An slowly weakening area of low pressure located somewhere near the
state of Iowa to start the period will move east, then east-
southeast to somewhere near Ohio by late Sunday evening. At the same
time, an area of high pressure centered just south of James Bay will
remain pretty much stationary through this same time frame. This
will help to ensure the track of the low remains south and west of
NYS, keeping us on the `cool` side of the system. The associated
warm/occluded front will approach form the southwest later Saturday
night. This will bring the chance for snow showers into western NY
after midnight, with the main area of precip expanding northeastward
to the Genesee Valley/Finger Lakes region by Sunday morning. At this
point it appears the surface warm front will not make it further
north than Ohio/Pennsylvania, and that the occluded portion of the
boundary extending east from the low will be what pushes into our
region on Sunday. This also means any true warmer air will never
make it into western and north central NY. That said, it will get
warm enough aloft across western NY, possibly as far east as the
Finger Lakes for a changeover from snow, to sleet/freezing rain and
plain rain for some areas across the Niagara Frontier and western
Southern Tier. Areas northeast of the Finger Lakes may keep snow as
the primary p-type through the event, with the best bet for all snow
remaining across the north country. The 12Z ECMWF/GEM remain in very
good agreement on the evolution of this scenario, with both also
trending a bit colder overall. The 12Z NAM is also in play now
through early Sunday evening and is also very similar to the
ECMWF/GEM. The outlier remains the GFS which tries to bring the nose
of the warm air aloft to far northeast. With all this in mind, have
trended the `all snow` line a bit further southwest, with the threat
for any frozen or freezing precip confined to the western Finger
Lakes and points west/southwest. Areas across far western NY and the
western Southern Tier have the best chance for seeing a changeover
to just plain rain from later Sunday morning through the afternoon.
Freezing rain amounts do not appear to be that much at this time,
but only takes a light glaze to create big travel problems. As for
snow amounts, there will be the possibility for a few inches of
accumulation for Monroe County and points east of the Genesee Valley
and south of Lake Ontario during the first half of Sunday, with this
potential then shifting northeast across the Eastern Lake Ontario
region during the afternoon. This situation will be closely
monitored over the next couple of days. Any shift in the track or
strength of the low could shift this "zone of uncertainty" in either
direction, so STAY TUNED.
Heading into Sunday night, weakening diffuse low pressure just to
our southwest will give way to a secondary area of low pressure
somewhere near the Delmarva or Jersey coast. This low will then
strengthen as it moves northeast just off the New England coastline.
The contribution of moisture from the coastal system and parent
upper low will keep snow, or a mix of rain and snow showers going
through Sunday night depending on your location, with the threat of
frozen/freezing precip no longer present as colder wraps in on the
back side of the low removing the warm nose aloft. Colder air will
deepen further on Monday, with just about all areas going over to
all snow. Air aloft will become cold enough for lake enhanced/effect
snow showers, mainly south of the Lakes on a cold northerly upslope
flow. Any leftover snow showers will taper off Monday night as
the low moves further away and drier air filters across the region