344 FXUS61 KALY 062204 AFDALY AREA FORECAST DISCUSSION National Weather Service Albany NY 504 PM EST Sat Feb 6 2021 .SYNOPSIS... The combination of a developing coastal storm and approaching cold front will bring accumulating snow to the region on Sunday. Some moderate totals are possible over portions of western New England and the Mid Hudson Valley, with mainly light totals elsewhere. The snow will taper off to snow showers Sunday evening, and end by Monday morning. Colder temperatures return for Monday and Monday night, with another period of snow possible on Tuesday. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... As of 350 PM EST, strong subsidence in the wake of this morning's shortwave has resulted clearing skies and drying for most of the region. Deep mixing to nearly h700 has allowed temps to "overachieve" in many valley areas, reaching the mid 30s to lower 40s from Albany south and east, with temps mainly in the 20s to lower 30s to the north/west. Dewpoints have dropped into the single digits in many places. A Lake Effect snowband was still occasionally extending into far northern Herkimer County. However, upstream radars and VWP's suggest backing low level winds occurring in western NYS. This should eventually translate eastward into the Tug Hill region and SW Adirondacks shortly after sunset, allowing any lingering snow bands to lift back north before contracting closer to the lakeshore as inversion heights drop. A period of clear skies, very dry air and nearly calm winds should allow temps to drop rapidly after sunset, especially across the southern Adirondacks, where temps could fall below zero before midnight. Have indicated min temps well below NBM guidance due to this potential. Elsewhere, mainly single digits and lower/mid teens are expected. High/mid level clouds should increase for areas south of I-90 before daybreak, allowing temps to become steady. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY NIGHT/... Winter Weather Advisory from 7 AM to 7 PM Sunday for Ulster, Dutchess, Columbia, Berkshire and Litchfield Counties... Developing coastal low expected to track northeastward off mid Atlantic coast during Sunday, while a cold front approaches from the west. The combination of low/mid level moisture from the passing coastal low and approaching dynamics from the incoming cold front/upper level trough should support widespread light snow across the region Sunday afternoon, with snow developing across southern areas between 10 AM and Noon, and areas north of I-90 between Noon and 3 PM. There remains some uncertainty regarding overall QPF, forcing and resulting snowfall amounts for southern areas Sunday, with the NAM remaining most aggressive with QPF for SE areas, and most other global models quite a bit lighter. Consensus from the 12Z/HREFs still suggest up to 0.5" liquid equivalent for portions of Litchfield County CT, and southeast Ulster/southern Dutchess Counties in NY. Given potential for mid level F-GEN from coastal system and resulting banding within favorable dendritic growth zone, snowfall ratios may reach as high as 13:1 or slightly higher at times for southeast areas, resulting in snowfall totals of 4-6 inches for Litchfield County and close to I-84 in Ulster/Dutchess Counties, and 2-5 inches for the remainder of Ulster/Dutchess/Columbia Counties and most of Berkshire County. Therefore, Winter Weather Advisories have been issued for these areas. Farther north and west, generally 1-4 inches are expected, with with the higher amounts mainly across higher terrain of southern VT. Again, uncertainty remains greatest for Litchfield County, where banding potential could allow for localized higher amounts to occur. If this potential increases, the current Winter Weather Advisory would be upgraded to a Winter Storm Warning. The snow should decrease from west to east in areal coverage between 4 and 6 PM. However, there could be some snow showers congealing along the incoming cold front within the Mohawk Valley and Capital Region, perhaps with some embedded squalls, so trends will need to be watched in case this occurs with some additional bursts of snow. For Sunday night, additional snow showers will be possible along the cold front. Then in the wake of the front, there is a possibility for a Lake Effect snowband to develop and extend into the Mohawk Valley/Capital Region and Schoharie County, before gradually shifting southward and becoming multi-banded later at night. This could lead to some additional minor accumulations, especially for western Mohawk Valley and Schoharie County where the snow band may be more persistent. Otherwise, gusty west/northwest winds develop behind the front, with low temps reaching the single digits and teens by daybreak Monday. Generally fair conditions for Monday, despite cold temperatures with highs in the mid teens to lower/mid 20s. Clear/cold Monday evening, before clouds increase after midnight ahead of next fast moving impulse embedded within west/southwest flow aloft. Some light snow may develop prior to sunrise within developing mid level isentropic lift across portions of the Mohawk Valley/SW Adirondacks and eastern Catskills, with some possibility extending as far east as the Lake George/Saratoga region by sunrise Tuesday with minor accumulations of less than one inch. && .LONG TERM /TUESDAY THROUGH SATURDAY/... A very active February pattern will be in place during the long term with back to back weather systems to monitor in addition to a period of below normal temperatures. As