Forecast Discussion

Forecast Discussion for BUF NWS Office
FXUS61 KBUF 181929

Area Forecast Discussion
National Weather Service Buffalo NY
329 PM EDT Sun Apr 18 2021

Scattered shower activity this afternoon will diminish by this
evening as weak high pressure brings mainly dry weather through
Monday. A few passing weak disturbances aloft may produce a few
light, isolated showers at times. Temperatures will continue to
slowly warm through Monday. More significant weather, including the
possibility for some wintry precipitation, will then return by
midweek as a cold front and low pressure cross the region.
Unseasonably cold air will move back into our area for the second
half of this week behind this system.


Mid level ridge and weak surface high continues to expand into the
eastern Lake Ontario region this afternoon. However, diurnal heating
and relatively cool temperatures aloft have allowed scattered
showers to form over inland locations away from the immediate lake
shadow southeast of Lake Ontario. Showers also developing inland
over Canada will move across the Niagara Peninsula and may impact
Western NY later this afternoon. Otherwise, subsidence beneath the
mid level ridge should generally keep shower activity light.
Temperatures will continue their slow recovery, with highs in the
mid to upper 50s in most areas, cooler along the Lake Erie and Lake
Ontario shore.

A weakening mid level shortwave will move northeast out of the Ohio
Valley into Pennsylvania. Weak forcing and just enough available
moisture may be enough to spark off a few scattered showers across
northern PA, with possibly a stray shower getting into far inland
portions of the western Southern Tier toward the NY/PA line. Low
temperatures tonight will range from the mid 30s to the lower 40s.

Warm air advection ahead of a front dropping into the northern Great
Lakes will aid in boosting temperatures Monday into the upper 50s to
mid 60s, likely making it the warmest day of the week. Weak
shortwave crossing the area could touch off a few afternoon showers,
but otherwise expecting Monday to remain mostly dry.


A sharp mid level trough and associated surface low will move from
the upper Great Lakes Monday night to Quebec Tuesday, with a
trailing cold front crossing the eastern Great Lakes. Cooler air
will filter into our region late Monday night and Tuesday behind the
cold front. The stronger synoptic scale forcing will pass well north
of the area, with forcing and moisture along the trailing cold front
diminishing with time and southeastern extent. The front may produce
a few light showers Monday night through the first half of Tuesday,
with the greatest chance close to the Canadian border and the lowest
chance near the PA state line. Most of the showers should end
Tuesday afternoon as the front lays out parallel to the mid level

Our attention then turns to another strong mid level trough, digging
into the Upper Midwest Tuesday night before reaching the Ohio Valley
and eastern Great Lakes later Wednesday. A strong baroclinic wave
will develop along the frontal zone in response to increasing
forcing and flow adjustments downstream of the mid level trough,
with the resulting surface low running down the boundary from the
Ohio Valley Tuesday night to eastern NY by Wednesday afternoon.
Strong frontogenesis and differential temperature advection on the
cold side of the surface boundary will support widespread
precipitation later Tuesday night through the first half of
Wednesday over the eastern Great Lakes.

While the large scale pattern is well agreed upon, the precise
details of frontal position and low track will be critical in terms
of the surface temperatures, thermal profiles, and snow potential.
Model guidance has shown a good deal of run to run changes on these
details, not atypical for an event still 3 days out. A swath of
accumulating snow will almost certainly occur to the northwest of
the low track, but model guidance has varied on placement of this
from over western and north central NY to north of Lake Ontario
mainly on the Canadian side of the border. There may be a narrow
ribbon of sleet and freezing rain as well in the transition zone
between rain and snow.

For this cycle, trended the forecast quite a bit colder for later
Tuesday night and Wednesday with a rain/snow mix through that time
frame, especially in areas close to the Canadian border. The current
forecast represents a solution a little farther north and warmer
than the 12Z GFS/ECMWF/GEM to blend in some previous, farther north
model runs. It should also be noted that past history shows this
type of system has a propensity to track farther north and west than
model guidance would suggest several days out. The range of
potential outcomes runs from very little snow at all to
accumulating, impactful snow for late Tuesday night and Wednesday.
Stay Tuned.

Wednesday night cold air will pour into the eastern Great Lakes
behind this system, with wrap around scattered snow showers
areawide. The airmass will grow cold enough for lake effect snow
showers southeast of Lakes Erie and Ontario later Wednesday night.


As the surface low departs northeast out of the area, another
shortwave will pass through the now upper level closed low, which
will interact with the leftover wrap around moisture Thursday to
continue to support the lake enhanced showers snow showers in the
early morning before switching to all rain due to the addition of
sun for places across the Finger Lakes region and to its east. While
a much colder air mass overhead would typically support colder
temperatures (to the tune of near freezing), thanks to the higher
sun angle this time of year high temperatures will warm up into the
low to mid 40s.

Upper level ridging late Thursday night through Friday night will
promote mainly dry conditions. Looking into the weekend, a shortwave
attached to the next incoming upper level trough may roll through
supporting a frontal boundary to approach and eventually cross the
area sometime Saturday or Sunday. However, this far out the model
guidance is in disagreement with timing of the feature with both the
ECMWF and the Canadian guidances slower to bring the boundary
through. Therefore, have chances for rain showers Saturday through
Sunday. Otherwise, upper level ridging will help advect warm air
back into the region, rebounding temperatures into the 50s for the
end of the work week and weekend.


Mainly VFR conditions as mid-level deck of diurnal cumulus continues
to develop across much of the area through this afternoon. Radar
imagery indicating scattered showers across the area away from the
lake shadow southeast of Lake Ontario. Shower activity looks to be a
greater concern for far western terminals this afternoon,
particularly KIAG and KBUF. CIGS may briefly lower to MVFR in any
passing showers. Quieter conditions with continued VFR conditions
expected moving into this evening, with a passing mid-level deck
from time to time.


Monday...Mainly VFR.
Tuesday...MVFR to VFR with a chance of showers.
Tuesday Night and Wednesday...IFR/MVFR with rain showers becoming
Thursday...MVFR/IFR with scattered snow showers and some lake effect
snow showers east of the lakes. Windy.


Southwest winds around 10 knots on Lake Erie and 10-15 knots on Lake
Ontario will continue to produce some light to moderate chop today.
In any case though, winds and waves will remain below Small Craft
Advisory criteria. Winds will then diminish tonight, with generally
light southwest winds on Monday, freshening a bit Monday afternoon
on Lake Erie and western Lake Ontario.





SHORT TERM...Hitchcock

NWS BUF Office Area Forecast Discussion