Scientific Forecaster Discussion

000 fxus61 kaly 180936 afdaly Area forecast discussion National Weather Service Albany New York 436 am EST Mon Feb 18 2019 Synopsis... low pressure tracking across Pennsylvania will redevelop east of New Jersey and pass south of Long Island today, bringing periods of snow across the area. The snow will taper to scattered snow showers and flurries by late this afternoon into the early evening. High pressure will bring mainly dry and seasonably cold temperatures tonight through Tuesday night before another storm system arrives late Wednesday into Thursday. && Near term /until 6 PM this evening/... Winter Weather Advisory remains in effect through 4 PM EST this afternoon for the Mohawk Valley, greater capital region, helderbergs, Mid Hudson valley, Taconics, eastern Catskills, Berkshires and Litchfield County, Connecticut... As of 435 am EST, bandlets of mainly light snow have redeveloped across the region, particularly areas along and north of I-90. Another area of snow with some mixed sleet/freezing rain was occurring across portions of the Mid Hudson valley and northwest CT. Thus far, snow has remained fairly light, and grainy in texture limiting snowfall accumulations. This may be due, at least in part, to the fact that best upward motion remains well below the dendritic growth zone. There has been a lull in overall precipitation much of the night, however a surge of isentropic lift and increased DPVA appears to be allowing precipitation to increase in areal coverage once again. Best forcing through this morning appears to be mainly north of the I-90 corridor, across the Mohawk Valley, southern Adirondacks, Lake George/Saratoga region into southern Vermont. In these areas, an additional 1-3 inches of snow is expected today, mainly this morning. To the south and east, snow should be more intermittent, with additional accumulation of less than one inch across the Mid Hudson valley, southeast Catskills, Litchfield County and southern Berkshires, with perhaps 1-2 inches closer to the capital region and northern Berkshires. Model soundings suggest a lack of ice nuclei in the clouds for a period this morning and early afternoon from the I-90 corridor south and east, implying some spotty light freezing rain/drizzle could occur. In fact, as temps warm slightly across portions of the Mid Hudson valley, some plain rain/drizzle could occur briefly later this morning. Snow should taper to snow showers from northwest to southeast later this afternoon as the mid level trough axis shifts south and east. Some mesoscale models suggest a small area/band of snow may persist and/or reintensify late this afternoon across portions of the capital region, eastern Mohawk Valley and helderbergs, in association with low level confluent flow. Trends will need to be watched for this additional development, which could produce an additional 1-2 inches of snow in isolated areas where any such areas or bands of snow persist. Temps are tricky today, as low level cold air continues to settle southward down the Hudson River valley, at the same time a remnant occluded front attempts to brush southern and central areas. Have undercut most guidance for high temps today, and perhaps not by enough, with forecast highs only in the lower/mid 20s across the southern Adirondacks, Lake George/Saratoga region, Mohawk Valley and southern VT, with upper 20s closer to the capital region and Berkshires, and lower/mid 30s across the Mid Hudson valley and lower elevations of northwest CT. However, there is a possibility that temps do not rise much at all for many areas, remaining in the upper teens to mid 20s, especially northern portions of the Hudson Valley. && Short term /6 PM this evening through Wednesday/... tonight, snow showers/flurries may linger across portions of the capital region, northeast Catskills and Berkshires within aforementioned remnant low level confluent flow. These should taper off toward and after midnight, with clearing occurring. With a fresh snowpack in place, and clearing skies, temps may drop off rapidly late tonight in some areas, particularly across the southern Adirondacks, where subzero mins are forecast. Elsewhere, expect widespread single digits and lower teens by daybreak Tuesday. Tuesday-Tuesday night, mainly clear skies are expected, with the exception of some lake effect clouds across portions of the eastern Catskills Tuesday, and the western Mohawk Valley and southwest Adirondacks Tuesday evening. Some flurries could even occur in some of these areas, as low level winds back more into the west and southwest. Otherwise, expect cold temps Tuesday with highs mainly in the teens and 20s, with another very cold Tuesday night expected, with lows ranging from zero to 10 below across the southern Adirondacks, with single digits and teens elsewhere. Wednesday, the next storm system will approach from the southwest later in the day. After some morning sunshine, expect increasing clouds, with light snow developing by late afternoon from southwest to northeast. Some minor accumulations will be possible by sunset, especially central and southern areas. Highs mainly in the 20s to lower 30s. && Long term /Wednesday night through Sunday/... flat upper ridging across eastern North America is expected to contribute to the weakening and deamplification of upper systems that track out of the central U.S. And Canada. There should also be a lack of deep moisture along with the weakening upper dynamics and relatively weak low level forcing. One system is timed to affect our region Wednesday night and Thursday with warm advection increasing through Wednesday night. Isentropic lift increases as well and snow gradually transitioning through mixed precipitation is expected Wednesday night into Thursday morning. There could be some light sleet and freezing rain in some areas, too. During the day Thursday, temperatures should warm well above freezing so that precipitation becomes mainly rain. Highs Thursday in the 40s but near 50 southern areas and mid to upper 30s northern areas. The system departs through the day and evening of Thursday and a dry and quiet weather period is expected through Saturday. Although, another system will be approaching and timing is very uncertain, some clouds and leading area of scattered showers could be in our areas by later Saturday. Highs Friday in the upper 30s to lower 40s but lower 30s northern areas. Highs Saturday in the lower to mid 40s but mid 30s northern areas. Decent consensus in long range guidance/ensembles for the next system to track through the northern periphery of the upper ridging and bring precipitation into our region Saturday night and Sunday. Highs Sunday well into the 40s but some upper 30s northern areas. && Aviation /09z Monday through Friday/... periods of light snow will affect all taf sites through this morning as a weak area of low pressure tracks south of the region. There is not much deep moisture with this system, so the snow will be light with intermittent periods of near moderate snow. Ceilings and visibilities will be predominantly MVFR but visibilities will lower to IFR in the bursts of near moderate snow and brief periods of ceilings just under 1000 feet are likely. Snow will end by 19z and ceilings will lift to VFR at kalb and kpou later Monday afternoon while lifting to around 3000 feet at kgfl and kpsf. Light winds will become north to northwest between daybreak and noon and then increase to 10-15 kt with gusts 20-25 kt through Monday afternoon. Outlook... Tuesday night: no operational impact. No sig weather. Wednesday: moderate operational impact. Chance of snow. Wednesday night: high operational impact. Likely snow...sleet. Thursday: moderate operational impact. Chance of rain showers...ra. Thursday night: no operational impact. No sig weather. Friday: no operational impact. No sig weather. && Hydrology... light to moderate snow will taper off later today into this evening. Another seasonably cold and dry stretch is likely tonight through most of the day Wednesday. Some thickening of ice is possible on the main Stem rivers, lakes and streams. Another storm system is expected late Wednesday into Thursday and this storm will bring snow changing to a wintry mix and/or rain to the region. As of right now, about a quarter to half inch of liquid equivalent is expected. Drier weather looks to return late in the week with slightly above normal temps, but overnight lows should fall below freezing with any snow melt refreezing. As a result, river and stream levels will generally hold steady through the end of next week and widespread snow melt, ice movement or flooding is not expected at this time. 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 until 4 PM EST this afternoon for ctz001-013. New York...Winter Weather Advisory until 4 PM EST this afternoon for nyz038>040-047>054-058>061-063>066-082. Massachusetts...Winter Weather Advisory until 4 PM EST this afternoon for maz001-025. Vermont...none. && $$ Synopsis...kl/wasula

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