Area Forecast Discussion
Issued by NWS Albany, NY

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000 FXUS61 KALY 271145 AFDALY AREA FORECAST DISCUSSION National Weather Service Albany NY 645 AM EST Sat Feb 27 2021 .SYNOPSIS... A storm system will push across the area today with snow and a wintry mix changing to rain. Drier weather returns tonight as high pressure builds into the area. Another system will move across the region later Sunday with periods of rain and perhaps a wintry mix across the higher terrain. Temperatures this weekend will run slightly above normal. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... A Winter Weather Advisory is in effect for western Ulster and Greene counties until 11 AM EST... A Winter Weather Advisory is in effect for the southern Adirondacks and the southern Green Mountains of southern Vermont until 2 PM EST... As of 628 AM EST... An area of low pressure will lift northeastward from the Great Lakes into Quebec today as a warm front lifts northward across New York and western New England. Precipitation continues to expand northward across the area as the main band of snow has already reached northern areas (Lake George Saratoga Region into southern Vermont). Within this band, visibilities have been reduced to a half of a mile or less at times. A few early reports across the region have observed around an inch or less of snow. South of this main band, precipitation coverage has lessened and become more scattered in nature. Pops were adjusted based on the latest radar and projected model trends. A changeover to a wintry mix and/or plain rain is expected to occur within the next couple hours across southern areas and then areas farther north through the morning. Forecast soundings suggest that cold air will become trapped near and just above the surface across some areas this morning while air aloft rises above freezing. This will allow snow to mix with and change over to sleet and/or freezing rain for a time. This will be most common across the higher terrain areas (eastern Catskills, southern Adirondacks and southern Green Mountains) where a deep snowpack remains in place (around 12 to 24 inches). As a result, Winter Weather Advisories were issued for these areas. Expect snowfall amounts to generally range from 1 to 3 inches with flat ice amounts up to a tenth of an inch. Outside of the Winter Weather Advisory areas, generally less than one inch of snow is expected this morning. Most of the precipitation will depart to our east during the afternoon with just some lingering scattered showers possible until sunset (greatest coverage across the Adirondacks). Total QPF amounts will range from 0.25 to 0.50 of an inch across the area, except the Capital District to the Mohawk and Schoharie valleys where precipitation shadowing is expected to occur (generally 0.10 of an inch or less expected here). High temperatures this afternoon will range from the mid- to upper 30s across some higher terrain areas to the mid-40s in the valleys. && .SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY NIGHT/... As this system departs to the east, high pressure will build into the region tonight. Clouds will partially clear with winds going calm. Despite weak cold air advection behind this system, temperatures could fall quickly later tonight as suggested by MOS guidance, especially if prolonged clearing occurs. Expect lows in most areas to bottom out in the 20s. On Sunday, the high will move off to the east as the next system approaches from the south and west. This feature contains both a northern stream feature (tracking from the Great Lakes toward Hudson Bay) and southern stream feature (tracking from the Ohio Valley to the mid-Atlantic coast). Despite the split flow, some precipitation is expected to spread across the region as another warm front lifts through our region. Guidance continues to slow on the arrival of this precipitation, not bring much in until the afternoon hours from southwest to northeast. So, POPs were adjusted accordingly. Temperatures should rise above freezing across most areas before the precipitation starts so we are looking at a mainly rain event. However, should any cold air remain trapped (especially in the higher terrain areas), some light snow, sleet or freezing rain will be possible once again. High temperatures will reach the upper 30s across some higher terrain areas to the lower and mid-40s in the valleys. We will remain in the warm sector for much of Sunday night before the cold front pushes from west to east toward daybreak Monday. So, occasional rain showers are expected across the area. As colder air arrives along and in the wake of the front, precipitation may mix with and/or change to snow, especially across higher terrain areas, before ending. Low temperatures will drop into the upper 20s in the higher terrain to the mid- 30s in the valleys. && .LONG TERM /MONDAY THROUGH FRIDAY/... The extended forecast will feature an arctic cold frontal passage Monday afternoon into the evening with a threat of isolated to scattered snow showers and snow squalls. Blustery and very cold conditions will follow in the wake of the boundary. High pressure ridges in Tuesday into Wednesday with fair and dry weather with temperatures rising back to normal or slightly above normal readings for the mid week. A cold front approaches late Thu into Friday with isolated rain or snow showers and temperatures settling back to early March readings. Mon-Mon Night...A pair of cold fronts will impact the region. The first boundary goes through in the morning into the early afternoon. A strong mid and upper level short-wave with an arctic cold front moves across NY and New England in the late afternoon into early evening. The Snow Squall Parameter based on the 0-2 km RH, mean wind speed, and potential instability (theta-e decreasing with height) is greatest from the Capital Region and the Berkshires north and west on the NAM and to an extent the GFS. There is also some instability with the steepening lapse rates. Isolated to scattered snow squalls are possible especially in late afternoon into the early evening. The timing of the front is faster on the NAM compared to the GFS. We will continue to mention this possible threat in the HWO. Snow amounts will likely range from a few tenths to an inch or so with any snow showers or