Area Forecast Discussion
Issued by NWS Buffalo, NY

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069
FXUS61 KBUF 230603
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
103 AM EST Thu Feb 23 2017

.SYNOPSIS...
Unseasonable warmth will continue through Saturday morning along
with a few passing showers. A strong cold front will move through
Saturday. This may be preceded by some thunderstorms. Following the
front, expect breezy to windy conditions, along with a return to
some lake effect snow east of the lakes by Sunday.

&&

.NEAR TERM /THROUGH TODAY/...
A deepening surface low over northern Michigan early this morning
will track across Ontario and into Quebec today. Surface pressure
falls to our north ahead of this low, coupled with high pressure off
the Mid-Atlantic coast will all for a strengthening southerly flow
early this morning, turning more southwesterly during the day today
as the low tracks eastward. The result is a very warm and moist
airmass in place (dew points around 50 degrees), with downsloping
across WNY, the Genesee Valley and northern Finger Lakes, and even
off the Tug Hill near Watertown. The result is very mild
temperatures that are unlikely to fall below 50 degrees through
morning across the western two-thirds of the forecast area. While
the North Country may see some upper 40s by sunrise.

Have also scaled back the fog formation even more in the forecast.
The southerly winds will keep any advection fog off Lake Erie
directed into Ontario Province and the Niagara Peninsula. Have
thus dropped the dense fog advisory for Niagara and northern Erie
counties. Some areas of fog may finally roll off the lakes to near
Buffalo and Watertown, during the day today, as the winds turn more
southwesterly to westerly, as the shortwave tracks to our north.
However, this may only last a few hours at any given spot as the
winds turn, and then drier air filters into the region behind the
weak frontal passage.

As that trailing surface front spills across the region, it may
spark off a few showers today, however the front is rather moisture
starved, and forcing across our area will be weak with the parent
wave well north into Canada. The greatest chances for a few
scattered showers will be across the North Country, closer to the
better forcing.

Temperatures will remain extremely mild yet again today, with little
change in airmass, except for the weak surface front waving through
the region later today. Highs will mainly be in the upper 50s, with
the warmest reading of mid 60s across the typical warm downslope
region of the Genesee Valley and northern Finger Lakes.

&&

.SHORT TERM /TONIGHT THROUGH SUNDAY NIGHT/...
The weather will be anything but uneventful during this period...as
a deep storm system will cut to our west and mark a change in the
overlying pattern across the country. Our region will initially be
unseasonably mild with near record temperatures...but as we progress
through the weekend...notably colder air in the wake of the passing
cyclone will send the mercury plunging back towards normal levels.
At the peak of this process...there will be the risk for strong to
damaging winds as well. If that were not enough...there will be some
accumulating lake snows in the typical snow belts east of both
lakes. Lets break this down into the day to day details.

A vigorous shortwave...seen in WV imagery coming ashore in northern
California at midday...will cross the Inter-Mountain West tonight
and Thursday. This will lead to significant cyclogenesis over the
central plains. The resulting surface feature will consolidate into
a deep cyclone over northern Missouri Thursday night...while a
strengthening warm front will extend to the east across Lake Erie to
northern Pennsylvania. As the front slowly pushes north Thursday
night...clouds will thicken across our forecast area with rain
spreading across the western counties during the latter portion of
the night. Have raised pops to likely for the bulk of western New
York while introducing chc pops for the North Country.

The surface low will approach Chicago on Friday as the associated
warm front will grudgingly push north to Lake Ontario. There is
still uncertainty as to the speed of this northward push but little
doubt that the bulk of the region will pick up at least a little
rain in the process. Once again...have chosen to raise pops...this
time to categorical for the counties near and east of Lake Ontario.
Since there will be a fair amount of elevated CAPE...the warm front
could also generate some embedded thunderstorms. The big question
for Friday will be the extent of any clearing over the western
counties...and in particular the Southern Tier. Once in the warm
sector where H85 temps will be in the vcnty of 10 to 12c...any
clearing would promote/support near sfc temps that could soar into
the 70s. This would be near record warmth in many areas (BUF 67/1906
ROC 70/1906). It should be stressed though that this kind of warmth
will NOT come during the typical mid afternoon time frame. Our
warmest weather Friday will come very LATE in the day or during the
evening. Again...this will all hinge on the speed of the northward
push of the warm frontal boundary. Stay tuned.

