Area Forecast Discussion
Issued by NWS Buffalo, NY

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000
FXUS61 KBUF 170844
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
344 AM EST Tue Jan 17 2017

.SYNOPSIS...
A period of rain, with light freezing rain will push across the
region today and tonight, with showers of rain and snow tapering off
through the day Wednesday. It will remain mild through the remainder
of the week, with warmer air reaching the region this weekend.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
This morning a surface low is found near Chicago with a warm front
pushing northeastward across the southern Ohio Valley, and cold
front draped back across the Mississippi Valley and through
Texas. Water vapor imagery displays two shortwaves, one near the
surface low over northern IL, while a second shortwave is back
across MN.

With the upper level trough over the surface low, there will not be
much additional deepening to this surface low through the
period...as the low tracks across Central Great Lakes today, and the
Eastern Great Lakes tonight. However both shortwaves will maintain
the presence of an upper level trough over the region, and this
will maintain chances for precipitation through the period.

For today surface temperatures remain around the freezing mark
across WNY, and into the lower 20s east of Lake Ontario. The leading
edge of precipitation ahead of the warm front has reached WNY this
morning. With surface temperatures around the freezing mark this has
led to a light glaze where the freezing rain has occurred. Will
maintain headlines as is for this update.

The precipitation will continue to push eastward through the day
reaching the North Country by this afternoon. A light northeast wind
through the Saint Lawrence Valley will replenish the cold air
through the boundary layer and maintain subfreezing temperatures
through the SLV for much of today and into tonight. Here there may
be the greatest ice accumulation with upwards to a quarter of an
inch possible. Otherwise much of the region will remain a tenth of
an inch or less...with many areas just a light glaze.

Through the day across WNY surface temperatures will warm well above
freezing with highs reaching the 40s, and upper 40s along the Lake
Erie shoreline where a downslope flow will exist. This will end the
freezing rain threat, though there will continue to remain a light
rain. There also may be some thunder this afternoon and evening
across the So. Tier. As the surface low nears, and tracks just to
the north of our region, some elevated instability of 100 to 200
J/KG may reach our region, along with TT`s reaching into the lower
50s. Will include slight chances for thunder across our Southern
Tier.

Tonight a cold front will track across the region as the surface low
pushes eastward. This cold front will continue chances for
precipitation (mainly rain across WNY, and a wintry mix of freezing
rain/sleet across the North Country) tonight. There will be minimal
cold air behind this front, such that the snow growth zone will
remain rather high...and likely in a layer just above the abundant
low level moisture. This will make for a tricky forecast as surface
temperatures drop tonight. There will likely remain some light rain
showers/drizzle late tonight...that may turn to a freezing drizzle
across some of the colder spots of the Southern Tier.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY NIGHT/...
A weak area of surface low pressure will move northeast up the Saint
Lawrence Valley during Wednesday. Cyclonic flow and abundant low
level moisture will keep chances for precipitation lingering through
the day, particularly across upslope areas. The precipiation for the
most part will be light, with some lingering drizzle or light rain
or flurries. As temperatures cool aloft, this could change to some
light snow for the high terrain, but any accumulations look very
minor.

Moisture will eventually pull away from the area Wednesday night as
a ridge axis to our south and west will start to build into the
region. Temperatures will lower to within a couple degrees of
freezing.

Fair dry weather is expected Thursday and Thursday night, as ridging
will amplify over the Lower Great Lakes. This will be accompanied by
some weak warm advection, with temperatures Thursday afternoon
climbing to near 40 to the lower 40s, possibly even mid 40s.
A little more cloudiness over the eastern Lake Ontario region will
likely keep that area in the mid 30s.

Conditions will then deteriorate Friday afternoon and night...as a
weakening shortwave will track northeast across the forecast area.
Will maintain chc pops to cover this light pcpn event, which again
could include some spotty freezing rain, especially across the North
Country.

&&

.LONG TERM /SATURDAY THROUGH MONDAY/...
A highly amplified split flow will be found across the continent
during the period with the Great Lakes region being dominated by
Pacific modified air within the southern branch. While this will
keep above normal temperatures in place over our region...the period
will be highlighted by what could be a soaking to problematic rain
on Monday. More on this in a moment.

As we open this period on Saturday...a weak mid level shortwave and
its attendant sfc trough will stall over our region. Given the
consistency between the various operational packages that depict a
swath of relatively deep moisture that will accompany the weak
lift...have add low chc pops to our area for some light rain. The
silver lining to the more pessimistic pcpn forecast is that it will
be quite mild. Temperatures Saturday afternoon are expected to climb
well into the 40s...with some of the valleys west of the Finger
Lakes approaching 50.

Ridging should become dominate over our forecast area on Sunday...
but do not let the improving trend fool you. A deep closed low over
the Lower Mississippi Valley on Sunday will open the door for rich
GOMEX moisture to stream northwards across the Ohio Valley towards
our region. As we proceed through Sunday night into Monday...the
large storm system will drift northeast to the Upper Ohio valley.
While this will shift the origins of the sub tropical plume to the
Caribbean and Gulf stream of the western Atlantic...it will still be
directed at our forecast area. This will set the stage for what
could be a significant rain event for our region on Monday.

