Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 250220

Area Forecast Discussion
National Weather Service Buffalo NY
1020 PM EDT Fri Mar 24 2017

A slow moving frontal boundary draped across the region will slip
back south of the area tonight and Saturday...before slowly lifting
back north across the region as a warm front Sunday and Monday.
Several disturbances sliding along this boundary will bring frequent
bouts of precipitation through the weekend and early next week...
with cooler temperatures prevailing north of the boundary and
milder temperatures found to its south.


As of 02z...regional surface obs and analysis show that the
surface frontal boundary has sagged to a rough southern Erie to
Ontario county axis. This southward shift will continue through
the near term period as strong Canadian high pressure builds
eastward across Ontario and Quebec...with the surface front
expected to reach the NY/PA border by late tonight...before
sagging further southward into Pennsylvania during the day
Saturday. In terms of temperatures...this will result in a tight
thermal gradient across the area with overnight lows ranging
from around or slightly below freezing across the North Country
to near 50 close to the Pennsylvania border...with highs on
Saturday then again ranging from around 50 near the PA line to
the upper 30s and lower 40s elsewhere.

As the frontal boundary sags southward tonight...rain will also
likely redevelop along and to the north of the front...then will
persist across much of the region through at least the first half
of Saturday...before gradually diminishing from north to south
during the afternoon as the front and best synoptic forcing shift
south across Pennsylvania. Across the North Country...boundary
layer temperatures will likely cool to around or a little below
freezing overnight...and with at least some warmer air lingering in
place aloft...this will result in the rain mixing with some sleet
and freezing rain from about the Tug Hill northeastward...which
will then persist until temps warm back above freezing later
Saturday morning. Given the likelihood of as much as a tenth to
an eighth of an inch or ice accumulation across this latter region...
a winter weather advisory has been issued as outlined below.

In addition to the above...a few thunderstorms will also be possible
along the front itself as it drifts southward through the overnight
hours...thanks to the presence of some weak elevated instability.
The overall pattern will also be favorable for the formation of at
least some patchy fog along and north of the boundary tonight...
with this then lasting into Saturday morning.


An unsettled pattern will continue this period as a frontal boundary
oscillates across the Lower Great Lakes.

Saturday night the frontal boundary will sag southward, stalling
across the Southern Tier as a strong Canadian high pressure system
moves into Quebec. This will bring a break in rain showers overnight
to the North Country and locations south of Lake Ontario, except for
the far Southern Tier. Temperatures will fall into the 30s north of
the front and even the mid 20s along the Saint Lawrence Valley where
strong northeast flow from the Canadian high becomes established.
The far corner of the Southern Tier will remain in the mid to upper
40s with scattered rain showers.

For Sunday through Sunday night, the strong low pressure system
currently seen on WV imagery churning over the central plains will
eject northeastward across the Great Lakes and the forecast area as
it starts to get picked up by the mean mid-latitude flow. In the
process, this will bring plentiful Gulf of Mexico moisture advection
and warm air advection sending the warm front northward. This push
of the frontal boundary will be accompanied by scattered rain
showers in the morning across Western NY. As the warm front
progresses northward on Sunday, expect to see a sharp rise in
temperatures across western NY from the 30s in the morning to the
upper 50s to low 60s by mid-day and early afternoon, especially if
there is a well defined break in the precipitation and possibly the
cloud cover. For the North Country, the surface temperatures in the
20s to low 30s in the morning may prove troublesome, as showers
along the front move northward, there could be a period of freezing
rain at the onset of precipitation before surface temperatures rise
into the 40s for the afternoon. The best chance of widespread
rainfall then come Sunday night with the mild, moist airmass in
place ahead of the approaching cold front and vorticity advection
with the parent upper level low. QPF amounts for Sunday and Sunday
night are only expected to add up to a quarter to a third of an
inch, with some locally higher pockets up to a half inch possible.
Temperatures overnight will be very mild, with many locations across
western NY in the upper 40s to around 50, with low 40s in the North

By Monday, a mild airmass will be left in the wake of the largely
cut-off low pressure system exiting to our east along with height
rises. This will result in lingering partly to mostly cloudy skies,
but rain showers tapering off from west to east, and becoming more
widely scattered by the afternoon. In fact, much of western NY will
likely see plenty of dry time by Monday afternoon. High temperatures
will top out in the mid 50s to low 60s across western NY, warmest in
the typical downslope regions of the Genesee Valley and northern
Finger Lakes. The North Country will remain somewhat cooler, in the
mid to upper 40s. Scattered shower chances will remain in place
Monday night as another wave is set to track just to our south.
Temperatures will remain mild overnight, in the 40s for most


The lengthy unsettled period will last into Tuesday as the stalled
complex frontal zone remains nearby. Both the GFS and ECMWF based
guidance suggest one more wave moving along the frontal zone and
passing to our north on Tuesday, producing another round of showers.
Temperatures will remain mild given the northerly low track, with
highs at least into the 50s and possibly into the 60s for the
southern half of the area.

Tuesday night and Wednesday a mid level trough will amplify across
Quebec and finally drive the frontal zone well south of our area,
with moisture and showers diminishing from northwest to southeast.
Cold advection associated with the trough will knock temperatures
back a few notches, with highs in the 40s Tuesday.

A slow warming trend should then ensue for the second half of next
week as the trough over Quebec moves offshore of the Canadian
Maritimes and height rises/weak warm advection overspread the
eastern Great Lakes. Model guidance diverges by next Friday with
respect to the track of the next system. The GFS keeps most of the
energy and deeper moisture suppressed well to the south across the
Ohio Valley and southeast States, while the ECMWF takes a much more
northerly track through the Great Lakes and would be a warmer and
wetter solution. Given the time range and inherent uncertainty, have
just included chance POPS for now.


A frontal boundary draped across western New York will slowly drop
back southward into Pennsylvania through the TAF period. Rain will
develop along and north of the boundary as it slips southward tonight...
then will persist across much of the region through at least the first
half of Saturday...before gradually diminishing from north to south
during the afternoon as the front and best synoptic forcing shift
south across Pennsylvania. Across the North Country...the rain will
mix with freezing rain and sleet overnight...with the mixed precip
then persisting into Saturday morning. A few thunderstorms will
also be possible along the frontal boundary itself at it drifts
southward overnight...mainly along and south of a rough KBUF-
KDSV axis.

In conjunction with the developing precipitation...a developing
north to northeasterly upslope flow on the back side of the
departing boundary will allow widespread IFR/LIFR conditions in
lower stratus and/or fog to develop from north to south tonight...
then persist across areas south of Lake Ontario through much of
Saturday. Across the North Country... some eventual improvement
to MVFR and then VFR is expected during the course of Saturday
as drier air arrives from the north.

Saturday night through Tuesday...MVFR/IFR cigs with rain likely
at times.


A frontal boundary draped across Lake Ontario will slip back southward
tonight and Saturday...with a northeasterly flow developing across the
Lower Lakes region. This will especially be the case on Lake Ontario...
where winds and waves will increase enough along much of the south shore
to require a small craft advisory from late Saturday morning through
Sunday evening.


NY...Winter Weather Advisory until 11 AM EDT Saturday for
MARINE...Small Craft Advisory from 11 AM Saturday to 11 PM EDT Sunday
         for LOZ042-043.



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