Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 262021
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
421 PM EDT Wed Apr 26 2017

.SYNOPSIS...
A narrow ridge of high pressure will shift eastward into New England
overnight while keeping mostly clear to clear skies in place across
the region. A very warm airmass will keep temperatures quite mild
tonight, with high temperatures soaring into the 80s on Thursday. A
line of thunderstorms, with a few potentially damaging wind gusts
and heavy rainfall, will cross the region late Thursday. Relatively
cooler, yet still above normal, temperatures will linger through the
weekend.

&&

.NEAR TERM /THROUGH THURSDAY/...
Water vapor satellite imagery shows an occluded low pressure system
pinwheeling slowly northward along the northeast coastline,
meanwhile another sharp trough is digging through Texas and a
narrow ridge axis extends northward through the Ohio Valley into
western NY. Under this ridging building in over the forecast area,
visible satellite imagery shows skies becoming clear in most areas
late this afternoon as the shallow low level moisture from this
morning mixes out. The one exception is across Lewis County where
more clouds will persist into early evening.

As we go into this evening a band of thin cirrus will move across
the region while the remaining diurnal cumulus will diminish with
loss of solar insolation. Overnight skies will become clear to
mostly clear. However, as a pressure gradient develops across the
region between a surface ridge axis shifting to our east and
pressure falls over the upper Great Lakes expect increasing
southeasterly winds. The persistent warm advection and downslope
flow will keep temperatures tonight quite mild, in the upper 50s to
even low 60s in the lake plains.

On Thursday, current PV max rounding the base of the broad trough
over the central plains will eject northeastward crashing the
amplified ridge across the northeast CONUS. The result for the
forecast area will be the poleward transport of a very warm airmass
(850 mb temps +15 to nearly +20C) combined with gusty (25 mph)
downslope winds on Thursday. Temperatures will soar into the 80s for
much of the region, with the warmest readings (mid to upper 80s)
across the Niagara Frontier to Genesee Valley where downslope flow
will be maximized. At the same time, moisture advection into the
region will push dew points into the upper 50s, if not near 60 in
spots. This will result in strong diurnal destabilization under a
warm nose aloft, which will keep us capped through the day. However,
later Thursday afternoon, as the ejecting PV max nears western NY,
height falls aloft will help erode the capped layer, supporting the
development of thunderstorms along a pre-frontal trough. Timing of
this thunderstorm develop has trended about 2 hours faster per 12Z
model guidance, which would place all of western NY under optimal
daytime heating. Combine this with the increasing speed shear (0-6km
of 40 to 50 knots) associated with the wave, and any thunderstorms
that develop will be capable of strong to potentially damaging wind
gusts. This best potential for a few severe thunderstorms will in
the typical corridor southeast of Buffalo from about Jamestown to
Rochester to the Genesee Valley. As the storm evolve eastward toward
central NY and the North Country overnight, storms will weaken as
diurnal instability wanes.

The actual cold front boundary will lag the best thunderstorm
potential by a few hours and will probably feature a few widely
scattered weaker showers or thunderstorms, but should be a more
uneventful passage. Cooler air will filter in behind the front
overnight, with lows bottoming out in the upper 40s in western NY to
the mid 50s toward central NY.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/...
After a stormy night Thursday night, western and north-central New
York should get a dry break on Friday as a zone of post-frontal
subsidence, accompanied by mid-level ridging moves across the
region. While there should be sunny breaks through the day, there
will likely be at least passing mid-level cloudiness, as fragments
of upper level energy eject across the region out of the Ohio
valley. While the cold frontal passage will yield markedly cooler
temperatures as compared to Thursday`s heat wave...highs will
actually still be a couple of degrees warmer than
average...generally in the mid 60s...with 50s found to the northeast
of the lakes, thanks to post-frontal southwesterly flow and
afternoon lake-breeze circulations.

The forecast becomes much trickier as we move into Friday night and
Saturday. In terms of the big picture, a Pacific jet diving across
the inter-mountain West will reinforce the longwave trough over the
Rockies and High Plains, while the sub-tropical ridge will remain
displaced to the west, across Florida and the southeastern states.
The convergence between southerly return flow around this anti-
cyclone and the cooler, drier air located within the longwave trough
will set up a baroclinic zone that will extend from the southern
Plains to the lower Great Lakes. While this boundary will certainly
serve as the focus for the development of showers during this as a
series of waves move along it, models continue to disagree both with
regards to its exact placement/orientation, as well as the timing of
the waves moving along the boundary. As a result, some guidance
packages suggest a wet start to the weekend, with periods of showers
Friday night into Saturday, as suggested by the GFS/NAM, while the
ECMWF keeps the showers at bay at least until Saturday night. For
the time being, will stick to broadbrushed chance pops, pending
further model runs.

