Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 252009
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
409 PM EDT Tue Apr 25 2017

.SYNOPSIS...
Low pressure will move northward along the east coast tonight with a
few showers persisting east of Lake Ontario. Drier weather and
summer-like warmth will then 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
and produces a round of showers and thunderstorms.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
Radar imagery showing the area of more widespread light rain moving
north across Lake Ontario and the eastern Lake Ontario region late
this afternoon. The light rain will taper off from south to north
through early evening east of Lake Ontario. Otherwise the rest of
the area will remain dry and cloudy, with just a few sprinkles or
light showers possible from the western Southern Tier to the western
Finger Lakes.

Low pressure will move slowly north along the east coast tonight and
Wednesday with the bulk of the more significant impacts staying well
east of our area. A weak inverted trough and deeper moisture will
drift across eastern NY tonight and early Wednesday morning, with
the western edge of that clipping the eastern Lake Ontario region
with a few showers. Otherwise the rest of the area should remain dry
tonight and early Wednesday, with clouds lingering along the western
periphery of the circulation of the east coast low.

Wednesday afternoon the coastal low will move into southern New
England, with a push of drier air moving out of the Ohio Valley and
into the lower Great Lakes. Any lingering light showers will end
east of Lake Ontario. Farther west, expect increasing amounts of
sunshine across Western NY.

As far as temperatures go, it will remain mild tonight with lows in
the lower 50s in most areas, and upper 40s in some of the cooler
Southern Tier valleys and Tug Hill region. Ongoing warm advection
and increasing sunshine will allow temperatures to rise into the mid
70s Wednesday afternoon across Western Ny, with upper 60s to around
70 for the North Country.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY 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.

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 /SATURDAY THROUGH TUESDAY/...
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 /20Z TUESDAY THROUGH SUNDAY/...
Steadier light rain over and east of Lake Ontario will taper off
from south to north by early this evening, replaced by scattered
light showers from the western Southern Tier to the western Finger
Lakes. One more round of light rain may clip areas east of Lake
Ontario tonight, but the light nature should keep VSBY mainly VFR.

CIGS are mainly VFR and will remain so through this evening.
Overnight low level moisture will deepen and support increasing areas
of MVFR especially across higher terrain and east of Lake Ontario,
with some patchy fog and local IFR possible as well. Any fog and low
stratus will dissipate by mid morning Wednesday, with a return to
VFR as mid level clouds slowly decrease from west to east.

Outlook...

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 will move slowly northward along the east coast through
Wednesday and support a continuation of easterly winds on the Lower
Great Lakes. Choppy wave action will continue on the west half of
Lake Ontario through tonight but will stay under Small Craft
Advisory conditions, with winds and waves slowly diminishing
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...HITCHCOCK
NEAR TERM...HITCHCOCK
SHORT TERM...RSH
LONG TERM...RSH
AVIATION...HITCHCOCK
MARINE...HITCHCOCK


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