Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 202024
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
424 PM EDT Wed Mar 20 2019

.SYNOPSIS...
An area of low pressure will approach the region tonight, bringing
light rain to western zones, that will spread across eastern zones
through tomorrow morning. Another area of low pressure forming off
the Carolina coastline tonight will advance northward along the
eastern seaboard, and then rapidly strengthen tomorrow night and
Friday. This system has the potential to produce heavy, wet snow to
areas east of Lake Ontario Friday through Friday night, with a mix
of rain and snow farther westward...that will become all snow Friday
night.

&&

.NEAR TERM /THROUGH THURSDAY/...
Late this afternoon there is plenty of sunshine to go around
with surface high pressure departing along the eastern seaboard,
and upstream surface low remaining back across the Upper Lakes.
Visible satellite imagery displays the leading edge of cirrus
clouds spreading into Western New York. Many locations have
warmed to around 50F.

For tonight, clouds will continue to slowly increase from west to
east as the surface low draws closer to WNY. The upper level trough
and best lift will drop southeastward across the Ohio Valley tonight
and this will slow the eastward progression of mostly rain showers.
The greatest threat for rain showers will be across far western
zones late tonight where surface convergence is maximized along a
weak warm front. Areas to the east may remain dry through the night
as the surface low weakens under what is now a shortwave ridge of
high pressure aloft over New England and eastern NYS.

Increasing clouds will likely prevent freezing temperatures across
WNY, though the later arrival of clouds tonight east of Lake Ontario
will produce some spotty temperatures just below freezing.

Chances for mostly rain will then spread eastward across our eastern
zones tomorrow morning before the initial surface low weakens over
WNY through the afternoon hours. Within the presence of this
weak surface low over our region, there will continue to be
chances for light rain showers through the day.

Precipitation tonight and tomorrow morning will predominately be
plain rain, though higher terrain may have a mix of wet snow and
rain. Even here snow accumulations will be little to none.

As the upper level trough sharpens over the Southeast States
tonight, a secondary surface low will develop along the lee side of
the Appalachian mountains tomorrow morning. This surface low will
begin to deepen and drift northward along the eastern seaboard to
about the Delmarva peninsula. As this low deepens a LLJ will
increase, with a S to N oriented jet across the eastern mid-Atlantic
States. Convergence along this jet axis will bring likely rain
showers to areas east of Lake Ontario by late in the afternoon
hours.

With no cold air drawn southward tomorrow afternoon temperatures
will again push into the mid 40s to around 50F.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/...
Latest operational and ensemble forecasts continuing to come
together on a late week complex pattern featuring two troughs which
will result in a deep closed circulation over New England.

First shortwave trough will cross the region Thursday night followed
by the main upper trough Friday. Dynamic support for precipitation
increases substantially over the area during this time.
Precipitation coverage which initially will be fairly spare
early Thursday night will increase overnight especially in
favored upslope areas. Thermal profiles will continue to be
warm enough for rain at lower elevations, with some wet snow
mixing in across higher terrain. Low temperatures will be in the
mid 30s in most locations and lower 30s for higher terrain.

Friday and Friday night, the deepening and coastal low will
allow for deep northwest cyclonic flow to develop across the
eastern Great Lakes. Abundant wrap around moisture, developing
lake instability, and upslope flow will all contribute to
widespread precipitation later Friday and Friday night.
Precipitation type will still be a mix of rain and wet snow
through midday friday before changing to all snow by late Friday
afternoon or early evening as strong cold advection develops in
the wake of the coastal low. Widespread wrap around snow will
then likely continue through Friday night. It will turn quite
windy as well, with gusts over 35 mph possible as cold air
pours back into the region.

Most guidance suggesting a good potential for significant snowfall
over the higher terrain east of Lake Ontario. A Winter Storm Watch
will be issued to cover the potential of 7 or more inches from
Friday into early Saturday. Most guidance suggests at least some
accumulation across other parts of the entire region. The
higher terrain of the Southern Tier and southern Finger Lakes
will have the better chances to see accumulating snowfall of
several inches.

The northwest flow lake effect and upslope snow will continue
through Saturday morning before tapering off from west to east
Saturday afternoon as the strong coastal low begins to move into the
Canadian Maritimes and away from the region. Additional light snow
accumulations are possible Saturday morning. Temperatures will be
well below normal, with highs in the 30s.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
High pressure will track across the Lower Ohio Valley, Appalachians
and off the southern Mid-Atlantic coast Sunday. This dry airmass
will promote dry and warm conditions Sunday with temperatures
climbing into the 50`s away from the lakeshores.

To the north, a cold front will be stretched from west to east from
Lake Superior to Montreal Sunday evening. As high pressure continues
to retreat off the east coast, this frontal boundary will begin to
move southward Sunday night. There continues to be question as to
the track and speed of an area of low pressure that will be
developing across the Central Plains. The GFS continues bringing it
further north where widespread rain or snow showers will spread
across western and north central NY late Sunday night through Monday
while the ECMWF keeps low pressure further south with little
interaction with the cold front as it moves across the eastern Great
Lakes Monday. There is a large spread with the amount of liquid
precipitation right now so kept chance rain or snow showers Sunday
night through Monday.

One thing that does look certain is the amount of cold air that will
move into the eastern Great Lakes beginning Monday night. Cold air
advection will continue through Tuesday night with 850mb
temperatures falling to a low of around -15C. Although dry, expect
winter-like temperatures for the first half of next week.

&&

.AVIATION /21Z WEDNESDAY THROUGH MONDAY/...
VFR flight conditions will last through 06Z. Light rain will
enter far WNY around midnight. An upper level low that is
forcing this rain will dive to the south of our region, leaving
little forcing and eastward push to these showers. Greatest
threat for rain showers will be across far western NY late
tonight where surface convergence is maximized along a weak warm
front. This will result in cloudy skies, with clouds still
mainly in the VFR flight category late tonight and into
Thursday.

With forcing dropping southward tomorrow rain shower activity
through the first half of Thursday will be spotty, with VFR flight
conditions likely. As moisture increases from the south Thursday
afternoon flight conditions will lower to MVFR/higher terrain IFR
and rain showers will increase some, especially towards the east
ahead of a LLJ along the eastern seaboard.

Outlook...

Thursday night...MVFR/IFR in rain showers changing to snow late.
Friday...MVFR/IFR with rain continuing to changing to snow.
Saturday...VFR/MVFR with a chance of snow showers.
Sunday...VFR.
Sunday night and Monday...VFR/MVFR in snow showers and perhaps rain
showers.

&&

.MARINE...
An area of low pressure will approach the lakes tonight, though the
pressure gradient will remain modest with winds generally 15 knots
or less through tomorrow night.

A secondary low will form tomorrow night along the Carolina
coastline and then rapidly strengthen Thursday night and Friday
along the New England coastline. The increase pressure gradient with
this system will bring gusty west to then northwest winds across the
Lakes Friday and Friday night, with waves pushing over 4 feet on
open waters. A period of small craft conditions is then likely to
continue through Saturday on the waters.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Winter Storm Watch from Friday morning through Saturday
     morning for NYZ006>008.
MARINE...None.

&&

$$

SYNOPSIS...Thomas
NEAR TERM...Apffel/Thomas
SHORT TERM...Hitchcock/TMA
LONG TERM...HSK
AVIATION...Apffel/Thomas
MARINE...Thomas



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