Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 150334
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
1134 PM EDT Sat Apr 14 2018

.SYNOPSIS...
A frontal boundary will stall just south of the region through
Sunday morning, with several periods of freezing rain and sleet to
the north of the front. Significant ice accumulations may result in
damage and power outages in some areas. Low pressure will then track
across the area with warming temperatures and a period of heavy rain
Sunday night and Monday, which may result in flooding.

&&

.NEAR TERM /THROUGH SUNDAY/...
The ice storm remains on track overnight. While there has been
a bit more sleet to start off with across Niagara Frontier, all
indications are that we will see a transition back to freezing
rain there after midnight. This will still give plenty of time
for significant ice accumulations, and likely numerous downed
trees and powerlines when combined with the gusty northeast
winds of 35 to 45 mph which have already been observed this
evening.

00Z KBUF sounding shows an incredible inversion from nearly -8C to
+8C between 2.5kft and 4.5kft. With this sounding, its no surprise to
see sleet reports from Buffalo northward to Lake Ontario. Meanwhile
slightly more shallow cold air is in place just south and east of
Buffalo with most reports predominately freezing rain, including the
Rochester area. As the main low pressure system approaches, this
will start to erode the deep layer of cold air from south to north
after midnight tonight. As this occurs, the far Southern Tier will
start to change over from Freezing Rain to Rain, meanwhile the
Niagara Frontier will change from predominately sleet to freezing
rain. The warmer air will arrive last across the North Country, not
until later Sunday night.

Synoptic Setup...

A strong and very dynamic system will move across the mid
Mississippi Valley tonight and reach the western Great Lakes and
Ohio Valley on Sunday. Downstream of the main system, a very strong
baroclinic zone will stall across the eastern Great Lakes, acting as
a focus for several strong waves to move along. Large scale ascent
from each wave will combine with strong frontogenesis and
differential temperature advection to produce deep layer ascent on
the cold side of the surface frontal zone. Deep southerly flow ahead
of the main system will transport Gulf moisture into the frontal
zone, setting the stage for several rounds of significant
precipitation. The first round will move into the area will continue
through this evening. This will be followed by somewhat of a lull
late tonight, with lighter, more intermittent precipitation. Another
stronger wave will arrive Sunday morning, supporting increasing
coverage and intensity of precipitation.

Ice, Sleet, and Snow Accumulations...

Expect freezing rain accretion to reach a half inch in many areas
from the Niagara Frontier eastward across the Genesee Valley and
areas southeast of Lake Ontario, and also into the Tug Hill region.

The North Country will likely see an extended period of sleet and
snow tonight into Sunday morning. This will reduce the amount of
freezing rain expected for the northern half of Jefferson and Lewis
counties, but up to an inch of sleet accumulation is possible. There
may also be some snow near the Saint Lawrence River with several
inches of accumulation possible.

Winds...

Fairly strong northeast winds will continue through the rest of the
afternoon, tonight, and Sunday. The strongest winds will be found
across the Niagara Frontier and along the south shore of Lake
Ontario, with northeast winds of 20-30 mph and gusts up to 40 mph.
Farther inland, winds will be 15 to 20 mph with gusts up to 30 mph.
The stronger winds, combined with added weight from ice accumulation
will increase the potential for tree and powerlines damage. Our trees
are very susceptible to northeast winds, which is the opposite of the
prevailing wind direction.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/...
Surface low pressure will track up across Michigan and into Quebec
Canada bringing with it a rich supply of moisture with the potential
for flooding across Western and North Central New York through
Monday night.

Now for the details, as the aforementioned low track north-northeast
into and across Michigan Sunday night a strengthening LLJ 60-70
knots will enter Western New York. Typically, this isn`t much of a
concern under a warm air advection pattern. However, with a 130-140
wind flow in the lower boundary layer coupled with the strong winds
aloft just off the surface(1-2K feet)damaging down sloping winds off
the Chautauqua Ridge will likely become a concern Sunday evening and
Sunday night. With saturated soils across the area it`s likely that
if these strong winds do materialize downed trees and power outages
will become a real possibility overnight into Monday. Given latest
guidance, confidence in this scenario playing out with strong winds
from the Chautauqua ridge to the lake Erie shoreline have increased
so have added a high Wind Watch for Southern Erie and Chautauqua
County. Continuing with the high wind threat the strengthening LLJ
(nearing 80+ knots) across the forecast area will move east-
northeast into North Central New York overnight. With that said, as
the LLJ encounters the Tug Hill a potential for strong winds east of
lake Ontario will increase Late Sunday night and during the day
Monday, especially for the Black River Valley, and the northern Tug
Hill area into the Fort Drum area. Again, these winds will be from
downslope/mountain wave development on the north side of the higher
terrain. A high wind watch remains in effect for Jefferson and Lewis
Counties for potential wind gusts to 60 mph.

