textproduct: Binghamton

WHAT HAS CHANGED

Confidence in a significant snowfall event for parts of the area continues to increase Friday afternoon, Friday night and into Saturday morning. Some mixed precipitation and freezing rain is forecast across the Central Southern Tier of NY and the Wyoming Valley region of Northeast PA. Winter Storm Watches have been issued for where the highest confidence in significant snow and/or a combination of snow, sleet and ice exists.

KEY MESSAGES

1)Generally quiet and seasonable weather through Christmas day, very cold temperatures expected Thursday night.

2) A quick-moving system will produce snow, some heavy at times and a wintry mix (for parts of the area) Friday afternoon through Saturday morning.

3) A busy weather pattern is expected to continue with another system pushing through the area Sunday into Sunday night, bringing rain and pockets of freezing rain along with gusty winds.

4) A strong cold front moves through Monday morning. Lake effect snow, blustery and much colder weather is expected Monday through at least the middle of next week, with another clipper system possible around next Wednesday.

DISCUSSION

KEY MESSAGE 1..

High pressure settles over the area this evening with partly cloudy skies. A weak warm frontal system moves through the area after midnight tonight, which could initiate a few light snow showers or flurries. There is a low chance the spotty precip late tonight could also be in the form of very light freezing rain or freezing drizzle. A fairly strong cold front drops down from the north midday on Christmas. This front could also have some flurries or patchy freezing drizzle with it, and behind it. Temperatures tonight will be in the mid-10s to mid-20s for lows, then warming up into the mid- 30s to low 40s for highs on Christmas Day. A strong Canadian high pushes in from the north, with a light northeast flow Thursday night. Skies partially clear and temperatures are expected to drop below zero north of the Mohawk Valley. Expect single digits to mid- 10s for the rest of the area overnight into early Friday morning.

KEY MESSAGE 2...

Most model guidance is starting to come into better agreement on a quick hitting low pressure system and winter storm for our area Friday afternoon, Friday night and perhaps into Saturday morning. Most of the ensemble guidance, including the ECS, GEFS and CMC Ens is showing a stripe of accumulating snow, oriented NW to SE right through the core of our CWA. There are minor differences in the placement of the rather narrow snow band, with the CMC Ens and GEFS being slight north of the ECS still. The latest 19z NBM is following closely in the footsteps of the previous 13z NBM run; showing the highest probabilities for 6" or more of snow along a line from near NYC to BGM (40-60%) with a much broader footprint of elevated 4" or more probabilities spreading out over most of NE PA (except Luzerne), the Twin Tiers, Susquehanna region and east to Delaware county...this is where 40-80% probabilities for 4" or more of snow exists on the 19z NBM. The 50th percentile 19z NBM is very close to our official forecast (which heavily incorporated WPC QPF)and has a stripe of 6-9" of snow extending across Sullivan county, Pike, Wayne, Susquehanna, Delaware, Broome, Tioga, Cortland and Chenango counties....if anything the 19z NBM seems to have shifted slightly north and east with the axis of these possible higher snow totals. Further west/south the snow may end up mixing with sleet and perhaps freezing rain Friday night as a warm layer in the 750-800mb range attempts to push into the region. Just northeast of where this above freezing layer aloft pushes with likely be where the higher end snow totals from this event set up.

There remains quite the spread in the 25-75th percentile, for example between about 3-8 inches at Binghamton, 2-7 inches at Elmira and Scranton, 4-10 inches at Monticello and 3-7 inches at Ithaca. Along the axis of highest probabilities, totals and confidence the Winter Storm Watch was issued for the heavy snow potential. Further west and south, the Watch was issued for the combination of several inches of snow, sleet and some freezing rain. There does exist the potential for up to around a tenth of an inch of ice if the warm layer aloft is thick enough, out across portions of Steuben, Bradford and Luzerne counties. The axis of potentially heavy snow will be supported by a strong push of warm air advection and frontogenesis in the 700-850mb layer, noted by the GFS cross-section over BGM at 7 PM EST Friday. The surface low tracks well south of the area, from near Chicago to Pittsburgh, then off the Delmarva coast Friday night. Model guidance is however showing a negatively tilted 700mb trough and even weakly closed low skirting through the local area Friday night. This could cause local enhancement and better mesoscale snow banding over portions of the Twin Tiers, Catskills and Poconos of NE PA.

