Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 140216

Area Forecast Discussion
National Weather Service Buffalo NY
1016 PM EDT Sun Aug 13 2017

High pressure will settle across the region overnight with mainly
clear skies...with remnant weak ridging then remaining in place
through the first half of the week. This will provide dry weather
most of the time, although a few widely scattered showers and
thunderstorms cannot be ruled out during the afternoon and evening
on Monday and Tuesday. Low pressure moving into the Great Lakes will
then bring a better chance of more numerous showers and
thunderstorms on Thursday.


Surface high pressure will settle across NY/PA overnight...with our
current mainly clear skies giving way to a modest increase in cirrus-
level cloudiness overnight. There may also be an increase in lower
clouds late tonight across the higher terrain of the western
Southern Tier as SSE return flow develops. Good radiational cooling
conditions will allow lows to drop into the upper 50s to around 60
on the lake plains, with low to mid 50s in the cooler Southern Tier
valleys and Lewis County. Expect typical Southern Tier valley fog
late tonight and early Monday morning. Patchy fog may also develop
near other inland bodies of water, such as the Seneca/Oswego Rivers,
Black River Valley, and near some of the lakes of the North Country.

On Monday high pressure will drift off the New England coast, with
weak southerly return flow developing in the low levels. This will
allow a plume of somewhat more moist and unstable air to advect
northward out of PA and into Western NY and the western Finger Lakes
during the afternoon. A weak/subtle mid level trough will move
through the Upper Midwest tonight and reach our region Monday
afternoon, providing some weak large scale ascent. A weak low level
inverted trough will also develop, and interact with mesoscale lake
breeze and terrain forced boundaries to increase low level
convergence during the afternoon and evening. The aforementioned
forcing and moisture, while not impressive, may be enough to support
a few widely scattered showers and thunderstorms during the
afternoon and evening across far western New York and the Genesee
Valley/Finger Lakes Regions. Expect highs within a few degrees of 80
across lower elevations, with mid 70s across higher terrain and
along the immediate lakeshores as lake breezes develop.


By Tuesday, a shortwave trough currently back over Manitoba will
pivot across the forecast area on the southern periphery of a large
trough near the Hudson Bay. The region will be embedded in westerly
to west-northwesterly flow as the plume of moisture advection and
DPVA moves through on Tuesday. Instability will be fairly modest,
and any convection that develops will be placed inland from the lake
breeze boundaries. Given the west-northwesterly flow direction, this
best potential for showers and thunderstorms would be the Niagara
Peninsula, southeastward between Buffalo and Rochester to the
western Finger Lakes. Otherwise, outside of any scattered
showers/thunderstorms, and within the lake shadows, expect a mainly
dry with seasonable temperatures.

Weak ridging will build across the region on Wednesday in the wake
of this shortwave passage. The result will be fair weather with
continued seasonable temperatures as 850 mb temps remain around
+14C. Nighttime lows will be near normal as well each night, Monday
night through Wednesday night, mid 50s to low 60s. The warmest night
will be Wednesday night as warm advection ensues ahead of the next
approaching weather system, with upper 50s to mid 60s and increasing
cloud cover.

A low pressure system will then cross the region sometime Thursday
into early Friday, with timing differences between the various
global models. This will bring out next best chance for widespread
showers or thunderstorms across the region. Have increased PoPs to
low end likely on Thursday, keeping in mind timing will certainly
need to be fine tuned as the day approaches.


While an omega block centered over Hudson Bay will dominate the
northern half of the continent during this period...a broad...low
amplitude trough will be found over the Great Lakes region. This
high confidence forecast for the large scale pattern will be
balanced out by plenty of uncertainty in the smaller scale features.
The result will be a relatively low confidence forecast in the
timing and coverage of shower activity. That being said...
significant rainfall is not expected during this period...nor will
there be much (if any) risk for severe weather.

As we open this period on Friday...a relatively shallow...broad
based trough will be found over the Great Lakes region. Energy
tracking east within the longwave trough will cross the Lower Great
Lakes...and it will be accompanied by some semblance of a surface
reflection...whether it is just a trough that extends to the sfc or
an organized sfc low. This is the range of solutions advertised by
the bulk of the medium range ensembles. In either case...there
should be at least the chance for some showers over the region. H85
temps in the vcnty of 12c will support afternoon temps in the mid to
upper 70s f.

Subsidence in the wake of the shortwave should minimize...but not
completely eliminate...the potential for showers Friday night.

The next shortwave within the broad trough is expected to cross the
region on Saturday. This would support another round of showers and
isolated thunderstorms. Will continue to use just chc pops due to
the model to model and run to run inconsistencies within the

General height rises across all of the Great Lakes Saturday night
and Sunday will lead to a slow improvement in conditions for our
region. Until more consistency is seen in the medium range ensembles
though...will maintain slgt to low chc pops from continuity.


Surface high pressure will settle across NY/PA overnight...with our
current mainly clear skies giving way to a modest increase in cirrus-
level cloudiness overnight. Valley fog will develop across the
western Southern Tier late tonight and early Monday morning with
local IFR, and some of this will likely impact KJHW. Some patchy fog
may also bring spotty IFR elsewhere, especially near rivers and
lakes inland from the Great Lakes. Otherwise...conditions will be

On Monday a modest increase in moisture and instability will allow
diurnal cumulus to build again from far western New York into the
Finger Lakes during the late morning and afternoon hours...with a
few widely scattered showers and thunderstorms also possibly
developing during the afternoon and evening. While VFR will prevail,
any heavier shower or storm could produce brief/localized MVFR to
IFR conditions.

Tuesday...Local IFR in southern Tier valley fog early. Otherwise VFR
with isolated showers and thunderstorms during the afternoon and
Wednesday...Local IFR in southern Tier valley fog early, otherwise
Thursday...Areas of MVFR with showers and thunderstorms likely.
Friday...Mainly VFR with a chance of showers.


Surface high pressure will build into the Lower Lakes region
overnight before drifting off the New England coast Monday, although
a weak ridge will remain in place back into the Lower Great Lakes
through Wednesday. This will bring an extended period of light winds
and flat wave action with local lake breezes each afternoon
producing weak onshore flow.





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