As the surface low passes by to our west it will send its trailing
cold front towards the Eastern Great Lakes. Copious amounts of
moisture ahead and along the front will stream northward into the
region aided by a potent LLJ. As this occurs, PWATS will ramp
up to near record territory closing in on 1.25-1.35 inches
across the forecast area. Surging moisture, in combination with
convergence, and large scale lift will bring an area of moderate
to heavy rainfall into the lower lakes. Additionally, the
possibility of a few embedded rumbles of thunder with elevated
instability found along the axis of the front with 100-200 J/KG
of MUCAPE. This deepening moisture environment coupled with the
embedded thunderstorms will lead to the potential for localized
heavy rainfall amounts and subsequent flooding issues with 2.0
to 2.5 inches of rainfall. Monday evening, behind the axis of
heavier rain flooding concerns will begin to include the larger
creeks and rivers. This concern will translate eastward with
time to include areas east of Lake Ontario (where there still
remains a sizable snowpack on the Tug Hill). The MMERF
(GEFS/NAEFS) maintains several of our gauged creeks/rivers
reaching above flood stage across the Niagara Frontier and
Western Southern Tier. At this time a Flood Watch will remain in
effect across the forecast area through Tuesday afternoon.

Behind the cold front, colder air advection will ramp up across
the Lower Great Lakes which will slowly transition the rain
showers over to snow as H850T fall to -3/-6C over the course of
the remainder of the day. The moderate to heavy rain will exit
our eastern zones late Monday and Monday evening. Strong cold
air advection will continue Monday night into Tuesday with light
accumulating snows across the higher terrain of the Western
Southern Tier and east of Lake Ontario (Tug Hill). As the
upper-level trough and core of the coldest air aloft arrives
Tuesday with H850T falling to -8/-10C numerous snow/rain
showers and some lake enhanced snows will be ongoing across the
forecast area. These snow/rain showers and lake snows will be
enhance by several impulses rotating around the upper-level low
as it tracks across the region Tuesday. Accumulations will
continue to remain on the light side due in part to mid April
diurnal influences. However, its not out of the question for an
inch or two of accumulation across higher terrain.

Tuesday night, the upper-level low slowly tracks further to our
north into Ontario Canada. Meanwhile, building heights with upper-
level ridging moving into the lower lakes will effectively shut
down any remaining rain/snow showers.

Temperatures wise, Tuesday will be some 15 to 20 degrees below
normal with highs in the mid to upper 30s across the region. Some
clearing will occur Tuesday night which will allow for temperatures
to drop back into the upper 20s to lower 30s.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
The good news first. The deep...slow moving storm system that
produced very unsettled weather across our region during the first
part of the week will finally exit across the Canadian maritimes
Wednesday and Thursday. The bad news is that another storm will
quickly follow in its wake. While the medium range ensembles of the
GEFS and ECMWF are in general agreement with the presence and
subsequent passing of this second system...there is some disparity
on the timing of the onset of the associated pcpn.  Here are some
day to day details.

As mentioned...the persistent storm system that will have plagued
our region for the days leading up to this period will be exiting
across Maine and the Canadian maritimes late Wednesday. Meanwhile...
a shortwave ridge will quickly scoot across our forecast area ahead
of the next storm system. This will give much of our region a little
breather from the inclement weather late Tuesday night and for the
bulk of Wednesday. By the way...this is where there is a large
difference in the timing of the onset of pcpn...so confidence in
rain moving into the region is low at this point.

As we push through Wednesday night into Thursday...the somewhat
compact `bowling ball` low will absorb a large leftover `piece` of
the previous storm system...and the result will be another lumbering
giant that will slow and take its time to clear our region. Once the
pcpn does get started...whether it is late Wednesday or sometime
Wednesday night...we can anticipate at least 24 hours of fairly
widespread rain and wet snow.

