Area Forecast Discussion
Issued by NWS Albany, NY

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000 FXUS61 KALY 201803 AFDALY AREA FORECAST DISCUSSION National Weather Service Albany NY 103 PM EST Wed Feb 20 2019 .SYNOPSIS... An approaching low pressure system will bring light snow late this afternoon and into this evening, changing to a wintry mix later tonight. It will become milder and mainly dry for Thursday into Friday. Another storm system could bring a wintry mix changing to rain Saturday night into Sunday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Winter Weather Advisory in effect for eastern New York and western New England late today through early Thursday morning... As of 1225 PM EST, not much change to the forecast at this time. Deeper moisture continues to work its way into the forecast area from the Gulf of Mexico per latest layered GOES16 water vapor imagery. There are some light returns on radar entering the mid-Hudson valley but NYS mesonet webcams only indicate snow in Suffern and Warwick, which is far southern New York. However, as the column saturates, snow should begin falling in the Poughkeepsie area and then work its way northward throughout the late afternoon and evening. Prev Disc... As of 950 am, high cirrus has overspread the region with overcast skies throughout the forecast area. Temperatures are tracking the current forecast well. Virga beginning to spread into southern reaches of the forecast area, but given the excessively dry airmass in place (PWAT 0.12/0.20 on the 12Z KALY/KOKX soundings, respectively), it will take some time to saturate the column. Closest snowfall observation is near Williamsport/East Stroudsburg, PA, which is in line with latest CAMs. Little changes were needed to the going forecast at this time. Previous discussion... The system that will impact our region later today into tonight is currently producing quite a bit of deep convection across the Ohio Valley region and points south. Models suggest that this convection translates eastward through the day, remaining closer to elevated instability near and south of the Ohio River. Heavier precipitation associated with this convection is therefore expected to remain south and east of the region, with additional heavier precipitation tracking into the Great Lakes region closer to the main upper level system. The deeper convection to our south may reduce moisture transport into our region, resulting in relatively lighter QPF for our region with this system. However, will have to watch trends closely in case the heavier precipitation and embedded convective elements to our south decrease more than expected, which could allow for greater moisture transport and higher QPF into our region. So, assuming we have the lighter QPF, clouds will continue to thicken/lower through the day, with light snow developing across southern areas (SE Catskills, mid Hudson Valley and NW CT) between roughly 3-6 PM, and across central areas (the Capital District of NY, Saratoga region, Mohawk Valley, and Berkshires) between 6-8 PM. Snowfall accumulations of 1-2 inches could occur by 7 PM across the eastern Catskills, mid Hudson Valley, central and southern Taconics, and NW CT, with perhaps up to an inch across the western Mohawk Valley, Capital Region and central Taconics and Berkshires. Areas farther north (southern Adirondacks, Lake George region and southern VT) should have the snow begin generally after 8 PM. Highs today mainly in the mid/upper 20s by mid afternoon, although temps may fall a few degrees shortly after snow begins due to wet bulb cooling effects. && .SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY NIGHT/... Tonight, snow will continue to overspread the entire region between 8 and 10 PM. A few moderate bursts of snow will be possible, especially across the Mohawk Valley and SW Adirondacks, where isentropic lift will be strongest and should coincide with added orographic effects. Snowfall rates of up to one half inch per hour could occur, however the potential for greater snowfall rates may be limited by the increasingly grainy texture of the snow, due to relatively warm temperatures near cloud top levels (generally -6 C to -10 C), with dry air above H600 limiting cloud depth and potential for dendritic snow crystals, especially after 10 PM. The snow should then change to sleet fairly quickly from SW to NE between roughly 10 PM and 1 AM, as a robust warm nose aloft impinges on the region from the southwest, and then for areas near and south of I-90, should mix with and/or change to freezing rain after 1 AM. There could be some bursts of moderate sleet at times. Precipitation should begin to decrease in areal coverage and intensity after 4 AM, as a deeper layer of mid level dry air sweeps across the area from the west/southwest. However, low levels will remain rather moist, so areas of freezing drizzle/light freezing rain and some now grains should occur during this time across most of the region. Total snow/sleet amounts should range from 1-3 inches, although locally higher amounts could occur across portions of the eastern Catskills, and higher terrain of the southern Green Mountains and northern Berkshires. Total ice accretion from freezing rain should generally average one tenth of an inch or less, although there could be some isolated amounts up to one quarter of an inch across the southern Berkshires and Litchfield Hills, and possibly the western Mohawk Valley. As a strong low level jet translates northeast across the region, strong wind gusts may occur across higher terrain of the SW Adirondacks, eastern Catskills, and the climatologically favored areas of the southern Greens, Berkshires and north/central Taconics, where southeast winds may gust up to 30-40 mph for a short duration, roughly between 10 PM and 2 AM. Low temperatures will be this evening, mainly in the 20s, with slowly rising temps after midnight, reaching the lower/mid 30s across many areas south of I-90 by daybreak, with upper 20s to lower 30s to the north. For Thursday, areas of freezing drizzle and drizzle may linger through mid morning, with the freezing