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135
FXUS61 KBUF 132100
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
500 PM EDT Sun Oct 13 2019

.SYNOPSIS...
An upper level low will bring moisture and cooler air across our
region tonight and Monday, resulting in narrow bands of lake
effect rain to the northeast and then east of the Great Lakes.
It will generally be quiet Monday night and Tuesday with high
pressure nearby before a strong area of low pressure brings
gusty winds, rain and possibly thunder mid-week.

&&

.NEAR TERM /THROUGH MONDAY/...
Surface high pressure continuing to slide off to our east this
afternoon. Deep occluded low over Lake Superior with surface cold
front arcing down through lower Michigan. The remainder of the
afternoon into this evening will continue to feature mainly clear
skies, before clouds start to work into our area early tonight.

The deep low over the northern Great lakes will slowly rotate
into Ontario tonight with the surface cold front starting to
impinge on the area by around 06z. Moist cyclonic flow and a
developing favorable over-water thermal regime with 850 mb
temperatures dropping to near 0C will result in a band of lake
effect rain, which will be enhanced along the incoming surface
boundary. Uniform south-southwest flow through about 10kft will
initially set up the band of lake effect rain off Lake Erie near
Niagara county around midnight or so, then we will see the band
becoming more organized as it slowly shifts to the south as the
low level flow veers westerly behind the passage of the cold
front.

By Monday morning, the band of lake effect rain off Lake
Erie will extend along the shoreline inland across the Buffalo
southtowns into Wyoming county. The later arrival of colder air
and surface front will delay the development of the lake induced
rain to the northeast of Lake Ontario, but should be getting
underway by early Monday morning.

The area is expected to remain firmly under the influence of
mid level low pressure and attendant moist cyclonic flow right
through the day Monday, as the low is expected to move very
slowly to the northeast only reaching the vicinity of James Bay
by Monday afternoon. 850 mb temperatures continuing to cool to
near -2C will maintain favorable over-lake instability although
incoming drier air and diurnal effects will gradually weaken
the lake effect rain bands during the afternoon.

Temperatures on Monday will be rather chilly only reach into
the lower to mid 50s, with a few upper 40s across higher
terrain. A brisk west wind will make these readings feel even
cooler.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/...
Monday night and Tuesday surface high pressure will move east from
the Ohio Valley to the Mid Atlantic. Subsidence and dry air
extending north of the surface high will bring dry conditions to the
majority of the area outside of lake effect areas. It will turn
quite chilly away from the lake effect clouds, with lows in the mid
to upper 30s away from the immediate lakeshores with some frost
possible from the Niagara Frontier eastward across the Genesee
Valley. Meanwhile lake effect clouds should prevent frost across
most of the western Southern Tier and across Oswego County.

Meanwhile, a westerly flow with 850mb temps around -2C will support
a marginal lake effect setup, with lake induced equilibrium levels
slowly falling from about 9K feet to 7K feet Monday night and early
Tuesday morning. Off Lake Erie, expect a few scattered light showers
or drizzle to persist Monday night across the western Southern Tier
with light rainfall amounts. Off Lake Ontario, a few scattered
showers across the Tug Hill in the evening will drift a little
farther south into Oswego County overnight. A weak band of rain
showers will then remain across Oswego County through early Tuesday
morning before rapidly moving out into the lake and dissipating as
boundary layer flow turns southerly late Tuesday morning. Rainfall
amounts should be fairly light in this band, up to a tenth of an
inch or so given the marginal synoptic scale moisture and relatively
shallow inversion heights.

Once the lake effect rain ends southeast of Lake Ontario, the rest
of Tuesday will be dry with a good deal of sunshine filtering
through a modest increase in cirrus level clouds. Temperatures will
be close to average, with highs around 60 at lower elevations across
Western NY, with mid 50s higher terrain and North Country.

