Forecast Discussion

Forecast Discussion for BUF NWS Office
FXUS61 KBUF 200539

Area Forecast Discussion
National Weather Service Buffalo NY
139 AM EDT Sat Apr 20 2024

A trough will pass over the eastern Great Lakes Saturday with
scattered showers. A few of these showers may produce some small
hail or graupel. Dry weather will return Sunday through much of
Tuesday as high pressure builds east across the Ohio Valley and
Mid Atlantic. Cool temperatures and gusty winds this weekend
will give way to a warming trend early next week.


Composite radar shows a broken line of weak echos stretching
from northern New York to northern Ohio late tonight. This is
mainly mid-level moisture as it has been hard to find any
observed precip. This activity will move east and weaken
overnight with partial clearing across western NY to the Saint
Lawrence Valley by daybreak.

Saturday, a sharp mid level trough will move from the central Great
Lakes in the morning to western New England by evening, with a
strong vorticity maxima crossing the eastern Great Lakes in the
afternoon. An associated cold front will cross the region in the
afternoon. While forcing will be strong with this feature, it will
be moisture starved.

Cold air aloft will contribute to strong low/mid level lapse rates
with daytime heating and support diurnal showers from late morning
through early evening. Expect a classic lake breeze boundary and
stable lake shadow configuration to the showers Saturday. The most
concentrated band of showers will likely be from the Niagara
Frontier extending ESE into the western Finger Lakes where enhanced
and channeled WSW flow off Lake Erie converges with WNW flow found
just south of Lake Ontario. The cold air aloft and steep lapse rates
suggest a few of these showers may contain graupel or small hail,
even in the absence of thunder. Meanwhile, stable lake shadows over
and east of Lake Erie and Lake Ontario will keep shower chances
lower, and the amount of sunshine higher for areas east of the

Temperatures Saturday will run close to 10 degrees below average,
with highs ranging from the upper 40s for lower elevations to the
low to mid 40s across higher terrain. It will be quite breezy again
as well, with gusts of 25-35 mph across the area.


Broad mid-level troughing across the lower Great Lakes and the
Northeast Saturday night will allow a shortwave trough to round the
base of the trough Sunday. The passage of the shortwave will pull
the longwave trough northeast, allowing for mid-level ridging to
spread across the Great Lakes.

Despite the deep cyclonic flow overhead, expansive high pressure
centered over the Central Plains and expanding east across the Ohio
Valley will support mainly dry weather throughout the weekend into
the start of next week. However, with the passage of the shortwave
and the longwave trough axis aloft, a couple of moisture starved
cold fronts will push southwards across the region Saturday night
and then Sunday night. While both of these fronts will be
precipitation free, cold air will advect into the region supporting
below normal temperatures Sunday and Monday. Highs Sunday and Monday
will range in the 40s across the North Country and upper 40s to low
50s elsewhere.


Soggy weather will return to the forecast as we move further into
the workweek, with a cooler airmass wrapping back into the region
leading to a couple of days of temperatures running a few degrees
below normal.

High pressure will shrink off the eastern seaboard Tuesday as a
positively tilted shortwave pivots out south-central Canada and into
the northern Plains/upper Midwest region. As this feature moves east
into the Great Lakes region Tuesday night, it will partially phase
with a deeper closed low wobbling about the vicinity of Hudson Bay.
This will cause the southern trough to dig southward and
progressively become more negatively tilted as it marches east
though Wednesday. Concurrent broad surface cyclogenesis will lead to
an elongated area of low pressure that will extend from the Midwest
all the way northeast across Quebec. Deep southerly flow out ahead
of the system`s main cold front will allow it to tap into a plume of
GOMEX based moisture, with a subsequent wide swath of rain showers
plowing through the region Tuesday night into Wednesday. Cooler air
will filter into the region behind the system, though strong high
pressure building across the Great Lakes should taper off the
potential for wrap-around precipitation fairly quick. With the loss
of sunlight and cooler air moving in, rain could briefly mix with
wet snow across the Tug Hill Wednesday night before ending. Mainly
dry weather and clearer skies are then expected Wednesday night
through Friday.

Long range guidance can be fairly sensitive to these types of
partial phasing setups, which can quickly lead to poor model
consensus and large run-to-run jumps in projected solutions. In this
case, the latest from the ECMWF/CMCNH are in decent agreement are
less bullish on the amount of phasing between the northern and
southern stream waves, in stark contrast to the operational GFS
which has consistently been more aggressive in this regard. Have
leaned on the former which show a slower arrival time of precip
Tuesday afternoon and evening. Both operational models advertise
areawide dry weather until rain showers move into WNY after sunset,
though have stayed close to NBM and left Chc PoPs for Tue afternoon
as there remains uncertainty in the exact timing at this range. Less
phasing of the two systems also implies the deeper cold air staying
confined to the north in Canada, with just seasonable cool advection
in the wake of the system. Should this favored trend hold, the
already tenuous potential for wet snow on the backside of the system
will be minimized even more.

In regards to sfc temps...Tuesday should be on the mild side in the
upper 50s and low 60s as the area sits within the warm sector of the
incoming system. Wednesday through Thursday will then be much cooler
with highs in the upper 40s to low 50s. Owed to good radiational
cooling conditions, temps Wednesday night will be quite chilly,
bottoming out in the upper 20s to low 30s. High pressure moving east
of the region should then initiate a warming trend by late next


VFR conditions will prevail across western and north central NY
overnight. A brief shower or sprinkle is possible east of the
TAF sites through daybreak.

The boundary layer will become well mixed Saturday as an upper
level trough moves overhead. Diurnally driven rain showers will
form outside of the stable lake airmasses. A convergence zone
will likely set-up inland and south of Lake Ontario where the
medium confidence of scattered showers will be located, mainly
from KIAG/KBUF to KROC and eastward. Small hail may mix in with
some stronger showers around midday. Prevailing VFR conditions
are expected however ceilings will be between 030-050 ft
especially south of Lake Ontario. Showers will dissipate towards
evening with dry conditions Saturday night.


Monday...Mainly VFR.
Tuesday...Mainly VFR. A chance of showers later in the
Tuesday night and Wednesday...Areas of MVFR with showers.


Another trough will cross the eastern Great Lakes Saturday,
producing another round of solid westerly flow Small Craft
Advisory conditions on Lake Erie and Lake Ontario. Winds will
temporarily diminish again Saturday night, then increase again
Sunday with another period of solid westerly flow Small Craft
Advisory conditions on Lake Erie and Lake Ontario. Overall, a
poor weekend for boating with chilly temperatures, strong winds,
and high waves much of the time.


MARINE...Small Craft Advisory from 10 AM this morning to 8 PM EDT this
         evening for LEZ020.
         Small Craft Advisory from 7 AM this morning to 11 PM EDT
         this evening for LEZ040-041.



NEAR TERM...Apffel/Hitchcock/HSK

NWS BUF Office Area Forecast Discussion