Area Forecast Discussion
Issued by NWS Albany, NY

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000 FXUS61 KALY 261710 AFDALY AREA FORECAST DISCUSSION National Weather Service Albany NY 1210 PM EST Fri Feb 26 2021 .SYNOPSIS... High pressure will move over New York and New England today, and then shift off the New England Coast tonight. A low pressure system moving across the Great Lakes Region and a warm front will bring some snow and light mixed precipitation transitioning to rain on Saturday. Milder weather is expected on the weekend, as another disturbance will bring some light precipitation back into the region to close the weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Clouds quite slow to exit but they are making slow progress east and many areas are seeing sun, or increasing sun. Those trends will continue through the afternoon as low level ridging is centered over us, but this dissipating small piece of upper energy with its area of clouds just has to exit. Winds will be light through the afternoon. Highs will be in the mid to upper 30s with lower 40s mid Hudson Valley and NW CT, and around 30 higher terrain.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY/... Tonight...A split jet stream will impact the forecast area with a north stream disturbance approaching from the upper Midwest and Great Lakes Region, and a southern stream disturbance moving from the TN Valley to the Mid Atlantic States. In the quasi- zonal west to southwest flow aloft clouds will quickly thicken and lower with the isentropic lift increasing on the 290/295K surfaces. The low-level baroclinic zone strengthens over NY and New England between the departing sfc high east of Nova Scotia and the southern stream low pressure system moving towards the mid Atlantic States. The column is cold enough for light snow to break out prior to daybreak once it moistens. Expecting coatings to a few tenth on an inch in the valleys with an inch or so over the southern Adirondacks, and the eastern Catskills as the south to southwest low-level jet increases. Lows will be in the 20s with upper teens over the southern Dacks and southern Greens. Temps will likely steady or slightly rise after midnight. Saturday...An anomalous LLJ of 40-60 knot moves over the region ahead of the warm front and low pressure system moving over southeast Ontario towards southwest Quebec by the afternoon. Strong upward vertical motion due to the differential thickness advection and isentropic lift overspreads the forecast area. A burst of snow will continue over the southern Adirondacks, and then the pcpn may mix with some sleet or a very brief period of elevated patchy light freezing rain. The snow may transition quickly over the southern Greens and Berkshires in the early pm to rain. WPC guidance and the HREFs FRAM output is showing some light freezing rain over the higher terrain in the forecast area, but looking carefully at the model soundings from the NAM/GFS, the profiles look isothermal. We did add a low chance of freezing rain over the high peaks of the southern Dacks and southern Greens for a couple of hours with minor accums of a coating to a few hundredths. The cold air is not expected to remain in place and we expect a quick transition to rain in many locations. In fact, the H850 0C line quickly moves north of the entire forecast area by about 18Z/SAT. 2-4" snow amounts are possible in the southern Adirondacks, 1-3" over the southern Greens, eastern Catskills, and the northern Berkshires, and a half an inch or less in the valley areas, except the Lake George/Glens Falls/northern Saratoga Region may get 1-2". Expect a shadow effect diminishing the pcpn over the eastern Mohawk Valley, Capital Region, and even the Schoharie Valley with the strong southwest flow in the H850-500 layer. The pcpn should quickly taper off the in the early to mid afternoon as low pressure move across southern Quebec and a warm front moves through. Highs on Saturday will be in the low to mid 40s from the Capital Region and the Mohawk Valley south and west with some upper 40s possible. Expect mid 30s to lower 40s north and east. Saturday Night...A few rain/snow showers linger over the southern Adirondacks, but then a brief period of fair and dry weather occurs over the forecast area, as a 1025 hPa or so sfc high builds in from the lower Great Lakes Region over NY and New New England. Lows fall back into the 20s to lower 30s. Some high mid and high clouds increase toward sunrise ahead of the next southern stream short-wave approaching from the Midwest and Ohio Valley. Sunday...A big change from the previous forecast is the slower timing of the next disturbance and the subsequent leading edge of the pcpn. The clouds will thicken and lower from southwest to northeast and the isentropic lift does not increase for measurable pcpn to move in until 15Z-18Z from the Capital District south and west. This will allow the column to warm for the pcpn to be mainly rain with perhaps a little snow. The latest 00Z CMC/NAM/ECMWF all have the warm advection pcpn barely getting to Albany by 18Z. All this said, the threat for some light freezing rain was removed do to the slower onset and collaboration with the neighboring offices. Looking for mainly light rain and a light snow/rain mix over the northern zones. Likely and high chance PoPs were used. Highs will be in the upper 30s to mid 40s across the region. