Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 242215

Area Forecast Discussion
National Weather Service Buffalo NY
615 PM EDT Mon Apr 24 2017

High pressure will move away tonight. Low pressure over the
southeastern states will slowly push northward along the east coast
over the next several days. This will spread showers into our region
late tonight and Tuesday. It will then become summer-like by mid
week, as the mercury will soar into the 70s for Wednesday and well
into the 80s Thursday.


The axis of the large surface high will push east to the Canadian
maritimes tonight, while a cut-off low over the southeast CONUS
makes slow progress northward. Strengthening low-level southeast
flow will develop north of the low, which in turn will advect
increasing amounts of Atlantic moisture back up across our
forecast area. This should result in a gradual uptick in
precipitation starting late tonight mainly after 08z with
precipitation starting out light and spotty owing to relatively
weak ascent this far northwest of the low and the relatively dry
low levels that will necessitate moistening/saturation for
steadier precipitation to develop.

Precipitation should blossom into some steadier shower activity
Tuesday morning as better lift arrives and lower levels saturate
out. The shower activity will diminishing 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 ranging from a tenth of an
inch or less south of Lake Ontario to one to two tenths of an inch
across the North Country.


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 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.


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.


High pressure centered near Hudson Bay will extend to the south
across New England into this evening, and this will allow for
flying with nearly cloud free skies. The fine VFR weather will
continue through at least the first half of tonight, then
clouds will lower and thicken from the southeast during the wee
hours of Tuesday morning. There may be some light showers over
the western counties by the end of the night.


Tuesday...Mainly VFR with showers likely.
Thursday...VFR/MVFR with a chance of showers and thunderstorms.
Friday and Saturday...Mainly VFR with a slight chance of
showers and thunderstorms.


High pressure centered near Hudson Bay will nose southeast across
the St Lawrence Valley and New England into early evening. This will
continue to generate a northeasterly flow across the Lower Great
Lakes region, with small craft advisory conditions expected in
the nearshore waters of Lake Ontario from the Niagara River to
Mexico Bay. The choppiest conditions will be west of Irondequoit

As the axis of the surface high pushes east to the Canadian
maritimes tonight, the flow will veer to the east and this will
redirect the choppiest conditions into Canadian waters. Weaker winds
and less wave action will be found on Lake Erie.

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.


MARINE...Small Craft Advisory until 8 PM EDT this evening for



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