of now, confidence is increasing in a more widespread event (likely producing mainly snow) occurring on Tuesday but guidance still shows disagreements on the timing and placement of systems thereafter including possibly Thursday/Friday and this weekend. Read on for details. A large closed low positioned in south central Canada will be responsible for sending a conveyor belt of amplifying shortwaves towards the Northeast over the next 5 - 7 days. After a brief break of high pressure on Monday, the next intensifying shortwave will be progressing through the Great Lakes on Tuesday with downstream ridging resulting in a surge of increased isentropic lift and a moisture connection to the Gulf of Mexico and even the western Atlantic. In previous deterministic runs, the ECWMF has been showing the shortwave digging a bit more compared to the GFS and CMC which kept the shortwave slightly flatter. As a result, there was a split between the GFS and CMC showing a weaker precipitation shield while the ECMWF was more generous with even a secondary low developing over southern New England in a "Miller B" type fashion. In today's 12 UTC runs, the GFS and CMC have trended slightly wetter, although still not nearly as wet as the ECMWF, and also suggest a secondary low near New England will possible. Therefore, we had enough confidence to show widespread chance POPs for Tuesday. Given the antecedent cold air mass in place, precipitation should fall as all snow. Fast zonal flow is maintained in the wake of the departing system which results in surge of cold air advection Tuesday night into Wednesday. Strong westerly winds advecting arctic air over the still warm Lake Ontario waters looks to lead to lake effect snow during this period for our western Adirondack areas. Under such a set-up, cloud coverage should persist into Wednesday and with continuing CAA, temperatures turn much chillier with highs only reaching into the low to mid 20s. High pressure centered in the Midwest will be pushing eastward resulting in a tightening pressure gradient over the Northeast as well which will lead to breezy conditions and make it feel even colder. By Wednesday night into Thursday, upper level ridging builds overhead with winds aloft veering to the southeast. This should shut- off lake effect snow and allow winds turn calmer but also lead to a chilly night. Temperatures look to fall well into the single digits throughout the region as high pressure moves overhead. High pressure says in place on Thursday but guidance shows a very potent shortwave rotating around the main closed low in south central Canada. This looks to result in an amplifying ridge downstream in the western Atlantic as the shortwave digs into Great Plains. The shortwave looks to send a blast of very cold air into the Central CONUS with 850hPa isotherms ranging -30C to -35C which is 2-3 standard deviation below normal. As a result of the amplifying pattern, yet another intensifying shortwave should combine with increased southerly flow to produce another surface low and widespread area of precipitation. Of course, exact details this far out in time are still uncertain but there is generally decent consensus that the enhanced southerly flow and ridge over the western Atlantic as well as the predicted storm track may send a warm tongue far enough north that precipitation type issues may be more of an issue (i.e snow may transition to wintry mix). The weekend stays active with guidance showing potential for additional storms as the 500hPa pattern remains busy. && .AVIATION /22Z SATURDAY THROUGH THURSDAY/... Through 18z/Sun...VFR conditions expected through tonight at all TAF sites. SCT-BKN stratocumulus clouds at or above 5000 feet will continue this afternoon, then dissipate and give way to a mainly clear sky this evening. Mid- and high clouds will increase overnight. Clouds will thicken and lower Sunday morning as the next storm system approaches from the south. Snow will spread northward across the TAF sites, arriving first at KPOU and last at KGFL. Cigs will lower to at least MVFR around the onset of snow as vsbys drop to IFR and perhaps LIFR in some areas by 18z/Sun. Wind will remain gusty out of the west to southwest at 10-15 kt with gusts to around 25 kt this afternoon, then diminish this evening before going calm overnight. Wind will be variable at less than 10 kt Sunday morning. Outlook... Sunday Night: Moderate Operational Impact. Breezy. Scattered SHSN. Monday: No Operational Impact. NO SIG WX. Monday Night: Moderate Operational Impact. Chance of SN. Tuesday: High Operational Impact. Likely SN. Tuesday Night: Moderate Operational Impact. Chance of SN. Wednesday: No Operational Impact. NO SIG WX. Wednesday Night: No Operational Impact. NO SIG WX. Thursday: Low Operational Impact. Slight Chance of SN. && .HYDROLOGY... No hydrological issues are expected through next week. Light to moderate accumulating snow is expected Sunday. Another system could bring light snow on Tuesday. Temps will mainly remain below freezing, which should allow ice to expand and thicken on area waterways through the upcoming week. 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...Winter Weather Advisory from 7 AM to 7 PM EST Sunday for CTZ001-013. NY...Winter Weather Advisory from 7 AM to 7 PM EST Sunday for NYZ060-061-063>066. MA...Winter Weather Advisory from 7 AM to 7 PM EST Sunday for MAZ001-025. VT...None. && $$ SYNOPSIS...KL/Thompson NEAR TERM...KL SHORT TERM...KL LONG TERM...Speciale AVIATION...Rathbun HYDROLOGY...KL/Thompson