Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 131848
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
248 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 stacked storm system will exit across the St Lawrence Valley on
Thursday...while ridging slowly approaches from the Upper Great
Lakes and Ohio Valley. Chilly cyclonic flow over our region along
with deeper moisture for at least the first half of the day will
continue to support lake effect rain showers for sites southeast of
the lakes. The activity will weaken during the course of the day
though...as the limiting inversion will lower to around 6k ft while
synoptic moisture will start to be stripped away in the afternoon.
Otherwise...it will be a very cool day with many areas not being
able to climb out of the 40s.

Surface ridging will start to cross the Lower Great Lakes Thursday
night. This will keep lowering the subsidence inversion to under 5k
ft while synoptic moisture will become scarce. Leftover rain showers
southeast of both lakes will taper off and end as a result with
temperatures in most areas dropping into the 30s. The exception will
be southeast of Lake Ontario due to the thicker lake induced cloud
cover and direct influence from the warmer lake.

Ridging at all levels will cross our forecast area Friday and Friday
night. This will promote fair dry weather. Though temperatures
rising into the mid 50s will be warmer than the chilly day we`ll see
on Thursday, but still will fall short of normal.

On Saturday...there are timing issues among the various guidance
packages concerning the passage of a weakening Pacific based cold
front. Even if the front were to move through during the day...the
dynamics associated with the front look meager. At this time, GFS is
most aggressive with the front where the ECMWF and Canadian look
pretty non-eventful. Will continue to only use slgt chc pops for the
fropa.

&&

.AVIATION /19Z 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.

A SCA will continue on Lake Erie through Monday evening, with
strongest winds and highest waves tonight and Monday.

On Lake Ontario winds and waves will likely increase into SCA
thresholds 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...Hitchcock/JLA/RSH
AVIATION...Thomas/TMA
MARINE...Thomas/TMA


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