Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 312348

Area Forecast Discussion
National Weather Service Buffalo NY
748 PM EDT TUE MAY 31 2016

Canadian high pressure will remain in control keeping fair
weather...above normal temperatures and comfortable humidity levels
going across the region through Wednesday. Warm and increasingly
humid conditions will then return later Wednesday night into
Thursday with showers and a few thunderstorms developing ahead of
the next cold front that will move east of the region Thursday
night. Dry weather and lower humidity will then return for the end
of the week into the first part of the weekend.


A weak moisture starved cold front will slide southeast of the
area this evening. This will result in mostly clear skies outside
of some high thin cirrus which will move across the area.

Mid and upper level ridging building over the Northeast combined
with reinforcing Canadian high pressure nosing in at the surface
will provide calm and dry weather across the area tonight. The
combination of dry air, light winds and little in the way of cloud
cover will provide a good setup for radiational cooling. Winds
will diminish the most inland from the lakes across the Western
Southern Tier where there may be patchy valley fog. Low
temperatures will range from the upper 40s to the mid 50s across
our area.

Wednesday, expect mainly sunny skies and northeasterly to easterly
winds as surface high pressure shifts eastward across eastern
Quebec. This will allow the normally cooler areas just to the east
of the lakes to warm a bit more, while inland areas south of Lake
Ontario will be the coolest. Expect a slow increase in cloud cover
toward the end of the day across southwestern New York State as the
leading edge of some more humid air begins to push north into the
area. High temperatures will be a few degrees warmer than today with
upper 70s to mid 80s across the region.


Wednesday evening some of the latest 12Z model guidance develops
convection across western NY along a weak warm frontal boundary
and surge of higher dewpoints. The 12Z NAM is the most aggressive
with this, developing a region of higher QPF and thunderstorms
across western NY. Other global models such as the Canadian GEM
and ECMWF do not develop this convection. The NAM and to some
extent the GFS seem far too aggressive in advecting higher
dewpoints into the area late Wednesday afternoon, with the NAM
forecasting upper 60s dewpoints across the western Southern Tier
by 00Z Thursday. This seems unreasonable given the dry airmass
currently moving into the area, and only modest southeasterly
return flow into the Southern Tier Wednesday afternoon. These high
forecast surface dewpoints produce unrealistic instability in the
model, and too much convection.

With this in mind, have followed the ECMWF and GEM guidance and kept
the bulk of Wednesday night dry. A few showers may develop late as
the cold front and associated pre-frontal trough approach the area.
Temperatures will remain mild, with lows in the lower 60s on the
lake plains and mid 50s in the cooler Southern Tier valleys and Tug
Hill region. Temperatures may rise a few degrees late as southerly
flow increases.

On Thursday a mid level trough will shift east from northwest
Ontario province to western Quebec, with an associated surface low
taking a similar track. The trailing cold front will cross the area
during the afternoon and evening. The GFS and NAM remain among the
faster model guidance, while the ECMWF and GEM are several hours
slower. It appears the GFS and NAM may be suffering from some
gridscale convective feedback, with composite outflow in the model
producing too fast of a cold frontal passage. With this in mind,
have again leaned towards the somewhat slower ECMWF/GEM guidance
with the higher rain chances moving into western NY during the
morning, then spreading east across the rest of the area during the
afternoon. The combination of ample moisture and reasonable dynamics
along the front justify high likely POPS. Enough instability will be
found along the front to support a few scattered thunderstorms.

Thursday night the cold front will push east with drier and more
stable air moving into the region from west to east. This will allow
any showers to slowly end across western NY overnight, with
lingering scattered showers across eastern areas ending Friday
morning. On Friday skies will at least partially clear, although
lingering low level moisture will likely support diurnal cumulus
development along and inland from lake breeze boundaries. Stable
lake shadows will develop east of the lakes with full sunshine
during the afternoon. Temperatures will be knocked back some behind
the front, with highs in the mid 70s in most locations along with
lower humidity.

Friday night and Saturday a bubble of high pressure will build into
the Great Lakes with mainly clear skies. The somewhat cooler and
drier airmass will allow for some radiational cooling Friday night,
with lows in the mid 50s on the lake plains and upper 40s in some of
the cooler Southern Tier valleys. Highs Saturday will rebound into
the mid to upper 70s.


The beginning of next weekend, including Sunday, will feature a
changing weather pattern across the CONUS, and will feature cooler
more unsettled weather for the region.

By Saturday night into Sunday, a large ridge will build across the
western CONUS, with downstream development of throughing across the
eastern half of the country. During the day Sunday, a trough digging
through the western Great Lakes will place the forecast area in the
optimal region of QG forcing, with DPVA and warm air advection ahead
of the low. Widespread showers and a few thunderstorms are possible
across the region. Temperatures on Sunday will remain near to just
above normal, in the mid to upper 70s, with a warm airmass in place
but plenty of cloud cover and showers keeping temperatures from
pushing into the 80s.

Sunday night into Monday, as the main surge of upper-level forcing
and associated surface low exit to the NW of the region, the broad
upper-level through will settle over southern Quebec. Cyclonic flow
aloft and steepening mid-level lapse rates under the low will keep
showers and some rumbles of thunder in the forecast, although likely
not a widespread soaking day expected. Temperatures will start
trending downward on Monday, as cold air advection follows behind
the surface low, and 850 mb temperatures fall to +6 to +8C. Highs
will be in the low 70s in the lower elevations to the upper 60s in
the higher terrain. Cloud cover will remain fairly persist through
the day with plentiful moisture under the through.

Tuesday will start off as a carbon copy of Monday, but with
temperatures continuing to cool in the cold air advection behind the
departing low. Drier northwesterly flow will slowly infiltrate across
the region from NW to SE through the afternoon as shortwave ridging
builds in behind the main through. Expect some increasing sunshine
is likely later in the day as this drier air moves in. Thus Tuesday
will likely not make it out of the 60s for any location as 850 mb
temperatures fall to only about +4C.

Looking further down the road...there remains strong consensus among
the GFS and ECMWF ensemble members that a closed low will be found
within a significant (if not anomalously deep) longwave trough over
eastern Canada during the entire first full week of June. This will
favor cooler than normal conditions for much of the week
...especially in regards to daytime highs. Normal max temps for this
time of year are generally in the mid 70s.


Widespread VFR conditions will prevail tonight through Wednesday
as high pressure remains in control across the region. There will
also be a thin cirrus shield aloft that will hang in through much
of the overnight. The only exception will be a some patchy valley
fog which may spread into JHW late tonight where vsby may be
variable for a few hours. Otherwise, VFR conditions should
continue through Wednesday.

Wednesday night...VFR.
Thursday...VFR/MVFR with showers likely and a chance of
Friday and Saturday...Mainly VFR
Sunday...VFR/MVFR with a chance of showers.


Dry conditions expected through Wednesday under high pressure.
Northeasterly to easterly winds increasing to around 15 knots on
Wednesday will produce choppy wave action but still below small
craft advisory criteria. Highest waves of 1-3 feet will be found
across the southern Lake Ontario shoreline on Wednesday. A cold
front passing through the area on Thursday may bring some gusty
winds and higher waves in thunderstorms. High pressure will then
build into the area again for Friday and Saturday.





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