drizzle mainly for the southern Adirondacks, Lake George Saratoga region and southern Vermont, where temps may be slower to rise above the freezing mark. For this reason, have extended the end time of the northern portion of the Winter Weather Advisory until 10 AM Thursday morning. As an occluded front sweeps eastward, deeper mixing should commence from west to east later in the morning through early afternoon, allowing for a spike in temps. So, highs may reach the 40s in valley areas by early afternoon, and perhaps near or over 50 across the mid Hudson Valley. It also should become windy by afternoon, with west winds increasing to 15-25 mph, with some gusts of 30-40 mph possible. Lots of clouds should dominate areas along and north of I-90 for Thursday night into Friday morning, with some snow showers even possible across the SW Adirondacks. Clearing is expected from SW to NE Friday afternoon, with mainly clear and chilly conditions expected Friday night. && .LONG TERM /SATURDAY THROUGH TUESDAY/... System that originates from the SW U.S. ejects NE tracking through the central U.S. and into the Great Lakes by Sunday. There is an increasing consensus that the upper system is a closed low that tracks around the northern periphery of mean flat upper ridging in eastern North America. The closed upper low then tracks north of the U.S./Canada border Sunday through Monday. Clouds and precipitation spread into our region by Saturday evening, which should be mainly rain but some mix of rain and snow in higher terrain. Highs Saturday in the upper 30s to lower 40s but mid 30s higher terrain. Precipitation mixes with some sleet and freezing rain in northern areas and parts of the eastern Catskills, Schoharie Valley, Berkshires and southern VT as some wet bulb cooling of low level temperatures is possible. There should be a cold rain in all other areas. Stronger warm advection Sunday morning is expected to change the mixed precipitation to rain. Rain becomes showers as coverage decreases when the upper system and associated cold front depart. Highs Sunday in the mid 40s to around 50 but lower 40s northern areas. There is an increasing consensus that the low level pressure gradient will increase significantly with the rapid deepening of low pressure. Some very strong west to northwest winds are likely late Sunday afternoon through Sunday night and much of Monday. Wind headlines may be needed once we get closer to the weekend and more details about specifics are available. Dry weather is expected Monday and much of Tuesday with winds diminishing Monday afternoon and night as low level ridging centers itself over our region. Highs Monday in the mid 30s to around 40 but mid to upper 20s and some lake effect snow shower activity into the southern Adirondacks. Highs Tuesday with clouds potentially increasing ahead of the next system, in the 30s but lower to mid 20s northern areas. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... Moisture continues to spread into the region from the south as high pressure shifts east. Virga appearing on area radars suggests column is beginning to saturate. This process should occur from south to north with flight categories falling to borderline MVFR/IFR in light snow beginning at KPOU around 20Z, KALB/KPSF around 22Z, and KGFL around 00Z. The snow should begin mixing with sleet after around 3-5 hours from the time it starts, then to freezing rain 1-2 hours later. Forecast soundings suggest the potential for some freezing drizzle during lighter periods of the snow. This will be addressed in future amendments if it appears plausible. Cigs/vsby in the overnight period should hover near the border of MVFR/IFR. As the steadier precipitation tapers off around 10-12Z Thu, some patchy drizzle will be possible (perhaps freezing drizzle at KGFL where temps will remain below freezing) which could allow for a period of IFR conditions through around 14-15Z. Cigs/vsby should begin to improve after 15Z as diurnal heating and the approach of drier air begins to mix out the low-level moisture. Winds will generally be from the south at 10 kt or less through the overnight period, shifting to west-southwest at 5 to 15 kt with some gusts in excess of 20 kt late Thursday morning into the afternoon. A brief period of marginal low-level wind shear conditions are expected between about 02-10Z, although southerly surface winds at KALB may be elevated enough to avoid LLWS concerns. Outlook... Thursday Night: Low Operational Impact. Breezy NO SIG WX. Friday: No Operational Impact. NO SIG WX. Friday Night: No Operational Impact. NO SIG WX. Saturday: No Operational Impact. NO SIG WX. Saturday Night: High Operational Impact. Likely RA...SLEET. Sunday: High Operational Impact. Breezy Likely SHRA...RA. && .HYDROLOGY... Hydrological impacts are not expected through at least Saturday. Seasonably cold weather is expected through today, promoting additional ice expansion on area waterways. The next system arrives late this afternoon into Thursday morning with snow transitioning to a wintry mix. Liquid equivalent amounts of generally a quarter to a half an inch are expected. Temperatures are expected to run a bit above normal Thursday into the weekend. Another period of rain or mixed precipitation is possible Saturday night into Sunday. 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 4 PM this afternoon to 7 AM EST Thursday for CTZ001-013. NY...Winter Weather Advisory from 4 PM this afternoon to 7 AM EST Thursday for NYZ047-058>060-063>066. Winter Weather Advisory from 7 PM this evening to 7 AM EST Thursday for NYZ038-040-048>054-061. Winter Weather Advisory from 7 PM this evening to 10 AM EST Thursday for NYZ032-033-039-041>043-082>084. MA...Winter Weather Advisory from 7 PM this evening to 7 AM EST Thursday for MAZ001-025. VT...Winter Weather Advisory from 7 PM this evening to 10 AM EST Thursday for VTZ013>015. && $$ SYNOPSIS...KL/Thompson NEAR TERM...KL/Thompson/JLV SHORT TERM...KL LONG TERM...NAS AVIATION...Thompson HYDROLOGY...KL/Thompson is the U.S. government's official web portal to all federal, state and local government web resources and services.