Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 202121

Area Forecast Discussion
National Weather Service Buffalo NY
421 PM EST Tue Feb 20 2018

Low pressure over the Straits of Michigan will track northeastward
into Quebec tonight...then on into Labrador on Wednesday. This system
will provide us with springlike warmth through early Wednesday morning...
along with some additional showers late this afternoon and evening...
followed by another period of widespread rainfall on Wednesday as
its trailing cold front crosses our area. While colder weather will
return in the wake of the cold front...our temperatures will still
remain above normal through the end of the week.


A warm front draped across Lake Ontario and the North Country will
slowly push northward to the Upper Saint Lawrence Valley by early
this evening...before shifting completely north of the area during
the first half of the night. Through early this evening...ongoing
warm air advection/isentropic upglide will lead to periodic showers
along and north of the front...while to its south a passing mid
level shortwave will push an attendant weakening area of showers
across portions of western New York. The bulk of these latter showers
will affect areas along and north of a rough Jamestown to Rochester
line...while locations to the south of this line will experience more
widely scattered to isolated activity with increasing southeastward

Once we get past the late afternoon to early evening hours...we can
then expect mainly dry and unseasonably mild conditions to prevail
across our region for the majority of the burgeoning
warm sector expands northward across our area in the wake of the
departing warm front. Overnight lows will range from the mid 50s to
lower 60s...with readings in fact likely to hover above these levels
(i.e. in the lower to mid 60s) through the bulk of the night. Such
temperatures will be more typical of midsummer than of late winter...
and will range an astounding 40 to 50 degrees above normal late
February overnight lows. With such a warm and moist airmass crossing
the much colder lake waters...areas of fog will remain possible over
and near the lakes tonight.

On Wednesday...the parent surface low will track northeastward from
Quebec into Labrador...and in the process will push its trailing
cold front across our region from northwest to southeast. After a
mostly dry start to the day...the frontal passage will usher in a
3-6 hour period of fairly widespread rainfall...with the bulk of the
rain falling behind the boundary due to its markedly anafrontal
nature. The majority of the rainfall will take place between the
morning and early afternoon hours...with the precip then steadily
tapering off from northwest to southeast during the afternoon as
high pressure and drier air begins building into the region from
the Upper Great Lakes. As for temperatures...the frontal passage
will also bring a rather abrupt end to our springlike warmth...
with mild morning highs in the mid 50s to mid 60s giving way to
steadily falling readings as cold air advection and precipitation-
driven cooling take over in the wake of the boundary...with temps
falling into the 40s areawide during the afternoon.


Wednesday night will start off with a frontal boundary stalled
somewhere to the south of the area. Model consensus differs on its
position considerably, which eventually leads to differences in the
track of a weak wave of low pressure late Wednesday night through
Thursday. 12Z runs of the NAM and GGEM show the range of
possibilities with the NAM virtually dry for our area and the GGEM
bringing precipitation across the entire cwa. The best chance for
precipitation is across the Southern Tier on Thursday with
diminishing chances to the north. There are also differences in
forecast thermal profiles with rain, snow, or mixed precipitation
possible. Any snow accumulation would be light (less than 2 inches)
since any persistent warming in the mid-levels from steady
precipitation would result in a change over. For temperatures, high
pressure will pass just north of the region Wednesday night which
may provide a narrow window of opportunity for radiational cooling
across the North Country. In general, expect lows on Wednesday night
to be in the upper 20s, but temperatures may fall into the teens in
the North Country. Given the cloud cover and likelihood of
precipitation the forecast hedges on the cool side Thursday with
forecast highs in the mid to upper 30s.

High pressure to the north will briefly expand into the region
Thursday evening which will result in mainly dry conditions for
Thursday night outside of perhaps a few lingering showers across the
Western Southern Tier. Lows will range from the lower 30s near the
Pennsylvania border to the lower 20s across the North Country.

The next low pressure system will approach Friday as the high
exits into the Gulf of Maine. A weak surface low is forecast to
track into the Upper Great Lakes region, with nearly all guidance
bringing an area of strong mid-level warm air advection across our
region. Given model agreement and synoptic scale lift, there is high
forecast confidence in a period of precipitation on Friday which
will taper off late Friday night. This may start off briefly as snow
or mixed precipitation across the North Country but will quickly
change to all rain as 850 mb temperatures warm to around +6C.
Precipitation will taper off late Friday night, but temperatures
will remain on the warm side with lows in the 30s.


An active weather pattern will continue this weekend with mild
temperatures and chances for precipitation. The large scale weather
pattern will remain relatively unchanged with a stubborn ridge over
the southeast CONUS and large scale troughing over the intermountain
west. This pattern will continue to supply above normal temperatures
and increased precipitation chances with the flow of Gulf of Mexico
moisture wide open.

