Area Forecast Discussion
Issued by NWS Buffalo, NY

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168
FXUS61 KBUF 210845
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
345 AM EST Tue Feb 21 2017

.SYNOPSIS...
A weak cold front producing light rain showers will cross the region
this late afternoon and evening. Temperatures will remain well above
normal today through Friday night, at which time a stronger cold
front will cross the region with additional rain showers, chances
for thunderstorms and gusty winds.

&&

.NEAR TERM /THROUGH TONIGHT/...
Surface analysis this morning places an area of high pressure over
eastern Quebec, ridged southward through New England. An area of low
pressure is just south of Hudson Bay, with a cold front passing
across the upper Great Lakes. Rain showers ahead of this cold front
are just now reaching Chicago.

For today mid and high level clouds will stream across the region
through the afternoon hours, with some breaks of filtered sunshine.
This sunshine, combined with light southerly winds ahead of the cold
front and 850 hPa temperatures +6 to +8C across the region will
bring upper 50s this afternoon across the lake plains of WNY, and
upper 40s to lower 50s across higher terrain of WNY, and east of
Lake Ontario.

IR satellite imagery this morning displays moisture flowing
northward from the Gulf of Mexico over the Mississippi Valley
region. This moisture will eventually feed the rain showers this
afternoon and evening. A shortwave crossing the Great Lakes region
will flatten the strong ridge of high pressure over the region...but
will weaken within the process.

Rain showers along with the cold front should reach far western
portions of the CWA around 4pm, with the showers spreading eastward
across the region. Highest PoPs will be closer to the lakes, while
inland, where forcing will not be as strong with the flattening
shortwave, Pops will be a shade lower.

The cold front will cross the region this evening with chances for
rain quickly ending by late evening, and just past midnight through
the region. There may be some lingering low level moisture late
tonight, that will bring patches of fog to the region, as well as
some low stratus across the hills of SW NYS.

Air temperatures will remain above freezing tonight, with many areas
across WNY remaining in the lower 40s.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY NIGHT/...
Flat ridging follows in the wake of the front for Wednesday. This
should allow for dry weather, with at least partial sunshine
developing by afternoon. Little change in airmass will result from
the front, and have continued with temperatures well above
climatology. Afternoon highs of 60 to 65 are expected for the
western counties, with cooler temperatures east of Lake Ontario
where highs will be closer to 50.

By Wednesday night, a southwesterly low level flow will develop as
low pressure moves well to the north and west of region. This will
begin to induce some isentropic lift and a slow increase in
moisture. This may be enough to touch off a few light rain showers
late Wednesday night. Temperatures will remain quite mild,
especially in the west with lows in the mid 40s to near 50, with
areas east of Lake Ontario possible sneaking down into the upper 30s.

On Thursday, there are some hints that a weak cool front could sink
south of the Canadian border with the possibility for scattered
showers, but there is a lot of disagreement in guidance. Based on
the mid level ridging expected to be over our region, siding with
the warmer and somewhat dryer scenario, although have maintain a low
chance for some showers. It will be another mild day with most high
temperatures well in the 50s to the lower 60s. This will especially
be the case over the Finger Lakes and Genesee Valley.

Jet energy digging south along the West Coast will deepen the
existing trough as it translates across the Rockies. Strong
cyclogenesis will result. A deepening surface low will track into
the upper Midwest Friday morning before drifting into the western
Great Lakes by Friday night. Weakly coupled jet structure will
emerge as longwave pattern amplifies, dominated by the southern jet,
allowing isentropic ascent to ramp up. Baroclinic zone will lift
back north across the forecast area bringing the likelihood of
showers to the area Friday. Consensus is essentially set on a warm
surface low track to the west of the area, with afternoon
temperatures likely to warm into the 60s within the warm sector
across western New York, but probably remaining in the 50s north of
the boundary across central New York. Confidence in Friday afternoon
high temperatures remains low at this point, as this is greatly
dependent on how far north the surface warm can progress. If skies
were to clear enough to allow for prolonged afternoon sunshine these
temperatures may not be nearly warm enough, with lower 70 degree
readings not out of the question. It is worth noting that the
potential exists for a run at the all-time February high
temperature at Buffalo of 71F/2000.

