Area Forecast Discussion
Issued by NWS Albany, NY

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000 FXUS61 KALY 180950 AFDALY Area Forecast Discussion National Weather Service Albany NY 450 AM EST Sat Nov 18 2017 .SYNOPSIS... A low pressure system will approach from the west today, resulting in clouds and rain chances both increasing throughout the day. Rain will be widespread overnight with temperatures steady or increasing. A strong cold front will sweep across the area Sunday morning, resulting in windy conditions and falling temperatures. Precipitation will become less widespread and begin to mix with snow over the higher terrain. Lake effect snow will occur in favored regions Sunday night into Monday. && .NEAR TERM /THROUGH TONIGHT/... Early this morning, an elongated area of low pressure is located across the Central Plains and Upper Midwest. This low is downstream of a positively tilted shortwave trough crossing Colorado. An area of showers was located from southeast Ontario into eastern Ohio in a warm advection pattern along a strong low-level jet. This forcing is forecast to weaken somewhat as it encounters the remnants of an upper ridge and a dry airmass over the northeast US. Locally, mid and high clouds are continuing to stream into the area. Expect these clouds to continue to thicken and lower throughout the day. As the low-level jet increases modestly throughout the day, resulting in midlevel theta-e advection, showers will become possible. However, a stubborn dry layer will be in place at low levels, so expect only light/spotty precipitation for much of the daylight hours. Given the antecedent cold/dry airmass, precipitation could begin as a wintry mixture of rain and sleet for parts of the Adirondacks and Catskills, but impacts are likely to be minimal given the light precipitation expected. It may become a bit breezy in favored locations within the Hudson Valley with channeled south/southeasterly flow. Could see some gusts around 30 mph. Isentropic lift cranks up this evening into the overnight hours as H850 winds increase to 50-65 kt ahead of the aforementioned shortwave which will become neutrally tilted as it enters the northeastern US. PWATs of around 1-1.25 inches are forecast to advect into the local area. All sources of guidance are indicating widespread coverage of showers overnight. H850 temperatures increase to around 5-7C. Some concern that temps in the Adirondacks will hover near the freezing mark after sunset, which brings the specter of freezing rain in sheltered valleys. Consensus does favor temps remaining at or above freezing and rising especially by the end of the night. Included a slight chance for freezing rain where the surface wetbulb temp was at or below 32. Will continue to monitor this potential, but for now it appears any freezing rain will be spotty and short lived. && .SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/... Fairly good consensus among deterministic models and GEFS members in tracking the strengthening surface low up the St. Lawrence Valley, with sea level pressures in the upper 970s by the time it`s in southeastern Quebec by 00Z Monday. The low will drag a sharp cold front across the forecast area Sunday morning, with the frontal position roughly situated across the Hudson Valley at 12Z Sunday. H850 temps are forecast to drop from roughly 7C at 09Z Sunday to -6C by 18Z Sunday. The strong cold advection and strong pressure gradient in the southwest quadrant of the low leads to the concern for strong winds Sunday. CSTAR research has shown this particular low track to be favorable for strong winds over portions of the forecast area. However, H850 winds are not terribly strong at around 45 kt, and it is questionable how deeply the boundary layer will mix given what is likely to be a fairly generous coverage of clouds. In coordination with neighboring offices, will forego any wind headlines attm, given the uncertainty and the timing which will still be in the 3rd forecast period (post 12Z Sunday). Favored locations for strong wind gusts exceeding 40 mph are higher terrain above 1500 feet along with the Mohawk Valley and Capital District. Steady rainfall will taper to showers behind the front Sunday. With the influx of colder air, lingering precipitation will mix with and change to snow through the day. With Lake Ontario surface temps averaging around 10C, the lake should be activated quickly behind the frontal passage. Accumulation of up to 2 inches is possible over the Southern Adirondacks and Green Mountains Sunday. Parts of the western Mohawk Valley will likely see some snowfall, but given warmer temps at lower elevations, accumulation is relatively less likely during the daytime hours. Overnight, surface to 850 mb delta-T increases to near 20C and inversion heights rise to nearly 3 km agl per forecast soundings at Utica. Wind trajectories favor a band of snow with a possible multi-lake connection from Georgian Bay and possibly Lake Superior. Trajectories favor this band setting up across portions of the western Mohawk Valley. Given favorable inland extent parameters, the snow band may extend into portions of the Schoharie Valley and possibly into the Capital