Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 252330

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

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.


Radar imagery showing the area of more widespread light rain moving
north through the Saint Lawrence Valley this evening, with a few
scattered showers left across the eastern Lake Ontario region.
Farther west, an area of scattered sprinkles and light showers has
expanded through the Southern Tier, Genesee Valley, and western
Finger Lakes. These light showers will continue to move northeast
this evening before tapering off by around midnight.

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
from late tonight through early Wednesday, with clouds lingering
along the western periphery of the circulation of the east coast

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.


Western and Central NY will be within the warm sector of a low
pressure centered over the Michigan UP on Wednesday night. A
nocturnal inversion with +15C to +18C air at 850mb along with
dewpoints in the 50s will hold temperatures very mild overnight
making for a nice night to keep the windows open. Low temps are only
expected to slip back into a range of the mid 50s to about 60.

The surface low over the Michigan UP is forecast to lift north into
northeastern Ontario Canada through Thursday with a trailing cold
front approaching western NY late in the day. An increasing southerly
flow ahead of this front will continue to advect unseasonably warm
and somewhat humid air north across the eastern Great Lakes. Mixing
of near +18C 850mb air will make for a summer-like day Thursday.
Most areas should see max temps in the low to mid 80s with a
potential for readings to reach 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.

While most of the day will be dry with above normal temperatures,
the approaching cold front will bring the threat of late afternoon or
evening thunderstorms Thursday. The combination of the very warm and
modestly humid airmass looks to support surface-based CAPE values
over 1000 j/kg and possibly above 2000 j/kg per 12z GFS. This
available energy will also combine with 0-6km bulk shear values of 40-
50 kts making for am environment which could support strong to
severe thunderstorms along and ahead of the cold front. The key for
potential severe storms Thursday will be timing of convective
initiation. If storms begin to fire in the mid to late evening where
instability values are still quite high then the severe risk will be
higher than if storms do not arrive until near or after sunset. The
front looks fairly progressive so while any thunderstorm can contain
heavy downpours, its looks less likely that training cells will
bring a potential for any flash flooding. Gusty to damaging winds
looks more likely with the high level of shear. Have held onto will
likely POPs for showers and thunderstorms Thursday night shifting
quickly west to east. Temperatures will remain mild behind the cold
front on Thursday night with lows only expected to dip into the
lower 50s.

The cold front looks to be cleared to the east of the forecast area
by Friday morning while the tail end stalls out somewhere across
central PA. A narrow wedge of high pressure building in behind the
front will make for a pleasantly warm and dry weather day.
Temperatures look to still run above normal with highs expected in
the mid to upper 60s with 850mb temps only slipping back to around

Friday night and Saturday, the surface ridge exits to New England
while a weak surface wave with associated 40kt low level jet shifts
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 the surface wave 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
stretched across western and central NY although the 12z GFS
suggests an inverted ridge of high pressure may make for a mainly
dry night ahead of our next weather system. Temperatures Friday
night will again slip back to around 50 with no access to a dry
continental airmass then warm into the low to mid 60s Saturday with
70 possible south of the front near the PA border. Temps are
forecast a bit cooler with a light northeast flow Saturday night
expected to slip back into the mid to upper 40s.


Sunday will feature more widespread chances of showers and
thunderstorms as forcing and instability are enhanced by a low
pressure system strengthening over the heart of the country.
Southerly flow ahead of this system will bump the stalled front a
little further north with moisture and instability interacting with
the warm front causing the chances for showers and thunderstorms

The low pressure system looks to further deepen on Monday while
lifting across Wisconsin. A cold front associated with this storm
will approach the western NY Monday afternoon then shifting into
central NY Monday evening bringing the risk for another period of
showers and thunderstorms. While still pretty far out, instability
should develop in the warm sector of the low across the eastern Great
Lakes. While GFS CAPE profiles are not very impressive, we will
again have some decent wind shear associated with a low level jet
ahead of the cold front which could bring a risk of a few strong to
severe storms.

The cold front is forecast to shift across central and into eastern
NY Monday night with a chance of showers and storms during the
overnight. Frontal timing will be key again here for zeroing in on
who sees showers and storms and who should be dry behind the front.
On Tuesday, the surface low is forecast to shift northwest of
Buffalo toward James Bay. This is a favorable track for a risk of
gusty gradient winds downwind of the lakes as a 40-50+ knot low
level jet mixes down in cold advection. Otherwise, the cold
advection within a plume of low level moisture circulating the low
will support a chance of some scattered showers.

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.


Scattered sprinkles and light showers will continue this evening
from the Genesee Valley and Southern Tier eastward across the Finger
Lakes to the eastern Lake Ontario region. The rain will remain
light, with mainly VFR VSBY. Most of the showers will end by around
midnight, except for east of Lake Ontario where a few showers will
continue overnight.

CIGS are mainly VFR and will remain so through this evening.
Overnight low level moisture will deepen and support increasing
areas of MVFR with some local IFR possible across the higher terrain
of the Southern Tier. The stratus will continue into Wednesday
morning before lifting and scattering out into a VFR cumulus field
by early Wednesday afternoon. These clouds will steadily diminish
Wednesday afternoon with VFR prevailing.


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


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 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.





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