By Friday...the large storm system will be exiting across the
Canadian maritimes. This will allow the widespread pcpn to taper off
from west to east through Friday night.

As we head into the weekend...a somewhat more robust ridge will move
across the Ohio Valley to the Lower Great Lakes. This will provide
our region with uneventful (dare I say `nice`) weather for the
weekend.

Temperatures through out this period will average below normal...
especially during the day when max temps will average 5 to 8 deg
below normal. By the weekend though...we should be looking at a
gradual day to day warming trend that will likely continue through
Sunday into Monday.

&&

.AVIATION /04Z SUNDAY THROUGH THURSDAY/...
Expect mainly IFR conditions to dominate overnight in a wintry
mix of freezing rain and sleet across the forecast area. As we
push through the overnight...there may be more intermittent
MVFR conditions as precipitation becomes lighter.

On Sunday...warmer air will move into the region, allowing
freezing rain to change to rain from southwest to northeast.
CIGS/VSBY will remain IFR through at least midday, with some
improvement possible in the afternoon.

Outlook...

Sunday night through Monday...MVFR/IFR with periods of rain and
possibly a thunderstorm.
Tuesday...Rain and snow showers with MVFR.
Wednesday and Thursday...VFR/MVFR. A chance of showers.

&&

.MARINE...
A strong gradient between strong surface high pressure over northern
Ontario and low pressure moving through the midwest states will
produce northeast gales on Lakes Erie and Ontario through Sunday
evening, before diminishing later Sunday night as winds become more
southerly and the pressure gradient relaxes.

&&

.HYDROLOGY...
There is a risk for flooding in the Sunday night through Tuesday
timeframe. Total precipitation amounts of 2.0 to 2.5 inches are
likely, with model consensus showing the greatest amounts are
likely to be along or north of the I-90 corridor. Some of this,
may fall as frozen precipitation but warmer temperatures Sunday
into Monday are likely to melt this and possibly some of the
existing snow pack in the Black River basin. Ensemble river
forecasts and official RFC forecasts suggest that there is a
risk for at least minor flooding for many of our rivers and
creeks. In addition to the area rivers, small streams, low-lying
areas and urban areas may see flooding problems as early as
Sunday night and early Monday from the moderate to locally
heavy rain Sunday night into Monday morning. A Flood Watch will
continue for the entire area.

&&

.TIDES/COASTAL FLOODING...
Northeasterly winds will result in significant wave action which
will result in lakeshore flooding and erosion along the southwestern
shores of Lake Ontario. A lakeshore flood warning is in effect
for Niagara, Orleans, and Monroe counties. The most susceptible
areas are the numerous bays and inlets, especially Braddock Bay
and surrounding ponds.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Flood Watch from late Sunday night through Tuesday afternoon
     for NYZ001>003-010>013-019>021-085.
     Ice Storm Warning until 2 PM EDT Sunday for NYZ001>006-010>014-
     085.
     High Wind Watch from Sunday afternoon through Monday morning
     for NYZ019-085.
     Flood Watch from Monday morning through Tuesday afternoon for
     NYZ004>008-014.
     Winter Storm Warning until 2 AM EDT Monday for NYZ007-008.
     High Wind Watch from late Sunday night through Monday
     afternoon for NYZ007-008.
     Lakeshore Flood Warning until 2 PM EDT Sunday for NYZ001>003.
     Winter Weather Advisory until 8 AM EDT Sunday for NYZ019>021.
MARINE...Small Craft Advisory until 5 PM EDT Sunday for LEZ020.
         Gale Warning until 6 PM EDT Sunday for LEZ040-041.
         Small Craft Advisory until 5 PM EDT Sunday for LOZ030.
         Gale Warning until 6 PM EDT Sunday for LOZ042-043-062>065.
         Small Craft Advisory until 8 PM EDT Sunday for LOZ044-045.
         Small Craft Advisory until 5 PM EDT Sunday for SLZ022-
         024.

&&

$$

SYNOPSIS...Church/Hitchcock
NEAR TERM...Church/Hitchcock/RSH
SHORT TERM...AR/Thomas
LONG TERM...RSH
AVIATION...Church/Hitchcock
MARINE...Church/Hitchcock
HYDROLOGY...Apffel/Hitchcock
TIDES/COASTAL FLOODING...Apffel/Hitchcock



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