squalls. The threat should diminish shortly before or just after midnight. It will become blustery and very cold with west to northwest winds of 15-25 mph with some gusts 30-45 mph. A wind advisory may be needed later is more frequent gusts of 46-57 mph look probable. H850 temps plunge to -24C to -29C from northwest to southeast by Tues morning on the GFS. Wind chills may reach advisory levels in the southern Adirondacks around -20F with zero to 15 below zero readings over the rest of the region. Highs on Monday will be in the upper 30s to mid 40s in the valleys with a few upper 40s over the mid Hudson Valley into NW CT, and upper 20s to mid/upper 30s over the higher terrain. The sharp drop in temps may also cause a flash freeze situation in some locations. Lows Monday night will be zero to 5 below over the southern Dacks, and single digits to lower to mid teens over the rest of the forecast area. Tuesday-Wednesday night...Blustery and cold conditions will continue on Tuesday in the wake of the front. Temps will run below normal Tuesday by 10-15 degrees. Highs will only be in the teens to lower 20s over the mtns, and mid 20s to lower 30s in the valley areas. High pressure will build in from the OH Valley and lower Great Lakes Region to the Mid Atlantic Coast during the afternoon. The winds will subside towards nightfall. The mid and upper level flow becomes less amplified Tue night. Another cold night will be on tap with lows mainly in the single digits and teens. The sfc anticyclone moves off the coast with warm advection occurring into Wednesday. Some mid and high clouds may increase during the day and there is a small threat of an isolated sprinkle or shower southeast of the Capital Region, as the latest 00Z GFS/ECMWF and the majority of the Ensembles have any coastal system passing well to the south. Highs on Wed will be more seasonable with 30s over the mtns and upper 30s to mid 40s over the hills and mtns. Lows will be mainly in the 20s. Thursday into Friday...The southern stream coastal wave passes southeast of the forecast area. The mid and upper level trough amplifies over the northeast. Temps will continue to be normal to slightly above normal on Thu. A short-wave in the northwest flow and a moisture starved cold front may move through Thu night into Friday. A slight chance of rain/snow showers was placed in the gridded forecast. Temps may cool down to seasonable values to close the week. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
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A low pressure system approaching from the Great Lakes Region and warm front will continue to bring snow and a wintry mix transitioning to rain to eastern NY and western New England this morning into the afternoon. An occluded front will move through in the late afternoon into the early evening with drier conditions returning. Widespread low MVFR/IFR flight conditions are occurring at KGFL/KALB/KPOU/KPSF this morning with snow across the region. Expect the pcpn to change to rain quickly at KPOU by about 13Z/SAT, and then 15Z/SAT at KALB. Some rain may start to mix with snow at KPSF between 14Z-18Z/SAT. Further north, KGFL will remain snow the longest but will start to mix with some sleet and rain between 16Z-18Z/SAT. The precipitation will lighten and be plain rain or drizzle in the afternoon, but in the deeper moisture, widespread IFR conditions will persist with low cigs and IFR/MVFR vsbys (2-5SM). Some LIFR conditions are also possible especially near KPSF, as some melting of the snowpack will contribute to the lower vsbys there and possibly at the other TAF sites. Once the occluded front moves through between 21Z/SAT-00Z SUN, expect the cigs/vsbys to improve to MVFR levels and steady additional improvement to VFR levels is expected prior to midnight in the 01Z-05Z/SUN time frame. Scattered to broken cirrus may be around after midnight. The south to southeast winds will increase to 8 to 15 kts in the late morning into the afternoon with some gusts 20-25 kts at KALB/KPSF. The winds will shift to southwest to west at 8-12 kts in the late afternoon into the evening. West to northwest winds of 5-12 kts will occur early this evening before becoming light to calm early Sunday morning, as high pressure builds in. LLWS will continue prior to 18Z/SAT as 2 kft AGL winds will be 35-50 kts from a south/southeast direction and sfc winds will be 5-12 kts. We kept the LLWS going at KPSF until about 20Z but ended it at KALB/KGFL/KPOU at 18Z/SAT. Outlook... Sunday Night: High Operational Impact. Likely SHRA. Monday: Low Operational Impact. Breezy. NO SIG WX. Monday Night: Moderate Operational Impact. Windy With Gusts To 34 kts. Chance of SHSN. Tuesday: Low Operational Impact. Breezy. NO SIG WX. Tuesday Night: No Operational Impact. NO SIG WX. Wednesday: No Operational Impact. NO SIG WX.
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&& .HYDROLOGY... No major hydrologic issues are foreseen through the middle of next week. Some melting and sublimation of the snowpack in the valleys is expected during the day time over the next several days. NERFC forecasts show minor up and down changes in river flows due to the diurnal freeze/thaw cycle. River ice is not expected to break up over the next several days. Two separate systems will move across the region this weekend. The first on Saturday will bring snow and a wintry mix which will change to rain. The second on Sunday will bring mainly rain. Total QPF amounts for the Saturday system will range from 0.25 to 0.50 of an inch for most of the region, except generally less than 0.10 of an inch across the Capital District and Mohawk and Schoharie valleys. Total QPF for the Sunday system will range from 0.10 to 0.30 of an inch. A strong cold front with snow showers is expected to move through later Monday through Monday night. Much colder air returns Monday night and Tuesday. 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...Winter Weather Advisory until 11 AM EST this morning for NYZ058-063. Winter Weather Advisory until 2 PM EST this afternoon for NYZ032-033-042-082. MA...None. VT...Winter Weather Advisory until 2 PM EST this afternoon for VTZ013-014. && $$ SYNOPSIS...Rathbun NEAR TERM...Rathbun SHORT TERM...Rathbun LONG TERM...Wasula AVIATION...Wasula HYDROLOGY...NAS/Rathbun

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