Friday night...the cyclone will deepen a bit while advancing to Lake
Huron. With the aforementioned warm front far to our north...our
forecast area will be firmly well entrenched in the warm sector.
Temperatures across the region will be steady or will slowly fall in
the evening...then will rise during the overnight hours. The max
temps for the day may very well come between nightfall and midnight
for some areas. That being said...there should be little if any pcpn
within the warm sector. Most of the rain will be focused over the
North Country in the evening in the vcnty of the exiting warm
front...and close to Lake Erie towards daybreak ahead of a powerful
cold front.

A strong 50 knot low level jet will move across the western counties
ahead of the approaching cold front late Friday night. While an
inversion will prevent the bulk of these winds from being mixed to
the sfc...there could still be some gusts over 35 mph across the
higher terrain and adjacent downslope areas.

On Saturday...the deep storm system will further intensify to under
985mb as it will track across western Quebec to the east shores of
James Bay. Its associated cold front will plow across our forecast
area during the morning (midday North Country). While a 50 mile wide
band of moderately heavy showers and possible thunderstorms will
accompany the frontal passage...the main concern will be the strong
winds that will follow. Lets be clear though. At this point...the
event is looking less and less impressive from the standpoint of a
`classic` high wind event...but there is still plenty of potential
for advisory criteria winds. In the column favoring strong winds
will be the track and pressure trend of the storm system...but
opposing this will be the lack of significant subsidence with the
residual low level jet immediately behind the front and the delay
time before near sfc winds veer to the southwest. If this scenario
ere to verify...parts of the region would be looking at winds
gusting into the 40s rather than 50+ mph.

The near advisory criteria winds on Saturday will aid with the
strong cold advection that will be underway. H85 temps that should
be in the double digits (celsius) at daybreak are forecast to drop
off to around -5c by evening. This will certainly not be cold enough
to initiate true lake effect...and the mesoscale process will be
further limited by low level ridging immediately behind the front.
While true lake effect will hold off til after dark...some nuisance
lake enhancement will be possible east of both lakes.

As the cold air deepens Saturday night...H85 temps will plunge to at
least -12c. The burgeoning lake induced instability will then result
in some lake snows east of both lakes. Otherwise...it will be brisk
and much colder than recent days with temperatures Saturday night
falling into the 20s.

The accumulating lake snows and general return to more seasonable
conditions will continue on Sunday and Sunday night. The thermal
trough associated with this scenario will move across our forecast
area on Sunday...with H85 temps averaging -12c. This will make
Sunday the coldest day of the forecast package with highs in the mid
30s...right near climatological norms. While lake snows will remain
in place east of both lakes...the late season diurnal effects will
disrupt any solid bands and somewhat limit daytime snow
accumulations.

Warm advection will then begin over the region Sunday night as low
level ridging will push to our east and the upper level pattern will
flatten out. Lake snows will weaken in the process...especially east
of Lake Erie.

&&

.LONG TERM /MONDAY THROUGH WEDNESDAY/...
Mother Nature will reload the upper level pattern for yet another
significant `cutter` storm during this period. This pattern...more
typical of the second half of March through April...will lead to
renewed warming with anomalous warmth once again possible by mid
week. If early indications form the medium range ensembles are
correct...this next cyclone could carry a notably higher risk for
strong winds. This will certainly deserve to be watched.

As we open this period on Monday...a relatively low amplitude flow
will be found over the Great Lakes region while a weak cold front
will try to pass through our forecast area. Since there is little
supported suggested with this front...will leave mention of pcpn out
of the package. Temps will be near normal with highs of 35 to 40.

