Area Forecast Discussion
Issued by NWS Albany, NY

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000 FXUS61 KALY 251150 AFDALY Area Forecast Discussion National Weather Service Albany NY 650 AM EST Sat Feb 25 2017 .SYNOPSIS... An anomalously warm and humid air mass will be over eastern New York and western New England into this afternoon. A strong cold front will bring heavy rain showers, scattered thunderstorms and gusty winds to the region this afternoon into early this evening. Much colder air will filter into the area with some light accumulating snowfall especially over the higher terrain tonight, as blustery and cold conditions finish the weekend with temperatures more typical of late February. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... A Flood Watch remains in effect for the western Mohawk Valley, the upper Hudson, the southern Adirondacks, Lake George Saratoga region and southern Vermont from today through Sunday. See the Hydrology section for details... The entire forecast area is in a Slight Risk for the possibility of severe thunderstorms this afternoon into early this evening with damaging winds the main threat. As of 648 AM EST...The sfc map this morning looks similar to May 25th rather than Feb 25th for a large portion of the forecast area with temps in the 50s to lower 60s, except for a portion of the southern Adirondacks, and Lake George Region, where the warm front back southward as a cold front and became stationary with temps in the the 30s to lower 40s this morning. For example, KGFL is 39F at 633 am, and KDDH is 62F! Sfc dewpts are in the 40s and the 50s for a large portion of the forecast area with a southerly flow advecting in the milder temps and dewpts due to the ridge downstream and the strong flow ahead of the upstream upper level trough that will be turning negatively tilted as it moves across the Great Lakes Region and Midwest into southeastern Canada. The sfc cyclone associated with the negatively tilted upper trough will pass well north and west of the region towards James Bay this afternoon. However, a strongly forced cold front supported by impressive upper level dynamics /for example, the right entrance region of the H250 northern jet stream will interact with the left front quadrant of the subtropical branch of the jet stream over the mid-Atlantic States/ will swing across the region with chances of thunderstorms, some of which could be severe. The morning will start out with a cluttered warm sector with lots of stratus around. The stratus has been most evident across western New England and parts of the Hudson River Valley and into the Taconics. Some isolated showers or pockets of drizzle are possible this morning, but it looks likes the leading edge of the showers and scattered thunderstorms get close to the western portion of the ALY forecast area based on the latest 3-km HRRR and NAM at 20Z. The pre-convective environment is a classic cool season high shear-low CAPE set-up. 0-6 km bulk shear values of 50-75 kts, and 0-1 km values of 30-40 kts ahead of the front with low amounts of sfc based instability generally less than 100 J/kg based on the NAM/GFS. However, the MUCAPE values are 100-350 J/kg on the GFS with DCAPE values of 200-700 J/kg. Mid level lapse rates on both the GFS/NAM are in the 6.5C-7C/km range with a very strong sfc-H850 theta-e gradient from west to east with the front. PWATS will be in the two thirds of an inch to 1 inch range, as these values are 1 to 3 standard deviations above normal based on the latest GEFS. A strongly forced low topped line of convection is likely with perhaps some QLCS segments early on before fusing into a narrow cold front rainband between 20Z-01Z/SUN across the region. The latest 3-km HRRR has the QLCS elements getting into the western Adirondacks between 20Z- 21Z.The low-level helicity values are also high and SPC did include a 2% contour for tornadoes, however, we agree that damaging winds will be the main threat, and we foresee several special weather statements /SPSs/ focusing on the winds and heavy rainfall, and potentially some SVR`s. In the gridded forecasts we included the wording heavy rainfall and gusty winds with the thunderstorms. The GEFS does have a strong +v component of the wind anomaly /strong southerlies/ over the region between 18Z to 00Z. The h925 winds do increase to 30-40 kts ahead of the front. We have some southerly wind gusts of 30-40 mph ahead of the boundary. These fell short of the advisory level. Temps will not have far to go in many locations once the stratus burns off in the late morning into the early afternoon ahead of the front. We have highs in the lower to mid 60s in the valley areas with some upper 60s near the mid Hudson valley and mid 50s to lower 60s over the hills and mountains. Some locally heavy downpours are possible, but FFG values remain high outside of the Flood Watch for snowmelt and runoff in our area, so we did not expand the watch at this time. && .SHORT TERM /6 PM THIS EVENING THROUGH MONDAY/... Tonight...We are looking at a 10C difference in H850 temps over a narrow east to west corridor across the front with temps falling below 0C over the western Adirondacks at 21Z, and temps close to +8C over the Hudson River Valley into western New England. By 03Z, H850 temps on the GFS/NAM are below 0C across most of western New England and -8C to -9C over the Adirondacks/eastern Catskills, and the western Mohawk Valley. The scattered thunderstorms should diminish around 7-8 pm, but in the strong cold advection in the wake of the front, expect a quick transition to snowfall especially over the higher terrain, and then the lower elevations. 