Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 220221

Area Forecast Discussion
National Weather Service Buffalo NY
1021 PM EDT Mon Oct 21 2019

Widespread rainfall will reach far western New York late tonight
and move across the region Tuesday as a cold front slowly moves
through. Tuesday night and Wednesday will be cooler with some
lake effect rain showers northeast of the lakes. There will be more
unsettled weather for the latter half of the week, followed by
high pressure and dry weather over the weekend.


Dry weather will continue late this evening with the 00Z Buffalo
sounding showing lots of dry air in the low levels which will
take some time to saturate. Temperatures will remain steady (or
even rise) across much of western New York due to a
southeasterly breeze which will downslope and keep the boundary
layer mixed. There may be some limited radiational cooling east
of Lake Ontario where winds are still light, but winds will pick
up here too shortly after midnight with the approach of a
frontal system.

The next weather maker is a vertically stacked system sitting
across the Upper Mississippi Valley. This system will slowly
track across Lake Superior through Tuesday, with a LLJ and front
extending from this system moving across our region. Its
trailing cold front will ever so slowly move east from lower
Michigan across Lake Erie tonight. Ahead of this front, a
40-45kt LLJ will be found at ~925mb or 2k feet aloft, right near
the top of a fairly strong inversion. While this magnitude of a
LLJ may not seem overly alarming its important to remember the
surface wind flow and the presence of an inversion. The current
forecast is for a south to southeast wind flow which isn`t the
most favorable direction for a typical down sloping wind event
off the Chautauqua ridge. However, it is just enough of a LLJ
and with trees still bearing their foliage with winds possibly
exceeding 45 mph that some trees could come down. A wind
advisory remains in effect for Chautauqua county tonight.

The cold front is forecast to slowly push into Western NY early
Tuesday. Low level convergence along the front will lead to a period
of widespread light to moderate rainfall pushing across the area
during the day Tuesday. It appears per latest guidance, basin
average rainfall amounts have trended a bit downwards, at least for
point west of the Finger Lakes. With that said, have lowered QPF
amounts to average between a third up to half an inch. However,
further east as the front crosses the Finger Lakes region a wave
riding along this boundary will enhance precipitation amounts from
the Finger Lakes into the North Country. Look for basin average
precipitation on the order of half an inch up to an inch for this
region. QPF aside, the large scale forcing provide high
confidence in measurable precipitation at all locations, with
at least several hours of rain expected.

Precipitation will taper off quickly behind the front, resulting
in mainly dry weather for far Western NY late Tuesday afternoon.
Further east, rainfall will continue into the early evening
hours for our far eastern zones. Otherwise, behind the front it
will start to turn cooler as a much cooler air mass filters in
with H850T falling to +2/3C by Tuesday night. Some scattered
lake enhanced rain showers will develop northeast of Lake Erie
toward sunset.

Highs on Tuesday will not be all that much different from overnight
lows with upper 50s to lower 60s across the forecast area.


Vertically stacked and occluding upper low just north of Lake
Superior in northern Ontario remains nearly stationary from Tuesday
night into Wednesday morning. As widespread rain over mainly the
eastern Lake Ontario region diminishes later Tuesday evening,
gradually cooler air will advect over the Lower Great Lakes on sw
low-level flow. There could also be some scattered showers that
sweep across Lake Ontario into the northern portions of western NY
as this cooler air begins to arrive. Eventually, H85 temps drop to
around 0 to -1C by daybreak Wednesday before slowly moderating by
Wednesday night. Though there is secondary shortwave rotating south
and west of Lower Great Lakes later Tuesday night through Wednesday
morning, synoptic moisture only slightly improves compared to the
limited deep moisture that we`ll start off with on Tuesday night on
back side of dry slot in wake of the cold front that moves through.

In terms of lake effect, net result is little additional forcing and
moisture for lake responses downstream of Lake Erie and Lake Ontario
Tuesday night into Wednesday. Certainly, unidirectional sw flow in
the lake convective layer is favorable for development as we`ll get
everything the lakes have to offer in terms of persistent fetch and
moistening, but even so, model soundings at end of the fetch of sw
winds at BUF and ART only show the inversion rising up to 6-8kft and
lake equilibrium levels reaching only around 10 kft. In comparison,
the lake event last week had inversions more in the neighborhood of
8-10 kft and lake equilibrium levels more in the 15-20kft. Likely
pops still seem reasonable vcnty of Buffalo and over much of
Jefferson county, but total qpf late Tuesday night through Wednesday
looks light, probably coming in under 0.25 inch. Suppose we could
see slight uptick in the lake response over eastern Lake Ontario
region Wednesday afternoon as edge of deeper moisture tied to
primary upper low over Ontario slowly edges across Quebec. Even
though the lake effect on Wednesday looks light, that is not to say
where the lake effect is ongoing it will be a pleasant day by any
stretch as the light rain showers will be blown about by 15-25 mph
winds while temps stay in the mid 40s to near 50F. Elsewhere without
the additional synoptic lift and moisture, it will just be mostly
cloudy from cold advection stratocu with less wind and temps
reaching into the low or maybe mid 50s if we get more breaks in the
cloud cover in the afternoon.

