Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 201528

Area Forecast Discussion
National Weather Service Buffalo NY
1128 AM EDT Mon Mar 20 2017

High pressure draped over our region will slide east into New England
today...allowing a weak cold front to cross the region tonight along
with a few rain and snow showers. A secondary arctic front will then
cross the region Tuesday night and usher in renewed chances for some
snow showers...while also sending temperatures plummeting back to mid-
winter levels for midweek. The return to much colder weather will be
brief a steady day-to-day warming trend will begin on
Thursday...and will eventually allow temperatures to climb to well
above average levels by the start of the upcoming weekend.


It will be a largely uneventful day across the region weather-wise,
as a narrow ridge of high pressure shifts across New York state. A
weak shortwave crossing eastern Ontario is generating a few limited
returns on radar that may result in a few flurries in the North
Country, but the bulk of any precipitation associated with this wave
will not even reach the ground. Otherwise, expect dry and cloudy
conditions across the area today as warm advection aloft and a
decent amount of low-level moisture will ensure a veil of clouds
will hang around throughout the day. Warm advection will help
temperatures climb into the low to mid 40s by late afternoon.

The main focus across this part of the country will be on an MCS
that is currently over SW Ohio. Guidance suggests that this system
will be replaced by a second MCS forecast to develop over NW OH this
afternoon as a mid-level trough crosses the region. This trough, a
pre-frontal trough extending across Ontario all the way into
northern Quebec, will cross our forecast area tonight. The bulk of
the guidance, with the exception of the GFS, keeps the MCS
associated with this trough south of our area, across PA/WV this
evening, which makes sense given the orientation of the thermal
fields across the region. As such, expect the trough passage to be
largely uneventful, with only a slight chance of showers tonight
across most areas, with the greatest chances being found across the
North Country, where synoptic forcing is slight better. Even  here,
we are only looking a a low chance of showers later tonight. With
little change in airmass and plenty of cloud cover hanging around,
look for temperatures to only fall about 10 degrees overnight, into
the low to mid 30s.


As is typical for this time of year...we will experience a roller
coaster ride of temperatures during this three day period. A
shortwave seen in WV imagery over the oilfields of Alberta this
morning will make its way across the Canadian Prairies this
afternoon while phasing with an arctic shortwave. This second
feature will be accompanied by a chunk of arctic air that had broken
loose from the notorious polar vortex over the weekend. In any
case...the combined efforts from the two shortwaves will dig a deep
trough over the Great Lakes and eastern Canada...with the core of the
coldest air crossing Quebec. The fringes of this airmass will clip
the Thousand Islands region...although all of our forecast area will
experience a shot of mid winter weather for a brief 24-36 hour

The good news is that the progressive pattern will not allow for the
cold air to really take up it will quickly exit
across the Labrador Sea during the second half of the week. This
will be followed by a significant warm up...courtesy of the next
main shortwave. The next feature was seen over the open Pacific...
south of the Aleutians this morning. This feature will help to carve
out a trough over California by mid week with significant ht rises
immediately taking shape downstream over the nations mid section.
The resulting broad ridge between the east and west coast troughs
will lead to the big warm up for our region that will take place
late in the week. This warming will be covered in more detail in the
long term section below.

As for the day to day details...Tuesday will be largely dry as an
arctic cold front will approach our region from southern Ontario.
The only area for unsettled weather will be east of Lake Ontario
where some light rain or wet snow showers could be generated by the
combined efforts of an upslope flow and the passing of vigorous
shortwave over northernmost New York. Otherwise...fair weather will
be accompanied by temperatures that should easily climb into the low
to mid 40s.

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 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. The cold air
will be made to feel even colder by gusty northwest winds that will
help to generate wind chill values in the single digits. Negative
single digit wind chills will be found east of Lake Ontario.

On Wednesday...arctic high pressure will build southeast from the
Upper Great Lakes. H85 temps as low as -20 C will accompany this temperatures are only expected to top out in the 20s F
for the afternoon. Parts of the North country may not make it out of
the teens. These readings will be roughly 20 deg f below normal.
While the vast majority of the region will experience at least
partial sunshine under the 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
lake induced convection will be shallow. Late season diurnal mixing
will also work against an organized lake snow
accumulations will NOT be significant.

Any clouds will clear out Wednesday night as the heart of the arctic
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 good portion of the Srn

While still on the cold side of `normal`...Thursday should be a
beautiful day across the region. The large surface high will
gradually drift away to our southeast...but not before supplying us
with mainly blue skies and light winds. It will not be
nearly as cold as warm advection aloft will already be busy
modifying our airmass. Afternoon temperatures are expected to 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.


