Area Forecast Discussion
Issued by NWS Buffalo, NY

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784
FXUS61 KBUF 251444
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
Issued by National Weather Service Cleveland OH
1044 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 today... 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 TONIGHT/...
During this period...a cutoff upper level low and its associated
surface reflection will slowly meander its way northeastward
along the Carolina and Virginia coastlines. A southeasterly feed
of Atlantic moisture wrapping around the northern side of this
system will continue to spread increasing/thickening clouds across
our region from south to north this morning...with the west-east
oriented swath of mainly light showers along the Interstate 90
corridor moving northward into Canada through early this afternoon
in tandem with its responsible low level jet.

The above developments will result in a rough 3-6 hour period where
most locations will see light rain showers...with the bulk of these
coming this morning south of Lake Ontario...and between mid morning
and early this afternoon across the North Country. After the passage
of these...shower chances should then generally tend to diminish
from west to east this afternoon and tonight as the deeper moisture
and better forcing from this system slide off into eastern New York
and New England. This said...it is possible that there could be
another brief uptick in light shower activity across interior
portions of the North Country late this afternoon and evening...as
the main swath of showers attendant to the coastal low lifts
northward and passes by just to our east...and its western edge
potentially brushes portions of Oswego and Lewis counties. Rainfall
amounts out of this system will be on the light side... with totals
ranging from a tenth of an inch or so across far western New York to
a quarter to a third of an inch across the eastern Finger Lakes and
North Country.

Temperature-wise...highs today will range from the mid to upper
50s across the North Country to the lower to mid 60s elsewhere...
with lows tonight then settling into the upper 40s to lower 50s.

Forecast reasonably on track and have only slowed the main area
of rain/showers by a few hours...trend though is there for
tapering across the majority of the area. Also slowed the
temperature rise, but overall highs should work out.

&&

.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
While this period will be highlighted by near record...summer like
warmth on Thursday...temperatures will average above normal through
out the period. The pattern responsible for the warm weather will
include a broad based longwave trough that will be locked in place
across the western half of the country and an amplifying ridge along
the Southeast coast. The genesis for this pattern can be traced to
an unusually strong East Asian jet that...at one point...spanned
nearly the entire northern Pacific. Energy within this +150kt river
at H25 carved out the western trough...and during the course of the
next couple days...the corresponding downstream ridge will take
shape. Meanwhile in the low levels...the first of two significant
Pacific based storm systems will open up the Gulf and encourage a
surge of sub tropical air to make its way north to the Lower Great
Lakes. Now that we have looked at the broad overview...lets get into
the details.

Wednesday will feature a day of improving conditions...as a
shortwave ridge pinched between an exiting East Coast storm system
and an organizing low over the the Plains will pass over our
forecast area. While showers from the previous night are expected to
be mainly east of our region by daybreak Wednesday (exception...
eastern Lk Ont region)...the associated cloud cover will linger into
at least the midday hours for sites east of the Genesee Valley...
and particularly across the North Country. Given the increased
sunshine...the airmass will become well mixed for the afternoon so
that we will be able to maximize H85 readings of 12c into max temps
in the 70s. It should be a beautiful afternoon.

The shortwave ridge will then pass east of our region Wednesday
night...while the weak warm advection aloft will continue. This will
not only assure us of fair dry weather...but will set the stage for
a warm night. Time to get the window fans and possibly the air
conditioners out...as temperatures across the lake plains will
likely not drop below 60 degrees. These readings will be 20 deg f
above typical late April values. The summer like night will be
followed by well advertised...true summer weather on Thursday.

A sub 995 low over Lake Michigan Thursday morning will move to the
confluence of the Upper Great Lakes by evening...while its
associated cold front will bear down on our region from the west.
Unseasonably warm and somewhat humid air will surge north ahead of
the front...with H85 temps forecast to climb into the upper teens c.
Taking advantage of a fully mixed boundary layer...this on its OWN
would yield max temps of at least the low to mid 80s f...but there
will be more localized effects that could elevated temperatures to
even higher levels. Winds below H925 should be from the south to
southeast. This will not only negate the cooling effects from the
lakes...but will offer some downslope warming over the lake plains.
Most of the western counties will experience max temps in the mid
80s...with readings likely reaching the upper 80s across the Genesee
Valley. These will threaten record high temperatures across the
region...which includes the following...84 at Buffalo (1984)...86 at
Rochester (1990)...and 85 at Watertown (2009). This will certainly
make it feel more like July rather than the end of April.

