Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 252352

Area Forecast Discussion
National Weather Service Buffalo NY
752 PM EDT Thu May 25 2017

An upper level low will track just to the south of the region
tonight and tomorrow, maintaining cool, cloudy conditions with
scattered light rain showers. Temperatures will moderate back to
normal for the weekend, though there will remain a chance for a
shower early Saturday, and then more widespread showers and perhaps
a thunderstorm later Sunday and Sunday night.


A closed upper low will move across Pennsylvania this evening
and into Southern New England later tonight. Meanwhile latest
surface analysis shows a weak surface reflection across eastern
Lake Erie, with model guidance suggesting a developing coastal
low will take over later tonight.

This main shield of rain has lifted to the north of the area
into the Saint Lawrence Valley. There are spotty showers and
some drizzle across Western New York this evening, which are
likely to continue to be spotty in nature overnight. As the
surface low passes, a subtle northerly flow will mix two already
moist air masses with lots of low level moisture and some fog
likely to develop south of Lake Ontario late this evening.

Tomorrow the surface low will become better organized off the mid-
Atlantic coastline, though a surface trough will linger westward
behind this low. Within this trough, and under a west to northwest
flow will remain chances for a few sprinkles/light rain showers
through the day Friday. As the deeper moisture slides eastward
tomorrow the light shower activity will end through the day.

Temperatures will remain nearly steady tonight under the thick
cloud cover with lows in the lower 50s. With the upper level
trough still overhead, highs tomorrow will only rebound back to
the low to mid 60s.


Weak surface-based ridging will slide eastward into our region from
the Central Great Lakes and Ohio Valley Friday night and Saturday.
In addition, heights aloft will build over the region as shortwave
ridge pushes east into the region. A wave embedded within the
northern edge will slide across the region with the possibility of a
few stray showers Friday night and Saturday morning with the
Southern Tier having the best chance to see any measurable
precipitation. The arrival of somewhat drier air behind the wave
from mid day through the afternoon should help to bring some partial
sunshine. Weak warm air advection and sunshine should allow
afternoon highs to reach the upper 60s to lower 70s.

Surface and upper ridging remains over the area for much of Saturday
night. Lead wave ahead of main upper trough will drop into the Great
Lakes as associated surface wave moves into the Ohio Valley. For the
most part Saturday night will be dry, before the leading edge of
some scattered shower activity returns to far western sections
toward Sunday morning.

Latest models continuing to highlight the Sunday and Sunday time
frame with increasing chances for showers and embedded
thunderstorms, as the deepen trough moves in from the west. Models
remaining inconsistent on timing, but with the combination of
falling heights and warm air advection on the eastern flank we
should see showers and embedded thunderstorms fill in during the
day, especially by afternoon and continuing into Sunday night.
Temperatures look to remain above average with highs in the lower to
mid 70s Sunday followed by lows in the mid to upper 50s Sunday night.


For much of next week a large upper level low will slowly meander its
way across the Great Lakes and southern Canada. As a result
temperatures will trend from slightly above normal values Monday
(highs in the low 70s ) to slightly below normal values by mid-week
(highs in the 60s). Several shortwaves embedded in the general
cyclonic flow will support numerous opportunities for scattered
showers across the region, with a few embedded thunderstorms also
possible with the steep lapse rates aloft.


Flight conditions are expected to deteriorate further tonight.
IFR conditions are already quite prevalent at the start of the
00Z TAF cycle, and as the weak surface low passes to the south a
light northerly flow will cause upsloping and mix two already
moist air masses resulting in very moist boundary layer
conditions. IFR or lower conditions are expected south of Lake
Ontario at BUF/IAG/ROC/JHW, with LIFR/VLIFR conditions possible
in very low CIGS and fog later tonight. This trend is indicated
by forecast BUFKIT soundings, and supported by HRRR and MOS
guidance. Otherwise, there will be some light showers or
drizzle lingering overnight, but this will have little impact on
flight conditions.

Friday, with a still light westerly flow flight conditions will
slowly improve back to MVFR with daytime mixing and deeper moisture
exits to the east. This is likely to be a slow process, with IFR
conditions likely to linger through most (if not all) of the
morning hours south of Lake Ontario.

Friday night...MVFR/VFR with isolated showers.
Saturday...Mainly VFR. Chc of showers early to the west.
Sunday...Mainly MVFR with showers likely.
Monday and Tuesday...MVFR/VFR with a chance of showers.


An easterly wind will continue across Lake Ontario this
evening with small craft advisory worthy waves and winds on the
western shoreline. A slight northerly component to the wind
will also create some eddies in the wind field across the lower
Niagara River, near the Lake Ontario shoreline...and will
maintain the SCA here as well.

Otherwise an upper level low will track across Lake Erie and to the
south of Lake Ontario tonight and tomorrow. Winds will relax under
this feature and this will allow for the SCA to end overnight.


A deepening low pressure system will move closer with an
increasing ENE flow on Lake Ontario. Winds will remain 15 to 25
knots today and this evening...allowing waves of 3 to 6 feet. Given
the high lake levels...this is expected to generate lakeshore
flooding from Monroe county west to the Niagara River, with
additional shoreline erosion likely. A Lakeshore Flood Warning
is in effect from Thursday morning through Thursday evening.

The higher wave action and associated flooding risk should be
relatively short-lived, however. The low will move over head
Western New York by late this evening, resulting in sharply
diminishing winds, with waves subsiding shortly thereafter. A
baggy pressure gradient on the back side of the departing low
means that while northwesterly flow behind the low should
generate some choppy conditions Friday along the southern shores
of Lake Ontario, waves should remain in the 1-2 foot range, and
additional flooding issues are not expected.


Buffalo has exceeded the daily precipitation record of 1.21
inches established in 1874. Rochester is close to a recorded
rainfall, while the rain continues across Watertown. Daily
record rainfall for Rochester is 1.74 inches set back in 1943
and Watertown`s record for today is 1.13 inches set back in
1979. With rain continuing east of Lake Ontario, and possible
showers across Buffalo and Rochester final daily totals be known
after the climatic day (1 AM EDT to 1 AM EDT) ends.


NY...Lakeshore Flood Warning until 2 AM EDT Friday for NYZ001>003.
     Beach Hazards Statement until 10 PM EDT this evening for
MARINE...Small Craft Advisory until 9 PM EDT this evening for LOZ030.
         Small Craft Advisory until 11 PM EDT this evening for
         Small Craft Advisory until 2 AM EDT Friday for LOZ042.



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