Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 211036
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
636 AM EDT Tue Mar 21 2017

.SYNOPSIS...
A weak cold front will finish crossing the region early this morning...
bringing little more than some clouds and spotty light showers. A
secondary arctic front will then push across the region this evening
along with some scattered flurries and snow showers...with much colder
weather and very limited lake effect snow showers then following for
later tonight and Wednesday. Temperatures will then rebound markedly
Thursday and Friday as much warmer air works its way back into our
region...with wetter conditions also arriving in time for Friday and
Saturday.

&&

.NEAR TERM /THROUGH TONIGHT/...
An initial weak cold front will finish crossing our region from west
to east early this morning. As this boundary is accompanied by only
very weak forcing and limited moisture...it will continue to generate
little more than some light rain showers or sprinkles as it crosses
our area...with some limited snow showers/flurries possibly mixing
in with these across portions of the Finger Lakes and North Country.
Expect the best chances for any precip to lie across the North Country
and Saint Lawrence Valley where a passing weak mid level shortwave will
provide a little more in the way of support...however even there PoPs
will only reach the very low end of the chance range.

As we progress through the day today...weak surface-based ridging
and much drier air will build in behind the departing initial front...
which will result in sunshine increasing from west to east from about
mid morning onward. While this improvement will be somewhat muted across
the North Country owing to the later departure of the front from that
region...areas further west should see a good deal of sunshine develop
by midday or early afternoon. While weak cold air advection will be in
place with 850 mb temps falling to between -2C and -4C...this will be
offset by the influence of the strong March sun and improving mixing...
which will help temperatures to climb higher than what we experienced
on Monday. Expect afternoon highs to reach into the lower to mid 40s
across the North Country and to the mid 40s to lower 50s south of Lake
Ontario...with the warmest overall readings found across the Genesee
Valley and portions of the Finger Lakes.

Tonight a sharp secondary arctic front will quickly slide southward
across our region. With moisture also looking to be rather limited along
this boundary...it will be hard pressed to generate much more than some
scattered snow and rain showers across the North Country and Finger Lakes
regions...with just some scattered flurries affecting areas further to
the south and west. Following the passage of the arctic front...a north-
northwesterly flow of much colder air will quickly flood southward across
our region overnight. This will send temperatures plummeting back to well
below average levels...with overnight lows dipping to between 10 and 15
across the North Country and to the mid teens to lower 20s south of Lake
Ontario. The incoming colder airmass will also help to generate a lake
response southeast of the lakes...though this should be rather muted given
the short fetch...a relatively low cap and the relatively dry nature of
the arctic-sourced air...all of which should keep any snow showers rather
light and scattered in nature...with only minor accumulations of less
than an inch expected.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY NIGHT/...
The calendar says Spring...but it will feel anything but...as a shot
of modified arctic air will place our temperatures some 15 to 20 deg
F below normal values to start this period. While the heart of the
cold airmass will pass by well to our north...it will still glance
our forecast area with H925 temps as low as -20c. Interestingly...
the degree of cold is BARELY 2 std below normal. This is due to the
large variance in temperatures that we experience during the early
part of Spring. For example...most days in March feature an 80
degree spread between daily record highs and lows. This is more than
any other month. It is just as `normal` for a day in the 20s F at
this time of year as it is to have a day in the 60s/near 70.

In any case...the fleeting shot of cold air will cross our region on
Wednesday...as a large Canadian high pressure system will build
southeast from the Upper Great Lakes. Afternoon temperatures are
only expected to top out in the 20s F across the western counties...
while parts of the North country may not make it out of the teens.
While the cold will be tempered by a fair amount of sunshine...there
could be some nuisance lake snow showers southeast of Lake Ontario.
Any lake response will be greatly limited though by a cap of 5k ft
and a very dry synoptic environment....not to mention the ill
effects of springtime insolation/diurnal mixing.

Any residual lake induced cloud cover will clear out early Wednesday
night as the center of the Canadian high will pass overhead. Given
the cold airmass and forecast light winds...this will lead to very
good radiational cooling and thus a very cold night. The mercury
should drop to within a few degrees of 10 for a large portion of
western New York...with single digit readings likely across the
North Country and the bulk of the Srn Tier.

While still on the cold side of `normal`...Thursday will be a
beautiful day across the region. The large surface high will
gradually drift away to our southeast...but not before supplying us
with azure blue skies and light winds. While still a little below
normal...it will not be nearly as cold as Wednesday as warm
advection aloft will already be busy modifying our airmass.
Afternoon temperatures will climb through the 30s to near 40 over
the western counties...while it will be a little chillier east of
Lake Ontario with max temps close to the freezing mark.

Thursday night...the broad ridge over the Mississippi Valley will
push east to the Ohio Valley and Great Lakes. Ahead of this
feature...a tightening baroclinic zone will become established from
Wisconsin and Lower Michigan to Lake Erie. The associated isentropic
lift along this elevated boundary will generate some showers...with
some of that activity spreading across our far western counties. Any
light pcpn will fall as a mix of light rain or wet snow showers.
Given the strength of the warm advection...temps after midnight will
actually start to rise...climbing back above freezing for counties
near Lake Erie.

