Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 311756
AFDBUF

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

.SYNOPSIS...
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 ahead of the next cold front that will move east of the
region by Thursday night. A return to dry weather and lower humidity
will then return for the end of the week into the first part of the
weekend.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
Weak moisture starved cold front will press south across New York
State this afternoon with Canadian high pressure once again building
across the region as we head into this evening. Visible satellite
imagery now showing some diurnal cumulus clouds along and inland
from the lake breezes, as well as across the higher terrain. The
northern edge of a thin cirrus shield will also be seen western New
York. Highs today will be in the mid 70s to around 80.

The high pressure centered north of our region will press further
into New York State and the northeastern states. This will maintain
a dry and cool flow across the area on north to northeast winds,
generally less than 10 mph overnight. Low temperatures will fall to
the upper 40s to lower 50s across inland regions and to the mid 50s
along the shores of Lakes Erie and Ontario. Expect to see valley fog
in the Southern Tier once more.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
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.

&&

.LONG TERM /SATURDAY NIGHT THROUGH MONDAY/...
Moving on into the latter half of the coming weekend, things will
become more unsettled across the Lower Great Lakes as a pronounced
shortwave progged to dive out of the Canadian Rockies and across
the Upper Great Lakes arrives on our doorstep Saturday Night.
Guidance begins to diverge slightly from this point onwards, with
the 12Z ECMWF favoring a slightly faster and less amplified
solution...a logical assumption given our time of year and the GFS
tendency to over-do these kinds of systems early on. Either way,
expect at least a chance of showers breaking out Saturday night
across Western NY.

By Sunday, the entire forecast area will be in the bullseye of the
upper level trough and accompanying surface low. While airmass
running out ahead of this system will not be nearly as hot/muggy as
we saw the last few days, temperatures on Sunday will still run 5
to 10 degrees above average. Given abundant synoptic forcing and
decent instability, expect scattered to numerous showers and
thunderstorms Sunday. Aforementioned synoptic forcing may allow
convection to linger well into Sunday night with another round
possible Monday as the upper level low center potentially stalls
over New England.

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 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.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
Widespread VFR will prevail this afternoon through Wednesday as
high pressure continues to build across the region from the north.
There will some scattered diurnal stratocumulus found along and
inland from the lake breezes again this afternoon, as well as
across the higher terrain. The only exception will be a low chance
for MVFR/IFR VSBY in fog at KJHW tonight as Southern Tier valley
fog forms between 08Z and 11Z. Have included some MVFR fog in the
KJHW TAF to highlight this potential.

Outlook...
Tonight and Wednesday...VFR.
Thursday and Friday...Mainly VFR with a chance of showers and thunderstorms.
Saturday...VFR.

&&

.MARINE...
Mainly dry conditions expected through Wednesday under high
pressure. Winds will increase to around 15 knots which will produce
choppy wave action but still well below small craft advisory
criteria. A cold front passing through late Thursday may bring
thunderstorms with gusty winds and higher waves. High pressure will
build into the area late Friday and Saturday.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...None.

&&

$$

SYNOPSIS...JM/WCH
NEAR TERM...JM/WCH
SHORT TERM...HITCHCOCK
LONG TERM...RSH/WOOD
AVIATION...JM/WCH
MARINE...CHURCH/WCH



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