The stacked storm system will be quite dynamic as it nears our
region on Monday...with strong upper level jet dynamics and a
distinct divergent upper level flow helping to produce deep lift
over our region. This should lead to widespread rain over our
region...with the influx of sub tropical moisture enhancing the
potential for moderate to heavy rain.

There could also be strong downsloping winds between Lake Erie and
the Chautauqua Ridge later Sunday night into Monday...as southeast
low level jet of 50 kts near the top of the inversion is being
forecast to be in place.

&&

.AVIATION /09Z TUESDAY THROUGH SATURDAY/...
For the 06Z TAFs flight conditions are beginning to deteriorate to
MVFR across WNY as moisture continues to deepen, and precipitation
nears the region. This precipitation may begin as a brief period of
light freezing rain, before a mild southerly flow warms the surface
and promoting plain rain. Freezing rain chances will be possible
through about 12Z across KIAG/KBUF and 15Z across KROC. There will
be lower chances for freezing rain across KJHW, where temperatures
are still in the mid 30s, and KART where temperatures through the
day may warm above the freezing mark before the precipitation
arrives.

Flight conditions will deteriorate to IFR through the morning and
early afternoon hours, with these flight conditions remaining
through a good portion of tonight. There may be come improvement to
MVFR through the later overnight period.

Light easterly winds this morning will become southwesterly this
afternoon...and westerly late tonight as a weak cold front passes.

Outlook...

Wednesday...IFR with showers transitioning to some
drizzle and fog.
Wednesday night through Friday...Mainly VFR.
Friday night and Saturday...chance of rain and some MVFR/IFR.

&&

.MARINE...
An area of low pressure will pass through the Great Lakes region
today, and an easterly flow ahead of the surface low will flow
across the Eastern Great Lakes. This flow will develop waves 4 to 5
feet on the western half of Lake Ontario, where winds will also
reach 20 to 25 knots. A small craft advisory will remain in place
for points west of Hamlin Beach.

A cold front will cross the region tonight, and these easterly winds
will veer around to southwesterly and then westerly. There will be
minimal cold air behind this cold front, and conditions on Lakes
Erie should remain just below SCA tonight and into
Wednesday...though waves and winds may reach the lower thresholds
of SCA on Lake Ontario Wednesday.

&&

.CLIMATE...
The main story for next week and beyond will be the extended
period of above normal temperatures not only in our region, but
for much of the eastern 2/3 of the nation. Over the next two
weeks, a strong closed low will remain parked over the Bering
Straits, forcing a strong Pacific East Asian jet to extend farther
east than normal. This will continue to bring a parade of Pacific
systems into the western United States, while also supporting
zonal flow and a flat ridge downstream across the central and
eastern part of the country. The westerly flow across the
continent will support strong Chinook warming off the Rockies,
with warmth spreading to the east coast and even well north into
southern and central Canada.

The warmth will last for another 12 days or so, but there is a
significant pattern change brewing beyond that. A Sudden
Stratospheric Warming event has just occurred in the northern
hemisphere. These events occur when planetary waves propagate
vertically into the stratosphere, with wave breaking and dampening
processes acting to rapidly warm the stratosphere over the high
latitudes and greatly distort the Stratospheric Polar Vortex.

This warming and disruption in the stratosphere has been shown in
numerous studies to slowly feed back into the troposphere, with a
strong tendency for high latitude blocking to increase about 2
weeks after the warming takes place. High latitude blocking
increases the ability of polar air to spread southward into the
mid latitudes, and increases the chances of cold and wintry
weather locking in for a longer period of time.

It appears the long range guidance is beginning to capture this
idea, with the GEFS and NAEFS ensembles suggesting a more highly
amplified flow starting late this month, with a ridge developing
over Alaska and the West Coast while a deep longwave trough
begins to establish across central and eastern North America. The
developing ridge in Alaska may also promote a period of cross
polar flow, draining frigid Siberian air into northern Canada.
GEFS ensembles also support a more negative NAO and AO pattern
towards the end of the month. Putting all this together, it
appears the pattern should become much colder and more wintry
around January 27-29. Past stratospheric warming events suggest
this cold pattern may last for quite some time, and may support
the potential for periods of well below normal temperatures by the
end of the month and first half of February. Stay tuned.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Winter Weather Advisory from 7 AM this morning to 4 AM EST
     Wednesday for NYZ007-008.
     Freezing Rain Advisory until 4 PM EST this afternoon for
     NYZ005-006.
     Freezing Rain Advisory until 1 PM EST this afternoon for
     NYZ003-004-013-014.
     Freezing Rain Advisory until 10 AM EST this morning for NYZ001-
     002-010>012-019>021-085.
MARINE...Small Craft Advisory from 7 AM this morning to 4 PM EST this
         afternoon for LOZ042.

&&

$$

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


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