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Area forecast discussion
National Weather Service Buffalo New York
1037 PM EDT Sat Jul 21 2018

low pressure lifting north from the mid Atlantic region will bring a
soaking, and at times heavy rainfall to the region overnight into
Sunday morning. Chances for rain showers and even some thunderstorms
will then increase again later Sunday with unsettled weather and
above normal temperatures then persisting through much of the
upcoming week.


Near term /through Sunday/...
radar shows widespread light rain has overspread western New York late
this evening ahead of a low shifting up the Delmarva penninsula.
This leading area of rain is being forced ahead of an unseasonably
strong 50 kt 850 mb jet on the north side of the low to our south
advecting a slug of deep moisture into western and north-central New
York. As the core of the jet approaches closer to our region after
midnight then lifts north across Lake Ontario, periods of heavy rain
are possible first across western New York the the Eastern Lake Ontario
region. Expect that the bulk of the steady rain overnight will fall
across most of western New York (1-1.5 inches) with much less (0.25-
0.5) expected in the Eastern Lake Ontario region. The bulk of the
rainfall will occur overnight, tapering off to showers by mid-
morning Sunday morning as the low weakens and tracks northward into
southern Ontario. The cloud cover, easterly winds and rain will help
keep temperatures mild overnight. Lows are only expected to dip back
to between the mid 50s and mid 60s.

Easterly component winds will pick up late overnight into Sunday
morning with the approach of the still quite strong surface low.
Northeasterly winds gusting to 40 mph along the south shores of
Lake Ontario and southeasterly winds downslope of the
Adirondacks may result in a few small downed tree limbs given
the full foliage.

Sunday afternoon the above system will push further northward
and away from our region, while a much larger vertically
stacked low over the Ohio Valley extends a surface trough
northward into the western southern tier. Initially, a southerly
flow should provide some downsloping and mainly dry weather
across the region for the middle of the day. The trough coupled
with diurnal warming and some weak destabilization may result in
scattered showers and thunderstorms late Sunday afternoon.
Expect the warmest temperatures to be across the lake plains
east of Rochester with highs in the lower to mid 80s with highs
in the mid to upper 70s most other locations.


Short term /Sunday night through Tuesday night/...
very complex scenario, hence difficult forecast will continue
through this period. Main players will continue to be strong high
pressure/ridging at all levels remaining anchored across the western
Atlantic Basin and a weaker elongating mid/upper trough stretching
from the western Great Lakes into the deep south. Meanwhile surface
low pressure will continue to spin across the southeastern U.S. Deep
southerly flow between these two features will continue to draw up
very deep Atlantic moisture across our region through the period,
keeping very warm and humid conditions in place.

Sunday night through Monday night, there will not be any real
features to focus any showers and thunderstorm activity on. However,
weak cyclonic flow aloft and plenty of moisture will keep a general
threat for showers/low chance thunderstorms throughout the period,
with dry periods built in there as well. Showers/embedded storms
will be most widespread Monday afternoon as instability increases
with daytime heating. The main threat from any storms will be for
areas of locally heavy rainfall if any training of cells manages to
set up, with the currently forecast 25-35 knots of flow aloft
otherwise likely to help keep things moving along. Otherwise, the
showers and storms will likely bring some beneficial rainfall to
portions of the region. Lows Sunday night will be mainly be in the
60s, with lower elevations likely not dropping below 70f Monday
night as conditions become increasingly humid. Highs Monday will be
some 5-10 degrees warmer than Sunday as deep southerly flow becomes
established across the region pushing most areas into the 80s.

Tuesday through Tuesday night, next mid-level shortwave will begin
to dig across the upper Great Lakes, while stronger upper level jet
dynamics develop just north of the area. Our region will also be
under the favorable right rear quadrant of this said strengthening
upper jet. The combination of these two features will help to focus
an axis of heavier rain across our area during this period. Where
exactly this axis sets up would be very hard to pin down at this
point. For temperatures, very warm and humid conditions will
continue, however with extra cloud cover and precipitation more
likely, temperatures will be tempered down a bit with highs
generally ranging from the upper 70s to lower 80s. With no change in
airmass, lows Tuesday night will again not fall back much with lows
generally ranging from the mid 60s to around 70.