1-3 inches is possible over the western Adirondacks, portions of the eastern Catskills, and the southern Greens, and possibly the northern Berkshires. Valley areas north of the mid-Hudson Valley will likely have an inch or less. The western Mohawk Valley may get around an inch. The colder temps will try to slow down the runoff from the rain, but we believe the Flood Watch for rain and snowmelt still looks good for the northern half of the hydro service area where two thirds of an inch to and inch and a quarter is possible. We are expecting a half inch or less further south and east from the Capital Region and into the mid-Hudson Valley and NW CT. WPC placed the eastern Catskills and portions of the Capital Region north and west into a Marginal Risk of exceeding the FFG guidance, but with little QPF the past 10-12 days and higher zonal FFG values compared to BGM`s area upstream, we believe our current Flood Watch looks fine. Low temps tumble back to the 20s to lower 30s with a few teens over the southern Dacks by day break. The west winds will increase to 10 to 20 mph with some gusts in the 30-40 mph range. Sunday...A blustery and cold day is expected with the best mixing anticipated late in the morning into the afternoon. West to northwest winds of 15 to 25 mph will be possible with some gusts in the 35 to 45 mph range in the Capital Region...Mohawk Valley...Taconics...Berkshires...and the eastern Catskills. Our confidence was not high enough for a 3rd period wind advisory, and based on collaboration with neighboring WFO`s, we feel the gusts fall short at this time. A brief lake connection with the mixed layer winds veering to the northwest will keep some multibands snow showers/flurries going for the western Adirondacks/western Mohawk Valley/Schoharie Valley/eastern Catskills going through the morning into the afternoon with light accums of an inch or less. Much colder temps with mid 30s to lower 40s in the valley areas, and 20s to lower 30s over the hills and mountains. It will feel more like late FEB. Sunday night into Monday...High pressure builds in from the Mid Atlantic Region late Sunday into Sunday night...and then drifts offshore. Mid and upper level heights rise, and some low to mid level warm advection kicks in. Some scattered snow showers are possible over the western Adirondacks Sunday night into Monday. Lows Sunday night will be in the teens and 20s. Sunshine mixes with clouds well in advance of the next cold front on Monday with temps rising about 5-10 degrees above normal again with mid 40s to lower 50s in the valleys, and upper 30s to mid 40s over the mountains. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... Active weather will persist through much of the long term period, with a transition from zonal flow at upper levels to a broad trough over the northeastern CONUS and below normal temperatures by next weekend. The period starts out with high pressure over the region Monday evening, gradually shifting eastward off the east coast by late Monday night. With a zonal flow aloft, the next low pressure system will quickly approach from the central plains and mid Atlantic regions on Tuesday. The surface warm front associated with this system will lift through Tuesday afternoon/evening, spreading precipitation across the area, but will mention slight chance pops Monday night to account for wider time window if the system movement speeds up. Thermal profiles indicate potential for some mixed snow/rain at the onset, especially for areas north of Albany and over the higher terrain. Temps should warm enough for plain rain by late Tuesday morning or early afternoon. As the surface low lifts across the Great Lakes, precipitation will remain possible from Tuesday afternoon through Wednesday afternoon. A stronger system is then forecast to track from the Upper Great Lakes northeastward into southeast Canada by Wednesday. Our region will be on the warm side of cyclone initially, with the potential for warming into at least the upper 40s to lower 50s despite rainfall. If breaks of sunshine can occur, temperatures would be even warmer. The system`s cold front will push through in the Wednesday night time frame, with a chilly air mass filtering in behind the front. Rain looks to transition over to snow on the backside of the system, with chances for snow across the high terrain Wednesday night/Thursday. As the core of the upper trough moves over New York on Friday, another low pressure system will pass through the forecast area, bringing a chance for snow showers area- wide. Strong cold advection ensues Friday night, with lows potentially dropping into the single digits across the Adirondacks and into the teens elsewhere. Winter isn`t over yet. After a period of significant warmth this week, expect below normal temperatures for the first full week of March and the potential for snow on the ground in many locations. