Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 221051
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
651 AM EDT Fri Jun 22 2018

.SYNOPSIS...
A storm system will slowly track across the Ohio Valley and the
Eastern Great Lakes region this weekend, sending bands of rain
showers and thunderstorms across the area later today and through
out the weekend. There will be dry periods in between the bands of
precipitation through the weekend. Some sunshine across northern
areas today will bring forth afternoon highs near 80, before clouds
limit high temperatures Saturday and Sunday to around 70 in a
moderately humid airmass.

&&

.NEAR TERM /THROUGH TONIGHT/...
IR satellite imagery displays cirrus continuing to encroach upon
WNY, with drier air associated with a Canadian airmass dissipating
the cirrus as it reaches the Finger Lakes and Eastern Lake Ontario
region.

Surface analysis places an area of low pressure near IL/IN, while
water vapor imagery displays a well defined shortwave centered near
western IL. Regional radars display a leading band of rain showers
across OH/PA and nearing SE Chautauqua county...with this
activity very light as surface observations display just a few
hundredths of an inch of rain measured at observing sites.

For today the surface low will slowly track eastward, and begin to
weaken this afternoon as the upper level low vertically stacks over
the surface low. Drier air across central NYS/New England will
erode the initial band of showers over OH/PA this morning. This
drier air will also bring a mostly sunny day to the northern Finger
Lakes and Eastern Lake Ontario region.

As the saturation level lowers through the day across our western
zones, and a belt of 20 to 25 knot low level winds and moisture
convergence pushes into the So. Tier precipitation will become
likely, with another wave of showers to reach our So. Tier around
noontime. The slowing and weakening to the surface low coupled with
drier air to the east will limit the eastward push to the
precipitation. The precipitation will likely fall apart across the
Niagara Frontier and Genesee Valley this afternoon.

As the low to our west pushes slowly towards Ohio through the
evening and overnight hours, additional bands of rain showers will
push deeper into WNY through the remainder of the evening and
overnight hours. There remains limited instability with this
activity, with just a few hundred J/KG of elevated instability
overnight. Will place isolated thunder into the grids, keeping
generic showers the main qualifier.

Rain showers chances will expand eastward across the Eastern Lake
Ontario region late tonight. Here rainfall amounts will be light,
less than a tenth of an inch. To the west an early start to the rain
will allow a tenth or two of an inch of rain.

North of the So. Tier sunshine will allow for highs in the upper 70s
to around 80F. Thickening clouds across the So. Tier will hold
temperatures to the lower 70s today. Tonight under cloudy skies lows
will range from the upper 50s to lower 60s. Dewpoints will also be
some 15 degrees or so warmer tonight, going from the lower 40s this
morning to the upper 50s by late tonight.

&&

.SHORT TERM /SATURDAY THROUGH MONDAY/...
On Saturday a weakening upper level low and its surface reflection
will track across the region. A diffluent flow aloft along with low
level moisture and an associated warm front will be sufficient to
generate fairly widespread showers. There will be limited
instability south of Lake Ontario, with some embedded thunderstorms
possible. Despite the high probabilities of rain, it should be noted
that there will be breaks, with periods of dry weather between the
areas of showers. Persistent cloud cover will limit warming with
high temperatures in the upper 60s to lower 70s.

Saturday night the surface low will slowly elongate across our area
while steadily weakening into a remnant trough which will slide east
across New England. Consequently large-scale forcing for ascent
across our region will also become weak with showers scattered in
nature. Cloudy skies will persist, with BUFKIT profiles showing lots
low moisture and the possibility of fog as cloud decks lower across
the Southern Tier. Radiational cooling will be limited with lows
mainly in the lower 60s.

On Sunday a larger upper level trough over Ontario and Quebec will
steadily sharpen and push southeastward into our region, along with
an attendant surface cold front. Increasing height falls and frontal
convergence will interact with our still-moist airmass to produce
the likelihood of another round of showers. Weak instability across
the Southern Tier and interior portions of the Finger Lakes may
result in some thunderstorms. With lots of cloud cover and 850mb
temperatures of only around +10C across Lake Ontario, expect highs
to be in the upper 60s to lower 70s.

A few showers may linger Sunday night with the trough axis still
across the region and an northerly flow promoting some upsloping
south of the lakes. High pressure will then expand across the entire
Great lakes region late Sunday night with showers ending from west
to east.

Model consensus suggests total rainfall amounts over the weekend to
be around a half inch, with locally higher amounts to an inch
possible. These would most likely be with thunderstorms across the
Southern Tier. While the timing of the rain is not ideal in that it
will be coming over the weekend, it will certainly still be very
welcome from an agricultural standpoint.

&&

.LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
High pressure will ridge into the region on Monday, with increasing
subsidence and drier air leading to clearing skies during the day.
Temperatures will be comfortable with highs in the lower to mid 70s.

High pressure will continue to move southeastward across the eastern
Great Lakes Monday night and Tuesday. This will make for dry and
seasonable weather during this time. The next system of concern will
be a a mid-level trough that will traverse the Northern Plains and
western Great Lakes mid-week. This will bring a return to warmer and
more humid conditions as return flow around departing high moves off
the Mid-Atlantic coast. A potential for showers and thunderstorms
will increase Wednesday-Thursday and slightly normal temperatures
are expected during this time. 00Z model consensus is a bit faster
than previous guidance so raised PoPs slightly for Wednesday. While
there still is considerable uncertainty in timing, most long range
guidance shows a fairly strong winds aloft which could potentially
support strong thunderstorms. Given timing uncertainty there is not
enough forecast confidence to place this risk in the HWO yet.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
VFR flight conditions are found at the start of the 12Z TAFS,
with just some cirrus passing across portions of WNY. A surface
low, over the corn belt states this early morning, will slowly
spiral eastward, with bands of rain showers inching closer to
WNY.

Expect some isolated to scattered shower activity to reach the
western So. Tier, including the KJHW terminal through the day,
with any activity light with VFR flight conditions. Will place
a VCSH in the KJHW TAF as activity should not be widespread. As
moisture lowers, ceilings will lower into the MVFR range across
the higher terrain this evening...and will place this into the
KJHW TAF.

Tonight the surface low will track to Ohio, with bands of showers
passing across WNY. Activity sparse during the early evening hours
will likely pass across WNY in two waves, with one centered around
midnight (VFR/MVFR), and a second around dawn Saturday morning
(MVFR).

Outlook...
Saturday...MVFR...Showers likely with a chance of thunderstorms.

Saturday night...MVFR/IFR with showers likely and chance of
thunderstorms.

Sunday...Mainly MVFR. A chance of showers and thunderstorms.

Monday and Tuesday...VFR.

&&

.MARINE...
An east winds will increase on Lake Ontario today, but this wind
direction will keep the bulk of the wave action over the open waters
and Canadian waters, with waves 2-3 feet along the southern Lake
Ontario shoreline.

A low pressure system will track across the lower Great Lakes this
weekend with some showers and thunderstorms possible. Wind speeds
and waves are expected to remain below SCA conditions.

Northerly winds will increase some late Sunday and into Monday
following the passage of a cold front, through winds will remain
weak enough to continue sub-SCA conditions on the lakes, with these
sub-SCA conditions then continuing into the start of next week.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...None.

&&

$$

SYNOPSIS...Thomas
NEAR TERM...Thomas
SHORT TERM...Apffel/JJR
LONG TERM...Apffel/HSK
AVIATION...Thomas
MARINE...Thomas



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