Long term /Wednesday through Saturday/...
this period will continue to remain wet, with seasonable
temperatures as an upper level trough passes across the Great Lakes

A weak frontal boundary will lie across the region Wednesday, with
another piece of energy from a former closed upper level low passing
across western New York. Precipitable waters will remain high, close to 2 inches
across our region, and with a low level boundary to focus rain
showers upon...will have categorical pops for our region for
Wednesday. This activity will wane some at night, though chances for
showers will continue as we remain unstable through the night.

Thursday a stronger cold front will near the region, and initiate
showers and thunderstorms. While moisture and instability are
favorable for storm development, a weak wind field (winds 20 knots
or less through 10k feet through the afternoon hours) may limit
severity. As the front crosses the region later Thursday and
Thursday night, precipitation will end from west to east.

Friday and Saturday there will remain chances for convection as an
upper level trough remains nearby, with precipitation mainly along
lake breeze boundaries. This activity will likely have less coverage
area than the Wednesday-Thursday timeframe.


Aviation /03z Sunday through Thursday/...
widespread light rain has overspread wny late this evening and is
expected to also reach the Eastern Lake Ontario region later
overnight. Cigs have already dipped to MVFR at kjhw at 02z. A slug
of deeper moisture and periods of heavy rain is expected to light
across western and north-central New York ahead of a strong low pressure
approaching from the south. Cigs/visible are expected to deteriorate
during the course of the overnight, as the steadier and at times
heavier rain lifts north. The worst conditons and heaviest rain will
fall across western New York. Cigs/vis will gradually deteriorate with IFR
to MVFR in the steady and heavy rain mainly across the rest of
western New York between 06z and 16z for kbuf/kiag/kroc. Kart should see
some heavy rain but for a shorter period mainly between 09-12z which
will bring IFR visible but ceilings expected to only slip to MVFR.

Expect most areas to start off Sunday IFR/MVFR but improve
quickly when the low tracks to the north and our winds shift to
the south which will dry out the lower levels. Expect mainly dry
weather with VFR conditions Sunday afternoon. Another slug of
moisture looks to arrive later Sunday from the southeast which could
bring some scattered thunderstorms late in the day. Confidence on
this convection is too low to include in the tafs at this time.

Sunday night...VFR/MVFR with a chance of showers and
Monday...mainly VFR with scattered showers and thunderstorms
and associated local/brief MVFR.
Tuesday and Wednesday...VFR/MVFR with showers and thunderstorms
Thursday...VFR/MVFR with a chance of showers and thunderstorms.


low pressure will continue to track north across the Delmarva and
Pennsylvania overnight to Lake Ontario Sunday morning. This is an
unusually strong surface low which will result in winds increasing
overnight into Sunday morning before diminishing behind the system
Sunday afternoon. This will result in a brief period of winds
solidly meeting small craft criteria in a NE-southeast flow. Small craft
headlines were issued for most of the waters with the exception of
the upper Niagara and eastern portions of Lake Ontario.

Looking further ahead to the coming work week...unsettled weather is
likely over the lower Great Lakes through at least mid week.
Fortunately...winds and waves during this period should be below
Small Craft Advisory levels.


Buf watches/warnings/advisories...
New York...beach hazards statement from 6 am EDT Sunday through Sunday
afternoon for nyz003-004.
Beach hazards statement from 6 am EDT Sunday through Sunday
afternoon for nyz001-002.
Marine...Small Craft Advisory from 5 am to 5 PM EDT Sunday for lez040-
Small Craft Advisory from 5 am to 5 PM EDT Sunday for



near term...apffel/Smith

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