Scientific Forecaster Discussion

000 fxus61 kbgm 201827 afdbgm Area forecast discussion National Weather Service Binghamton New York 127 PM EST Wed Feb 20 2019 Synopsis... another light wintry mix today and tonight will move across the region, along with gusty south winds. Mostly quiet conditions later in the day Thursday through Friday into early Saturday. The next low pressure system will impact the region later Saturday through Sunday into Monday with more wintry mix and strong winds. && Near term /through Thursday/... Early this afternoon, light snow continues to slowly to advance northward into the southern tier. However, observations to our southwest are showing a fairly quick transition to sleet already and this has been reflected with this update. Both the dry air and early onset of a wintry mix have resulted in a slightly lower forecast with snow totals now. Highest totals look to be in the southern Catskills, Oneida County and in NE PA of an inch or two. Where a few moderate bursts occurred this morning, a few totals may still end up around 3 inches. The Winter Weather Advisory continues with the main concern continuing to be icing tonight. As of mid-morning, the leading edge of the snowfall is being eroded away by a considerable amount of dry air in place. With saturation being slower, snow totals were slightly reduced in portions of NE PA. The general expectation though of light snow this afternoon going to a wintry mix tonight and light rain or drizzle by Thursday morning is still in place. 340 am update... main concerns in the near term remain focused on the incoming wintery mix of snow, sleet and freezing rain later today and tonight...along with strong S/se winds across The Finger lakes tonight and noticeably warmer temperatures on Thursday with lingering light rain/snow showers to the north. High pressure at the surface shifting off to the east this morning but still having enough influence on the area to keep weather conditions quiet. High clouds have moved in, and will continue to see clouds thicken through the morning before snow moves in from the S/SW around 9 to 10 am into NE PA. Atmosphere still expected to be cold enough for all snow through most of the afternoon with the snow shield spreading to the northeast, and dropping 1-2 inches across central New York and 2 to 3 inches into NE PA. This part of the forecast remains relatively unchanged. However, there have been slight adjustments made to the total snow and ice accumulations...especially during the evening and early overnight hours. Model guidance has come into slightly better agreement with respect to the the depth and amt of warm air aloft and cold air near the surface. At this time there appears to be a greater potential of sleet rather than freezing rain...although light ice amounts are still this result has caused total snow amounts to be slightly higher than the previous forecast, although not substantially higher. With the p-type leaning more toward sleet, this will cut back on the ice accretion...with most areas of central New York less than 0... areas of NE PA 0.10" or less. Still expecting a change over of snow to sleet from west to east during the late afternoon and early evening time frame...and then a couple hours later, mixing with freezing rain. The freezing precip may end up actually being fairly light...more likely freezing drizzle as the column loses ice crystals aloft and the dry wedge moves in from the west. The sfc pressure gradient tightens this evening as the surface low to the west deepens slightly and moves east...and the high off the coast takes its time moving out of the area. These two features will cause sustained south/se winds around 10 to 20 mph and gusts up to 30 mph into The Finger lakes. Gusty winds are possible in the higher terrain of the Catskills and the Allegheny plateau, but the strongest winds will be from downsloping into The Finger lakes. Wintry mix will taper off west to east after midnight and change to mostly liquid (drizzle or light rain) for most of the area by or just after sunrise Thursday morning. The air mass behind the departing system will be fairly cold once again...and allow for a weak lake reaction across the far nrn counties into Thursday afternoon. Surface temperatures will warm into the upper 30s north and into the lower 40s south. Even with temperatures above freezing, the air mass aloft will likely be supportive of light snow or drizzle off the lake into mainly Oneida County. Areas south of the thruway will likely be dry most of the day Thursday as the dry punch and surface ridge axis pushes east. && Short term /Thursday night through Friday night/... 310 am update... fairly benign period expected in the short term with little if any precipitation behind the front Thursday night, then a gradual breakup of stratocumulus Friday into Friday night. Weak cold air advection will continue Thursday night along with west-northwest flow. The moisture that will exist will be quite shallow; confined to a sharp inversion around or below the 800mb level. While it appears that there will likely be stratocumulus for most of the area, the depth of the moisture will make precipitation hard to come by. The top of the layer reaches to about minus 10 celsius Thursday evening, which should prevent drizzle/freezing drizzle by then. However, a few scant flurries cannot be ruled out in central New York north of Cortland-Norwich and mostly east of Syracuse. With the clouds, temperatures will be prevented from dropping any lower than 20s for lows. Stratocumulus layer will thin with time of Friday, and as usual it will linger longest in north central New York while others will start getting into more sunshine especially in afternoon. High pressure will pass across the region Friday afternoon- evening, then just east by dawn Saturday. Highs of mid 30s-lower 40s Friday, will be followed by lows of upper teens-mid 20s Friday night thanks to a mostly clear sky allowing for radiational cooling. && Long term /Saturday through Wednesday/... 