Timing for this event looks to have the steady snow quickly overspread the area Friday afternoon, becoming heavy at times late afternoon and evening. Mixed precip could arrive for our southwestern zones Friday evening, with periods of snow continuing elsewhere well into Friday night. The snow tapers off and becomes lighter, while lingering along the 700mb trough axis into Saturday morning.

Temperatures during this event will be cold. Starting off in the 10s to mid-20s Friday afternoon and holding fairly steady, but perhaps rising a few degrees for the evening and overnight hours. Everywhere remains well below freezing for the entire event. Snow to liquid ratios should be rather high where it remains all snow, likely between about 10-15:1. The snow will end up being weighed down, and much heavier/wetter to move around where mixing occurs.

Winds will be southeast during this event, between 5 to 15 mph for most locations. Some minor blowing and drifting is possible of the dry, powdery snow, but it should not be significant.

We will continue to closely monitor the latest model guidance trends and if/when confidence increases warnings and/or advisories will be posted. This system will likely have a big impact on post holiday travel, so be sure to check back for critical updates.

KEY MESSAGE 3...

The next weather system pushes into the area Sunday afternoon into Sunday night. There will be lingering low level cold air near the surface, but temperatures aloft will reach +5 to +8C at 850mb. This can set the stage for a mix of rain and pockets of freezing rain Sunday afternoon into Sunday night, especially for areas along and east of I-81, including the Catskills and Mohawk Valley. Overall confidence is low on just how much, if any freezing rain will occur...due to uncertainty in the exact thermal profiles near the surface. Temperatures should rise Sunday evening into Sunday night over the region, as increasing south winds and warm air advection take hold out ahead the low pressure center.

KEY MESSAGE 4...

The strong cold front moves through, likely Monday morning for most of the area. Temperatures aloft fall to -12C by Monday afternoon. Exact timing of the front and just how fast temperatures fall during the day Monday remains uncertain at this time. Lingering rain showers will changes to wrap around and lake enhanced snow showers during the day or afternoon on Monday. West-northwest winds increase Monday, Monday night and Tuesday, with strong gusts of at least 25- 40 mph certainly possible at times. The setup looks favorable for more lake effect snow (possibly significant) Monday night into Tuesday. PoPs where raised and blowing snow was added into the forecast for this time period. As usual, exact flow and therefore lake effect band position and inland extent are not certain this far out in time. Outside of the main lake effect, it will be very cold and blustery early to mid week with 850mb temperatures possibly getting down near -20C Tuesday morning. Will need to keep tabs on just hold cold it will be and very cold wind chills could be a factor at times. Watching another fast moving clipper out in the extended that will be approaching by next Wednesday, no details known on this system yet...but it is likely to produce more snow showers and/or lake effect for the region.

AVIATION /00Z THURSDAY THROUGH MONDAY/

VFR conditions through at least mid morning. As west-southwest flow picks up just off the surface ahead of an approaching dry cold front, marginal Low Level Wind Shear conditions are figured for BGM-ELM-AVP for a few hours around dawn; confidence too low or magnitude negligible farther north. Then, dry front passes during later morning-midday and winds will veer northwesterly while picking up somewhat through afternoon, with 15-20KT gusts. MVFR ceilings are anticipated to form behind the front for KSYR-KRME-KITH-KBGM. While depth of moisture does not suggest measurable precipitation, there is a small chance for brief patchy drizzle/freezing drizzle behind the front in late morning-midday at KBGM-KRME.

Outlook...

Thursday night to Friday midday...Mainly VFR.

Friday afternoon into Saturday morning...Snow with associated restrictions. Sleet may mix in at times for KELM-KAVP Friday night-early Saturday.

Saturday afternoon through Sunday early morning...Mostly dry but patchy flurries or even spotty freezing drizzle possible with lingering ceiling restrictions.

Sunday midday through Sunday night...Rain and restrictions likely.

Monday through Monday night...Cold frontal passage and gusty winds as rain showers change back to snow showers, especially NY terminals as lake effect becomes dominant.

BGM WATCHES/WARNINGS/ADVISORIES

PA...Winter Storm Watch from Friday afternoon through Saturday morning for PAZ038-043-047. Winter Storm Watch from Friday afternoon through Saturday morning for PAZ039-040-044-048-072. NY...Winter Storm Watch from Friday afternoon through Saturday morning for NYZ022>024. Winter Storm Watch from Friday afternoon through Saturday morning for NYZ025-044-045-055>057-062.