Regarding temperatures, again, there is quite a bit of uncertainty,
as the temperatures will be affected by the final position of the
stationary front relative to the forecast area. The general trend as
forecasted currently though will be for temperatures to cool
somewhat on Saturday, pending a cloudier/wetter regime, though once
again readings should be, at worst near average for late April.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
Time for a change in the pattern.

A hemispheric WV loop clearly depicts a robust shortwave rotating
around the base of an expansive Aleutian low early this morning.
This feature will eject to the east this afternoon and is forecast
to make landfall along the British Columbia coast Thursday evening
before diving into a persistent longwave trough over the western
half of the country. This will lead to significant cyclogenesis
across the southern Plains during the course of the weekend...with a
deep `cutter` low lifting north and eventually closing off in the
vicinity of the Upper Great Lakes early next week. This will
encourage the base of the persistent longwave trough over the west
to become centered over the center of the continent...setting the
stage for notably cooler air to make its way to the Lower Great
Lakes. As is usually the case...the pattern change will be marked by
a round of very unsettled weather. More on that in a moment.

As we open this period on Sunday...the aforementioned `cutter` low
will be in the process of lifting north across the plains states. A
burgeoning downstream ridge ahead of this storm system will help to
lift the old frontal boundary from Friday night back across our
region as a warm front. This could touch off some showers...but more
importantly...it will usher in another round of very mild weather.
This will be realized by highs that will mainly be in the 70s for
Sunday...particularly across the Southern Tier where it is not out
of the question that some spots could reach 80. This would depend on
the speed of the warm front and the amount of clearing in its wake.
In any case...this will set the stage for a warm night with mins
across the western counties struggling to fall below 60.

The stacked low over the Upper Great Lakes will swing its associated
cold front across our region on Monday. This will produce a round of
showers and thunderstorms...and again...pending the timing of the
actual fropa...the mercury could re-visit the 70s.

Notably cooler weather can then be expected on Tuesday...as the
opening longwave trough will pass to our north. H85 temps will
settle into at least the lower single digits...and possibly below
zero c. This will translate into high temperatures Tuesday afternoon
that will be in the 50s...which is actually below normal. A novelty.

A look further down the road suggests that temperatures may stay
near to below normal for much of the remainder of the week...as
general troughiness if preferred by the majority of the medium range
ensemble members of the GEFS and ECMWF. This agrees with the 8 to 14
day temp forecast from CPC...which favors cooler than normal weather
for the first week or two of May.

&&

.AVIATION /21Z WEDNESDAY THROUGH MONDAY/...
High pressure will shift across the region through this afternoon
and into New England overnight. VFR conditions will prevail the rest
through tonight with light winds. There may be some IFR CIGS or some
patchy fog developing across interior Southern Tier tonight, but at
this point expect this remain inland near ELZ/OLE, and is not
expected to expand westward to JHW.

On Thursday, VFR conditions will again prevail but with
strengthening southerly winds gusting to around 20 to 25 knots in
the afternoon at KIAG/KBUF/KROC. A line of showers and thunderstorms
will then cross the region late Thursday afternoon and evening, with
erratic gusty winds and locally heavy rainfall. Localized IFR
conditions possible in these storms, with VFR/MVFR otherwise.

Outlook...

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

&&

.MARINE...
High pressure will move slowly east of the region tonight and into
New England on Thursday, while a low pressure system deepens over
the upper Great Lakes. Light winds this evening will become
southeasterly overnight to southerly on Thursday. Winds and waves
will continue to be well below small craft thresholds into Thursday
afternoon.

A cold front will cross the region Thursday night, with showers and
thunderstorms likely ahead of the front. Winds and waves are largely
expected to remain below SCA threshold on the Eastern Great Lakes,
however locally higher winds and waves are possible with any
thunderstorms that develop late Thursday.

&&

.CLIMATE...
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.


Buffalo

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

1........51.3.........1921
2........51.1.........2010
3........51.0.........1955
4........50.9.........2008
5........50.8.........1878

Current April average temperature through April 25th: 49.0F


Rochester

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

1........52.6.........1878
2........52.5.........1921
3........52.4.........2010
4........52.3.........2008
5........51.4.........1915

Current April average temperature through April 25th: 49.9F


Watertown

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

1........49.1.........1987
2........48.7.........1955
3........48.7.........2010
4........48.3.........1968
5........48.2.........2008

Current April average temperature through April 25th: 45.9F

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

&&

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

&&

$$

SYNOPSIS...CHURCH
NEAR TERM...CHURCH/HITCHCOCK
SHORT TERM...WOOD
LONG TERM...RSH
AVIATION...CHURCH/HITCHCOCK
MARINE...CHURCH
CLIMATE...THOMAS


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