Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 191424
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
1024 AM EDT Sun Mar 19 2017

.SYNOPSIS...
A remnant trough of low pressure across western Pennsylvania and New
York will dissipate this morning...with high pressure then building
across the area this afternoon and tonight. Skies will gradually
clear out from northeast to southwest this afternoon into
tonight as drier air moves into the region. Low pressure
tracking across northern Quebec will then push a couple of cold
fronts across the region Monday and Tuesday...with much colder
air briefly returning in their wake for midweek...before milder
weather returns for the end of the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Plenty of cloud cover can still be found across the bulk of Western
and North-Central New York this morning thanks to a combination of
inverted troughing, lingering low-level moisture, and light upslope
northeasterly flow that continues to produce widespread low clouds
and patchy fog south of Lake Ontario, and across the Southern Tier
in particular. There is clearing across the North Country this
morning however, as drier air advecting out of Canada is slowly
eating away at the cloud cover. This clearing will continue to
slowly advance southwestward across the forecast area through the
day, as the inverted trough is replaced by a narrow ridge of high
pressure advancing from the west and the March sun aids in mixing
out the lower levels of the atmosphere. However, given that
northerly flow off of Lake Ontario will persist throughout the day
across Western New York, expect ceilings to rise some, but cloud
cover to remain throughout the day. With that in mind, have lowered
forecast highs by a couple of degrees, with mid to upper 30s
expected across the bulk of the forecast area.

Tonight the axis of the aforementioned ridging will build directly overhead.
This will result in a dry and quiet night...with any leftover lower
clouds across the Southern Tier finally giving way to some partial
clearing, as northerly flow gives way to light southerly courtesy of
the ridging moving overhead. Expect overnight lows to exhibit a
decent gradient from east to west... with clearer skies allowing
readings to dip into the mid teens across the North Country...while
partly cloudy conditions will preclude readings from falling below
the mid 20s across the lake plains of far western New York.

&&

.SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/...
While `meteorological` Spring began several weeks ago (at the start
of this month)...it will officially kick off at 6:29 AM EDT as
we open this `Short Term` period. Unfortunately...any semblance
to Spring will be swept away by an arctic front as we push into
the middle of the week.

Mid level energy coming ashore in British Columbia this morning will
track across the Canadian Rockies this afternoon and tonight. This
feature will phase with an arctic shortwave that will dive south
from the Canadian Archipelago on Monday. The phased northern branch
will dig out a significant trough over eastern Canada Monday night
through Wednesday...one that will direct a chunk of arctic air
across Quebec. The fringes of this much colder airmass will clip our
forecast area...particularly across the Thousand Islands region
where the mercury will plunge to more than 20 deg f below normal.
The short lived change to mid winter weather will be marked by the
passage of an arctic front Tuesday night...with a burst of
moderately heavy snow possible in the process. As for the details...

A flattening ridge will pass over our forecast area on Monday...
while a weak cold front will approach from the west. While the bulk
of the day will be precipitation free...a slug of moisture and
marginal hgt falls in advance of the front could support some
scattered rain showers during the afternoon. For the first day of
Spring...temperatures will average within a degree or so of
normal...ranging from the mid 40s over the western counties to
around 40 east of Lake Ontario.

Surface based ridging will build across the region behind the front
Monday night. Given the light flow below 10k ft...clearing will be
slow to take place with clouds and spotty light rain or wet snow
showers remaining in place through a good portion of the night.

On Tuesday...the first of two fronts (possibly just a pre-frontal
trough) will push through our forecast area. It will not have much
moisture or synoptic forcing to work with...so am only anticipating
a swath of clouds to accompany its passage. All in all...this should
be a problem free weather day with only a minimal chance for a rain
or wet snow showers across the North Country. It will be a few
degrees cooler with highs ranging from 40-45 over the western
counties to the mid and upper 30s east of Lake Ontario.

It will then become a little interesting Tuesday night as an arctic
cold front will plow south across our region. A burst of snow
usually accompanies the passage of such fronts...and this one is not
expected to be any different. While the burst will only generate a
inch or so of snow for many areas...it could be moderately heavy
with greatly reduced visibility during its passage. Temperatures
across the region will drop into the teens away from the lakes...
with single digit readings possible in Lewis County.

