Area Forecast Discussion
Issued by NWS Buffalo, NY
FXUS61 KBUF 211906
Area Forecast Discussion
National Weather Service Buffalo NY
306 PM EDT Tue Mar 21 2017
A weak ridge of high pressure over western NY late this afternoon
will keep mainly fair conditions in place until later this evening.
Then an arctic frontal boundary, accompanied by scattered snow
showers, will move across the region ushering in much colder
temperatures and some lingering lake effect snow showers through
Wednesday morning. 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
.NEAR TERM /THROUGH WEDNESDAY/...
Quiescent conditions across western and north central NY late this
afternoon under a weak ridge of high pressure will give way to an
influx of much colder air and scattered snow showers later this
evening. First, ahead of the arctic frontal boundary, a pre-frontal
boundary / gravity wave feature has developed a line of showers
north of Lake Ontario across Ontario and southern Quebec provinces.
As this feature tracks eastward, the southern end of the line may
spark off some scattered rain/graupel/snow showers in the North
Country between 22 to 00Z.
Otherwise our attention turns to the main arctic cold front
boundary, which can easily be picked out in surface observations,
satellite imagery across northern Michigan and Ontario province. In
the wake of the frontal passage, temperatures are dropping from the
30s/40s to the teens/20s across upper Michigan and Ontario.
Convective snow showers associated with steep lapse rates under the
upper-level low are also being enhanced by lake induced instability
over the upper-Great Lakes with numerous streamers developing off
Lake Superior. This trend will continue into western and north
central NY later this evening as the boundary crosses the region.
Have maintained scattered snow shower wording in the forecast as
upstream data supports a broken line of snow showers moving through
with the front, then scattered lake effect snow showers lingering
southeast of Lakes Erie and Ontario behind the front overnight.
Highest PoPs are positioned southeast of the Lakes where added lake
moisture and instability will make snow showers and light
accumulations more likely. Regarding snow accumulations, expect
these will be very light, on the order of a coating to an inch or
two in the most persistent lake streamers overnight. The main reason
for such limited amounts will be the very dry nature of the arctic
airmass, combined with a the shorter/non-ideal northwest to
southeast fetch across the lower Great Lakes. Temperatures by
Wednesday morning will bottom out in the teens, with even some
single digits in the north country. It will be a rude awakening for
most as you head out the door Wednesday morning when factoring in
the wind chill, it will feel like near 0F across western NY and 5 to
10 BELOW zero in the North Country.
Temperatures will recover little through the day on Wednesday, as
arctic high pressure builds in across the region. Lingering lake
effect snow showers will fizzle out as the capping inversion lowers,
along with diurnal effects and a very dry airmass. There will be
some breaks to more sunshine by the afternoon, however with 850 mb
temps -teens to -20, highs will only be in the 20s for most
.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/...
Western and North-Central New York will enjoy a period of fair and
tranquil weather from Wednesday evening through Thursday afternoon,
as an expansive arctic high passes over the region. Clear skies and
light winds Wednesday night will promote widespread radiational
cooling, and given the residual cold and dry air in place across the
region, temperatures will plunge into the single digits across the
Southern Tier and potentially below zero in the North Country, with
low teens along the lake plains. These will likely be the coldest
readings we will encounter until next winter, as temperatures will
rebound into spring by the end of the week. Temperatures on Thursday
will remain slightly below average, as the last vestiges of Arctic
air make their way east as the center of the high moves to the
Increasing return flow will advect increasingly warm and moist air
northwards into the Great Lakes starting Thursday night. This will
lead to increasing clouds and a much milder night Thursday night,
relatively speaking, with lows ranging from the lower 20s in the
North Country to just below freezing across far western New York.
With this increasing warm advection, we will start to see
precipitation develop across the forecast area Thursday night into
early Friday morning from west to east, as isentropic uplift and
DPVA aloft increases across the area. With temperatures still below
freezing, there will be a risk for snow and/or mixed precipitation
before temperatures warm above freezing later in the night and
precipitation changes over to rain.
By the time we move into Friday, warm advection will be in full
force across the region, with increasing baroclinicity and
frontogenesis across the Great Lakes and upper Midwest as warm air
surges northwards across the region while anticyclonic flow around
high pressure over northern Manitoba brings cold and dry air south
towards the Great Lakes. This, in addition to deformation along the
emerging boundary, will lead to the development of widespread,
persistent, and occasionally heavy rainfall across the region and
the forecast area starting Friday and lasting through much of the
weekend. While precipitation will be all rain during the day on
Friday, as temperatures should range from near 50 in Western NY to
around 40 in the North Country, given the aforementioned baroclinic
gradient that will be in place across the region, temperatures in
the North Country, and in the Saint Lawrence valley in particular,
will be close enough to freezing Friday night to maintain a concern
for a changeover back to mixed precipitation overnight.
.LONG TERM /SATURDAY THROUGH TUESDAY/...
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
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 /19Z TUESDAY THROUGH SUNDAY/...
In the wake of a weak cold frontal passage...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
Wednesday...Scattered snow showers/flurries and associated MVFR
southeast of the lakes dissipating...otherwise VFR.
Friday...Deterioration to MVFR/IFR with mixed rain and snow
developing...then changing over to all rain.
Saturday and Sunday...MVFR/IFR with rain likely.
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
After that...strong high pressure will build across the region
later Wednesday through Thursday while bringing a return to
light winds and negligible waves.
MARINE...Small Craft Advisory from 8 PM this evening to 2 PM EDT
Wednesday for LEZ040-041.
Small Craft Advisory until 2 PM EDT Wednesday for
Small Craft Advisory until 2 AM EDT Thursday for LOZ043-
Small Craft Advisory until 5 PM EDT Wednesday for LOZ042.
Small Craft Advisory from 8 PM this evening to 5 PM EDT
Wednesday for LOZ045.