Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 250623
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
223 AM EDT Tue Apr 25 2017

.SYNOPSIS...
Low pressure over the southeastern states will slowly make its way
northeastward along the east coast over the next couple of days. After
this system brings a brief round of showers into our region Tuesday...
drier weather and increasingly summerlike warmth will spread across our
area Wednesday and Thursday...with temperatures surging well into the 80s
in many places on Thursday. The next chance for rain will then arrive
late Thursday and Thursday night...when a cold front will cross our
region along with some showers and thunderstorms.

&&

.NEAR TERM /THROUGH TODAY/...
Overnight...a cutoff low over the southeastern states will continue
to make slow but steady progress northeastward. The strengthening
southeasterly low level flow around the northern side of this system
will advect increasing amounts of Atlantic moisture into our area...
which will manifest itself in the form of increasing/thickening
clouds south of Lake Ontario...where shower chances will also gradually
increase from north to south over time. Temperature-wise...readings
are already at or close to expected lows...and should generally tend
to hold fairly steady or rise during the balance of the night.

Precipitation should blossom into some steadier shower activity
Tuesday morning as better lift arrives and lower levels saturate
out. The shower activity will diminish from west to east
Tuesday afternoon and Tuesday night as the deeper moisture and
better forcing slide off into New England. Rainfall amounts out
of this system will be fairly light with totals less than a
quarter inch in most areas. Expect highs on Tuesday to range from
the upper 50s to mid 60s.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/...
A slow-moving cutoff low will continue to make its way up the East
Coast as we move through Tuesday night and into Wednesday. While
most of the shower activity should be tapering off as we move into
Tuesday night, as the bulk of the deeper moisture and synoptic
forcing will be moving off into New England, nonetheless there will
be enough of a southeasterly fetch of Atlantic moisture to maintain
at least a chance of showers  across the eastern half of the
forecast area through much of the night.

Things should dry out as we move into Wednesday, and the low
pressure system continues to fill as it moves off the coast of New
Jersey. The moist southeasterly flow will give way to warmer and
drier southerly flow that will help clear out lingering cloud cover
while boosting temperatures into the 70s.  We should see mostly
clear skies Wednesday night into Thursday, as a sharply amplified
upper level ridge transits the region. Warm air and downsloping
southerly flow will keep temperatures in the mid 50s Wed night, with
readings in the low 60s along the Lake Erie plain, making it feel
more like July than April.

Thursday will be the warmest day we have seen so far this year, as a
combination of subsidence that will boost 850mb temps to in excess
of +18C. The subsidence, abundant sunshine, and slight downsloping
on south-southeasterly flow will translate to highs that should
easily top out in the mid-80s for many locales, with temperatures
potentially approaching 90 in the Genesee valley.

Things get more interesting as we move into Thursday night and a
cold front approaches the region. Convection occurring along a pre-
frontal trough is forecast to move across the forecast area
overnight. While there may be a potential for some of these storms
to be strong and possibly severe, particularly across far Western
New York in the evening, when instability will be maximized,
vertical shear as depicted in the models is marginal for severe
weather, and moisture is limited. In addition, should the front be
held up by even a few hours, the pre-frontal trough will cross later
in the night, when diurnal instability will be greatly reduced.
Nonetheless, it is often the case that when we see a dramatic warmup
such as the one expected Thursday, it is followed by a bout of
severe weather...so this is a scenario that will bear close watching
over the next couple of days...

As a final note, high temperature records for April 27th are 84 at
Buffalo (1984)...86 at Rochester (1990)...and 85 at Watertown
(2009)...with it appearing increasingly likely that the records at
Buffalo/Rochester will at least be approached if not threatened on
Thursday. After that...modest cool air advection setting up behind
the cold frontal passage will allow lows to fall back into the mid
and upper 50s Thursday night...though such readings will still be
some 15-20 degrees above late April normals.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
The cold front mentioned in the Short Term Discussion above is
forecast to be in the process of shifting across Central NY Friday
morning then clearing to the east of the forecast area by Friday
afternoon with while the tail end stalls just south of the NY/PA
border. Have left a chance of showers with a slight chance of
thunderstorms during the morning east of about a Watertown to Oswego
to Wellsville line with a slight chance of a shower to the west of
that line. Expect mainly dry weather for Friday afternoon with a
narrow wedge of high pressure building in behind the front. The
exceptions are a slight chance of a shower possible in the afternoon
for the eastern Lake Ontario Region lingering behind the cold front
as well as far western NY ahead of an approaching weak surface wave
moving into the Ohio Valley.

