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Area forecast discussion
National Weather Service Buffalo New York
515 am EDT Mon Aug 26 2019

high pressure drifting slowly east across New England will bring
more dry weather today with near normal temperatures. A warm front
will then move into the area Tuesday morning, followed quickly by a
cold front late Tuesday night and early Wednesday. This will bring a
several rounds of showers and possibly a few isolated thunderstorms.
Mainly dry weather will return Thursday as high pressure builds into
the Ohio Valley.


Near term /through tonight/...
infrared satellite imagery showing mainly clear skies across the region
early this morning, with just some high/thin cirrus drifting across
western New York. Some River Valley fog will continue across the western
southern tier in the typical locations through about 9am.

Surface high pressure will continue to drift slowly east across New
England and Quebec today. Associated subsidence and dry mid levels
will continue to support dry weather today. Model point soundings
show a layer of moisture around 850mb across western NY, and this
will likely support another round of cumulus/stratocumulus
development from about the Genesee Valley westward with daytime
heating. Areas east of Lake Ontario will see full sunshine with
little or no moisture left in the low levels. Temperatures will be
very close to average, with highs in the mid to upper 70s at lower
elevations and lower 70s on the hills.

The cumulus/stratocumulus will mostly dissipate this evening with the
loss of daytime heating. Mid/high clouds will then thicken and lower
from west to east overnight as warm advection and moisture ramp up
ahead of the next system. A warm front will approach western New York very
late tonight. Isentropic upglide and moisture transport supported by
a 40+knot low level jet will support an area of showers just ahead
of the warm front. These showers will enter western New York shortly
before daybreak Tuesday. Given the agreement amongst the global and
high-res model guidance, increased probability of precipitation to likely very late tonight
and early Tuesday morning west of the Genesee Valley. The increase
in clouds will keep temperatures milder than recent nights, with
lows in the low to mid 60s on the lake plains of western NY, and 50s
across the southern tier valleys and east of Lake Ontario. These
lows will likely occur around midnight, with rising temperatures
late tonight as clouds thicken and southerly winds increase.


Short term /Tuesday through Wednesday night/...
this warm front will then cross the area on Tuesday, as high
pressure retreats eastward off the New England coast.
Strengthening warm advection along the nose of a 40kt low level
jet will move across western New York Tuesday morning. The best warm
air advection/lift will be from The Finger lakes west where
there will be showers along the front through the first half of
the day, with areas toward the Eastern Lake Ontario region most
likely remaining dry. As the warm front moves north of the area,
believe all areas will see a brief dry period Tuesday afternoon
before showers associated with a cold front approach western New York
late in the evening. A strong south-southeast low level jet will cause some
gusty downslope winds near Lake Erie off the Chautauqua ridge
through early Tuesday afternoon. High temperatures on Tuesday
will be in the mid to upper 70s, with low 70s elsewhere. There
will be a noticeable uptick in the humidity, especially across
western NY, as dew points rise into the mid 60s.

A cold front will move into western New York during the second half of
Tuesday night and then slowly move east across the forecast area
during the day Wednesday. The main threat with this front appears to
be a period of heavy rain just ahead of the boundary with precipitable water
values rising to 1.75-2.00" within a ribbon of deep moisture pooling
just ahead of the cold front on the leading edge of 30-35kt low
level jet. Will keep just the chance for thunder in the forecast as
instability along the front is marginal. Deep southerly flow
combined with increased cloud cover will keep low temperatures
across most areas in the 60s Tuesday night, with some upper 50s
across the higher terrain east of Lake Ontario. Highs on Wednesday
will be in the mid to upper 70s for most areas, with some low 70s
across the higher terrain.

The cold front will push east of the area by Wednesday night,
with showers and embedded thunderstorms ending from west to east
Wednesday afternoon and evening. The front will usher in cooler
air aloft with consensus 850mb temperatures dropping to around
+8 to +9c across Lake Erie Wednesday night, with these values
moving over Lake Ontario by later Wednesday night into Thursday
morning. The combination of lingering moisture from an upper
level trough and the cooler air off the deck may support limited
lake effect/enhanced showers east and northeast of Lake Erie
late Wednesday night.


Long term /Thursday through Sunday/...
Lake effect/enhanced rain showers may still be supported east of
lakes Erie and Ontario Thursday morning as 850mb temperatures
continue to remain sub +10c through 18z with the upper level low
continuing to slowly shift to the east. Diurnal effects will end the
lake effect potential by Thursday afternoon, although a few cold
core showers cannot be ruled out over interior sections as
instability maxes out during peak afternoon heating.

Surface high pressure to our south will slide to the mid-Atlantic
region bringing in warmer and drier air Thursday night keeping it
dry, with this trend possibly lasting through the first part of
Friday. The 00z model suite has come into better agreement on the
timing of the next cold front coming through the region. Now appears
it will come through later in the day Friday into Friday night, with
at least the chance for some showers along the front as it swings
through. Then on Saturday as 850mb temperatures fall into the mid to
upper single digits c, there may be a Few Lake enhanced showers southeast
of the lakes Saturday morning, before diurnal effects weaken any
lake enhancement by afternoon. There may still be few instability
showers across inland areas during the second half of the day as
instability maxes out during peak heating.

Where the models differ is how far south of our area this boundary
eventually stalls out. This appears as though it will be dependent
on the placement of two areas of high pressure, one to the north and
one to the south of this boundary. Models then try to develop some
sort of wave along this now stationary front, then move it east
Saturday night into Sunday morning. For now will keep a chance of
showers in the forecast for Saturday night, with the best chance
south. High pressure nosing in from the north Sunday should be able
to suppress the stationary boundary a little further to the south,
taking most of the precipitation chances with it.

High temperatures will generally be within a few degrees either
side of the mid 70s, with lows in the 50s through this period.


Aviation /09z Monday through Friday/...
mainly clear skies will continue through this morning with just some
thin/high cirrus drifting across western New York. Typical southern tier
River Valley fog will develop, with local IFR from about 07z-13z.
This is not expected to impact the kjhw terminal.

Once the valley fog Burns off in the southern tier, VFR will prevail
today. Model guidance still shows a layer of moisture centered on
850mb across western NY, so expect a good deal of
cumulus/stratocumulus development during the midday and afternoon
from the Genesee Valley westward, with bases around 5k feet.

The cumulus/stratocumulus will mostly dissipate this evening, with
mid/high clouds then thickening and lowering from west to east ahead
of the next system. A warm front will approach western New York after
about 09z Tuesday, bringing with it an increasing chance of showers.
Ceilings/visibility will likely remain VFR in most locations through 12z
Tuesday as the low levels remain unsaturated with the initial
arrival of showers. The one exception may be across the higher
terrain of the southern tier, where MVFR ceilings in low stratus may
develop late tonight.


Tuesday through Wednesday...mainly VFR with some short periods of
MVFR from showers and thunderstorms.
Thursday and Friday...mainly VFR, some brief MVFR with showers


high pressure will continue to drift slowly east across New England
and Quebec today. Easterly winds will increase on Lake Ontario
today, producing choppy conditions on the west half of the lake.
Winds will become south-southeast tonight and increase to 15-20 knots late
tonight and early Tuesday. This will produce choppy conditions on
both lakes, but this wind direction will direct the greater wave
action into Canadian waters.

A cold front will then cross the eastern Great Lakes late Tuesday
night and early Wednesday. Winds will become southwest behind this
cold front, producing choppy conditions at the east end of lakes
Erie and Ontario.


Buf watches/warnings/advisories...
New York...none.




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