Late tuesday night and Wednesday our attention turns to the most
significant system of the week. A sharp mid level trough will move
east across the Great Lakes, with an associated deep surface low
moving across lower Michigan Tuesday night before reaching Georgian
Bay Wednesday. A trailing cold front will sweep east across the area
Wednesday.

12Z model guidance has trended just a few hours slower, which will
keep the majority of Tuesday night dry with showers arriving towards
daybreak Wednesday across Western NY. The majority of the rain will
fall in a 2-4 hour window just ahead of the cold front Wednesday.
Strong DPVA ahead of the mid level trough, increasingly diffluent
mid/upper level flow, and strong moisture transport/convergence in
the low levels supported by a 50+ knot low level jet will produce
widespread showers, a few of which could be briefly heavy. Model
guidance suggests a solid 0.50-0.75" of rain with this front.
Instability is limited, but the very strong forcing may be enough to
support a broken band of low topped thunderstorms along the cold
front. If these materialize, they may pose a risk of locally strong
wind gusts given the very strong flow aloft.

The track of the moderately deep surface low to our north and west
fits the pattern recognition for strong post-frontal winds in our
area. Low level lapse rates will steepen in the cold advection
regime behind the cold front, and southwest winds will channel
favorably down Lake Erie. Winds aloft behind the cold front are not
terribly strong however, in the 40-45 knot range a few thousand feet
off the deck. This may support wind advisory gusts in the typical
locations along the Lake Erie shore and extending northeast across
the Niagara Frontier to near Rochester.

There will be a brief break in the rain following the cold front.
Later Wednesday afternoon and Wednesday night deeper wrap around
moisture will arrive as the strong mid level closed low crosses the
eastern Great Lakes and heads into New England. The wrap around
moisture and forcing from the mid level trough will produce a few
scattered showers Wednesday night. More importantly, deepening cold
air will support growing lake induced instability. Flow may be
sheared initially, but should align better from the WNW later
Wednesday night as lake induced equilibrium levels rise to 15-20K
feet. This will support a robust lake response east and southeast of
the lakes, with rain showers becoming widespread. Deep moisture and
lift extending up through the graupel growth zone may support some
thunder as well.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
The upper level pattern will prove to be quite interesting during
this period. While a robust but progressive shortwave trough moving
through the Lower Great Lakes will support the most widespread lake
effect precipitation of the young cool weather season...a persistent
150 to as high as 175kt East Asian jet screaming across the open
north Pacific will set the stage for more Indian summer weather. As
for the day to day details...

A stacked storm system centered over New England for much of
Thursday will produce a deep cyclonic flow of chilly air over the
Lower Great Lakes. This will continue to support a fairly strong
lake response...with lake to cloud base delta t values averaging 15
deg c. Fortunately...H85 temps of zero to -2c will not be low enough
to support any snow...but the resulting lake driven convection could
include some heavier rain showers. Given the height of the -10c
isotherm (most likely region for graupel) and depth of the
corresponding mixed phase region...the heavier showers could be
electrified. Will add some lightning to these areas...which will be
mainly focused southeast of Lake Erie and especially southeast of
Lake Ontario. This whole scenario is about six hours delayed from
earlier forecasts... but aligns well with lower sheared environment
in deepening west to northwest flow. Otherwise...it will be a poor
day to be out and about as a gusty northwest wind and fairly
widespread lake driven rain showers within the ongoing cold
advection will prevent many areas from climbing out of the 40s.

Surface ridging will start to cross the Lower Great Lakes Thursday
night. This will lower the limiting subsidence inversion to under 5k
ft while the bulk of the synoptic moisture will be stripped away.
come scarce. Leftover rain showers southeast of both lakes will
taper off as a result (esp off Lk Erie) with temperatures generally
dropping into the upper 30s and lower 40s.

Ridging at all levels will cross our forecast area Friday and Friday
night. While there may still be a few nuisance lake showers east of
Lake Ontario Friday morning...this scenario will promote fair dry
weather. It will remain on the chilly side of normal though...as the
most efficient warm advection should become established over our
region until Friday night. Speaking of which...overnight mins Friday
night will likely take place by midnight with slowly rising mercury
readings through the pre-dawn hours of Saturday morning.

