.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
...Increasing potential for a long duration, impactful accumulating
snowfall during the mid week period...
A Winter Storm Watch is now in effect for all of western and north
central New York Wednesday night through the first half of Friday.
Southwest flow of milder air continues into the region ahead of an
approaching cold front Wednesday morning. Temperatures may reach the
lower to mid 40s, especially for the lake plains and Genesee Valley
into the Finger Lakes. Could see a few showers of rain or rain/snow
mix sneak into the region from the northwest Wednesday morning,
but its not until the afternoon on Wednesday until the deeper
northward push of moisture transport reaches the area within the
background of broadening system relative isentropic ascent
along and immediately ahead of the advancing cold front. This
introduces the initial stage of an expected longer duration
precipitation event.
Wednesday night through Thursday night...
Gradual height falls tied the lead northern stream wave shearing
into central Ontario will draw the system cold front across the area
Wednesday evening into Wednesday night. Sustained ascent driven by
very moist system relative isentropic lift working over the
advancing boundary ensures an expanding coverage of precipitation
commences during this time. Rain may still be the predominant
precipitation time Wednesday evening before steady cooling of the
column allows for a change over to snow from north to south
probably from late evening or around midnight through the overnight.
Transition timing will likely impact accumulating snow potential
Wednesday night and at this point do not see this as the period of
the heaviest snow accumulations although several inches are
certainly possible before morning if the change over occurs early
enough in the night.
At this point in the forecast process believe that the best
potential for widespread accumulating snowfall will be Thursday into
Thursday night as several rounds of stronger ascent continue to
engage the elevated frontal zone. Do see diminishing ascent
commencing late Thursday night. However, north-northeast flow of
incoming arctic airmass will start to bring in some mesoscale
processes with lake response south of Lake Ontario likely coming
into play by the time we reach Friday morning.
Overall snow to liquid ratios starting out very wet in the 6:1 range
transitioning to a more standard 10-12:1 ratio by Thursday night. A
general blend of guidance including the GFS/CMC/EC suggesting a high
likelihood for snowfall total to exceed 9 inches through this time
period with the potential for more as we go into Friday.