Friday night, the weak surface wave with associated 40kt low level
jet will shift from the Ohio Valley to western NY. In this process
it should lift the stalled front to our south back north as a warm
front, stretching across western and central NY. As this system
shifts along the stalled front it will bring a chance of showers
Friday night and Saturday morning with a chance of thunderstorms
possible in the Southern Tier Saturday afternoon where some
instability is possible south of the warm front. Saturday night, a
chance of showers will linger for all areas with the front still
stretch across western and central NY.

Sunday and Monday will feature more widespread chances of showers
and thunderstorms as forcing and instability are enhanced by a low
pressure system strengthening in the Midwest. Southerly flow ahead
of this system will bump the stalled front a little further with
moisture and instability interacting with the warm front causing
the chance for showers and thunderstorms. The low pressure system
looks to rapidly deepen on Monday while lifting over Michigan. A
cold front associated with this storm will approach the forecast area
Monday or Monday night bringing the risk for another day of showers
and thunderstorms. Its still pretty far out to be more certain but
there could even be a risk of severe storms as shear will be
enhances ahead of the cold front.

Temperature-wise, readings through will remain well above normal
with daytime highs Friday through Sunday still expected to range
between the mid 60s and lower 70s. Overnight lows look to run
comfortably in the upper 40s to low 50s. As mentioned in a previous
discussion, while temperatures are forecast above average, the exact
magnitude of these departures will be highly dependent upon the
exact position of the warm front. This feature will mark the
dividing line between pleasantly warm spring conditions to its north
and downright midsummerlike warmth to its south. Monday may be the
warmest day of the period as the warm front lifts north of our
region possibly setting the stage for another run toward 80 degrees
should showers and thunderstorms hold off until late in the day.

Looking out just beyond this period into Monday night/Tuesday. There
could be a risk of strong gradient wind gusts in the wake of the
front downwind of the lakes. This would be due to the track of the
surface low following a favorable track and 50+ knot low level jet
mixing in cold advection behind the front. This is a very early
assessment so stay tuned for future updates.

&&

.AVIATION /07Z TUESDAY THROUGH SATURDAY/...
During the TAF period...low pressure will meander its way northeastward
along or just offshore of the Carolina and Virginia coastlines. A feed
of Atlantic moisture wrapping around the northern flank of this system
will bring increasing/thickening clouds to the region overnight and
Tuesday morning...along with a period of fairly numerous light showers
between Tuesday morning and early Tuesday afternoon...with these lasting
between 3-6 hours at any given location. After that...shower chances will
then generally diminish from west to east through the balance of the
period.

In terms of flight conditions...expect these to lower through the VFR
range overnight and Tuesday morning as the clouds increase/thicken and
the showers develop...though expect most locations to remain VFR...save
for the higher terrain where some MVFR ceilings may develop. Once the
showers taper off...expect general VFR ceilings to then largely prevail
through the rest of the period across the lower elevations...with a
mix of MVFR and potential IFR ceilings found across the higher terrain.

Outlook...
Wednesday...Improvement to VFR areawide.
Thursday...Mainly VFR during the day...with showers/thunderstorms and
attendant MVFR then becoming likely late Thursday and Thursday night.
Friday and Saturday...Mainly VFR with a chance of showers and
thunderstorms.

&&

.MARINE...
A general east to southeast flow will remain in place across the
Lower Great Lakes Tuesday and Wednesday, as a very slow moving
coastal low will be found along the coast of the Carolinas. Again,
the choppiest conditions will be found in Canadian waters so no
additional marine related flags are anticipated.

&&

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

&&

$$

SYNOPSIS...JJR
NEAR TERM...APFFEL/JJR/TMA
SHORT TERM...WOOD
LONG TERM...SMITH
AVIATION...JJR
MARINE...APFFEL/JJR/TMA



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