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/... A strong cold front will sweep east across the TAF sites late this afternoon. A period of moderate to heavy rain showers, strong gusty winds, and even a few rumbles of thunder will be possible as the leading edge of the front moves through, with light to moderate rain likely lingering in its wake. So expect conditions to drop to IFR or lower within the stronger thunderstorms. There is also potential for rain to change over to snow behind the front but this depends on how quickly the cold air can invade the region. Shower chances should gradually diminish after about 06Z/Sun but fog and low level moisture will likely keep conditions at MVFR/IFR through the end of the forecast period. Winds will be southerly increasing to 10-15 kt by late this morning with higher gusts around 25-30 kt at KALB. Some low level wind shear may develop toward afternoon where surface winds are relatively light and a southerly low level jet moves overhead. LLWS may need to be mentioned in subsequent TAF issuances. Winds will shift into the west with the cold front and increase to 10-20 KT with gusts of 25-35 KT possible, perhaps even stronger in any embedded thunderstorms. Outlook... Sunday Night: No Operational Impact. NO SIG WX. Monday: No Operational Impact. NO SIG WX. Monday Night: No Operational Impact. NO SIG WX. Tuesday: Moderate Operational Impact. Chance of RA...SN. Tuesday Night: Moderate Operational Impact. Chance of RA. Wednesday: High Operational Impact. Likely RA. && .HYDROLOGY... Flood Watch in effect for the western Mohawk Valley, the upper Hudson, the southern Adirondacks, Lake George Saratoga region and southern Vermont from today through Sunday. Runoff will result from a combination of snow melt over the past couple days and heavy rainfall this afternoon into this evening. At this time minor flooding of some main stem rivers is expected, including the upper Mohawk, smaller rivers/streams in areas with significant snow depth in the southern Adirondacks and southern Green Mountains of Vermont, and possibly even portions of the upper Hudson basin. There remains the potential for flooding for areas south of the watch, but confidence is much lower with less rainfall and snowmelt expected. So will continue to mention the threat in the HWO for possible expansion of the watch if conditions warrant. A warm and and moist air will be over the region into this afternoon. A quick moving, strong cold front is expected to bring a period of moderate to heavy rainfall this afternoon and early this evening. Total rainfall forecast of around a half an inch to around 1.25 inches is forecast through tonight, with the lowest amounts in the Mid- Hudson Valley and Northwest Connecticut, and the highest amounts over the western/southern Adirondacks. The time frame for greatest potential for flooding is during and after the cold front passage due to heavy rain/snow melt combination and subsequent runoff. The precipitation will change to snow quickly behind the front especially over the mountains, which will slow down the run-off tonight. Drier and colder air will filter in behind the cold front for Sunday, with some lake effect snow possible across the western Adirondacks and western Mohawk Valley. Strong west to northwest winds of 15 to 25 mph with strong gusts will also slow down the runoff later in the weekend. 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. && .CLIMATE... All-time February high temperature records set yesterday at Albany and Poughkeepsie. Albany reached 74 degrees, which broke the old all-time February record of 69 set yesterday. Poughkeepsie reached 73 degrees, which broke the all time February record of 72 set back in 1954. Also, Glens Falls set a daily record high yesterday of 59 degrees breaking the old record of 55 degrees set in 1985. && .ALY WATCHES/WARNINGS/ADVISORIES... CT...None. NY...Flood Watch through Sunday evening for NYZ032-033-038>043- 082>084. MA...None. VT...Flood Watch through Sunday evening for VTZ013>015. && $$ SYNOPSIS...Wasula NEAR TERM...Wasula SHORT TERM...Wasula LONG TERM...JPV/JVM AVIATION...KL/JVM HYDROLOGY...NAS/Wasula CLIMATE...WFO ALY is the U.S. government's official web portal to all federal, state and local government web resources and services.