Area Forecast Discussion
Issued by NWS Buffalo, NY

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000
FXUS61 KBUF 241148
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
648 AM EST Sat Feb 24 2018

.SYNOPSIS...
An area of high pressure will pass to the north of the area today
with mainly dry weather outside of a few showers which may clip the
Southern Tier. Then strong low pressure will track from the Upper
Great Lakes region tonight and into Ontario on Sunday. This will
result in above normal temperatures over the weekend with a period
of heavy rain and windy conditions late tonight and Sunday.

&&

.NEAR TERM /THROUGH TONIGHT/...
High pressure building into southern Ontario will help push a
frontal boundary further southeast of the area this morning.
Model consensus tracks a weak wave of low pressure to our south,
with some showers associated with this system possibly clipping
the Southern Tier today. There will be a sharp cut-off on the
northern fringe of this system with dry weather elsewhere today
as surface high expands into southern Quebec. Expect at least a
partial clearing this afternoon north of I-90 from Buffalo to
Syracuse. Temperatures will be above normal with highs mainly in
the 40s.

The forecast gets more challenging after this with numerous
potential headlines to consider. The cause will be a dynamic storm
system which is forecast to track from the mid-west to Lake Superior
while deepening to around 986mb by daybreak Sunday. Model guidance
continues to be in good agreement with the track and timing with
some differences in the strength of the low.

There is high confidence that an area of precipitation will move
across the region from SW-NE tonight. This should enter far Western
New York just before midnight, with widespread rain across the
entire region by daybreak Sunday. A strong 60 kt LLJ will move into
the region late tonight in advance of an occluding cold frontal
boundary. Forecast thermal profiles show a sharp inversion
developing with the arrival of this jet with elevated instability
resulting in a period of heavy rainfall and possibly a thunderstorm
south of Lake Ontario late tonight. Rainfall amounts will average
between a half an inch and an inch which will result in high levels
but not flooding. The one potential area of concern is the Allegheny
River basin where there is a chance greater amounts of rain to the
south will cause forecast points to approach bankfull. The odds of
this happening are low, not enough to justify a Flood Watch at this
time.

In addition, there is a risk of strong to damaging downslope winds
late tonight. The strength and direction of the low level jet is
ample to support gusts to 60 mph however it will coincide with the
rainfall which may limit the strongest winds from mixing to the
surface. Given this uncertainty, will maintain the high wind watch
for downslope regions north of the Chautauqua Ridge and Tug Hill and
western Adirondacks.

Downsloping will result in temperatures rising into the upper
40s across the lake plains tonight, and across most of Western
New York through daybreak Sunday with a warm front. The notable
exception is across the Saint Lawrence Valley and eastern
portions of Lewis county where temperatures will be much slower
to warm tonight. In these locations, some spots will be below
freezing with the arrival of precipitation with rapid mid-level
warming showing a classic freezing rain forecast sounding. Any
freezing rain would be short-lived but still could result in up
to two tenths of an inch of icing in spots due to the moderate
to heavy rainfall rates. Any icing southwest of a Watertown to
Lowville line will be minimal due to warming from downsloping. A
winter weather advisory was issued for Jefferson and Lewis
counties.

&&

.SHORT TERM /SUNDAY THROUGH TUESDAY NIGHT/...
...HIGH WIND WATCH FOR WINDS GUSTING POTENTIALLY TO 60 MPH SUNDAY...

Anomalously strong low pressure over the Michigan UP Sunday morning
will deepen while tracking northeast to the southern tip of James
Bay. An occluded front associated with this low is forecast to shift
east across western and central NY through the day. Widespread
moderate to possibly heavy rainfall ahead of the front will shift
east exiting the forecast area by early to mid afternoon. An
additional one to two tenths in WNY and quarter to half inch east of
Lake Ontario will add to the one to three quarters of an inch of
rain expected tonight. This should be manageable in most areas with
the highest threat of potential river flooding being in the Allegany
basin. There may be some lingering freezing rain on the Tug Hill
east of Lake Ontario where surface temperatures are slow to rise
above freezing. Expect dry and sunny but gusty conditons following
the front Sunday afternoon. High temps should peak in the 50s to
about 60 ahead of the front before falling late.

