Area Forecast Discussion
Issued by NWS Albany, NY

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626 FXUS61 KALY 171413 AFDALY Area Forecast Discussion National Weather Service Albany NY 913 AM EST Fri Nov 17 2017 .SYNOPSIS... Cold and brisk conditions in store for today, as high pressure builds eastward across the region. A low pressure system will approach from the lower Great Lakes on Saturday, bringing the next chance for widespread precipitation. The storm system will intensify Saturday night as it tracks northeast through the Saint Lawrence River Valley, and will drag a cold front across our region by Sunday morning. Colder air will filter in by Sunday night, with lake effect snow developing downwind of Lake Ontario. && .NEAR TERM /THROUGH TONIGHT/...
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Clouds anchored to terrain with some breaks in the Hudson Valley to southern Berkshires and NW CT. Clouds will gradually erode through the day with gusty northwest winds. Area 12Z soundings show quite cold at the boundary layer and even with the mixing from the gusty winds, temperatures may be on the cooler side of guidance. There are still a few flurries into the Schoharie Valley and eastern Catskills that are diminishing. Just some minor adjustments to temperatures and sky cover through this afternoon. The previous AFD has a few more details through tonight and is below... Colder air continues to filter in with a gusty northwest wind. Flurries are expected to end later this morning, as a subsidence inversion develops associated with high pressure building east from the lower Great Lakes. It will remain breezy through much of the daylight hours, as the ridge axis will not move overhead until this evening. Winds will gust around 30 to 40 mph in favored spots (Mohawk Valley, Capital District, Berkshires), especially through this morning as winds speeds aloft beneath the inversion of 30-35 kt are forecast. Temperatures will be cooler than yesterday, with 30s across the higher terrain and lower to mid 40s in the valleys. High pressure will briefly move overhead tonight, which will allow for winds to diminish and mainly clear skies with only some high level cirrus clouds increasing overnight. These conditions should result in substantial radiational cooling with lows mainly in the teens to lower 20s across the area.
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&& .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... Strong winds possible behind a cold front Sunday... Saturday will start out cold and tranquil, although low pressure will be deepening as it tracks northeastward from the Midwest to the lower Great Lakes during the day. Clouds will continue to increase and thicken ahead of the strengthening storm system. Precipitation will develop generally from west to east during the afternoon as isentropic lift on the 290-295K surfaces increases ahead of the cyclone. Model trends each of the last several days have slowed the onset of precip. Due to the later arrival, low-level temperatures will have a chance to warm up after the cold start due to increasing S-SW flow. Still, there could be a brief period of snow/sleet in the Mohawk Valley and southern Adirondacks where a brief dusting is possible before changing over to rain. Much of the region will have just plain rain as temps warm into the 40s during the afternoon. The surface cyclone is forecast to deepen to a sub-980 mb low late Saturday night, as it tracks northeast along the St. Lawrence Valley. Isentropic lift will continue Saturday night ahead of the system`s cold front, so will maintain high pops through the night. Model guidance in generally good agreement regarding the track/intensity of the cyclone, except for the NAM which is a considerable southern outlier. Will side more towards the GFS/ECMWF/CMC solutions. The cold front should move sweep through late Saturday night into early Sunday morning. As temps aloft cool, some snow may mix back in across portions of the Adirondacks before sunrise Sunday. Behind the cold front, winds will shift to the W-NW and become noticeably stronger during the morning. The parent cyclone will continue to track northeast into southern Quebec as a sub-980 low, with cold advection resulting in deeper mixing to perhaps 800-750 mb. This could result in mixing down winds of 40+ kt to the surface, especially across favored areas in W-NW flow such as the Mohawk/Schoharie Valleys, Capital District and Berkshires. While it is too early to determine exact wind speeds this far out, will continue to mention the potential for at least advisory level winds with 45+ mph gusts on Sunday. With regards to precip, rain will end Sunday morning although snow showers will develop as multiple short waves move through the upper level trough. Some light accumulations will be possible in mainly higher terrain areas. It will be difficult to organize lake effect snow despite moderate lake induced instability due to the oscillating flow associated with the short wave passages. Lake effect snow may finally start to organize Sunday night along the Mohawk Valley as winds align from the W-NW and an upstream multi- lake connection likely develops with Lake Huron/Georgian Bay. Some lake effect snow bands may even make it down the Mohawk Valley and into the Capital District depending on the flow trajectory. Otherwise it will remain brisk, cold and breezy, although wind speeds will decrease somewhat compared to earlier in the day. && .LONG TERM /MONDAY THROUGH THURSDAY/... The extended forecast opens with Lake Effect snowfall impacting locations west of the Hudson River Valley. There is still some disagreement with the guidance on the orientation of the bands and the favored low-level trajectory. Our forecast remains close to the latest GFS with west to northwest flow with the Schoharie Valley, west-central Mohawk Valley and eastern Catskills being impacted on Monday early on, and then the band or bands lifting northward into the western Adirondacks, as the low to mid level flow backs to the west with high