Area Forecast Discussion
Issued by NWS Binghamton, NY

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000 FXUS61 KBGM 070248 AFDBGM Area Forecast Discussion National Weather Service Binghamton NY 948 PM EST Fri Dec 6 2019 .SYNOPSIS... Lake effect snow will be southeast of Lake Ontario tonight into early Saturday. Mainly dry weather is expected this weekend, followed by rain for Monday and Tuesday. && .NEAR TERM /THROUGH SATURDAY/... 945 PM Update...Increased PoP overnight across Onondaga County as lake effect band is now starting to form and snow appears highly likely. Also, just made some minor changes to hourly temperatures to align with current observations and trends. 625 pm Update...Water vapor imagery shows upper trough dropping into Central NY and into the Southern Tier. Forcing is enough to make snow shower activity more widespread than previously forecast, so have increased PoP for the next few hours across Central NY. Also, some of the showers have been quite heavy, so localized amounts of a quick half inch to possibly an inch will be possible. 330 PM Update: No real changes with this update apart from minor adjustments to taper rain chances off a little sooner in NE PA, with most of the precipitation now north of the PA border ahead of the cold front. Previous discussion: The forecast remains largely on track this afternoon, with much of the precipitation north of the southern tier of NY. A few rain/snow showers are being seen across the southern Tier, with any precipitation across PA looking like hit and miss periods of light rain. Otherwise, light snow continues mainly north of a line from Oneonta-Ithaca-Dansville, with a rain/snow mix in the lower elevations. Still looking like a general 1 to 2 inches from that line, increasing to around 3 to 4 inches of snow heading northward towards the I-90 corridor and the western Mohawk valley before snow associated with this clipper system winds down tonight. Overnight, a shift to NW flow will bring in another round of snow downwind of Ontario. The main changes with this update have been to increase the coverage of snow to allow for better chances for a few snow showers to develop across Oneida county. However, the thinking still stands that our best chances will be for bands to set up and extend across Onondaga, Cayuga, and northern Cortland counties, extending downwind into Chenango and Otsego counties with healthy NW flow and a connection to the Georgian Bay. Additional totals up to 2 to 4 inches will be possible across the I-90 corridor and western Mohawk valley with lesser totals below an inch elsewhere. With higher amounts still not looking likely, will hold off on any advisories. Otherwise, lingering lake effect snow showers wrap up into Saturday afternoon with a ridge building in and our flow turning lighter. Temperatures drop generally back into the teens to low 20s tonight with the passing cold front, peaking in the 20s Saturday afternoon with a colder airmass in place. && .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/... 306 pm update... Main concerns in the short term remain centered around a drastic shift in the weather pattern Sunday night into Monday with much warmer temperatures and a transition from a quick/light wintry mix to rain. Will also be watching the potential for minor flooding, mainly along the smaller tributaries of the Upper Susquehanna and Upper Delaware river basins, and near the Lackawanna river in ne PA...where there is around an inch of snow water equivalent and where the heaviest rain is expected. Weather conditions Saturday night and most of Sunday will be very quiet with high pressure sliding to the east. The primary concern Saturday night will be the potential for very cold temperatures as a good portion of the area will be under mostly clear skies with strong raditional cooling. Lows are expected to drop into the single digits above zero and teens. The high will shift to the east as the next system begins to move into the Ohio Valley/srn Great Lakes Sunday evening. A tight surface pressure gradient will develop across the Northeast/mid Atlantic which will allow for strong southerly flow to begin Sunday night. A strong stream of warm moist air from the southern Atlantic coast will advect north into PA/NY Monday morning and spread precipitation north to the south through the area. Thermal profiles and subsequent p-types will be challenging during this time as the cold air near the surface...around 30 deg...gets trapped under a rapidly warming air mass aloft. The initial push of precip will be light on the front end Monday morning, with a slight chance of sleet and freezing rain...but should change to all rain as the boundary layer warms above freezing and increase in intensity and cover through the late morning. A strong inversion just above the surface will likely also produce an abundance of low clouds and fog. The axis of moisture on Monday will ride up along the I-95 corridor during the day and likely brush the Poconos and Catskills with a solid half to 1 inch of rain. The rain will likely shift further east Monday night, but persist in the form of light rain showers into Tuesday morning. The surface low will track from the sern Great Lakes into srn Quebec by early Tuesday morning with a drawn-out slow moving cold front extending south along the Appalachian Mtns. Along and ahead of this front will be the focus for an extended period of light rain Monday night into Tuesday where there should be sufficient time and heating to melt a good portion of the snowpack. Surface dewpoints in the 40s will aid in the melting of snow during this time. Latest modeled snow water equivalent across the region is roughly 1-2 inches in central NY and along the nrn tier of PA. The combination of the initial push of mdt- hvy rain on Monday, combined with an additional quarter of an inch or so of rain and an inch of snow melt may put enough water into some area basins to rise smaller streams and creeks to bankful, and possibly cause minor flooding for the usually sensitive areas...especially the Upper Susquehanna and Upper Delaware. && .LONG TERM /TUESDAY THROUGH FRIDAY/... 306 pm update... Rain showers continue early Tuesday before the back edge of the precip moves through wrn NY and the front edge of the cold Arctic air moves in later in the day. The cold front will start to make strong progress east later Tuesday into Tuesday night with the upper trough catching up and kicking the system out to sea. The onset of much colder and drier air will arrive Tuesday afternoon/evening with any remaining rain showers transitioning to snow showers quickly as temperatures go from the lower 40s to the upper 20s in a short period of time. The focus then shifts to the potential for accumulating lake effect snow, mainly north of the Thruway Tuesday night through Thursday. Strong cold air advection and a persistent west wind will put the focus across the northern counties. There are still a lot of details to be worked out with respect to the LES potential, but the air mass will definitely be cold enough...850mb temps around -15 to -20 C...for heavy lake snow in some areas downwind of Lake Ontario. Much colder temperatures are on tap for the middle part of next week...with highs in the 20 and 30s...and overnight lows in the teens. && .AVIATION /03Z SATURDAY THROUGH WEDNESDAY/... 630 pm update... Lake effect snow has expanded across CNY early this evening with even some sprinkles at AVP. IN general MVFR conditions tonight improving to VFR Saturday. With the northwest flow AVP should only have MVFR cigs with mixed precipitation the first 2 hours then VFR. ELM mainly VFR too with the first 4 hours with a MVFR tempo in snow showers. RME will be east of the bulk of the snow showers. Up to 04z also a tempo for MVFR. As the flow shifts a little to the west late tonight a return to MVFR 9 to 15z. ITH fuel alternate MVFR to continue all night with some IFR up to 04z. Return to high end MVFR at 12z then VFR at 19z. BGM similar with fuel alternate MVFR all night improving to high end MVFR at 13z then VFR at 20z. SYR is expected to have the steadiest snow tonight. MVFR all night with possibly some IFR from 07 to 11z. VFR at 18z. Northwest winds tonight around 6 kts. West to northwest winds at 8 kts Saturday. Outlook... Saturday night through Sunday evening...VFR. Monday and Tuesday...Restrictions likely with a broad area of rain across the region. Wednesday...Restrictions possible in lingering snow showers. && .BGM WATCHES/WARNINGS/ADVISORIES... PA...None. NY...None. && $$ SYNOPSIS...BJG/HLC NEAR TERM...HLC/MPK SHORT TERM...BJT LONG TERM...BJT AVIATION...TAC

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