A typical summer day is not complete without the threat of late
afternoon or evening thunderstorms...and this will certainly NOT be
an exception. The very warm and somewhat humid airmass (Tds near 60
and PWAT values arnd 1.25") will not only support MLCAPE values over
1000 j/kg...but will have bulk shear values as high as 40 kts. This
environment will be in place as the aforementioned cold front will
slowly cross our region Thursday night. The only factor limiting the
severity of the convection will be the nocturnal timing of the
fropa. This should place the greatest risk for strong to severe
storms over the far western counties...where pre-frontal convection
will be more likely earlier in the evening. A larger threat though
could come from training storms.

It is a given that we will have an unusually warm and moist
environment in place Thursday night. The aforementioned cold front
will also be nearly parallel to the southerly mid level flow...as
the overlying upstream trough will become nearly negatively tilted.
This should slow the front to a crawl when it will cross our
region...and there are even some guidance packages that suggest the
presence of a wave...thus further slowing its eastward progress. All
of this could heighten the threat for another round of impactful
rains over the region. Will highlight this risk in the Hazardous
Weather Outlook (HWO). In any case...will increase pops to likely
for showers and thunderstorms Thursday night with this fropa.

As one would expect...in will be notably cooler in the wake of the
cold front on Friday. It is worth pointing out though that while it
will be cooler than the previous two days...temperatures will STILL
be above normal. H85 temps will be in the high single digits for the
majority of the day...so afternoon temperatures should top out in
the 60s to lower 70s. The trend back TOWARDS normal temperatures
will be accompanied by plenty of sunshine...courtesy of a bubble of
high pressure that will cross the region.

Another cold front will sag through our forecast area Friday
night...likely stalling just to our south across Pennsylvania. This
could produce some showers Friday night...and will very likely be
part of more unsettled weather as we push through the weekend.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
Confidence is very high that temperatures will remain well above
normal during this period. While the majority of this time frame
will be rain free...there will also be times of unsettled
weather...including the potential for locally heavy convective
rains.

In terms of a general synoptic overview...there will be little
change to the longwave pattern over the country during this
period...as a broad trough will remain anchored over the western
states. This will keep a relatively warm southerly feed of GOMEX air
across the Upper Ohio Valley...and for much of the time...across the
Lower Great Lakes as well. The devil will be in the details though
when it comes to the timing and amount of rainfall...but
unfortunately...there is a large spread of the daily placement of
frontal boundaries within the ensemble members of the GEFS and
ECMWF.

For Saturday...a cold frontal boundary that will have passed through
the region Friday night will be stalled along...or just south of the
Pennsylvania border. Meanwhile high pressure will be found over the
province of Ontario. This set up should keep most of the day rain
free across the region...but given the proximity of the front...
will leave chc pops in place with the greatest potential for showers
being across the Southern Tier. High temperatures will range from
the 60s near Lake Ontario the 70s across the Southern Tier.

A very robust shortwave will round the base of the western trough
late Saturday night and Sunday morning...and this will help to
consolidate and strength a surface low in the vcnty of Missouri. As
the deepening low pushes north towards Lake Michigan...the quasi-
stationary frontal boundary near our region will push back to the
north as well. This will increase our chances for showers and
thunderstorms during the day Sunday...with H85 temps returning to
the mid teens. Pending the amount of cloud cover and pcpn...parts of
western New York could again experience temperatures in the mid to
upper 70s.

Sunday night...the still deepening storm system will make its way to
the Upper Great Lakes while `our` frontal boundary should be pushed
north of Lake Ontario. This will place most of our region within a
warm sector...keeping overnight temperatures in the mid to upper 50s
for southern sections.

There is general agreement between the medium range guidance
packages that the deep stacked low over the Upper Great Lakes will
push a strong cold front across our region on Monday. Have thus
raised pops to likely for showers and thunderstorms...which could
include some heavy rain.

&&

.AVIATION /15Z 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 through this morning...along with a period
of fairly numerous light showers between this morning and early
this 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 through this morning as 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...
Low pressure along the Carolina coastline will slowly meander its
way northeastward along the east coast over the next couple of days.
This will produce a general easterly to southeasterly flow across
the Lower Great Lakes...which will direct the greatest wave action
into Canadian waters. As a result...conditions should remain below
advisory levels through Wednesday.

Wednesday night and Thursday winds will turn more southerly in
advance of an approaching cold front...which will then cross the
region along with some showers and thunderstorms late Thursday and
Thursday night.

&&

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

&&

$$

SYNOPSIS...CHURCH/JJR
NEAR TERM...OUDEMAN/CHURCH/JJR
SHORT TERM...RSH
LONG TERM...RSH
AVIATION...CHURCH/JJR
MARINE...CHURCH/JJR



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