pressure building in from the Carolinas. Some of the lake effect snow showers may extends into the Capital Region, northern and central Taconics, and the Berkshires with light accums. Locations further to the west may receive light to localized moderate amounts of snow. It will be cold and brisk with H850 temps running a couple of STD DEVs below normal based on the 00Z GEFS with actual H850 temps in the -10C to -14C range early in the day, and the warm advection occurs by the afternoon with the ridge building in. The isolated to scattered lake effect snow showers over the western Adirondacks/Mohawk Valley should end Monday night. Highs Monday will be mainly in the upper 20s to mid 30s in most locations, the exception will be the Capital District, Mid Hudson Valley, and southern Litchfield CTY where some upper 30s to around 40F readings are possible. Lows Mon night will be mainly in the 20s. Tue-Wed...High pressure ridges in from off the Mid Atlantic Coast with moderating temps to above normal readings. Mid and upper level heights rise across the Northeast ahead of the next northern stream short-wave trough. H850 temps rise to-1C to +4C from northwest to southeast across the forecast area. The medium range deterministic guidance and the ensembles have this short- wave trough arriving Tue night into Wed. In the warm advection pattern, not much pcpn is expected with the warm front, and it looks like the best moisture convergence is with the cold front late Tuesday night into Wed. A slight to low chance of rain to snow showers was kept in the forecast predominately north and west of the Capital Region. A brief lake connection is possible Wednesday afternoon west of the Hudson River Valley. Mild temps on Tue will be in the upper 40s to lower 50s in the valley areas, with upper 30s to mid 40s over the mountains. Lows Tue night fall back into the upper 20s to lower 30s. Highs on Wed will trend close to normal with the cold advection in the wake of the front with 40s from the Capital District south and east, and upper 20s to upper 30s for locations north and west. Wed night into Thu...The mid and upper level trough axis moves across the region Wed night with any multi-bands of lake effect snow ending over the western Mohawk Valley, northern Catskills, Schoharie Valley and western Adirondacks with light snow accums. The chilly cyclonic flow will continue aloft over the Northeast and southeastern Canadian with high pressure at the sfc building in from the Midwest and Ohio Valley for Thanksgiving. Temps will continue at slightly below normal readings for the holiday. && .AVIATION /14Z FRIDAY THROUGH TUESDAY/... Low pressure continues to move into the Canadian Maritimes this morning. The upper level trough continues to be over eastern NY and New England. High pressure will build in over the region this afternoon into tonight. VFR conditions will continue at KPOU/ALB this morning with cigs in the 3.5-5 kft AGL range. MVFR conditions persist at KGFL/KPSF. The cloud bases will rise to VFR levels between 12Z- 15Z at KGFL/KPSF. Expecting the subsidence in the wake of the cyclone, and the surface high building to erode the clouds completely in the very late morning with clear to mostly clear conditions by the early afternoon, and continuing into the early evening. High to mid level clouds will begin to move into the region after 06Z/SUN. The strong sfc pressure gradient between the departing cyclone into the Canadian Maritimes and high pressure ridging in from the Midwest will allow gusty winds this morning into the afternoon. Some deeper mixing from 1-2 kft AGL will allow for west to northwest winds of 10- 18 KT with some gusts in the 22-30 KT range into the early afternoon. The stronger gusts are expected at KPSF/KALB. The winds will decrease in the mid to late pm with northwest winds of around 10 kts, and they will become light to calm after 02Z/SAT. Outlook... Saturday: High Operational Impact. Likely RA. Saturday Night: High Operational Impact. Breezy Definite RA. Sunday: High Operational Impact. Windy Likely SHRA. Sunday Night: Moderate Operational Impact. Breezy Chance of SHSN. Monday: Low Operational Impact. Breezy Slight Chance of SHSN. Monday Night: No Operational Impact. NO SIG WX. Tuesday: No Operational Impact. NO SIG WX. && .FIRE WEATHER... Cold and brisk conditions in store for today, as high pressure builds eastward across the region. A low pressure system will approach from the lower Great Lakes on Saturday, bringing the next chance for widespread precipitation. The storm system will intensify Saturday night as it tracks northeast through the Saint Lawrence River Valley, and will drag a cold front across our region by Sunday morning. Colder air will filter in by Sunday night, with lake effect snow developing downwind of Lake Ontario. && .HYDROLOGY... No hydrologic problems are expected on the main stem rivers through the next week. High pressure will briefly build in today before a strong low pressure system approaches from the Great Lakes Region on Saturday. Widespread rain may begin as a mix with snow in the western Mohawk Valley and southern Adirondacks but then quickly change to to all rain that will continue through Saturday night. A cold front will sweep through Sunday morning with additional rain changing to snow over the higher terrain. At this time, total QPF from this system looks to range from a half inch to near an inch. A colder air mass will then build in Sunday night through early next week, with some lake effect snow downwind of Lake Ontario affecting the western Adirondacks and Mohawk/Schoharie Valleys. For details on specific area rivers and lakes, including observed and forecast river stages and lake elevations, please visit the Advanced Hydrologic Prediction Service /AHPS/ graphs on our website. && .ALY WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. MA...None. VT...None. && $$ SYNOPSIS...JPV NEAR TERM...NAS/JPV SHORT TERM...JPV LONG TERM...Wasula AVIATION...Wasula FIRE WEATHER...JPV HYDROLOGY...JPV

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