Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 232246
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
646 PM EDT Fri Jun 23 2017

.SYNOPSIS...
Occasional showers and scattered thunderstorms associated with a
cold front will continue through this evening before ending from
northwest to southeast overnight. An upper level trough will then
become established over the weekend with a brief shower or
thunderstorm possible both days, but the majority of the time will
be rain free. A better chance of showers will arrive Monday as the
trough sharpens over the Great Lakes. Temperatures will drop to
below normal over the weekend and early next week.

&&

.NEAR TERM /THROUGH SATURDAY/...
Radar imagery shows scattered to numerous showers across the
region at 630 p.m. There is been very little thunder so far
given the extensive cloud cover and showers limiting
destabilization with storm tops failing to rise high enough for
electrification. For this update have lowered PoPs due to the
diminishing areal coverage. However, PWAT is near 2 inches, so
any storms that develop may produce brief heavy downpours.
Severe weather risk is minimal given the anemic CAPE and poor
lapse rates.

The cold front is just on the doorstep and poised to move into
Western New York around sunset. There may be scattered showers
along this boundary, but thus far activity is limited upstream.
The rain will then end from northwest to southeast overnight as
the surface cold front crosses the area. The lake plains should
see some clearing late tonight as a push of dry air arrives out
of Canada and subsidence increases in the wake of the cold
front. Low clouds will likely persist across the higher terrain
of the Southern Tier and Tug Hill region in moist low level
upslope flow. Cold advection will increase behind the cold front
and allow lows to drop to drop into the lower 60s in most
locations by daybreak.

On Saturday a weak surface ridge will build into the Ohio Valley and
eastern Great Lakes. Meanwhile, a broad/weak trough will become
established in the mid/upper levels across the Great Lakes. A mid
level shortwave will move through the mean longwave trough and cross
the eastern Great Lakes during the afternoon. Meanwhile, mesoscale
convergence zones will setup across our region as enhanced gradient
onshore SW flow develops downstream of Lake Erie, with more westerly
flow across Lake Ontario. This should allow a well defined surface
convergence zone to develop from Niagara Falls east to Rochester,
eventually building all the way east to Central NY. The convergence
along this feature combined with the weak large scale ascent from
the mid level shortwave may support a few widely scattered afternoon
showers and thunderstorms, mainly in the corridor between the NYS
Thruway and south shore of Lake Ontario. An isolated afternoon
thunderstorm also cannot be ruled out across the higher terrain from
the interior Southern Tier into the Finger Lakes. It will be less
humid on Saturday, with highs in the mid 70s in most locations, and
a few upper 70s from the Genesee Valley into Central NY.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
Saturday night...The upper level pattern will feature a longwave
trough centered over the Great Lakes region with an upstream
intermountain ridge.  At the surface...a weak ridge will be in
place.  Thus any leftover scattered evening convection on lake
breezes, primarily S of Lake Ontario, should quickly dissipate
during the evening with a dry and cool remainder of the night - low
should be mostly in the 50s.

Sunday and Sunday night...Sunday should start out nice, but expect
the eventual development of scattered to possibly numerous showers
and thunderstorms developing on lake breeze boundaries.  Additional
development may form along a weak cold front moving SE into WNY
during the afternoon. Similar to Saturday night, expect convection
to dissipate fairly quickly with the loss of daytime heating.

Monday...The upstream cold pool aloft corresponding to the upper
level trough will pass overhead.  Strong insolation and resultant
mixing, together with plenty of moisture and cool air aloft without
any signs of a cap will result in fairly quick development of
showers and some thunderstorms, although CAPE values will be
unimpressive with a skinny profile seen in point forecast soundings.
 Still, with a freezing level somewhere near 8000-10000ft, cells
could easily support small hail. As noted earlier, there may even be
a hint of a lake response with a dry adabatic lapse rates over the
65-70+F waters. Once again, expect showers to be on the decrease
during the evening with little or no showers late.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
Tuesday a final upper level shortwave will round a longwave trough
over the Northeast, bringing additional chances for showers and
thunderstorms through the day.

The upper level trough will push eastward Tuesday night and
Wednesday, with just a small chance for a lingering shower across
the North Country. Surface high pressure will drift across the
eastern US, south of our region Wednesday, providing for some
clearing skies. Southerly winds behind this surface high Thursday
will bring increasing temperatures, along with an increase in
humidity levels. A shortwave rippling across the northern US may
trigger a few showers and thunderstorms later Thursday and Friday,
though timing at this point remains a bit uncertain.

Temperatures under the upper level trough Tuesday and Wednesday will
remain below normal. Southerly winds Thursday and Friday should push
temperatures into the upper 70s to lower 80s across the region.

&&

.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
Periods of showers and a few widely scattered thunderstorms will
continue late this afternoon and evening ahead of a cold front
moving through the central Great Lakes. Some of the heavier
showers will produce areas of MVFR VSBY, with local IFR in the
heaviest downpours.

The showers and scattered thunderstorms will end from northwest to
southeast overnight with the passage of the cold front. There
may be a period of lower conditions (IFR or lower) just ahead
of the front when there will be lots of low level moisture.
These are likely to last longest at JHW, but may also briefly
impact BUF/IAG/ART through this evening.

On Saturday a weak/broad mid level trough will become established
across the Great Lakes. While most of the time will be rain free, a
few isolated showers and thunderstorms may develop along lake breeze
boundaries, most notably along the KIAG to KROC corridor. Any
lingering IFR CIGS across higher terrain will improve, leaving VFR
to prevail Saturday outside of any isolated thunderstorms.

Outlook...
Sunday through Tuesday...Mainly VFR with a chance of
mainly afternoon showers and isolated thunderstorms.
Wednesday...Mainly VFR.
Thursday...Mainly VFR with a chance of a shower or thunderstorm.

&&

.MARINE...
Funneling has helped enhance the southwesterly flow on Lake Erie
just enough to require a brief and low-end Small Craft headline
southwest of Dunkirk. Waves just offshore should briefly
increase to 3 to 5 feet, in part aided by slightly stronger
winds just to the west of the NY waters. Winds will pick up on
Lake Ontario ahead of the front later this evening, but without
the funneling of the Chautauqua Ridge these are not expected to
get as strong.

West to southwest winds are likely to increase on Sunday on Lake
Erie as the pressure gradient increases ahead of a secondary cold
front crossing the eastern Great Lakes. The increase in winds is
less certain on Lake Ontario with considerable model differences
showing up. At least moderate westerlies will continue with choppy
conditions, and there is a chance of stronger Small Craft Advisory
conditions if the stronger GFS based guidance verifies.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Small Craft Advisory until 11 PM EDT this evening for LEZ040.

&&

$$

SYNOPSIS...HITCHCOCK
NEAR TERM...APFFEL/HITCHCOCK
SHORT TERM...ZAFF
LONG TERM...THOMAS
AVIATION...APFFEL/HITCHCOCK
MARINE...APFFEL/HITCHCOCK



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