High Winds...The forecast track of the surface low, within 500 mi
northwest of Buffalo and deepening trend is favorable for a wind
event Sunday. The track is a bit further west than the track of the
composite mean identified in a recent local high wind study while
the forecasted ~986mb low at 15z Sun is close to the mean of a study
defined Limited impact high wind event. The accompanying ~60kt 850mb
jet is also more favorable for a Limited impact type high wind
event. Subsidence, cold advection and rising pressure tendencies
support mixing down of the higher winds aloft along our typical
corridor east of Lake Erie stretching from Chautauqua county across
the Niagara Frontier to Monroe County. This is where a High Wind
Watch remains in effect 14z-22z Sunday. A deeper low and stronger
850mb jet would support a more widespread impact but guidance does
not suggest this will occur. With still more than 24 hours until
gusty westerly winds are expected to ramp up, we have opted to
continue the Watch while we see if the 12z guidance shows a
stronger/weaker trend. Ahead of the front, another High Wind Watch
which runs through 18z Sunday remains for Jefferson and Lewis
counties due to potentially strong gusty downslope winds.

Sunday night through Tuesday night, surface high pressure and mid-
level ridging will slide east from the Central Plains to eastern
North Carolina with ridging extending north across the eastern Great
Lakes. This will support fair dry weather with temperatures
remaining well above normal for this time of year. Highs Monday are
expected in the low to mid 40s then climbing into the upper 40s to
low 50s Tuesday.

&&

.LONG TERM /WEDNESDAY THROUGH FRIDAY/...
Where`s all the cold air??

There is high confidence for above normal temperatures through the
second half of next week as a low amplitude split upper level flow
over the country will include a pronounced sub tropical jet that
will extend across the Lower Great Lakes. This will help to
establish a feed of very mild air out of the GOMEX that will hold
our temperatures some 15 deg above seasonal levels for Wednesday and
Thursday but likely not without some rainfall. As we head into next
weekend...the mercury will gradually settle to near normal.

For those wondering about true cold air...an analysis of H85 temps
Friday evening showed a pool of sub arctic air (<-20c) near and east
of Hudson Bay...but this airmass will retreat poleward during the
coming days. By the time this forecast period begins (Wednesday)...you
will have to travel north of 65N...and more specifically to the
Yukon...to find any arctic air. Given the split flow over the Lower
48...there will no chance of tapping this marginally cold airmass.
The coldest airmass in the northern hemisphere though will remain
parked on the other side of the Pole...in Siberia.

A bulging ridge over the eastern third of the country will allow H85
temps to climb above freezing while maintaining enough subsidence to
keep fair weather in place. The warmer air aloft will encourage max
temperatures to reach well into the 50s across the western
counties...with readings generally holding in the 40s across the
North Country.

In terms of precipitation, Global models shift a warm front over or
just south of our region later Thursday into Friday. Since there are
likely some timing issues yet to be resolved we have kept chance
POPs on Wednesday increasing to likely POPs Thursday-Thursday night
followed by chance POPs Friday. P-type should largely be plain rain
with above normal temps but some snow may mix in during the night
periods where overnight lows dip toward or below freezing.

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
A frontal boundary will continue to move across the area through
daybreak with a general improving trend in conditions. Areas of IFR
or lower conditions will linger across higher terrain and east of
Lake Ontario through 14Z with mainly MVFR conditions elsewhere. After
this expect improving conditions this morning as drier air moves in
in the northerly component flow behind the front. Some patchy MVFR
cigs may linger south of Lake Ontario this afternoon with VFR
conditions expected elsewhere.

Expect mainly VFR conditions this evening, followed by active
weather starting around midnight. This will include a period of
heavy rain, and possibly even a thunderstorm. There also may be
LLWS late in the period as a low level jet moves into the region.

Outlook...

Sunday...Rain ending with improvement to VFR. LLWS early. Windy.
Monday through Wednesday...Mainly VFR.

&&

.MARINE...
High pressure will briefly build back across the Lower Great
Lakes today, before a strong area of low pressure tracks
northeastward across the Great Lakes on Sunday. This system will
bring at least a round of high end advisory-worthy conditions, with
gale force winds possible.

After this, a moderate southwesterly flow will result in near-
advisory conditions across eastern portions of the lakes Sunday night
into Monday. Then high pressure will build across the lower Great
Lakes late Monday and Tuesday.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Winter Weather Advisory from 1 AM to 10 AM EST Sunday for
     NYZ007-008.
     High Wind Watch from late tonight through Sunday afternoon for
     NYZ007-008.
     High Wind Watch from Sunday morning through Sunday afternoon
     for NYZ001>003-010>012-085.
     High Wind Watch from late tonight through Sunday afternoon for
     NYZ019.
MARINE...None.

&&

$$

SYNOPSIS...APFFEL
NEAR TERM...APFFEL
SHORT TERM...SMITH
LONG TERM...RSH/SMITH
AVIATION...APFFEL
MARINE...APFFEL



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