Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 140825

Area Forecast Discussion
National Weather Service Buffalo NY
425 AM EDT Mon Aug 14 2017

A few showers and thunderstorms will form across interior regions
this afternoon and evening as moisture increases across the Great
Lakes region behind a surface high pressure. Additional storms are
possible Tuesday before a surface high pressure returns dry
conditions with mid-summers warmth for Wednesday. Another area of
low pressure will reach the Great Lakes region Thursday spreading
widespread showers and thunderstorms across the region.


This morning surface high pressure is found over eastern NYS, and
this feature is providing for a quiet start to the workweek. IR
satellite imagery and surface observations indicate cirrus clouds
passing over much of WNY.

For today as this surface high pressure advances farther to the
east, a return southerly flow of moisture will ensue, focused upon
WNY where a weak inverted surface trough will be forming. In the mid
levels a fast moving, subtle shortwave will track across NYS this
afternoon, and this feature will bring lift in the mid levels, that
combined with daytime instability and surface convergence should
generate a few showers and thunderstorms. Moisture will be
limited, and instability modest, around 500 to 1000 J/KG of
SBCAPE...but a few isolated to scattered thunderstorms should form
across the interior So. Tier and then track northeastward towards
the southern North Country this evening as the flow becomes briefly
westerly behind the shortwave. Weak 0-3 km shear and modest
instability will likely keep such storms garden variety through the
afternoon and evening hours.

Storms will dissipate with the loss of daytime heating, and passage
of the mid level shortwave this evening. High temperatures today
will peak near 80F. Tonight will have a touch more humidity than the
previous night, and lows will be a few degrees warmer as well
...generally from the upper 50s to mid 60s.


On Tuesday, a weak shortwave will pivot across the area on the
southern periphery of a large trough near the Hudson Bay.
Instability will be modest, with forecast soundings showing a long
but thin CAPE where subtle differences in surface temperature and
dew points will make a difference. Following this, model QPF differs
considerably, with the NAM largely dry while most other guidance
shows at least some precipitation. The most likely outcome is that
scattered showers and thunderstorms will develop with the shortwave
from mid-day and through the afternoon hours. Otherwise,
temperatures will be seasonable with highs in the upper 70s to
around 80.

A weak cold front is forecast to drop across the region Tuesday
night as high pressure expands across the entire Great Lakes region.
This should largely be a dry frontal passage, with mainly cloud
cover and possibly a stray showers across the North Country. This
high will expand across the region on Wednesday, with dry weather
and increasing sunshine from north to south. Temperatures aloft will
be cooler on Wednesday, but this will be somewhat offset by the
sunshine with highs in the mid to upper 70s.

The high will shift into New England on Wednesday night, but 00Z
model consensus is a bit slower in doing this than previous runs. As
a result, the vast majority of the night should remain dry with only
a small chance for showers across far western portions late in the
night. This will also delay the cloud cover, allowing for good
radiational cooling conditions east of Rochester. Forecast trends
below consensus guidance, with lows in the upper 40s to lower 50s
across the Eastern Lake Ontario region.

On Thursday morning, model consensus places an area of low pressure
near Wisconsin. This low is forecast to track slowly toward the
Lower Great Lakes, reaching the area Thursday night. A warm front
will extend ahead of this system, approaching the region during the
day Thursday ahead of the surface low. There are timing difference
between the various global models but this still is likely to
produce widespread showers and thunderstorms in the timeframe.
Timing will certainly need to be fine tuned as the event gets
closer. The dynamic nature of this system suggests there is some
severe weather potential, but the risk appears greatest along and
south of the southern cwa boundary which has the best chance to
break into the warm sector.


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.

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.


For the 06Z TAFS the main concern will be river valley fog across
the So. Tier. Currently there is still a fair amount of spread
between the air temperatures and dewpoints, with satellite imagery
and surface observations depicting little fog forming as of yet. For
this reason will continue KJHW in VFR flight conditions through the
night, with fog forming in the vicinity. Cannot rule out some IFR
flight conditions here later...but for now confidence is low for
placing any flight restrictions in this TAF.

Otherwise high pressure will yield a VFR flight day for the TAF
sites. A few showers and thunderstorms forming across interior regions
this afternoon and evening may brush by an airfield, but activity is
expected to be isolated to scattered.

Tonight clouds will thin as eastward bound convection wanes through
the night. There will again be possible river valley fog in the So.
Tier, possibly impacting KJHW.

Outlook... Tuesday...Otherwise VFR with isolated showers and
thunderstorms during the afternoon and evening.
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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