On Tuesday...several robust Pacific shortwaves will dig into...and
amplify...a trough over the western states. This will amplify a
downstream ridge over the eastern half of the country...thereby re-
opening a direct flow out of the GOMEX to the Great Lakes. All of
this will take place while another round of cyclogenesis will be
taking place over the central Plains. While our region will be
mainly rainfree on Tuesday...there will be a low chc for some light
rain showers within the warming airmass.

The weather will deteriorate Tuesday night and Wednesday as the the
deepening cyclone will eject out of the Plains and makes its way to
the Great Lakes. This will lead to more rain for the region...which
could be followed by some strong winds Wednesday night.

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
The main threat for IFR fog and low stratus overnight will be across
the western Southern Tier (KJHW) where low level moisture will
interact with the higher terrain. Have scaled back the fog potential
for IAG/BUF with these TAFS, as the southerly winds will keep any
Lake Erie fog north in southern Ontario Province as out of the
Niagara Frontier overnight.

During the day today, winds will turn from southerly to
southwesterly to westerly by this afternoon as a weak frontal
boundary crosses the region. MVFR CIGs will be common with this
frontal passage, along with a few widely scattered rain showers.
However, this front may also pick up moisture from Lake Erie and
Ontario, and spread some potentially IFR fog into IAG/BUF/ART for a
few hours early this afternoon. However drier air will quickly spill
into the region behind the front, bringing an end to any fog that
develops by this evening.

Outlook...

Tonight...Mainly MVFR due to low ceilings. A chance of showers.
Friday...Morning Rain, but otherwise VFR.
Saturday...Periods SHRA with MVFR and local IFR, then windy.
Sunday...VFR but IFR to MVFR in lake effect snow SE of both
lakes.
Monday...VFR, possible MVFR...depending on low location.

&&

.MARINE...
A relatively weak pressure gradient with a neutral to warm temp
advective pattern will keep relatively light winds and manageable
waves in place across the Lower Great Lakes today. A weak front will
move through this evening. There will be areas of fog on the waters,
dense in spots.

The next real time of concern will be late Friday night and Saturday
when a powerful cold front will cross the Lower Great Lakes.
Strong...possibly gale force winds...will be found in the
wake of the front Saturday and Saturday night.

&&

.HYDROLOGY...
There is a potential for flooding across the Eastern Lake
Ontario Region starting late Saturday and lasting into next
week.

While the snow pack has largely melted across Western New York,
a significant snow pack remains east of Lake Ontario, including
the Black River basin. Snow water equivalent values are about
130% of normal, with this snow pack expected to become
increasingly ripe through the end of the week due to the warm
weather.

On Saturday, a strong system will pass to our north with
a prolonged period of warm (50+ degree) temperatures expected
Friday through Saturday until the passage of a cold front
drops temperatures below freezing Saturday night. This will be
combine with winds and moist air to rapidly melt a significant
portion of the snow pack in place. This system will also bring a
period of rain Saturday, with amounts expected to average
around an inch although exact amounts remain uncertain this far
out.

This may result in multiple issues east of Lake Ontario. First,
the combination of snowmelt and rain may cause areal flooding on
faster responding creeks and rivers starting late Saturday. Some
ice jams are also possible. After this, runoff will cause the
Black River and its basins to respond Sunday and lasting into
next week. MMEFS ensembles show a low probability for flooding
at McKeever and Boonville, but chances may be higher than
indicated if surface temperatures exceed the model consensus.
The risk is greater for the Watertown forecast point, extending
upstream to Lyons Falls with extensive snow pack contributing to
the runoff for the entire basin. This flooding potential is
discussed in the hazardous weather outlook. If forecast
confidence increases, a flood watch may be issued for all or a
portion of the Eastern Lake Ontario region.

&&

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

&&

$$

SYNOPSIS...CHURCH
NEAR TERM...CHURCH
SHORT TERM...RSH
LONG TERM...RSH
AVIATION...CHURCH
MARINE...CHURCH
HYDROLOGY...APFFEL



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