Forecast Discussion for BUF NWS Office
000
FXUS61 KBUF 171329
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
929 AM EDT Fri Aug 17 2018

.SYNOPSIS...
The center of a storm system will pass just to our north today,
bringing several rounds of showers and thunderstorms through
tonight. A cold front will drop across the Eastern Great Lakes late
tonight and early Saturday morning with more showers and
thunderstorms before high pressure brings a return of fair weather
with comfortable levels of humidity for the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
A weak surface low just south of Lake Huron will pass just north
of Lake Ontario, and then head into northern New England
tonight. Aloft two shortwaves exist near our region, one to the
NW of Lake Ontario, with a second and readily identified on
water vapor imagery, over northern IL.

An area of showers and thunderstorms has developed along the
north shores of Lake Erie and this is likely to bring some rain
to the Niagara Frontier late this morning. Raised PoPs for this
area, but otherwise made little changes to the previous
forecast.

There will be three concentrated periods for showers and
thunderstorms the next 24-hrs.

The first is ongoing, and is associated with the first
shortwave and surface low NW of Lake Ontario. These features are
aiding in pulling a warm front northward across our region,
with elevated instability and convergence along a 35 knot LLJ.
This is producing a steady area of rain which will be across the
Eastern Lake Ontario region through the morning hours.

The second period of storms will be towards this afternoon when
daytime instability yields scattered showers and thunderstorms.
SBCAPE values are expected to again top 1000 J/KG and storms may
blossom a bit earlier than yesterday owing to now a flat flow
aloft...opposed to a ridge aloft yesterday. Lapse rates will remain
poor, generally under 7 C/km above 850 hPa and wind fields weak,
especially to the west. Afternoon convection will again likely be
garden variety storms, with a few heavier storms bringing drenching
rainfall in a still very moist environment.

The third period of showers and thunderstorms will be along a cold
front. As the surface low tracks to New England and a shortwave
crosses from the Midwest to NYS it will push a cold front across our
region. Convergence along the front, coupled with additional lift
along the shortwave aloft will bring synoptic lift that will likely
bring more showers and thunderstorms to our region. The overnight
timing of the cold front passage, and continued weak wind fields
(winds less than 25 knots through 15K feet) will likely mean that
any thunderstorm will remain below severe thresholds. This cold
front will bring storms, first to the Niagara Frontier during the
evening hours, and then showers diminishing through the night to
points east and south. Southwest winds will veer to northwest behind
the front.

With little change in the airmass, we will again have dewpoints in
the upper 60s to lower 70s...though a cloudier day will likely hold
air temperatures a few degrees cooler in the low to mid 80s. Lows
tonight in a still humid environment will be in the 60s.

&&

.SHORT TERM /SATURDAY THROUGH MONDAY/...
Early Saturday morning, the cold front should be in the process of
shifting south out of New York with just a chance of some lingering
showers near the NY/PA before midday. Behind this front, high
pressure will be centered over Quebec with a ridge extended
southwest across the lower Great Lakes. This high will shift toward
the Canadian Maritimes through Sunday promoting fine weekend weather
across western and north-central NY. The 00z ECMWF is an outlier to
this forecast, showing showers slower to leave NY Saturday and some
afternoon showers and storms developing inland away from the lakes
Sunday. We expect our region will remain dry into Sunday night and
Monday with the lingering surface ridging even as models show
development of a coastal storm near Long Island.

Somewhat drier air associated with the surface high to our north
will help support slightly more comfortable humidity levels over the
weekend with dewpoints slipping back into the lower 60s. 850mb temps
around 14C and northerly flow will support temps close to normal for
late August. Highs will comfortably top out in the mid to upper 70s
with a few locations at lower elevations on the lake plains may see
low 80s. The lack of much lower dewpoint air will allow for
overnight temps to only dip into the upper 50s to low 60s each
night. Highs Monday have the best chance at reaching back to 80
degrees thanks to downslope southeast winds.

&&

.LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
Models show a mid-level trough crossing the midwest on Monday will
contribute to a developing surface low over Missouri or Illinois. As
this occurs, high pressure which brought us a fine weekend will
slide east off the New England coast. 00z ECMWF/GEM models and to a
lesser extent the GFS show this surface low deepening while shifting
just northwest of New York through Tuesday and Tuesday night. NAFES
ensembles show this low as potentially reaching 2SD below normal for
mid-August with central pressure of 1008mb. The operational EC/GEM
bottom the central pressure out at sub-1000 mb which would support
an even more anomalous storm system for this time of year. A strong
cold front should accompany this low and cross western and north-
central NY Tuesday.

Synoptic forcing will increase ahead of the approaching storm system
giving way to increasing shower and thunderstorm coverage through
Tuesday as the low tracks by to our northwest. High PW values of 2+
inches means any storms will likely contain torrential rainfall with
a marginal threat of flash flooding. Depending on the exact timing
of the low, there could also be a marginal threat for severe weather
with a swath of 35-40 knots of 0-6km shear and narrow ribbon of
SBCAPE sets up ahead of the cold front passage.

Moisture will quickly shallow out behind the cold front passage
Tuesday night through Wednesday as high pressure moves into the
central CONUS and supplies a northwesterly flow across the region.
Any convective coverage from Tuesday will quickly subside Tuesday
night, with numerous cumulus developing inland from the lake breezes
Wednesday afternoon that could result in an isolated to widely
scattered shower or thunderstorm. High pressure will continue to
build in across the region with a continued drying trend into
Thursday.

Temperatures through this period will run close to normal. Tuesday
will remain quite muggy, but much drier air will return behind the
cold front passage for Wednesday and especially Thursday when dew
points may finally return to much more comfortable 50s.

&&

.AVIATION /14Z FRIDAY THROUGH TUESDAY/...
For the 12Z TAFS showers continue to expand across WNY with the
main area of rain now just to the east of KROC, and in the
vicinity of KART. Flight conditions are likely to lower to MVFR,
and will place showers near KART for the first few hours of the
TAF package. Otherwise, some low CIGS across the SO. Tier will
begin to lift back to MVFR...though improvement to CIGS across
WNY will be slow.

Additional showers and thunderstorms will be possible this
afternoon, generally from the So. Tier to the Finger Lakes region,
as the airmass remains unstable. A cold front will drop across the
region late tonight, with a notable wind shift from SW to NW. This
front will also carry the last of the lingering showers eastward.
Some valley fog will be possible late tonight across the So. Tier,
with IFR flight conditions possible.

Outlook...

Saturday...Mainly VFR. Widely scattered showers.
Sunday and Monday...VFR.
Tuesday...MVFR. Showers and thunderstorms likely.

&&

.MARINE...
A southwest flow will increase on Lake Erie this morning, to around
15 knots with waves increasing to 3 feet as a surface low deepens a
little and passes by to the northwest and north of the Eastern Great
Lakes.

This surface low will drag a cold front across the Lakes tonight and
early Saturday. Winds will shift to northwest behind the front and
increase some, though both waves and winds will likely remain just
below small craft advisory criteria. Following the cold front surface
high pressure will build towards the region this weekend with fine
boating conditions on the lakes and rivers.

&&

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

&&

$$

SYNOPSIS...Thomas
NEAR TERM...Apffel/Thomas
SHORT TERM...Smith
LONG TERM...Church/Smith
AVIATION...Apffel/Thomas
MARINE...Thomas

NWS BUF Office Area Forecast Discussion