Friday night...the still deepening cyclone will track to Lake Huron
while its strong cold front will plow across southern Ontario to to
the Niagara River. Strong southerly winds ahead of the front will
keep very mild conditions in place across all of the forecast
area...with some sites form the Genesee Valley eastward probably
not falling below 50 for an overnight low. Any showers that will be
found over the region early in the night will become more common as
the front approaches...especially over the far western counties.

This should set the stage for a windy day on Saturday.

&&

.LONG TERM /SATURDAY THROUGH MONDAY/...
It will certainly be notably colder during this period as
temperatures will return to more seasonable levels. The change back
to winter will include some snow showers...especially in the
snowbelts east of the lakes where mesoscale processes (ie. lake
effect) will contribute to potentially significant accumulations.

As so often happens here during the cold season...the passage a deep
surface low to our west and north will mark the change in the
overall pattern across the country. Rather than having a trough in
the west and ridging in the east...a broad trough full of Canadian
air will dominate the Great Lakes region. Unfortunately...these
pattern changes are also usually marked by significant/damaging
weather events. This case may be no different.

When we open this period Saturday morning...a strengthening sub
990mb low will be pushing northeast from Lake Huron while its
powerful cold front will be bulldozing across western and north
central New York. The accompanying rain showers will be accompanied
by winds of at least 25 to 40 mph with the frontal passage...then
after a couple hours where winds will subside a bit...winds will
ramp back up...possibly as high as 50 mph. The storm track...
negative tilt to the supporting mid level trough...and suggested
subsidence all favor at least advisory criteria winds. The only
thing missing is a significant low level jet. Stay tuned.

Strong cold advection on the backside of the exiting cyclone will
send H85 temps to as low as -15c Saturday afternoon into MOnday.
This will be more than cold enough to promote lake effect snow
showers east of both lakes..with significant accumulations possible
east of Lake Ontario where an upstream connection and full fetch
will be likely. Outside of the lake effect areas...Sunday and Monday
will feature partly to mostly cloudy skies and scattered light snow
showers.

After temperatures fall from 50 Saturday morning in the wake of the
front...max temps will be in the mid 30s on Sunday and close to 40
for most areas on Monday. Mins through the period will be in the
20s.

&&

.AVIATION /09Z TUESDAY THROUGH SATURDAY/...
For the 06Z TAFS VFR flight conditions were found, and these flight
conditions should prevail through at least 21Z. At that time a line
of rain showers will be nearing the western TAF sites, with mainly
VFR flight conditions continuing through the light rain, though a
brief period of MVFR flight conditions is likely. Rain showers will
likely reach KART between 22Z and 01Z.

This cold front will cross the region this evening, with rain
showers tapering off late this evening, and early morning Wednesday.
There may be some IFR CIGS developing later tonight across the
Southern Tier, with patchy MVFR CIGS elsewhere behind the cold
front.

Light easterly winds this morning will become southwesterly this
evening, with speeds generally remaining 15 knots or less through
the TAF cycle.

Outlook...

Wednesday and Thursday...Mainly VFR.

Friday and Saturday...Periods of rain showers with MVFR and local
IFR. Windy on Saturday.

&&

.MARINE...
Light easterly winds on the lakes today will gradually veer to
southerly through the day. Winds will pick up some, but the
strongest winds may remain over the central waters and towards
Canada, and thus will not issue any small craft advisories as winds
should largely remain 15 knots or less.

A weak cold front will cross the lakes this evening, though with
very little cold air behind this feature waves and winds will have
little response.

Winds and waves should then remain below SCA thresholds, until an
easterly flow picks up on Lake Ontario Friday ahead of the next, and
more potent storm system.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...None.

&&

$$

SYNOPSIS...THOMAS
NEAR TERM...THOMAS
SHORT TERM...TMA
LONG TERM...RSH
AVIATION...THOMAS
MARINE...THOMAS



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