Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 272001

Area Forecast Discussion
National Weather Service Buffalo NY
401 PM EDT Thu Apr 27 2017

Summer-like conditions this afternoon will give way to stormy
weather by this evening as showers and thunderstorms cross the area
ahead of an approaching cold front. Some of these storms may produce
damaging winds this evening. Cooler air will move into the region
behind the front Friday and last through the weekend, with showers
possible through the weekend, as a frontal boundary stalls near the
lower Great Lakes.


Western and north-central New York is basking in midsummer-like
warmth this afternoon, as the area is firmly planted in the warm
sector of a low pressure system currently centered over the eastern
end of Lake Superior. The pleasant weather will come to an end by
the end of the day however, as a line of showers and thunderstorms
expected to develop within a pre-frontal trough move across the
forecast area from late this afternoon through the evening hours.

Regional MRMS products show this line beginning to form up from Lake
Huron down into eastern Ohio. As this line approaches western New
York, it should encounter an environment that will be primed for
strong to severe thunderstorms, with latest SPC mesoanalysis already
indicating around 1000 j/kg of SBCAPE, with several more hours of
heating to go, close to 50kt of bulk shear, and 700-500mb lapse
rates of 7.5 degC/km. The strong shear is largely unidirectional,
and relatively front-parallel, suggesting that any gust fronts
should remain close to the updrafts, favoring strong to damaging
wind gusts as the line moves across Western New York.  Mesoscale
guidance varies slightly from model to model on the timing of the
convection, but the current forecast bringing the convection into
WNY around 5-6pm looks on track. The severe threat is expected to
persist through the late evening, at which point the instability
will be diminishing and the line will approaching the eastern end of
the forecast area.

Another line of showers will likely accompany the cold front proper,
following the convective line a couple of hours. After that, expect
quiet weather for the rest of the night and into Friday as cooler,
drier air filters across the region behind the cold front, with
temperatures dropping into the 40s by daybreak across all but the
far eastern portions of the forecast area. Lingering post-frontal
cloudiness should give way to sunny breaks by late morning, as high
pressure moves across the region, before high clouds return once
again later in the day, courtesy of warm advection aloft.


A baroclinic zone will become established across the forecast area
Saturday and Sunday as we will be sitting on the northern periphery
of a ridge just off the southeastern coast. Weak waves will ripple
along this frontal boundary promoting a chance of showers through
much of the weekend, however the weekend will likely be far from a
washout as overall forcing is weak and sporadic. In fact mid-range
models are struggling with the subtle forcing along this boundary,
with the GFS/NAM solutions remaining wetter on Saturday, while the
EC continues to suggest mostly dry weather until later in the day.
For now have kept Saturday PoP at chance given the uncertainty.
Temperatures will be warmest across the Southern Tier and cooler
across the Lake Plains and North Country with highs ranging from the
low 60s to the low 70s.

By Sunday the boundary will evolve into a warm front pushing
northward as a deep low pressure system develops across the central
plains. As this low pressure system tracks toward the Great Lakes
region forcing will increase along the warm front, but it will also
move northward into southern Ontario and Quebec. Thus we may see a
period of showers early Sunday before breaking into the warm sector
later Sunday and Sunday night with a majority of that time being dry
and warmer. A sharp temperature difference can be expected across
the region as the warm front moves northward with highs in the low
50s in the North Country and along the lake Ontario shoreline to the
mid to upper 70s across the western Southern Tier.

By Monday, the anomalously deep low pressure system will track
through the upper Great Lakes while pushing a strong cold front
across the region Monday. Depending on the timing of this front, if
it lines up with peak diurnal heating, could result in strong to
potentially severe thunderstorms for the region, along with locally
heavy rainfall. The front will exit to our east Monday night giving
way to a drying a cooling trend. Very warm temperatures are expected
in the warm sector ahead of the approaching cold front with highs
well into the 70s and even the 80s across the lake plains and
Genesee Valley.


A seasonably deep surface low passing northwest of our region will
help usher in much cooler weather with below normal temperatures
expected. This airmass will arrive behind the cold front on Tuesday
along with a chance of some scattered showers and gusty winds.
Strong cold air advection with a source region over central Quebec
will lower 850mb temps a few degrees Celsius below zero which will
translate into surface temperatures that run very cool Tuesday
afternoon. Current expectations are highs which only top out in the

This strong cold air advection looks to also support very gusty
winds Tuesday with a 50+ knot low level jet streaking across the
eastern Great Lakes. The depth and track of the low and current
forecast strength of the low level jet in the 12z GFS could support
possible advisory level wind gusts. If the low level jet verifies
stronger such as the near 60 knot jet that the 12z EC shows, than a
late season high wind event may be possible. This threat of gusty
winds is included in the Hazardous Weather Outlook.

Winds will slacken off Tuesday night with below normal temperatures
then remaining in place Tuesday night through Wednesday and likely
Thursday with continued cold air advection as a mid-level trough
axis shifts east across our region followed by another trough
digging into the central states. Cool air instability showers will
be possible through Wednesday with the coldest core of below normal
air aloft passing by. Have continued low to slight chances of
showers for this. On Thursday medium range models show the digging
trough over the central states will kick off a surface low along the
Appalachians midweek which could lift some showers into our forecast
area from the south by Thursday. Lows Tuesday and Wednesday nights
look to dip into the upper 30s to low 40s then highs on Wednesday
and Thursday only rising into the low to mid 50s.


VFR conditions this afternoon will give way to showers and
thunderstorms towards evening, as a pre-frontal trough crosses the
area ahead of a cold front. A line of showers and thunderstorms is
expected to form over Ern OH/Wrn PA this afternoon and cross the
forecast area from west to east between 22Z-07Z, with most TAF sites
experiencing SHRA/TSRA for 2-3 hours at most. A second line of
mainly rain showers is expected along the cold front, following the
main line of SHRA/TSRA by 1-3 hours. Conditions will rapidly improve
behind the front, with mainly VFR cigs, MVFR over higher terrain,
scattering out by late morning on Friday.


Friday Night...VFR.
Saturday...VFR/MVFR with a chance of showers and thunderstorms.
Sunday...VFR/MVFR with a chance of showers.
Monday...MVFR to locally IFR with showers and thunderstorms likely.
Tuesday...VFR/MVFR with a chance of showers.


Generally quiet conditions on the lakes will give way to unsettled
weather late this afternoon into this evening, as showers and
thunderstorms cross the area ahead of an approaching cold front.
Some of these storms may be strong to severe, with locally strong
gusts and higher waves. Behind the front, expect freshening
southwesterly winds to generate moderately choppy conditions on the
east ends of the lakes later tonight into Friday.

Tranquil conditons will return to the lakes Friday night into
Saturday, as a weak area of high pressure moves over the lakes,
followed by a trough of low pressure that will set up across the
lakes, resulting in a weak pressure gradient. Northeasterly winds
will then freshen Saturday night into Sunday, as an area of low
pressure over the lower Missouri valley deepens and a warm front
lifts across the lakes.


The last days of April will finish with above normal
temperatures, warm enough that it will send our climate sites
towards a top 10 warmest April on record. The degree of
anomalous warmth has been greater towards the west, where
climate site Buffalo may reach the warmest April on record.
Below are the warmest Aprils on record.


Rank....Value (F).....Year


Current April average temperature through April 26th: 49.6F


Rank....Value (F).....Year


Current April average temperature through April 26th: 50.4F


Rank....Value (F).....Year


Current April average temperature through April 26th: 46.6F

Temperature records for Buffalo and Rochester begin 1871, while
Watertown`s history is a bit shorter, with temperature records
beginning in 1949.





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