Area Forecast Discussion
Issued by NWS Albany, NY

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893 FXUS61 KALY 181738 AFDALY Area Forecast Discussion National Weather Service Albany NY 1238 PM 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/...
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As of 1230 PM EST...Leading batch of precipitation did show some wet bulb processes for a wintry light mixture. This has since dissipated as we await for the main upstream precipitation to arrive which was progressing across the Catskills. Mesonet obs suggest temps into the Catskills were well above freezing so mainly wet conditions. Due to rather drier conditions across the remainder of the region, did delay the PoPs/Wx a bit per the trends in the HRRR. Otherwise, minor updates to the hourly grids. Prev Disc... An elongated areas of surface low pressure is located over the Midwest, associated with a positively tilted trough over the central Plains. Ahead of an approaching warm front, a strengthening low-level jet is in place over the region. This has allowed some light rainfall over central New York and central PA. Across our area over eastern NY and western New England, the low to mid levels are very dry (as seen in the 12Z KALY sounding). As a result, this approaching precip will likely evaporate as it heads towards our area for later this morning and into the early afternoon. Cannot totally rule out some spotty light rainfall, but most areas should stay dry, with just broken to overcast mid and high level clouds. Temps are currently in the mid 20s to low 30s across the area. Temperatures should gradually warm up above freezing across the entire area during the day today and this should occur before the steady precip arrives late today. Still, Any spotty precip that may arrive this afternoon could briefly have some light sleet or freezing rain over the high terrain of the Adirondacks at the onset, but no accumulation is expected and any impacts would be minimal and valley areas are not expected to see any frozen/freezing precip today. Based off the latest 3km HRRR, the steady precip will arrive from southwest to northeast between 5 PM and 8 PM today. With the strong low-level jet in place, 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.
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&& .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 SATURDAY/... 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 /18Z SATURDAY THROUGH THURSDAY/...
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Ahead of an approaching frontal system, flying conditions are currently VFR for all sites with bkn-ovc mid and high level clouds in place. A persistent southerly flow this afternoon will allow winds to increase to 5-10 kts, with a few higher gusts possible at KALB. Meanwhile, increasing moisture will allow ceiling heights to lower to MVFR levels by later this afternoon or early this evening. Although there may be a brief light shower this afternoon, steady rainfall won`t arrive until this evening from south to north (moving in between 22z and 00z). Visibility will drop to 3 to 5 SM in rainfall for this evening into tonight, with IFR conditions due to low ceilings likely for all sites. With a strong low-level jet aloft, some LLWS will be possible at KPOU/KPSF as surface winds generally remain under 10 kts, but winds around 2 kft will be around 40-45 kts. As the storm moves by to the northwest, steady rainfall will taper to just a few lingering showers for Sunday morning, with ceilings gradually improving through the morning hours back to VFR levels. After daybreak Sunday, winds will switch to the southwest and eventually west around 15-20 kts with some higher gusts, especially for KALB/KPSF. Outlook... 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.
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&& .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...Frugis/BGM/Thompson SHORT TERM...Thompson LONG TERM...IAA AVIATION...Frugis FIRE WEATHER...Thompson HYDROLOGY...BGM/Thompson www.weather.gov/albany

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