Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 190743

Area Forecast Discussion
National Weather Service Buffalo NY
343 AM EDT Sat Aug 19 2017

A weak upper level disturbance will cross the region today with a
few widely scattered showers and thunderstorms. High pressure will
then bring a return to dry weather Sunday through Monday.
Temperatures will be briefly cooler today before becoming very warm
and humid again early next week. A cold front will bring another
round of showers and thunderstorms Tuesday, followed by much cooler
and less humid for the end of next week.


A weak low level trough will continue to cross the region through
this morning, bringing areas of cloud cover to much of the region.
The combination of convergence along the weak boundary, cooling air
aloft, and developing lake induced instability will continue to
support a few lake enhanced rain showers this morning. Off Lake
Erie, these should remain isolated across the higher terrain east of
the lake before ending by mid morning. Off Lake Ontario, expect a
little better organization for a few hours this morning with a
broken band of showers across the Tug Hill region. This should
quickly break apart by midday as diurnal mixing disrupts the
delicate lake induced convergence zone.

During the afternoon a fairly sharp mid level trough will approach
the region with increasing DPVA. Moisture will be fairly shallow
with this feature, so it will need the help of mesoscale processes
to force convection. Expect lake breeze boundaries to play the
primary role, with widely scattered showers and thunderstorms
developing from the western Southern Tier into the western Finger
Lakes and southern Tug Hill region this afternoon and evening.
Stable lake shadows will develop northeast of the lakes this
afternoon and prevent any convection from the Niagara Frontier to
Rochester and across Jefferson county, and also provide more

A brief push of cooler air aloft will keep highs in the mid to upper
70s across lower elevations and lower 70s on the hills. It will
become breezy once again northeast of Lake Erie with gusts in the 20-
25 mph range.

The mid level trough will cross the region this evening. Widely
scattered showers and thunderstorms which develop in eastern Ontario
during the late afternoon will cross the eastern Lake Ontario region
through the evening as the trough swings through and overwhelms the
remnants of the stable lake shadow. Elsewhere the trough will just
bring a period of greater cloud cover. Overnight a few upslope
showers will linger east of Lake Ontario along with more cloud
cover. Farther west, increasing subsidence and drying will bring
clearing skies. Expect lows to range from the lower 60s on the lake
plains to the mid 50s across the interior Southern Tier and Lewis


A sprawling surface high will move through upper Ohio Valley Sunday
then off the mid-Atlantic coast Monday. A dynamic trough will dive
through the Great Lakes Tuesday sweeping a potent cold front across
the area Tuesday night.

Sunday and Monday will be characterized by building warmth and
humidity as return flow develops between the surface high moving off
the mid-Atlantic and the impinging trough over the upper Great
Lakes. Temperatures will be near seasonal normals on Sunday with 850
mb temps around +12 to +14C, while increasing southwesterly flow
Monday and especially Tuesday ahead of the cold front will push 850
mb temperatures to around +18 to +19C. The combination of the warmer
airmass and downslope flow across the Genesee Valley and northern
Finger Lakes will result in upper 80s readings both day, with a
potential for a few sites to see the 90 degree mark. Northeast of
Lakes Erie and Ontario, a stiff lake breeze will keep temperatures
slightly cooler, in the low to mid 80s. Dry weather and ample
sunshine will prevail with subsidence under the ridging aloft on
Sunday and Monday. This will provide ideal viewing conditions for
the solar eclipse on Monday afternoon. Monday night will be quite
warm and muggy ahead of the approaching front, with low temperatures
not likely to fall out of the 70s across the lake plains and dew
points in the upper 60s to near 70.

By Tuesday afternoon and into the overnight hours, shower and
thunderstorm chances will increase as the trough approaches and
crosses the region. A fairly dynamic shortwave rounding the base of
the trough will help provide forcing for ascent and also increasing
the wind shear Tuesday late afternoon and early evening. Current
model depictions of thermodynamic profiles suggest fairly tall,
skinny CAPE. However, given the strongly forced nature of the trough
passage with ample shear certainly cannot rule out a severe weather
threat of mainly damaging wind gusts. Severe weather potential is
still uncertain, and may change based on the timing of the front.


A cooler airmass will work its way across the northeast in the wake
of the cold frontal passage Tuesday night, bringing a fall feel to
the second half of the work week. 850 mb temperatures will fall to
around +6C for Thursday and Friday with drier northerly flow as a
sprawling Canadian surface high builds over the Great Lakes. The
result will be daytime high temperatures in the mid 70s Wednesday,
but in the upper 60s to low 70s for Thursday and Friday. Initially
some lingering moisture and upslope flow Wednesday will support some
isolated to widely scattered showers, especially over the higher
terrain where northerly upslope flow can help with orographic
ascent. Progressively drier air will build in, along with a lowering
subsidence inversion, with the surface high for Thursday and Friday.
Thus, despite the cooler temperatures aloft normally sufficient for
a lake response, don`t expect we`ll see much other than some
stubborn lake enhanced cloudiness south of the lower Great Lakes.


A few lake enhanced rain showers will continue east of the lakes
this morning with local/brief MVFR VSBY. Otherwise areas of clouds
will continue through the morning with mainly VFR CIGS at lower
elevations and areas of MVFR across higher terrain. The lake
enhanced showers will end by midday, to be replaced by a few widely
scattered showers and thunderstorms along and inland of the lake
breeze boundaries during the afternoon and evening. VFR will prevail
in most areas, although any thunderstorm may produce brief/local
MVFR to IFR conditions.

The convection will end this evening, although a few upslope showers
may continue across the higher terrain east of Lake Ontario where
some MVFR CIGS may also develop. Valley fog will develop late
tonight across the western Southern Tier with local IFR. Otherwise
VFR will prevail for the rest of the region.


Sunday and Monday...VFR except for late night and early morning
valley fog with local IFR.
Tuesday...Mainly VFR, with a chance of showers and thunderstorms
in the afternoon.
Tuesday Night...MVFR/IFR, with showers and thunderstorms likely.
Wednesday...VFR/MVFR with a chance of showers.


Low pressure will move slowly east across Quebec today and bring
another round of moderate to strong WSW winds to the eastern Great
Lakes. This will bring Small Craft Advisory conditions to much of
Lakes Erie and Ontario through this evening. Winds will then
diminish from west to east tonight. High pressure will bring a
return to lighter winds Sunday and Monday.


NY...Beach Hazards Statement through this evening for NYZ006-007-
MARINE...Small Craft Advisory until 11 PM EDT this evening for LEZ020-
         Small Craft Advisory from 8 AM this morning to 8 PM
         EDT this evening for LOZ042.
         Small Craft Advisory until 5 AM EDT Sunday for LOZ044-045.



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