Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 250105

Area Forecast Discussion
National Weather Service Buffalo NY
905 PM EDT Mon Jul 24 2017

An area of low pressure over eastern Lake Ontario will dissipate as
it moves to the Atlantic coast Tuesday. Scattered showers will
transition to thick low cloud cover and some drizzle through early
Tuesday morning. After a cool and cloud Tuesday clearing skies and
seasonable temperatures return mid week with high pressure. A cold
front will cross the region for the second half of the week with
scattered showers and thunderstorms, ushering in high pressure and
comfortable, dry weather for the weekend.


A stacked low pressure system over eastern Lake Ontario this evening
will slowly dissipate as it drifts toward the east coast on Tuesday.
Scattered showers this evening are organized along a frontal
boundary dropping southward on the back side of this surface low
across western NY.

Northerly flow with cold advection will continue to overspread the
region overnight as the low drifts southeastward off Lake Ontario.
This will drop 850 mb temperatures to around +7 to +9 overnight.
Meanwhile mid-level moisture will depart to the east as the upper
level trough swings southeastward. This combination will allow for
showers to diminish from west to east overnight and into Wednesday
morning. However, low-level moisture will be reinforced due to the
steepening low-level lapse rates over the relatively warm lower Great
Lakes. This will maintain thick low cloud cover across the forecast
area overnight as northerly winds cross Lake Ontario and upslope
into the western NY and the Finger Lakes. With the lack of mid-level
moisture across western NY, dont expect much in the way of shower
activity for the second half of the night toward morning, but would
not rule out areas of drizzle and even some fog in the higher
terrain south of the NY State Thruway. Meanwhile, east of Lake
Ontario, a bit more mid-level moisture will remain closer to the
upper-level low to support scattered showers overnight into Tuesday

During the day Tuesday, it will actually feel quite fall-like for
this area, with northerly flow and trapped low-level moisture under
a sharping inversion leading to overcast skies lasting much of the
day. The cool pool of air aloft will keep daytime highs below
normal, with highs only in the 60s to near 70. Thick low overcast in
the morning will likely lift some and break into a stratocumulus
deck that will linger through the afternoon. This process will also
allow for any morning fog/drizzle to dissipate as we get into the
late morning.


Expect dry and quiet weather Tuesday night through Wednesday as
surface high pressure and low amplitude mid-level ridging shifts
across western and central New York. Added some Southern Tier river
valley fog Tuesday night with the high cresting overhead. Expect
partly to mostly sunny skies on Wednesday. Expecting a cool night
Tuesday night with lows in the mid 50s inland to around 60 at the
lakeshores. Wednesday, southerly flow develops helping to boost
temperatures back to late July levels with highs forecast in the
upper 70s to low 80s except low 70s across the Tug Hill.

Most of Wednesday night should still remain dry ahead of an
approaching cold front. Have gone with a low chance of some showers
across the Niagara Peninsula and SLV Thursday morning either from a
narrow leading warm sector or well ahead of the cold front.
Otherwise, mugginess will return overnight as the lower Great Lakes
comes under strengthening warm and moist southerly flow. Temps may
actually rise late in the night. Expect lows to bottom out only in
the mid to upper 60s with 70 possible for lows near the lakeshores.

The next likely period of showers and thunderstorms will then arrive
Thursday with the passage of a cold front. There remains some timing
differences among the 12z guidance with some showing a morning
frontal passage and others later in the afternoon. This leaves
uncertainly in more exact timing so have held on to continuity which
better aligns with the 12Z ECMWF and brings the highers POPs across
our region in the afternoon hours. Instability at this range looks
weak but with better insolation ahead of the front we could be
looking at a risk for some strong/severe storms as 0-6km shear is
forecast to run about 40kts. SPC has not included a severe risk area
at this time. 850mb temps are forecast to rise to +13C to +14C which
will translate into highs in the upper 70s to low 80s. Combined with
dewpoints rising to the mid/upper 60s will make for a very
uncomfortable mid summer day across the region.

Showers and thunderstorms will taper off from northwest to southeast
with the passage of the front Thursday night. Northerly flow behind
the front will likely hold in cloudiness and possibly a few
scattered showers in wrap around moisture ahead of the trailing mid-
level trough axis. Dewpoints holding in the 60s will keep mild
overnight temps only bottoming out in the low 60s.


