Forecast Discussion

Forecast Discussion for BUF NWS Office
808
FXUS61 KBUF 240233
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
933 PM EST Thu Jan 23 2020

.SYNOPSIS...
Fair dry weather wil persist across the region through Friday...
then a large...slow moving storm system from the mid western states.
This mature system will spread rain across much of our forecast area
Friday night...then as colder air works back across the region
Saturday afternoon into Sunday...the precipitation will change over
to some accumulating snow. Most areas should pick up an inch or two
of accumulation by the end of the weekend with parts of the Southern
Tier and Eastern Lake Ontario region receiving as much as six
inches.

&&

.NEAR TERM /THROUGH FRIDAY/...
High pressure will remain nearly stationary east of the
Appalachians and into New England tonight. A closed low will
slowly move east across the Mississippi Valley tonight. Deep
moisture will surge from the Gulf of Mexico to the Mid-West
ahead of this system. The eastern Great Lakes will continue to
be under the influence of an upper level ridge and surface high
pressure keeping it dry. Warm air advection will continue across
the region and waves of mid to upper level clouds will pass
overhead tonight. Low temperatures will range from the low to
mid 20s across Western NY to the upper teens to low 20s east of
Lake Ontario.

High pressure will be stubborn to move east while low pressure
tracks into the Ohio Valley Friday. A surface trough will take shape
from Lake Erie to the northern Adirondacks while the pressure
gradient tightens between these two airmasses Friday. A
southeasterly flow will increase throughout the day for places south
of the surface trough where places along the axis of the trough
remain light. An easterly flow will increase to the north of
the surface trough mainly across Lake Ontario. A 35-40kt low-
level jet, transporting deeper moisture northward will remain
west of Western NY through the afternoon. The fringe of this
moisture just starts to move into eastern Ohio and western
Pennsylvania by Friday evening. The chance for rain showers
start to increase across Chautauqua county at this time. High
temperatures will reach the mid 40s across much of Western and
North Central NY Friday.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/...
A slow moving closed low, with a nearly vertically stacked surface
low beneath, will move from Indiana Friday evening to northern Ohio
by Saturday afternoon, then to eastern NY by Sunday morning. The
initial surface low will eventually give way to secondary
cyclogenesis along the Maine coast later Sunday. This closed low is
embedded within an otherwise very warm pattern, with high heights
dominating most of the nation. The airmass in the western quadrant
of the system will be marginally supportive of some wet snow for the
second half of the weekend.

Friday night into Saturday morning an initial band of deep moisture
associated with the warm/moist conveyor on the front side of the
system will be supported by increasing large scale ascent ahead of
the closed low, convergence along the occluded frontal zone, and low
level convergence on the nose of a strong SSE low level jet. This
will all come together to support a period of steady precipitation
arriving in Western NY Friday evening, then progressing slowly east
to the eastern Lake Ontario region by Saturday morning. The majority
of this first phase of the system will be rain, with most model
guidance supporting a wedge of warm air aloft and at the surface
ahead of the system. There is a chance that a few of the sheltered
valleys of Cattaraugus and Allegany counties may see a brief period
of freezing rain later Friday night, as suggested by NAM point
soundings. There is also a small chance of some spotty freezing rain
east of Lake Ontario Saturday morning through early afternoon.

Later Saturday afternoon through Saturday night the closed low will
move over or just south of the eastern Great Lakes. The associated
pool of cold air aloft will move overhead, and modest cold advection
will begin in the boundary layer. This will allow for a change to
wet snow, first at higher elevations where temperatures will be
slightly cooler, and last near the Lake Erie and Lake Ontario
shorelines. The majority of the precipitation will then be snow
later Saturday night through Sunday, although some rain may still
mix in at times across lower elevations. The wrap around phase of
precipitation Sunday and Sunday night will feature upslope
enhancement across the higher terrain of the western Southern Tier
and Tug Hill region as westerly flow increases in the wake of the
system. While there will be orographic enhancement, the boundary
layer never becomes cold enough for any appreciable lake
enhancement.

As far as accumulations go, the marginal thermal structure will
likely keep the accumulations highly dependent on elevation. There
will be virtually no accumulation anywhere through late afternoon
Saturday. Saturday night and Sunday it will become cold enough
across higher terrain to allow for accumulation to begin. Expect
total accumulations from Saturday night through Sunday to reach 3-6
inches across the higher terrain from the Boston Hills and Wyoming
County down through Chautauqua and Cattaraugus counties, and also on
the Tug Hill Plateau. Across lower elevations, temperatures will
struggle to get cold enough to allow for much, if any accumulation.
Expect a coating to an inch or two of slush at most across most of
the lower elevation locations, including Buffalo and Rochester.
These are early estimates and may change with later model guidance.

One final note on this system, the strong southeasterly jet may
support localized downslope winds along the Lake Erie shore Friday
night. Wind gusts of 35 to 45 mph area possible to the lee of the
Chautauqua Ridge for a few hours Friday night.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
Low pressure will depart through the Canadian Maritimes on Monday. A
trough will still hang back from New England through the eastern
Great Lakes, supporting a few more wet snow showers. The best
coverage will likely be across the higher terrain with northwest
upslope flow continuing. Any additional accumulations will be minor.

Another weak trough will then move from the western Great Lakes
towards the Mid Atlantic states Monday night through Tuesday. This
may support a chance of a few more light snow showers of little
significance. This trough and associated surface cold front will
usher in somewhat colder air by Tuesday night and Wednesday, with
temperatures returning back closer to average. High pressure will
allow for mainly dry conditions by Wednesday and Thursday with
the somewhat colder temperatures continuing.

&&

.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
Despite a gradual lowering of our high and mid level cloud cover...
VFR conditions will persists through at least midday Friday. Lower
strato-cu will then work into the Western Southern Tier later Friday
afternoon...and that could result in some MVFR cigs for sites like
KJHW and KELZ by nightfall.

Outlook...

Friday night...Deteriorating conditions to MVFR to IFR cigs with
increasingly widespread rain. LLWS.
Saturday...Widespread MVFR to IFR cigs with rain and wet snow.
Saturday night through Sunday...Widespread IFR conditions in snow.
Monday...IFR to MVFR cigs slowly improving to VFR.
Tuesday...Mainly VFR...but MVFR in scattered snow showers.

&&

.MARINE...
A strong surface high centered in the vicinity of James Bay will
support a freshening easterly flow across the Lower Great Lakes
overnight. This will especially be the case on the western half of
Lake Ontario where conditions will approach small craft advisory
criteria by Friday morning.

As the sfc pressure gradient tightens ahead of an approaching storm
system on Friday...the easterly flow will continue to strengthen
across Lake Ontario. This will lead to SCA conditions on the western
end during the midday and afternoon.

Fresh to occasionally strong easterlies will persist across the
western half of Lake Ontario into the first half of the weekend...as
the aforementioned storm system will slowly advance to Lake Erie.

Winds and waves on both lakes will subside Saturday night...as the
vertically stacked storm will make its way across the region. On
the backside of the system...winds and waves will once again
increase throughout the day Sunday.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Small Craft Advisory from 10 AM Friday to 4 PM EST Saturday
         for LOZ042.

&&

$$

SYNOPSIS...RSH
NEAR TERM...HSK
SHORT TERM...Hitchcock
LONG TERM...Hitchcock
AVIATION...RSH
MARINE...RSH

NWS BUF Office Area Forecast Discussion