Upper low center remains over northern Ontario and Hudson Bay
Wednesday night into Thursday, but H85-H7 trough axis shifting more
toward Atlantic Canada should bring drier weather to the region at
least on Wednesday night. Weak shortwave rotating west to east on
southern periphery of primary upper level trough along with another
cold front could bring some showers back into western NY Thursday.
Larger scale features are weaker though and more subtle, so there
are model differences in that idea, with outer reaches of the NAM
run keeping all of NY dry while GFS and ECMWF are most aggressive in
bringing qpf back into the fold, as early as Thursday morning. GEM
is more of a compromise solution, mainly favoring Thursday afternoon.
Will keep some pops in there, but with the lack of agreement, will
also keep them on the lower side. Looks like a mostly cloudy day as
even leaning toward drier idea from the NAM, there looks to be good
deal of mid clouds. After the cooler conditions on Wednesday, temps
on Thursday will return above normal, in the upper 50s to around 60F
with even lower or middle 60s possible from the Genesee River valley


Friday and Friday night a mid level trough will swing from the Great
Lakes into Quebec, de-amplifying with time. Meanwhile at the
surface, a baroclinic wave will develop along a stalled frontal zone
over the Ohio Valley in response to large scale forcing and
ageostrophic flow adjustments from the passing mid level trough. The
ensuing wave will pass over or just southeast of our area, bringing
a chance of showers Friday and Friday evening. The GFS is most
aggressive and well developed with the baroclinic wave, while the
ECMWF and GEM are weaker.

Behind this wave, a very modest lake response may develop east and
southeast of the lakes late Friday night and Saturday as colder air
moves into the eastern Great Lakes. 850mb temps get down to -3C to
-5C depending on model of choice. If this were to verify it may
allow a few wet snowflakes to mix in across the highest terrain late
Friday night. Given the marginal nature of the setup however, kept
the precip type all rain for now. The limited lake response will end
later Saturday afternoon as surface high pressure and associated dry
air move into the eastern Great Lakes.

Medium range guidance diverges significantly Sunday and Sunday
night. The ECMWF and GEM bring a substantial southern stream system
through the Ohio Valley Sunday and the eastern Great Lakes Sunday
night, spreading clouds and showers back into our region. The 12Z
GFS keeps this system suppressed over the deep southeast states.
Given the consensus between the ECMWF and GEM, have continued with
chance POPS Sunday and Sunday night. This system should be moving
east of the area by Monday, with drier and somewhat warmer weather


VFR conditions will continue through 06Z. A southerly 40-45kt
low level jet combined with a southeast flow at the surface will
result in low level wind shear overnight. Rain and low level
moisture will gradually spread into the region from west to east
late tonight and into Tuesday. Downsloping in the southerly
flow will keep CIGS in the MVFR or higher flight category for
most locations. The exception is across the Southern Tier
(including KJHW) where higher terrain and thus a lack of
downsloping will result in IFR cigs and possibly some fog.

Rain will end from west to east and conditions will gradually
improve to VFR across far Western New York (KBUF/KIAG/KJHW)
after 18Z Tuesday afternoon. Rain and MVFR cigs will last
through the afternoon hours at KROC/KART.

Tuesday night...MVFR/IFR within showers.
Wednesday...MVFR to VFR with scattered lake
effect rain showers northeast of Lakes Erie and Ontario.
Friday...MVFR/VFR with showers.


An easterly flow across Lake Ontario will shift to the southeast
overnight, but with waves still up to 5 feet across western
portions will maintain Small Craft headlines through 2 a.m.
Otherwise, gusty south to southeast winds ahead of approaching
cold front will support Small Craft Advisory headlines on
eastern portions of Lake Ontario and Lake Erie through Tuesday.
Once the cold front crosses and winds turn to the southwest,
expect more Small Craft Advisories to be needed over most of our
marine zones on both Lake Erie and Lake Ontario Tuesday night
through Wednesday evening. For Lake Erie, strongest winds,
gusting to around gale force, and highest waves behind the cold
front will occur late Tuesday night through most of Wednesday.
On Lake Ontario, worst conditions occur Wednesday afternoon into
Wednesday evening. Expect winds and waves to diminish steadily
Thursday on into the upcoming weekend as pressure gradient


NY...Wind Advisory until 8 AM EDT Tuesday for NYZ019.
MARINE...Small Craft Advisory until 11 AM EDT Tuesday for LEZ040-041.
         Small Craft Advisory from 2 AM to 5 PM EDT Tuesday
         for LOZ045.
         Small Craft Advisory until 2 AM EDT Tuesday for LOZ042.



LONG TERM...Hitchcock
MARINE...Apffel/JLA is the U.S. government's official web portal to all federal, state and local government web resources and services.