269 FXUS61 KBGM 050545 AFDBGM AREA FORECAST DISCUSSION National Weather Service Binghamton NY 1245 AM EST Tue Mar 5 2019 .SYNOPSIS... High pressure will build into the area early this morning bringing mainly clear skies to the area. A cold front will push through late on Tuesday bringing snow showers and possibly snow squalls in the late afternoon and evening. Very cold air and lake effect snow will hit the area behind the front, for much of the rest of the week. && .NEAR TERM /THROUGH TODAY/... 730 pm update... Cloud cover has scattered out more than previously thought...so decreased clouds in the forecast tonight, along with a lowering of precip chances...except for the far northern counties where lake effect snow showers are possible. The loss of clouds will lead to slightly colder temperatures as well, so made slight adjustments to the overnight lows downward. Rest of the forecast remains unchanged with a round of scattered snow showers...possibly a few snow squalls later tomorrow followed by an extended period of lake effect snow through Thursday. Previous discussion... Westerly flow developed early in the afternoon and pushed the lingering lake effect north clearing much of the area. Flow becomes southwest this evening ahead of the approaching wave so that single band developing pushes north of Oneida county. This will bring a mainly clear and cold night to the area with a fresh snow cover. Wave and cold front moves into the western zones late in the day Tuesday and clears the area by around 03Z Wednesday. March instability creeping into the forecast sounding with some cape as the front pushes through. This will result in snow squalls, especially over the NY zones and along nrn PA. A lake band will develop in the WNW flow behind the front and continues beyond the period. && .SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/... 400 PM Update... The midweek period will feature very cold Arctic air, and fluctuating lake effect snow for counties along the New York Thruway, with at least scattered snow showers and flurries down to the Twin Tiers. 850mb temperatures dive to about minus-20 Celsius for Tuesday night through Wednesday night, before starting to moderate slightly into Thursday. Thus the dendritic growth layer will reside in the lowest 5 kft agl, with just about any cloud cover or moisture producing some fluffy snowflakes. Also, in addition to the instability already offered by the very cold air mass aloft with 1000-500mb thicknesses falling to about only 500 decameters, the ever-increasing sun angle of March will also produce diurnal instability Wednesday and Thursday afternoons, to eke out additional snow showers and flurries. The airmass will indeed be very dry, limiting coverage and accumulations of snow in a general sense. However, the primary lake feed off of Lake Ontario will be capable of yielding significant snow across portions of Onondaga-Madison-Oneida counties. The steadiest period of lake effect snow will be late Tuesday night through the day Wednesday...but it will linger Wednesday night and even Thursday morning. The lake effect snow bands do fluctuate through this period some, but will be mainly focused on a 280-290 flow. Deep moisture up to around 700mb or 10k feet agl, along with good lift in the snow growth zone on the forecast soundings indicate the potential for very high snow to liquid ratios (20:1 or even higher). Confidence of getting greater than 7 inches in any 12 hour period or 9 inches in a 24 hour period is now greater than 50 percent, enough for a winter storm watch across Onondaga-- Madison and Oneida counties. The highest confidence areas are north-central Onondaga county, northern Madison county and western Oneida county, where storm totals of 9 to 15 inches are possible. Late Tuesday night to Wednesday afternoon, and again Wednesday night into Thursday AM may include a Huron-to-Ontario connection which would produce higher snowfall rates; perhaps 1 to 2 inches per hour for a time. Unsure at this time exactly how far south this banding gets; some portions of northern Seneca, central Cayuga, northern Cortland, northern Chenango and Otsego could get involved at times as well...but snow amounts look much lower in these areas...perhaps 2-5 inches over a 24-36 hour period. Will continue to better define the details over the next day or so and may eventually need to upgrade the current winter storm watch area to a warning and/or advisory. A weak disturbance moves through Wednesday night into Thursday morning and will bring a better chance for scattered snow showers across the entire forecast area. Outside of the lake effect snow accumulations will be light; mainly less than 1 inch. Lake effect tapers off to flurries later Thursday and Thursday night as a surface high moves across Pennsylvania and southern New York. Lows Wednesday night and Thursday night will be mainly single digits above zero, yet with wind chills often below zero. Highs Wednesday will be roughly 20 degrees below climatology by only reaching mid teens to near 20. Temperatures Thursday will bump just slightly higher, reaching the low to mid-20s. && .LONG TERM /FRIDAY THROUGH MONDAY/... 415 PM Update... Friday and Friday night: 12z GFS continues to show a weak system passing by to the south of the region...bringing some light snow mainly to our NE PA counties. Most other guidance is further south and dry for our forecast area. Maintained slight chance to low end chance PoPs for the southern half of the area until model guidance comes into better agreement on this system. Saturday: Looking dry as a transient upper level ridge and surface high pressure center move over the region. Temperatures warming toward seasonable levels, with highs in the mid-30s to lower 40s. Saturday night through Monday: A strong low pressure system is progged to move into the Great Lakes during this time. Current guidance is in fairly good agreement on the general timing, precipitation amounts and type with this system. Current timing indicates precipitation will arrive from southwest to northeast late Saturday night or Sunday morning, in the form of a wintry mix (snow, sleet and freezing rain). Held PoPs to chance Saturday night, but then went to likely when confidence increases on Sunday. Currently it looks like the wintry mix would be rather brief and change to rain during the day Sunday as strong warm air advection and southerly flow take hold on the east side of the low. South-southeast winds could certainly be breezy this period. After overnight lows in the mid-20s to around 30 it turns much warmer on Sunday, with highs well into the 40s. The cold front looks to move through Sunday night with the upper level low over the region for next Monday. It will gradually turn cooler with lingering rain showers changing over to snow showers. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/... 1235 am update... VFR will rule this morning. Low level flow is West to Southwest keeping lake effect north of the TAF sites. This afternoon a cold front will pass through the NYS terminals with brief IFR restrictions due to snow showers between 21Z-01Z. MVFR possible in CNY due to snow showers starting at 18z. Persistent MVFR cigs/vsby most likely at RME as lake effect shifts into northern Oneida County this evening as the flow shifts to west. AVP will remain well south of the lake effect. Possible brief MVFR restrictions in the evening with the cold front. West to southwest winds at 5 knots shifting early this morning. Late morning increase to 5 to 10 kts then a shift to west around 20z. Outlook... Tuesday overnight through Thursday...Occasional restrictions possible for primarily the NY terminals from lake effect snow. Mostly VFR at AVP. Friday and Saturday...VFR. && .BGM WATCHES/WARNINGS/ADVISORIES... PA...None. NY...Winter Storm Watch from this evening through Thursday morning for NYZ009-018-036-037. && $$ SYNOPSIS...DGM NEAR TERM...BJT/DGM SHORT TERM...MJM/MDP LONG TERM...MJM AVIATION...TAC