Conditions will further deteriorate on Friday...as the strengthening
baroclinic zone will evolve into a fairly pronounced warm frontal
boundary. This feature will push north across our forecast area
during the course of the day and serve as a focus of lift for the
wealth of moisture being pumped into the region from a 40kt low
level jet. The pcpn could initially start as a bit of wet snow...but
will quickly transition to just rain. The 60 mile wide band of pcpn
will push north during the course of the midday and afternoon...with
the axis of rain aligning with Lake Ontario and the North Country by
late in the day. This means that the Srn Tier will could be far
enough into the warm sector for the bulk of the pcpn to end...or at
the least considerably taper off. Max temperatures on Friday will
range from the low to mid 50s over the Southern Tier to the lower
40s north and east of the Tug Hill.

Friday night...while a mid level ridge will remain pinched in place
over the Lower Great Lakes...the conspicuous sfc frontal boundary
stretched the length of Lake Ontario will slowly be pushed south by
a strong area of high pressure near James Bay. The associated swath
of steadier rain will settle south to the counties lining the south
shore of Lake Ontario with an increasing chance for rain also across
the Finger Lakes and Genesee Valley. Despite colder air undercutting
the boundary...the pcpn should remain all liquid across the forecast
area.

&&

.LONG TERM /SATURDAY THROUGH MONDAY/...
Confidence remains very high that this will be a wet and unsettled
period across the majority of our forecast area.

The ECMWF and GEFS ensembles are in fairly strong agreement for
Saturday and Sunday with the general placement of the upper level
synoptic components...including the mid western closed low and its
downstream Lower Great Lakes ridge. The key feature though will be a
quasi-stationary east to west frontal boundary that will be in place
across our forecast area. This persistent front will continue to
offer a surface for which abundant low level moisture can over-run
to produce fairly widespread rain and even some wet snow. While the
two mainstream ECMWF and GFS packages are similar...am leaning more
on the ECMWF as it keeps the bulk of its pcpn in close proximity to
the tighter H925-85 baroclinic zone...where one would expect the
pcpn to be. It is simply more meteorologically consistent.

Have thus raised pops to likely/high likely for many areas Saturday
and Sunday...while maintaining the possibility for a wintry mix at
night. While it is not out of the question that cold air undercutting
the boundary from the north could support some freezing rain across
the North Country Saturday night...will only mention a mix of rain
or snow for now. As mentioned in previous discussions...it is not
climatologically favorable for ZR- in late March so will keep the
forecast for rain or snow...keeping in mind there is a small
potential for other forms of precipitation.

By Monday...the filling upper low will be exiting to our east with
flat ridging following in its wake. This should lead to
improving conditions over our region with only a low chc for any
residual pcpn.

In regards to temperatures...the sharp frontal boundary will offer a
wide range of temperatures across our region. Daytime highs Saturday
will range from the mid 50s near the Pennsylvania border to the
upper 30s near the Thousand Islands. On Sunday...the same areas will
range from the mid and upper 40s to the mid 30s respectively as
shallow cold air will ooze southwards across Lake Ontario. Max temps
on Monday will generally be in the 40s throughout.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
A weak initial cold front will finish crossing the region early
this morning...with just some spotty light rain and snow showers or
sprinkles/flurries marking its passage. Otherwise flight conditions
will be dry and primarily VFR...with just a brief period of MVFR
possible along and immediately behind the front.

In the wake of this initial boundary...weak surface-based ridging and
much drier air will build across the area through the rest of today.
This will bring increasing amounts of sunshine and improvement to
VFR from west to east.

A trailing secondary arctic front will then cross the region tonight
and bring some additional scattered snow and rain showers to the
Finger Lakes and North Country...with a north-northwesterly flow
of much colder air in its wake helping to generate some scattered
light snow showers and flurries southeast of the lakes. Expect the
potential for brief reductions to MVFR/IFR within any snow showers...
with general high-end MVFR to lower-end VFR conditions otherwise
prevailing.

Outlook...
Wednesday...Scattered snow showers/flurries and associated MVFR
southeast of the lakes dissipating...otherwise VFR.
Thursday...VFR.
Friday...Deterioration to MVFR/IFR with mixed rain and snow
developing...then changing over to all rain.
Saturday...MVFR/IFR with rain likely.

&&

.MARINE...
After a few days of relatively tranquil conditions...a freshening
westerly flow will develop across Lake Ontario in advance of an
approaching arctic cold front today...with fresh northwesterlies
then overspreading the entire Lower Lakes region following the
passage of the front tonight...then continuing through a good chunk
of Wednesday. To cover the resultant increase in winds and wave
action...Small Craft Advisories have been hoisted as outlined
below.

After that...strong high pressure will build across the region
later Wednesday through Thursday while bringing a return to
light winds and negligible waves.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Small Craft Advisory from 8 PM this evening to 2 PM EDT
         Wednesday for LEZ040-041.
         Small Craft Advisory from 5 PM this afternoon to 2 PM
         EDT Wednesday for LOZ030.
         Small Craft Advisory from 5 PM this afternoon to 2 AM EDT
         Thursday for LOZ043-044.
         Small Craft Advisory from 5 PM this afternoon to 5 PM EDT
         Wednesday for LOZ042.
         Small Craft Advisory from 8 PM this evening to 5 PM EDT
         Wednesday for LOZ045.

&&

$$

SYNOPSIS...JJR
NEAR TERM...JJR
SHORT TERM...RSH
LONG TERM...RSH
AVIATION...JJR
MARINE...JJR



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