Area Forecast Discussion
Issued by NWS Albany, NY

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000 FXUS61 KALY 151422 AFDALY Area Forecast Discussion National Weather Service Albany NY 922 AM EST Thu Nov 15 2018 .SYNOPSIS... A low pressure system will spread accumulating snow into the region from south to north this evening into tonight. The snow may mix with sleet and freezing rain for portions of the region. Wintry precipitation tapers off from west to east Friday late morning into the afternoon, with additional lake effect snow possible for the higher terrain. Continued colder than normal temperatures expected for the weekend with mainly dry conditions outside of the lake effect belts. && .NEAR TERM /THROUGH FRIDAY/... Winter Storm Warning in effect 7 pm today through 1 pm Friday for the southern Adirondacks and western Mohawk Valley Winter Weather Advisory in effect 4 pm today through 1 pm Friday for The Mid Hudson Valley, eastern Catskills, and central and southern Taconics in eastern New York, the southern Berkshires in western Massachusetts, and northwestern Connecticut Winter Weather Advisory in effect 7 pm today through 1 pm Friday for The Capital District, Schoharie Valley, central Mohawk Valley, Lake George Saratoga Region, northern Taconics, and Helderbergs of eastern New York, the northern Berkshires of western Massachusetts, and southern Vermont..... As of 922 am...Mid and level clouds have ovespread the entire region and they will continue to thicken through the day. as a large closed off upper low moves eastward up the Ohio Valley. With the Arctic surface high overhead today and the increasing cloud fraction another very chilly day is expected. The upper low will accelerate and become an open wave as it reaches near NYC by 12Z Friday. At the surface, a coastal low will become dominant and deepen around 12 mb in 12 hours from 00-12Z Friday as it moves from the Delmarva to near Long Island. Isentropic lift will increase rather quickly ahead of this system, especially 00-06Z, as SE winds on the 295K surface increase to near 60-70 kt. This will allow saturation to occur rather quickly despite the dry airmass. Trend in the guidance has been for a slower precip onset compared with yesterday at this time, such that the evening commute will be spared from the Mohawk Valley/Capital District/northern Berkshires and points north. South of there, snow should spread in and possibly impact the commute as it becomes moderate to briefly heavy. The onset of the system is reminiscent to the laterally translating band composite in CSTAR research, meaning that heavy bands will be transient for a particular area during this onset period, but could still approach an inch per hour at times 00-06Z. Lift will be enhanced by a coupled jet structure. From 03-09Z, most models suggest that a combination of a warm nose and dry slot aloft will allow precip to transition to sleet, freezing rain, and perhaps freezing drizzle from south to north. There is still uncertainty with how far north the mixture gets, with the ECMWF and some of its ensembles being on the colder/snowier side of the guidance compared with the GFS/NAM/HREF mean. Current forecast thinking is that a mixture could be seen as far north as the central Mohawk Valley to Glens Falls area (basically areas outside of the Winter Storm Warning). In the warning area, this is where we see the best 850 to 700 mb frontogenesis, as the pattern becomes more reminiscent of the CSTAR pivoting band composite, although not totally as the wave opens up so the heavier bands may be more progressive. Still, snowfall rates of one to two inches per hour are possible in the warning area just to the north and west of the dry slot. Snowfall accumulations here were adjusted upward accordingly. Further south, the eastern Catskills, Mid Hudson Valley, and Litchfield Hills and southern Berkshires could see around a tenth of an inch of ice, with locally higher amounts possible in the higher terrain. Combined with gusty winds, this could result in some isolated power outages. From about 12-15Z, the fgen/deformation band is expected to sweep eastward across the region, so areas that turned to mixed precip may turn back to snow around the morning commute. Precip appears to end rather quickly from west to east during the late morning and early afternoon behind this band, and many spots will warm back above freezing aside from the high terrain, which could aid snow/ice removal operations. On average, the best lift will be located below the DGZ, so lower snow to liquid ratios are expected compared with climatology. On average, expect that they will range from 8-12:1. This will result in a rather heavy, wet snow. QPF will be modulated by terrain with the strong low-level SE winds. Shadowing is likely in the lee of the higher terrain of western New England for portions of Washington County, the Taconics, and even eastern portions of the Capital District, and upslope enhancement likely on the eastern slopes of the Greens, Berkshires, and Catskills, and the southern Adirondack foothills. As far as headlines, upgraded the southern Adirondacks and western Mohawk Valley to Winter Storm Warnings as discussed above. Elsewhere, many areas are borderline advisory/warning criteria. Felt it would be a better idea to leave the door open for headline upgrades than to upgrade the borderline areas to warnings right now, so the day shift can reassess. && .SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY/... Friday afternoon into Saturday, lake effect snow will return to the western Adirondacks, tacking on around 1-5 additional inches. Some upslope snow is possible over the southern Greens especially through early Friday night, so another couple of inches is possible there. Otherwise, below normal temperatures will continue with partial sunshine Saturday outside of the lake effect belt. