Area Forecast Discussion
Issued by NWS Buffalo, NY

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644
FXUS61 KBUF 250834
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
434 AM EDT MON JUL 25 2016

.SYNOPSIS...
An upper level trough will slowly cross the region today producing
scattered showers and thunderstorms. A trailing cold front will
pass through our region this evening...followed by slightly
cooler and less humid weather Tuesday before temperatures and
eventually humidity levels trend upward again Wednesday and
Thursday. A weak area of low pressure will then cross the region
Friday and Saturday bringing the next chance of showers and
thunderstorms.

&&

.NEAR TERM /THROUGH TONIGHT/...
High pressure across New England will exit into the Atlantic as a
weak mid level trough and pre-frontal surface trough enter Western
New York this morning. There is consensus that this trough and a
modest 30+ knot low level jet will provide the primary focus for
convection today.  However model guidance continues to struggle on
the specifics with a wide range of possible solutions. Radar trends
early this morning are shedding some light on this, with the
steadiest activity north of Lake Ontario and so far only scattered
storms upstream of Western New York. Will continue to monitor
convection developing across Western Lake Erie which should track
across Western New York this morning.

This only supports largely chance POPS west of Rochester where many
areas may, again, miss out on the rainfall. Areas which do get
thunderstorms can expect a brief period of heavy rain which may
provide localized drought relief. Precipitable water values are
forecast to increase to above 2 inches. The severe weather potential
this morning appears small, however a few stronger storms with gusty
winds cannot be ruled out.

This afternoon, the pre-frontal trough will move across Central and
Eastern New York. This will provide a better opportunity for diurnal
heating ahead of this which will increase instability. Following a
consensus of mesoscale guidance this is likely to result in
thunderstorms across eastern portions of the cwa this afternoon
before this activity exits into Eastern New York later in the day.
Wind fields this afternoon will be moderately conducive for severe
weather, with 700 mb winds increasing to 35 kts and some directional
shear. This is not likely to produce widespread severe weather, but
some strong to severe storms are possible with wind the primary
threat and hail also possible. The window for severe weather will be
narrow, with a consensus of guidance quickly bringing drier air
behind this trough late afternoon.

The lake breeze convergence zone will also provide a focus for this
convection, in addition to residual outflow boundaries and
topography. Meanwhile a breezy southwesterly flow will help develop
a lake shadow down wind of Lake Erie this afternoon, with perhaps a
few afternoon storms in Niagara/Orleans county just north of this.
The actual cold front will not reach the area until after this, but
by then the boundary layer should be too dry to support any storms.

Today will be another hot day, with highs in the mid to upper 80s.
It also will be muggy, especially this morning when dew points rise
to near 70.

For tonight, a ridge of high pressure will expand into the region
providing fair weather and clearing skies. Temperatures will be a
bit cooler behind the front with lows in the 60s. Patchy fog is
possible across the Southern Tier valleys.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
Generally uneventful weather will unfold through this period as flat
zonal flow aloft, combined with surface high pressure expanding
across the Eastern Great Lakes region bring very warm afternoons and
mild nights. Tuesday 850 hPa temperatures in the 14 to 17c range
will bring low to mid 80s for highs, while on Wednesday 850 hPa
temperatures of 16 to 19c will bring mid to upper 80s for highs, and
possibly a few 90F readings in the Genesee Valley.

A fast moving shortwave will ripple by to our north on Wednesday,
though limited moisture should bring nothing more than a few more
cumulus clouds during the afternoon hours.

A weak cold front will sag southward later Wednesday night,
bringing a slight chance for a shower or thunderstorm to SLV late.

The better radiational cooling conditions this period will be
Tuesday night, with clearer skies and lighter winds which will allow
for temperatures to lower to the mid 50s to mid 60s. Wednesday night
will likely be a few degrees warmer.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
While drought busting rains are not anticipated during this
period...there is relatively high confidence that the pattern will
be more active...so many areas should pick up at least a little
rainfall. This will be due to a subtle shift in the dominant ridge
that has been in firm control of the country.

Unlike the past couple weeks when an expansive sub-tropical ridge
either flexed its muscles with anomalously high heights over the
nations mid section...or stretched from ocean to ocean across the
southern half of the Conus...this time frame will feature low
amplitude troughing over the Great Lakes region. Meanwhile...the
heart of the aforementioned ridge will have retrograded to the
Desert Southwest. This upper level transition will encourage a
little more baroclinicity across the Great Lakes region...which
should support a more active storm track.

At the surface...the period will open with a wavy frontal boundary
that will be stalled in the vcnty of the Mason Dixon Line. It is
interesting in that all of the real baroclinicity...lift and moisture
will be found a few hundred miles north of the sfc front. This
should initially keep the bulk of any showers and thunderstorms
north of the international border...but as push into Friday...a
fairly well organized wave will develop over the Mid West and slowly
track east along the front. The ensembles are all over the place
with the location...speed and track of this wave...but all are in
general agreement that the system will move close enough to our
region to help generate more widespread rainfall. The best
opportunity for some rain would be Friday and Friday evening with
basin average rainfall averaging under a quarter inch...but locally
up to three quarters of an inch.

Confidence drops off for the weekend as a second wave could bring
another round of beneficial showers and thunderstorms to the
forecast area. This will largely depend on the strength of the first
system though...so will only use relatively low pops to express this
potential.

In terms of temperatures...while mercury levels will generally be
lower than those of the past few weeks...there is high confidence
that they will remain close to...if not still a few degrees above
normal.

&&

.AVIATION /09Z MONDAY THROUGH FRIDAY/...
Largely dry VFR conditions should prevail underneath varying amounts
of mid and high cloud cover through 11 or 12Z. Patchy fog at JHW
will dissipate as high clouds move in toward sunrise.

A trough will enter Western New York this morning and then move into
Central New York this afternoon. This should provide the main focus
for showers and thunderstorms, however radar shows the only
scattered coverage currently upstream so will maintain VCTS for most
TAF locations. The highest confidence in a thunderstorm is at ART
where the later arrival should allow for some heating ahead of the
trough leading to more widespread thunderstorms this afternoon.
Convection will end from west to east this afternoon, with breezy
and dry conditions first developing at BUF due to lake shadowing.

Any lingering showers should be done by 00Z Tuesday with widespread
VFR conditions expected tonight outside of perhaps some fog in the
river valleys and at JHW.

Outlook...
Tuesday and Wednesday...Mainly VFR.
Thursday...Mainly VFR with a chance of showers and thunderstorms.
Friday...VFR/MVFR with a chance of showers and thunderstorms.

&&

.MARINE...
A cold front will move east across the lower Great Lakes today. A
fresh southwesterly breeze will develop ahead of this, supporting
low-end small craft advisories on Lake Erie and the Upper Niagara
River. Winds should be strongest near the shoreline where the lake
breeze will help enhance the flow.

Winds will diminish tonight following the passage of the weak front,
with winds and waves then expected to remain below Small Craft
Advisory levels through midweek.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Beach Hazards Statement from noon EDT today through this
     evening for NYZ010-085.
MARINE...Small Craft Advisory from noon today to 8 PM EDT this evening
         for LEZ020-040-041.

&&

$$

SYNOPSIS...APFFEL
NEAR TERM...APFFEL
SHORT TERM...THOMAS
LONG TERM...RSH/THOMAS
AVIATION...APFFEL
MARINE...APFFEL/THOMAS



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