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... Rain and snow showers will remain possible Sunday night as the first cold front associated with the surface low departing into Quebec crosses the area. The actual timing of the front remains uncertain amongst the guidance with some during the evening and others after midnight. In the wake of the front, precipitation should briefly wane or even come to an end as mid-level dry air punches into the region. With lingering clouds in place, low temperatures will only dip into the upper 20s across some higher terrain areas and the low to mid-30s in the valleys. On Monday, guidance is beginning to converge on a dry start with a more potent upper-level trough and arctic front passing across the region late in the day. Due to the mild start, surface temperatures will likely reach the 30s across the higher terrain and the Mohawk Valley to the 40s elsewhere. Guidance suggests steep low-level lapse rates as well as some weak instability develops ahead of the arctic front. This could lead to some convective rain and/or snow shower potential. Activity will likely remain to the north and west of the Capital District during the afternoon and then progress farther eastward during the evening. It is not out of the realm of possibilities a few heavier snow showers or even squalls form, but this remains uncertain. In the wake of the front Monday night, temperatures will plummet and winds will become gusty, possibly in the 25 to 35 mph range. Lake- effect and upslope snow showers will linger as well prior to the arrival of drier air. Low temperatures will dip into the single digits across the higher terrain to the teens elsewhere (except lower 20s in portions of the mid-Hudson Valley). High pressure builds into the region on Tuesday with drier but seasonably chilly weather. Winds will gradually lessen throughout the day as the pressure gradient weakens. Highs will only reach the 20s to mid-30s (5 to 10 degrees below normal). There may be additional chances for precipitation on Wednesday and Thursday, but model guidance continues to widely vary on possible solutions. Will just run with a blended approach at this time and go no more than low chance pops at this time. && .AVIATION /17Z FRIDAY THROUGH TUESDAY/... Through 12z/Sat...This TAF update increased cloud coverage across KALB/KPSF/KGFL this morning as the upper-level trough continues to produce a rather large area of stratocumulus clouds. Still, expect VFR conditions at these terminals with the exception of KPSF, where some brief MVFR periods are possible for a few more hours as bases are just below 3000 feet. These clouds have stayed away from KPOU, so expect SKC conditons there this morning. High pressure will then build into the region this afternoon with a decrease in clouds. Tonight, expect some high cirrus clouds from time to time in the evening with a quick increase and lowering of clouds toward daybreak as the next system approaches from the south. Some precipitation may break out prior to 12z/Sat, so will introduce VCSH for this update. A rain/snow mix may start at KPOU just before 12z/Sat. Wind will remain under 10 kt through much of the TAF period at various directions. Wind at KALB will pick up from the south at 10- 15 kt by the end of the TAF period. As a low-level jet approaches the area tomorrow morning, LLWS will become a concern for most terminals, but will likely begin at KGFL/KPOU just prior to 12z (as surface winds should remain nearly calm). Outlook... Saturday Night: No Operational Impact. NO SIG WX. Sunday: Moderate Operational Impact. Chance of RA. Sunday Night: Moderate Operational Impact. Chance of SHRA...SHSN. Monday: Low Operational Impact. Breezy. Slight Chance of SHRA. Monday Night: Low Operational Impact. Breezy. Slight Chance of SHSN. Tuesday: No Operational Impact. NO SIG WX. Tuesday Night: No Operational Impact. NO SIG WX. Wednesday: Low Operational Impact. Slight Chance of SHRA. && .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. Mainly light snow showers are expected this morning across the southern Adirondacks and the western Mohawk Valley. Additional light snow and rain is possible Saturday with temperatures rising above normal to close the weekend. Some snow melt and ripening of the snow pack is possible. Total QPF from the Saturday system will range from a tenth to third of an inch with some locally higher amounts over the southern Adirondacks, eastern Catskills, and the western New England higher terrain. Another system will bring light precipitation to close the weekend mainly in the form of rain. A strong cold front with snow showers is expected to move through on Mon-Mon night with below normal temperatures possible Tuesday before rising to near normal levels for the mid week. 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...Wasula NEAR TERM...NAS SHORT TERM...Wasula LONG TERM...Rathbun AVIATION...Evbuoma HYDROLOGY...NAS/Wasula

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