Earlier guidance packages suggested that a weakening Pacific based
cool front would pass through our region on Saturday. The freshest
guidance is even less impressed with this boundary as it is now
forecast to essentially washout across southern Ontario before it
even gets here. This will leave a southwest flow of milder air over
the Lower Great Lakes. H85 temps climbing into the upper single
digits c should easily be able to support afternoon temps of at lest
the low to mid 60s f...so Saturday should be a fairly nice day to
get out and enjoy the foliage.

An even nicer day is being advertised on Sunday...as a burgeoning
sub tropical ridge over the Southeast coast will help to pump our H5
hgts to near 580dm...levels more typical of late summer. H85 temps
may get into the mid teens by late Sunday. If this were to verify...
a large swath of our forecast area would experience max temps of 70
or better.

The warmth will very likely continue beyond this period into the
start of the new work week. The anomalously strong East Asian jet
mentioned earlier will ultimately be responsible for this warmth...
as they often lead to troughiness over the Inter-mountain region
which teleconnect to burgeoning ridges in the East. These features
also effectively cut off any intrusions of cold air from the
Canadian Archipelago. That being said...the pattern will remain
progressive so the troughiness (and associated cooling) over the
nations mid section will make its way across the Great Lakes for the
middle of the week.

&&

.AVIATION /21Z SUNDAY THROUGH FRIDAY/...
Unlimited VFR flight conditions across the area through at least 06z
tonight as surface high pressure slides to the Atlantic coast.
Southwesterly surface winds gusting to near 20 knots at KBUF and
KIAG on the northwest side of the high.

An upper level low to the west will spiral moisture and cooler
temperatures eastward tonight, that will likely bring lake effect
rain, with the rain forming on a surface trough that will mark the
onset of cooler temperatures. This will bring MVFR flight conditions
at times Sunday night to KIAG and KBUF for the second half of the
night.

The core of the Lake Erie band may remain just to the north of KJHW
Sunday night. A later arrival of moisture and cooler air over the
eastern end of Lake Ontario will likely keep KART VFR through Sunday
night.

Outlook...

Monday...A chance of lake effect showers and MVFR CIGS east and
northeast of the lakes, otherwise VFR.
Tuesday...Mainly VFR.
Wednesday...Showers likely with areas of MVFR. Gusty
Winds.
Thursday...A chance of lake effect showers and MVFR CIGS east
of the lakes, otherwise VFR.

&&

.MARINE...
An upper level low will slowly rotate northeastward through tonight
across southern Canada, and eventually towards James Bay by
Monday afternoon. Southwest winds on Lake Erie will freshen
tonight and tomorrow as a surface trough crosses.

Higher winds and waves are offshore and across Canadian waters this
afternoon. Winds and waves will increase along the New York Lake
Erie shoreline tonight and Monday. A Small Craft Advisory is in
effect on Lake Erie through Monday evening.

On Lake Ontario winds and waves will increase and Small Craft
Advisories are likely Monday as the trough crosses.

Colder air coming in aloft will bring the potential for waterspouts
on both Lake Erie and Lake Ontario late tonight and Monday.

Surface high pressure will push towards the Lakes Tuesday, with
winds and waves falling below SCA thresholds by late Monday night on
Lake Ontario. Winds and waves will be light Tuesday with the surface
high nearby before increasing once again as a deeper and colder
storm system passes through the Eastern Great Lakes midweek.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Small Craft Advisory until 11 PM EDT Monday for LEZ040-041.

&&

$$

SYNOPSIS...Thomas/TMA
NEAR TERM...TMA
SHORT TERM...Hitchcock
LONG TERM...RSH
AVIATION...Thomas/TMA
MARINE...HSK/Thomas/TMA