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... Below normal temperatures through the period as the region remains under a longwave trough with short waves rotating about an upper level low as it moves eastward across eastern Canada. Lake effect snows are expected to linger into Saturday evening then diminish by Sunday morning as weak surface high pressure builds in disrupting the favorable flow off Lake Ontario. Mainly fair weather is expected Sunday however the high will be quick to shift off the coast. There are some differences regarding the amplitude and timing of an approaching short wave and associated cold front as we head into next week. Have widespread chances for mainly snow showers Sunday night and Monday as these features approach and swing through. It may get warm enough Monday afternoon for some rain showers up the Hudson River Valley and across northwest Connecticut. With the passage of this cold front an even colder airmass is expected to be ushered in with lows expected to drop into the single digits and teens Monday night. As we head into Tuesday the uncertainty in the forecast grows. At this time, have chances for snow showers due to cyclonic flow and lake effect. && .AVIATION /14Z THURSDAY THROUGH MONDAY/... A coastal low has developed along the southeast coast. It will rapidly deepen today as it heads northeastward up the east coast and is expected to pass over Long Island early Friday morning. Snow will overspread the area from south to north late this afternoon and through the evening with conditions quickly dropping to IFR. It will remain cold enough for all snow KGFL and KALB, however at KALB some freezing drizzle is possible during the overnight. Warmer air will work in with a changeover to sleet and freezing rain KPSF and KPOU. At KPOU a period of plain rain should occur for a few hours before transitioning back to sleet and snow before 12Z/Friday as colder air filters back in. A light easterly flow will develop with winds turning more northeasterly especially in the evening then to the north as the coastal low approaches and passes to our south. Low level wind shear may need to be added to the KPOU and KPSF TAFs however confidence is not high enough to include at this time. Thick cirrus shield will remain across the region overnight with light and variable to calm winds with a surface high drifting directly over the region. A coastal low has begun to develop along the southeast coast. This low will rapid deepen Thursday as it heads northeastward up the east coast and will bring widespread wintry precipitation to the area. Snow will overspread the area late in the day into the early evening with conditions quickly dropping to IFR. It will remain cold enough for all snow KGFL and KALB through 06z/Friday. However, warmer air is expected to work in with a changeover to sleet and freezing rain expected at KPOU and KPSF during the evening. Light/variable to calm winds overnight with a light easterly flow developing Thursday. Winds will shift more northerly in the evening as the coastal low approaches. Low level wind shear may be needed for KPOU and KPSF by Thursday evening however confidence is not high enough to include in the TAFs at this time. Outlook... Friday: High Operational Impact. Definite SHRA...RA...SN. Friday Night: No Operational Impact. NO SIG WX. Saturday: No Operational Impact. NO SIG WX. Saturday Night: No Operational Impact. NO SIG WX. Sunday: Low Operational Impact. Slight Chance of SHSN. Sunday Night: Moderate Operational Impact. Chance of SHSN. Monday: Moderate Operational Impact. Chance of SHRA...SHSN. Monday Night: Low Operational Impact. Slight Chance of SHSN. Tuesday: No Operational Impact. NO SIG WX.Outlook... Friday: High Operational Impact. Definite SHRA...RA...SN. Friday Night: No Operational Impact. NO SIG WX. Saturday: No Operational Impact. NO SIG WX. Saturday Night: No Operational Impact. NO SIG WX. Sunday: Low Operational Impact. Slight Chance of SHSN. Sunday Night: Moderate Operational Impact. Chance of SHSN. Monday: Moderate Operational Impact. Chance of SHRA...SHSN. Monday Night: Low Operational Impact. Slight Chance of SHSN. Tuesday: No Operational Impact. NO SIG WX. && .FIRE WEATHER... Widespread wintry weather expected this evening through Friday afternoon. Mainly dry outside of lake effect belts but continued unseasonably cool through the weekend. && .HYDROLOGY... A low pressure system will bring widespread wintry precipitation to the region Thursday afternoon into Friday. The precipitation may become rain or freezing rain especially from the Capital District south Thursday night into Friday morning. QPF ranges from around 0.60 to 1.30 inches, with the heaviest amounts over the Mid Hudson Valley, Litchfield County, and the Berkshires where rivers are already running high. Flooding on the main stem rivers is not expected, but some urban and poor drainage flooding cannot be ruled out due to the saturated ground. Mainly dry for the weekend outside of lake effect snow over the western Adirondacks. && .ALY WATCHES/WARNINGS/ADVISORIES... CT...Winter Weather Advisory from 4 PM this afternoon to 1 PM EST Friday for CTZ001-013. NY...Winter Weather Advisory from 4 PM this afternoon to 1 PM EST Friday for NYZ058>061-063>066. Winter Weather Advisory from 7 PM this evening to 1 PM EST Friday for NYZ039>041-043-047>054-083-084. Winter Storm Warning from 7 PM this evening to 1 PM EST Friday for NYZ032-033-038-042-082. MA...Winter Weather Advisory from 4 PM this afternoon to 1 PM EST Friday for MAZ025. Winter Weather Advisory from 7 PM this evening to 1 PM EST Friday for MAZ001. VT...Winter Weather Advisory from 7 PM this evening to 1 PM EST Friday for VTZ013>015. && $$ SYNOPSIS...Thompson NEAR TERM...Frugis/Thompson SHORT TERM...Thompson LONG TERM...IAA AVIATION...IAA FIRE WEATHER...Thompson HYDROLOGY...Thompson

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