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Area forecast discussion
National Weather Service Buffalo New York
442 PM EDT Mon Oct 21 2019

widespread rainfall will arrive across the lower lakes late tonight
into Tuesday as a cold front slowly tracks east into and across the
region. Cooler, with some lake effect rain showers northeast of both
lakes on Wednesday. More unsettled weather for the latter half of
the week. High pressure over the Ohio Valley then builds into the
lower lakes with dry weather expected over the weekend.


Near term /through Tuesday/...
it was a spectacular day and fine weather will continue into
this evening. Temperatures late this afternoon are in the 60s to
near 70f and will gradually drop through this evening. Enjoy
this weather because it's about to come to an end. Our next
weather maker is sitting just to the west of the upper
Mississippi Valley with its trailing front moving east which
will influence our region beginning later tonight.

Speaking of which, the extremely large low to the west of the upper
Mississippi Valley will head towards the upper Great Lakes and arrive
over Lake Superior Tuesday. It will then send its trailing cold
front ever so slowly east from lower Michigan across Lake Erie
tonight. Ahead of this front, a 40-45kt low level jet will be found at ~925mb
or 2k feet aloft, right near the top of a fairly strong inversion.
While this magnitude of a low level jet 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 low level jet and with trees still bearing their foliage with
winds possibly exceeding 45 mph that some trees could come down. So
a Wind Advisory was issued and GOES into effect from 00z to 10z

Temperature wise, it will be a mild night given the expected cloud
cover and elevated wind. With that said, lows should occur fairly
early and following a non-diurnal temperature trend. Possibly even
rising overnight. Otherwise, look for temperatures to briefly fall
back into the 50s to low 60s across western New York. For our eastern
locations, it will be a bit cooler across the north country with
temperatures generally found in the lower 50s.

The cold front is forecast to slowly push into western New York 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 quantitative precipitation forecast
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. Otherwise, with the passage of the front the steady
precipitation will taper off fairly quickly across western New York then
expect mainly some residual scattered showers behind the front.
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.

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


Short term /Tuesday night through Thursday/...
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 New York
as this cooler air begins to arrive. Eventually, 850 mb 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 850 mb-700 mb 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 New York 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 New York dry while GFS and European model (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


Long term /Thursday night through Monday/...
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
European model (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 European model (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 European model (ecmwf) and Gem, have continued with
chance probability of precipitation Sunday and Sunday night. This system should be moving
east of the area by Monday, with drier and somewhat warmer weather


Aviation /21z Monday through Saturday/...
VFR area wide late this afternoon which will continue into this
evening. The largest concern during this taf period will be the
onset of low level wind shear tonight. A southerly 40-45kt low
level jet combined with a southeast flow at the surface will
potentially produce wind shear conditions. Additionally, ceilings
will likely remain at VFR levels for a majority of the night
before MVFR/IFR ceilings develop first across parts of the southern
tier just before daybreak.

Tuesday, the large low over the upper Great Lakes will send its cold
front across the forecast area with ceilings deteriorating to MVFR/IFR
conditions across area terminals along with lower visibilities.

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.


gusty south to southeast winds ahead of approaching cold front have
resulted in Small Craft Advisory conditions on portions of Lake
Ontario and along East Shore of 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


Buf watches/warnings/advisories...
New York...Wind Advisory from 8 PM this evening to 8 am EDT Tuesday for
Marine...Small Craft Advisory from 8 PM this evening to 11 am EDT
Tuesday for lez040-041.
Small Craft Advisory from 2 am to 5 PM EDT Tuesday
for loz045.
Small Craft Advisory until 11 PM EDT this evening for



near term...AR/apffel

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