310 am update... main concern in the long term period, is the increasing signal for a possible wind event as a deepening low pressure system passes through the region Sunday into Monday. Also, the same system will bring varying types of precipitation ahead of, during, and behind the system. A low pressure center is projected to exit the Central Plains Saturday, which then rapidly deepens Saturday night into Sunday while moving through the western Great Lakes into Ontario- Quebec. To differing degrees, yet with the same general idea, the European model (ecmwf) Canadian and especially GFS models have this occur as southern stream and northern stream upper waves phase with each other while lifting northeastward. Based on local studies there are several parameters meeting thresholds of past stronger wind events including 925-850mb winds exceeding 50 knots, low level lapse rates in excess of 8 deg c/km, as well as a strong pressure rise-fall couplet in terms of 6 hour pressure change. While zone of strongest winds and pressure rises appears to translate from western to northern New York and especially into Canada, areawide it appears that it will get quite gusty Sunday through Sunday night and perhaps into Monday as well. If a verbatim GFS solution were to pan out, damaging gusts are not out the question especially from The Finger lakes to Mohawk Valley areas but perhaps further south too. Sometimes the magnitude of a potential wind event looks high several days out, only to diminish as it gets closer. For now though, we will be adding mention of this potential to our local hazardous weather outlook for northern parts of our area to raise awareness, where potential is higher, and we will otherwise continue to monitor trends in coming days. Besides wind, the other impacts of this system of course will involve precipitation. Strong warm air advection will occur especially later Saturday into Sunday. As increasing moisture and lift occur on the front side of the system, a shield of precipitation will lift south to north across the area later Saturday through especially Saturday night. It is not totally impossible that a brief wintry mix could occur, especially higher terrain east of I-81, but overall it appears strength of warm air advection as well as relatively limited cold air damming in the low levels will make rain the predominant precipitation type. Temperatures will surge into Sunday with highs of at least upper 40s-lower 50s expected. Blast of cold air advection and gusty winds will then occur later Sunday through Monday. What is left of rain showers will change back to snow showers Sunday night. Some accumulating lake snows could occur into Monday in parts of central New York with gusty cyclonic flow on the back side of the system with potential to pick up Great Lakes moisture from well upstream. Then, brief ridging by Monday night into Tuesday appears to yield a temporary respite of quiet weather. && Aviation /19z Wednesday through Monday/... snow is moving into northeastern PA and the southern tier of New York early this afternoon and should reach krme and ksyr by mid afternoon. Ceilings and visibilities will gradually lower with the arrival of the snow this afternoon to the MVFR and IFR range. The highest chances for IFR visibilities reside in the early and mid afternoon hours. The onset of the snow may vary slightly from what the 18z tafs given some locations have gone very quick from VFR to IFR further south and others are much slower to form restrictions. Ceilings will likely some more tonight with the snow changing to freezing rain this evening. Sleet is possible as well still this evening. This set of tafs attempted to fine tune the timing of any sleet but some uncertainty still remains. Winds will be southerly with some gusts to 20 knots possible at kith. Low level wind shear is likely this evening as well with the highest chances is the 3-10z timeframe. Current thinking is that ceilings will be slower to lift tomorrow than what some of our tools show with IFR ceilings lifting to MVFR in the morning. Westerly wind gusts close to 20 knots are possible tomorrow morning. Outlook... Thursday afternoon and night... MVFR ceilings slowly lifting Thursday afternoon except at krme where some lake effect precipitation is possible. Friday and Saturday...VFR under high pressure. Saturday night through Monday...restrictions likely with rain, perhaps a brief wintry mix at the start through Sunday. Ceilings slowly improving on Monday. && Bgm watches/warnings/advisories... PA...Winter Weather Advisory until 7 am EST Thursday for paz038>040- 043-044-047-048-072. New York...Winter Weather Advisory until 7 am EST Thursday for nyz009- 015>018-022>025-036-037-044>046-055>057-062. && $$ Synopsis...bjt

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