District/northern Taconics/Berkshires. Around 1-3" of snow is forecast for the western Mohawk Valley with generally less than an inch elsewhere depending on where exactly the band sets up. && .LONG TERM /MONDAY THROUGH FRIDAY/... Monday as colder air continues to move across the relatively warmer waters of lakes Ontario and Erie. However as ridging builds in and the low level flow backs the lake effect will shift from across central New York, the western Mohawk Valley and eastern Catskills northward into the western and southern Adirondacks as the day progresses. Additionally short waves rotating about the upper low as it lifts northeastward across eastern Canada and upslope flow will keep showers in the forecast most of the day especially along and north of I-90. At this time looking at additional snow accumulations 1 to 3 inches for the western Mohawk Valley and western/southern Adirondacks with less than an inch elsewhere. The shower activity is expected to wind down during the evening hours as the ridge takes hold at the surface and aloft. Ridging should only briefly be over the region Monday night into Tuesday as it`s expected to weaken and shift eastward as short wave dives out of central Canada and digs a trough over the Great Lakes Tuesday night into Wednesday bringing another low pressure system across the region. There are differences in the models handling this short wave energy; it`s amplitude, timing and possible interactions between northern and southern system energy. Have followed lead of the Weather Prediction Center to maintain forecast continuity which prefers a more flow separation. Please refer to their extended forecast discussion for details (PMDEPD). With this said limited chances for snow and rain showers Tuesday night and Wednesday as the main low expected to pass well to our north along with limited moisture. As for Thanksgiving, expecting fair weather at this time for Wednesday night through Friday with the region between systems. Guidance indicates the weather should be unsettled for a least some of the weekend. With extensive cloud cover and cyclonic flow across the region Monday below normal temperatures expected with brisk winds making it only feel colder. Readings are expected to rebound Tuesday to normal or a bit above with highs mainly in the 40s with sunshine and light southerly winds. With the passage of a cold front a return to seasonable temperatures Wednesday and with the passage of a secondary boundary below normal for Thanksgiving and Friday; however winds should be rather light. && .AVIATION /09Z SATURDAY THROUGH WEDNESDAY/... As the ridge axis across the region weakens and shifts eastward overnight into Saturday high and mid level clouds will stream in. Clouds will thicken and quickly lower late in the day into the evening as a strong low pressure system approaches from the west and rain moves into and develops over the local area. Expecting widespread MVFR by 00Z and IFR developing by late evening as clouds lower further and rain becomes steadier and heavier which will continue through the overnight hours. Winds will remain very light to calm overnight with a southerly flow developing Saturday morning. Southerly winds will increase to 6 to 10 knots by late morning/early afternoon with gusts into the teens at KALB as flow funnels up the Hudson River Valley. Winds will remain southerly with a bit of a shift to the southwest and will increase some in speed and gusts at KALB and KPSF buy evening. Outlook... Sunday: Moderate Operational Impact. Windy. SHRA likely. Sunday Night: Moderate Operational Impact. Breezy. Chance of SHRA...SHSN. Monday: Moderate Operational Impact. Chance of SHRA...SHSN. Monday Night: No Operational Impact. NO SIG WX. Tuesday: No Operational Impact. NO SIG WX. Tuesday Night: Low Operational Impact. Slight Chance of SHRA...SHSN. Wednesday: Low Operational Impact. Slight Chance of SHRA...SHSN. Wednesday Night: No Operational Impact. NO SIG WX. Thanksgiving Day: No Operational Impact. NO SIG WX. && .FIRE WEATHER... A low pressure system will approach from the west today, resulting in clouds and rain chances both increasing throughout the day. Rain will be widespread overnight with temperatures steady or increasing. A strong cold front will sweep across the area Sunday morning, resulting in windy conditions and falling temperatures. Precipitation will become less widespread and begin to mix with snow over the higher terrain. Lake effect snow will occur in favored regions Sunday night into Monday. && .HYDROLOGY... No hydrologic problems are expected on the main stem rivers through the next week. A strong low pressure system will approach from the Great Lakes Region today. Widespread rain will occur throughout the forecast area mainly late this afternoon into tonight. 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, with isolated higher amounts over portions of the Green Mountains. 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...Thompson NEAR TERM...Thompson SHORT TERM...Thompson LONG TERM...IAA AVIATION...IAA FIRE WEATHER...Thompson HYDROLOGY...BGM/Thompson is the U.S. government's official web portal to all federal, state and local government web resources and services.