On Wednesday...arctic high pressure will build southeast from the
Upper Great Lakes. H85 temps in the minus teens C will accompany
this feature...so temperatures are only expected to top out in the
20s for the afternoon. Parts of the North country may not make it
out of the teens. These readings will be 20 deg f below normal.
While the vast majority of the region will experience at least
partial sunshine with this arctic high...there could be some nuisance
lake snow showers southeast of lake Ontario. The synoptic
environment will be quite dry though with a relatively low cap...so
lake induced convection will be shallow. Late season diurnal mixing
will also work against an organized lake response...so snow
accumulations are not forecast to be significant.

The arctic high will pass over our forecast area on Wednesday night.
Given the cold airmass and forecast light winds and lack of cloud
cover...this should be 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 for the North Country and
good portion of the Srn Tier.

&&

.LONG TERM /THURSDAY THROUGH SATURDAY/...
Guidance has generally come into better agreement during this
period...thus confidence in the forecast has increased
significantly. This is especially the case for Thursday into Friday.

Starting with a general over view...we can anticipate moderating
temperatures during this period as a broad...progressive ridge
centered over the Mississippi Valley will push to the East Coast by
the weekend. Meanwhile...the arctic surface high that will be
responsible for the abnormally cold weather leading into this period
will be pushed out to sea. This will open the door for a strong
southerly flow of GOMEX air to make its way northward to the Lower
Great Lakes with temperatures Friday and Saturday climbing into the
50s for the western counties. As is so often the case...the warmth
will be accompanied by some rain showers...so there will be somewhat
of a price to pay for the more tolerable temperatures.

As far as the day to day details...the aforementioned arctic high
will move off to our southeast during the day Thursday. This will be
our sunniest day of the long term period...and with on going warm
advection taking place...we can expect temperatures to climb back
through the 30s over the western counties with some of the warmer
valleys tickling the 40 degree mark. It will be cooler across the
North Country where Thursday afternoon max temps will  be closer to
30.

The fair weather will gradually come to an end Thursday night
though...as a burgeoning baroclinic zone over the Great Lakes region
will support some snow showers over our western counties during the
second half of the night. Its not out of the question that it could
be warm enough aloft for the shower activity to include some rain as
well.

On Friday...the semblance of a warm front will gradually push to the
north across our forecast area. This will generate some snow showers
early...with the vast majority of the pcpn falling as rain during
the late morning into the afternoon. As the boundary pushes north to
Lake Ontario in the afternoon...it will become pleasantly mild
across the western counties that will be firmly within the warm
sector. The warmer weather will be fed by a 40-50kt southerly flow
between H925-85 that will make its way north from the western GOMEX.
Max temps on Friday will range form the lower 50s across the western
counties...and in particular across the Genesee Valley and valleys
of the Srn Tier...to the low to mid 40s east of Lake Ontario in the
vcnty of the warm frontal boundary.

As the ridge passes over our forecast area Friday night...the
majority of our forecast area will be deep within the warm sector.
While this should only mean a chance for a couple rain showers...
there are medium range ensembles that suggest a rainier night with a
cold frontal passage. Will lean more towards the ECMWF...which keeps
the bulk of our region in the warm sector and generally pcpn free.

Finally for Saturday...a cold frontal passage will generate more
widespread showers while sending our temperatures lower for the
second half of the weekend. Confidence in the timing of this fropa
though is relatively low.

&&

.AVIATION /15Z SUNDAY THROUGH THURSDAY/...
Satellite imagery and surface obs continue to indicate widespread
LIFR conditions across the Southern Tier this morning, with some
improvement to MVFR cigs indicated across lower elevations, aided by
diurnal mixing. Meanwhile, widespread clearing is ongoing across the
North Country, including KART, as drier air advects across the area
from Canada. This drier air will continue to erode cloud cover as it
slowly advances southwest through the day. However, most of Western
NY will likely remain under MVFR solid MVFR cigs, with improvement
from IFR to MVFR this afternoon in the Southern Tier, thanks to
persistent upslope northerly flow off of Lake Ontario and the
presence of a subsidence inversion that will aid in trapping the
moisture. Widespread improvement to VFR can be expected overnight as
high pressure moves overhead and northerly flow gives way to
southerly flow, allowing for downsloping to replace upslope
northerly flow.

Outlook...
Monday and Tuesday...VFR/MVFR with a chance of rain and/or snow showers.
Wednesday...Localized MVFR/IFR possible in scattered lake effect snow
showers southeast of the lakes...otherwise VFR.
Thursday...VFR.

&&

.MARINE...
High pressure building across the Lower Lakes region and northeastern
states will bring a period of tranquil conditions today and Monday...
before a freshening westerly flow out ahead of an approaching cold front
brings at least some potential for advisory-worthy winds and waves to
Lake Ontario on Tuesday.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...None.

&&

$$

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



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