In particular, a low pressure system will eject from the four
corners region Saturday across the Great Lakes by Sunday. The result
should be a chance of widespread rainfall Sunday ahead of the
approaching low pressure system. As the low passes by to our
northwest, expect decent southwest winds to pick up behind in the
cold advection behind the front. Models vary on the strength of the
surface low, but there at least low potential for a high wind event
if surface low deepens sufficiently.

Quiet and drier weather returns Monday with surface high pressure
building over the Ohio Valley. Otherwise, highs will remain above
climo (+5F - +10F) with the daytime highs in the mid and upper 40s
likely for most locations. Sunday will likely be the warmest day, so
long as we briefly break into the warm sector, with at least 50s


A warm front draped across Lake Ontario and the North Country will
slowly push northward to the Upper Saint Lawrence Valley by early
this evening...before shifting completely north of the area during
the first half of the night. Along and north of the front...periodic
showers and lower clouds will lead to MVFR conditions and reductions
to IFR at times through early this evening. Meanwhile to the south
of the boundary flight conditions will mostly be dry and VFR through
tonight...except along and north of a rough KJHW to KROC line this
afternoon where another round of showers will likely produce a short-
lived round of MVFR conditions...with brief/localized IFR visibilities

Otherwise low level wind shear will also remain an issue much of the
time through tonight...with a persistent 45-50 knot low level jet
lingering around 2kft. The exception to this will be across far western
New York this afternoon...where increased mixing could lead to surface
gusts to 30 knots or so while helping to temporarily alleviate any
wind shear.

On Wednesday a trailing cold front will cross the region from northwest
to southeast...with a rough 3-6 hour period of rain accompanying and
following the frontal passage. Coupled with lowering ceilings as the
boundary layer moistens...this will result in an areawide deterioration
to IFR/MVFR flight conditions during the morning hours. As we move into
the afternoon...high pressure and drier air will begin building into
the region behind the front...resulting in the rain tapering off from
northwest to southeast...and flight conditions rebounding to MVFR and
then VFR in a similar fashion.

Wednesday night...Mainly VFR...with a chance of snow showers/MVFR
across the Southern Tier overnight.
Thursday...MVFR with some rain and snow likely across the Southern
Tier and Finger Lakes...and VFR/MVFR with a chance of rain and snow
Friday...VFR/MVFR with some rain developing.
Saturday and Sunday...VFR/MVFR with scattered to numerous rain and
snow showers.


In the wake of a warm front...a moderately brisk south to southwesterly
flow will continue across the Lower Lakes Region through tonight and
early Wednesday. While winds will be offshore and at marginal levels
in most locations...a slightly stronger flow will be in place across
Lake Erie and the Upper Niagara River/Buffalo Harbor through tonight...
for which Small Craft Advisories remain in place.

On Wednesday a cold front will cross our region from northwest to
southeast. In its wake...a brisk westerly to northwesterly flow will
set up across Lake Ontario late Wednesday morning and Wednesday
afternoon...before diminishing Wednesday night. This will bring
another round of advisory-worthy conditions to areas along the
south shore of that lake...for which a new round of Small Craft
Advisories have been hoisted.


There remains a risk for flooding in the Black River Basin, but the
chances for moderate (or major) flooding have diminished. So far
rainfall amounts have been slightly less than expected with total
amounts in the Black River basin now expected to average in the 0.75
to 1.50 inch range. There will be locally higher amounts to 2 inches
along the south face of the Tug Hill, but these will mainly be just
to the west of the Black River Basin.

Temperatures are still on track to melt the majority of the snow
pack in place in the Black River basin. The event started with a
basin average of 4-5 inches (water equivalent) with up to 10 inches
across higher terrain.

The greatest risk for flooding is at the Watertown forecast point
due to the widespread nature of the event. RFC forecasts have
trended down slightly, but still show the forecast point is likely
to just reach flood stage. Boonville and McKeever are less likely to
flood, with a bit less rainfall. These points still will be close
given the significant snow melt expected through Wednesday. There
will also be rises on the Salmon River. Ice jams also may be an
issue with some ice still in place in and along some waterways in
the basin.

Elsewhere, flows on many area creeks and rivers will be high but are
not expected to reach flood stage. An inch to an inch and a half of
rain is now expected across the Niagara Frontier which will cause
ponding of water in low-lying areas. The steadiest rains missed most
of the Buffalo creeks basins, with a few forecast points expected to
reach action stage but there is no out of bank flooding expected.


NY...Flood Watch through Wednesday evening for NYZ006>008.
MARINE...Small Craft Advisory until 10 AM EST Wednesday for LEZ020-040-
         Small Craft Advisory from 10 AM Wednesday to 1 AM EST
         Thursday for LOZ043-044.
         Small Craft Advisory from 10 AM to 7 PM EST Wednesday for



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