winds diminish towards sunset. && .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY/... As of 355 AM EST Saturday...The surface ridge then crests atop and east of the forecast area on Sunday night as return southerly flow becomes established over time. Skies should generally remain partly cloudy as filtered mid to high clouds advect eastward. No precipitation is expected as lows hold seasonably mild from the upper teens to mid 20s in the warmer valleys. By Monday clouds continue to slowly thicken under increasing southerly flow as an anomalously strong upper ridge becomes established across the eastern third of the nation into the western Atlantic. The low level flow will eventually advect higher moisture into the region with chances for showers or periods of light rain increasing markedly as the afternoon progresses. P-type issues shouldn`t be of concern with boundary layer temperatures climbing well above freezing into the lower and mid 40s through the day. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... As of 355 AM EST Saturday...Confidence is now quite high that another period of unusually mild temperatures will affect the area in the Monday night through Wednesday time frame as deep southerly flow remains entrenched across the area. There are still some minor variations in this morning`s models in regard to the overall strength of the subtropical ridge and the extent to which it governs the placement of the polar front on its northern periphery. However, the overall consensus is that it will lie well north of the region until Wednesday after which it should sweep south through the area with cooler temperatures in tow. In the interim period extremely mild, near record breaking warmth is expected with daily highs in the 50s to lower 60s on both Tuesday and Wednesday with periods of rainfall. Blended QPF output support prior forecasts in showing the steadiest/heaviest rainfall will occur across the northern tier of counties in closer proximity to the surface front. However, some dry periods are expected through this time frame, especially south. Given these conditions, the threat of rapid snowmelt, resultant river rises and potential flooding remain a real threat so the situation will continue to be monitored very closely (see hydro section below). By later Wednesday the front should swing south through the area as steadier rainfall comes to an end and temperatures level off or even fall slowly. Temperatures by Wednesday night continue to slowly fall, though still remain well above late February norms with lower to mid 20s expected north and west, and lower to mid 30s south. Looking further out into later next week our stretch of mild weather continues, though not quite to the extent of Tuesday and Wednesday. Weak high pressure should ensure mainly dry weather until next weekend when another surge of deeper moisture brings a renewed threat of rain and snow showers. High temperatures should top out in the 30s to around 40 on Thursday and Friday, then mainly into the lower and mid 40s on Saturday in an airmass of eastern Pacific origin. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
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Through 12Z Sunday...VFR under mainly SKC this morning will give way to increasing cirrus from west to east through the day. After 00Z Sunday, low clouds and snow will advance from the south associated with coastal low pressure, lowering ceilings to MVFR at all sites except KPBG and KMSS, and vsby to IFR at KMPV and KRUT. Snow exits after 09-10Z with vsby lifting to VFR, but MVFR ceilings remain. Winds trend southerly after 14Z at 5-15 knots. Outlook... Sunday: VFR. Isolated SHSN. Sunday Night: VFR. NO SIG WX. Washingtons Birthday: Mainly VFR, with local MVFR possible. Chance SHRA. Monday Night: Mainly MVFR, with local IFR possible. Definite RA. Tuesday: Mainly MVFR, with local IFR possible. Likely RA. Tuesday Night: Mainly MVFR, with local IFR possible. Likely RA, Chance SHRA. Wednesday: Mainly MVFR, with local IFR possible. Likely RA, Chance SHRA.
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&& .HYDROLOGY... As of 355 AM EST Saturday...A 48-hour period of anomalously warm temperatures will affect the region from Monday through Wednesday afternoon. Periods of rainfall, modest winds and dewpoint temperatures climbing into the 40s to lower 50s will foster rapid snowmelt across the entire area. Still some variability shown in this morning`s modeled 48-hr QPF, though the general consensus is for two day totals averaging from 0.5 to 1.5 inches, heaviest north. Taking this all into account, modest to substantial river rises look highly probable starting Monday night and continuing into Wednesday, supported by NAEFS/SREF MMEFS hydrograph data. While widespread open water flooding is not expected, several rivers may approach minor flood. Given the numerous ice jams in place from the substantial thaw this past January localized high water/flood concerns near these features will also remain a concern. As future data helps hone the forecast in the coming 36-hours, a Flood Watch will likely be necessary for most if not all of the forecast area during this period. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Lahiff NEAR TERM...Lahiff SHORT TERM...JMG LONG TERM...JMG AVIATION...Lahiff HYDROLOGY...JMG

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