There is high confidence that this will be a wet and unsettled
period across western and north central New York.

While the various medium range ensembles are in fairly close
agreement with the large scale pattern during this time frame...
they have some timing/placement issues with underlying surface particular a focusing east to west oriented frontal

Lets start with what we can `bank on` first. A closed mid level
storm system will emerge from the southern Rockies Thursday night
and will then drift across the central Plains on Friday. A broad
downstream ridge will cross the Ohio Valley and Great Lakes region
in the process. This will open up a deep southerly flow out of the
GOMEX with a plume of sub tropical moisture being directed towards
the Upper Great Lakes. Meanwhile at the surface...a baroclinic zone
will extend from the Upper Great Lakes across our forecast area.
This pseudo-warm front will gradually push north across our region
during the day Friday with the likelihood of showers. The showers
could initially be mixed with a little wet snow...but fairly strong
warm advection will quickly change any mix over to just rain. As the
front pushes north to Lake Ontario in the afternoon and evening...
the pcpn will taper off across the Southern Tier and Finger Lakes
regions. Temperatures within the warm sector (to the south of the
warm front) are forecast to climb into the lower 50s...with mid 50s
possible in some of the valleys. The mercury will not make it out of
the 40s east of Lake Ontario where the frontal boundary will become
stalled late in the day.

During the course of Friday night and Saturday...the closed low will
slowly make its way to the Upper Mississippi Valley. The mid level
ridge over the our region will then amplify a bit as it will become
increasingly pinched between the aforementioned closed low and a
deep digging trough over far eastern Quebec. This will keep a plume
of deep moisture streaming northwards from the GOMEX...although the
axis will shift east and will become focused over the Ohio Valley
and eventually our forecast area. This is the point where the
ensembles start to diverge on the placement of the increasingly
significant frontal boundary. The ECMWF solution appears to be more
realistic with stalling the boundary near Lake Ontario Friday night
and early Saturday...with only a slow southward push Saturday
afternoon. Other packages seem a little aggressive with the
southward push being supplied by a strong Canadian surface high near
James Bay. Will lean more on the ECMWF solution...which depicts
fairly widespread rain showers that will be focused across the North
Country and over counties lining the south shore of Lake Ontario.

The closed low will drift to the Mid West Saturday night and Sunday.
Again the ensembles differ on the speed at which the surface
boundary will push south...with the bulk of the GEFS ensembles being
the fastest. Will again differ to the ECMWF which is slower and more
realistic looking (as per the placement of the ridge). This being
said...the sfc boundary will push south across the region saturday
night and Sunday with widespread rain anticipated. Colder air
working into the moist environment could change some of the pcpn
over to some wet snow.

Despite all of the pcpn...the good news is that it will be
relatively mild for the bulk of this period. Temperatures over the
western counties...being in the warm sector for much of Friday and
Saturday...should be able to make it into the 50s. In the wake of
the slow moving sfc will cool on sunday with max temps
forecast to be within a a few degrees of 40. For all three days...
readings east of Lake Ontario will average some 5 degrees lower.


Low clouds and associated IFR conditions continue to plague the
North Country this morning as a stubborn pool of low level moisture
remains in place across the area. This low level moisture should mix
out this afternoon as surface temperatures warm, with improvement
expected around 18Z. Elsewhere, expect VFR cigs to persist through
the forecast period as mid-level clouds overspread the area under
warm advection aloft ahead of an approaching trough. This trough
will cross the area tonight, with little impact precipitation-wise
as the bulk of the moisture will be taken up by an MCS passing to
our south across OH/PA/WV this afternoon/evening. However, enough
shallow low-level moisture may still make it in to lower cigs to
MVFR overnight, with IFR possible in the Southern Tier.

Tuesday...Improvement to VFR...with a chance of snow and rain showers
east of Lake Ontario.
Tuesday Night and Wednesday...Localized MVFR/IFR possible in mainly
scattered snow showers southeast of the lakes...otherwise VFR.
Friday...MVFR/IFR with snow showers changing over to rain showers.


Expect relatively tranquil conditions to persist across the Lower Great
Lakes through tonight as high pressure slowly departs to our east...and
a very weak cold front crosses our region. Westerlies will then freshen
across Lake Ontario in advance of an approaching arctic front on Tuesday...
with fresh northwesterlies to northerlies then overspreading the entire
region in the wake of the arctic front Tuesday night and Wednesday. This
should eventually necessitate another round of small craft advisories
Tuesday into Wednesday...before strong high pressure builds across the
region Wednesday night and Thursday and brings a return to calmer





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