The axis of the upper level trough that is expected to bring the
showers and thunderstorms on Thursday/Thursday night will be
centered to the east of the forecast area by the time we get into
Friday, and the bulk of the precipitation should be clear of the
area. However, the 12Z ECMWF and GEM are both slower with the
progression of the trough than the GFS, and under this scenario
precipitation wrapping around a surface low over New England may
linger across the eastern half of the forecast area during the day
on Friday. Even if precipitation associated with the low stays clear
of the area, it is worth noting that 850mb temps falling to around
+9C in addition to lingering cyclonic flow aloft have the potential
to generate a few lake-effect showers south of Lake Ontario Friday
into Friday night. The precip potential may be limited by a dearth
of moisture aloft, as well as a short northerly fetch across the
lake. For the time being, will keep a low chance of pops in the
forecast pending better agreement on timing of the upper level
trough progression between models. As would be expected in this
scenario, temperatures will be a tad on the cool side for late July,
with highs in the lower 70s, with upper 50s to lower 60s Friday

Even if lake effect showers do not pan out Thursday into Thursday
night, we can expect lake-enhanced stratocu to hang around south of
Lake Ontario during this period. Clouds should diminish for the
weekend as the upper level trough continues to pull away from the
region and a col develops overhead in the upper levels, with broad
surface ridging in the lower levels. This should make for a pleasant
weekend across western and north-central New York, as high pressure
persists at least through Sunday and light north-northeasterly flow
helps keep dewpoints down in the upper 50s to around 60, with
seasonable highs in the upper 70s.


Widespread MVFR to IFR stratus will persist across the region
tonight into Tuesday. IFR conditions are likely to be the most
persistent overnight into Tuesday morning at JHW and ART with
upslope northerly flow into the higher terrain. Expect mainly low
MVFR at BUF/IAG/ROC but there is a possibility for these sites to
drop IFR for a couple hours after midnight as the cooler air moves
across Lake Ontario. Scattered rain showers this evening will
diminish and transition to some areas of drizzle with even some fog
possible over the higher terrain south of the Thruway and over the
Tug Hill.

On Tuesday, low stratus with patchy drizzle early will slowly lift
into a MVFR and eventually VFR stratocumulus deck for midday through
the afternoon. Any morning fog/drizzle will diminish by mid-day with
daytime mixing and heating.


Thursday...MVFR/VFR with showers and thunderstorms likely.
Friday and Saturday...Mainly VFR.


An area of low pressure over the eastern waters of Lake Ontario will
fade to the Jersey shoreline Tuesday. Small craft conditions will
continue on Lake Erie through around midnight. Meanwhile northerly
winds will increase on Lake Ontario for which small crafts have been
expanded to cover the entire southern shore of Lake Ontario. Winds
will subside through Tuesday afternoon allowing waves to drop below
SCA criteria by Tuesday evening.

Fine boating conditions are expect Wednesday before a cold front
crosses the lakes Thursday brining scattered showers and
thunderstorms and higher wind/wave action.


A period of stronger northerly winds is expected to set up across
Lake Ontario late tonight and Tuesday morning as low pressure departs
off to our southeast. With the wind direction now expected to be
a bit more northerly than previously forecast, especially
across the eastern end of the lake, have expanded the Lake Shore
Flood warning to cover the entire southern shoreline of Lake
Ontario. Conditions will worsen first across the western end of
the lake overnight with a more northeasterly wind direction
expected. Into Tuesday morning, impacts will expand eastward to
include northern Cayuga and western Oswego counties as winds
take a more northerly direction.


NY...Lakeshore Flood Warning from 6 AM to 4 PM EDT Tuesday for
     Lakeshore Flood Warning from 2 AM to 4 PM EDT Tuesday for
     Beach Hazards Statement until 11 PM EDT this evening for
MARINE...Small Craft Advisory until 2 AM EDT Tuesday for LEZ040-041.
         Small Craft Advisory until 8 PM EDT Tuesday for
         Small Craft Advisory from 6 AM to 4 PM EDT Tuesday for



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