NWS Area Forecast Discussion

000
FXUS61 KBUF 202035
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
435 PM EDT Fri Jul 20 2018

.SYNOPSIS...
Low pressure moving very slowly through the western Great Lakes will
bring a small chance of a shower across far Western NY tonight and
Saturday, otherwise the rest of the area will remain dry under the
influence of high pressure off the New England coast. Low pressure
will then move northward from the Mid Atlantic to eastern NY late
Saturday night and Sunday, with increasing chances of more
widespread rain. Unsettled weather is then expected to last through
at least the first half of next week as a frontal zone stalls across
the region. Temps range through the 80s with 90 here in Buffalo.

&&

.NEAR TERM /THROUGH SATURDAY/...
Satellite imagery showing plenty of sunshine across the region late
this afternoon, with just scattered diurnal cumulus and some
thin/high cirrus across portions of western NY.

Tonight through Saturday a vertically stacked, cutoff low will
continue to spin and drift slowly from Lake Michigan into northern
Indiana. The bulk of the deeper moisture and forcing for ascent will
remain west of our region through the period, held at bay by strong
high pressure surface and aloft parked along the New England coast.
Associated subsidence and dry air will only allow for a very slow
increase in cloud cover tonight and Saturday for the bulk of the
area. The one exception will be across Western NY, where more in the
way of cloud cover will move into the area tonight and Saturday on
the eastern periphery of the upstream cutoff low. Low level moisture
spreading northward through PA may also produce some low clouds late
tonight into a portion of Saturday across the higher terrain of the
Southern Tier.

The vast majority of the area will remain dry tonight and Saturday.
Across far Western NY, there may be a few brief opportunities for a
few isolated light showers. An initial mid level shortwave and
associated moisture wrapping around the upstream cutoff low will
move into Western NY this evening and weaken. There may be just
enough forcing and moisture left to support a few showers across
western Chautauqua County. If this does materialize this evening,
the showers would end overnight as the forcing weakens and deep
moisture thins. A few isolated showers may develop again Saturday
from late morning through mid to late afternoon across far Western
NY as marginal moisture and forcing approach from the southwest.

A 40 knot southerly low level jet will cross the region tonight. The
majority of this wind will stay aloft, but the downslope areas in
Western NY may see gusts of around 30 mph overnight into early
Saturday morning, namely the Lake Erie shore and other northward
facing slopes of Southern Erie and Chautauqua counties.

Temperatures will remain much milder tonight than recent nights with
some increase in cloud cover and a steady southerly breeze. Expect
lows of 65 to 70 on the lake plains, with upper 50s to lower 60s in
the coolest Southern Tier valleys and Lewis County. Highs on
Saturday will be a notch lower than today with increasing cloud
cover. Expect low to mid 80s on the lake plains, with 70s across
higher terrain. Portions of Allegany County may just reach 70 if low
clouds persist much of the day.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
This period overall will be warm and humid, with multiple chances
for some much needed rainfall.

Saturday night and Sunday the main area of surface low pressure will
settle southward across the Ohio Valley. Meanwhile at the same time,
a second much more compact and moisture laden surface low pressure
system will move north-northwestward from the Delmarva region toward
central/eastern New York State, eventually into southern Canada by
late Sunday. Guidance continues to support a slight shift westward
in the track, with rain chances increasing some across far western
New York, however the chance for more appreciable rainfall will be
across central/northcentral New York. Precipitation will be showery,
with the possibility of some heavy downpours possible. For
temperatures, lows Saturday night will range from the upper 50s
across interior portions of the Southern Tier/Eastern Lake Ontario
region, to the lower to mid 60s elsewhere. Extra cloud cover and
showers will help to hold high temperatures in the mid to upper 70s
on Sunday.

After the passage of Sunday`s system, there will likely be a lull in
the better precip chances for Sunday night as the first low and
associated moisture/dynamics depart to our north, and the low over
the Ohio Valley weakens and pivots toward the southeastern U.S. With
warm and humid conditions remaining in place along with a general
southerly flow, will keep a chance of showers in the forecast. With
cloud cover and humidity levels continuing to rise, low temperatures
will only fall back into the 60s area wide.

Monday and Monday night our area will be sandwiched in between an
elongated area of troughing/low pressure to the west and
ridging/high pressure over the western Atlantic basin. This will be
the beginning of a prolonged period of broad southerly flow that
will bring deep Atlantic moisture north across the eastern third of
the U.S. This will keep our weather generally unsettled with the
threat of showers and thunderstorms in the forecast into early next
week and beyond. There will be a narrower axis of enhanced moisture
lying within the deep southerly flow across the eastern third of the
nation. With modest instability and PWATs nearing 2.0 inches, where
exactly this axis of enhanced moisture sets up, will likely lead to
areas of heavier showers and thunderstorms. Training of storms over
the same areas does look like a possibility as well and the
possibility for flooding/flash flooding will need to be monitored,
especially beyond early next week. Warm and humid conditions will
continue with highs Monday pushing into the upper 70s to mid 80s,
with lows Monday night only falling back into the mid 60s to lower
70s.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
A persistent flow of Atlantic moisture will continue through late
Wednesday across the region before a cold front moves through with a
dryer airmass in its wake. This moist air is the result of southerly
flow associated with the weakening vertically stacked low pressure
system over the norther Gulf of Mexico and a strong area of high
pressure/ridging off the mid-Atlantic coast. At the same time a weak
stationary frontal system will be stalled across the region and
combined with the moist airmass the chance for showers/thunderstorms
will persist through Wednesday. High PWATs on Tuesday and Wednesday
will increase the potential for some heavier rain with any
showers/thunder storms. PWATs of 1.50-2.00 inches will be in place
across much of the area through late Wednesday night before the
first of two cold fronts move through.

These two cold fronts will be associated with an upper level trough
and surface low that will shift from central Ontario to northern
Quebec between late Wednesday and Friday. As the system moves
through Ontario and Quebec, the first cold front will drop southeast
early Thursday and weaken as it shifts across our region. The second
but stronger cold front will move through Thursday
afternoon/evening. Sufficient instability looks like it will be in
place for Thursday to have at least the chance for thunderstorms but
the decrease in moisture may limit precip/convection. Friday looks
mostly rain free as of current guidance suggestions.

Temperatures for Tuesday and Wednesday will range from near 80 to
the mid 80s for highs and mid 60s to around 70 for lows. Slightly
cooler temperatures are expected for Thursday and Friday with highs
in the mid 70s to around 80 and upper 50s to mid 60s for lows.

&&

.AVIATION /21Z FRIDAY THROUGH WEDNESDAY/...
High pressure along the New England coast will continue to provide
only scattered cumulus into this evening for the bulk of the area.
Some mid level clouds will spread into far Western NY this evening
through Saturday, with a small chance of a few isolated showers at
the far western end of the state. CIGS will remain VFR in most areas
tonight and Saturday. The one exception may be across the higher
terrain of the Southern Tier, where low level moisture moving
northward out of PA may produce some MVFR CIGS late tonight through
midday Saturday.

Outlook...
Saturday night and Sunday...VFR/MVFR with the likelihood for showers
and isolated thunderstorms.
Monday...Mainly VFR with scattered showers and thunderstorms and
associated local/brief MVFR.
Tuesday and Wednesday...VFR/MVFR with showers and thunderstorms
likely.

&&

.MARINE...
The gradient between high pressure over the New England coast and
low pressure over the Midwest will combine with stronger winds aloft
to bring an increase in southeast winds tonight and Saturday
morning. The strongest winds will be along the Lake Erie shore with
an added boost from downslope flow. The southeast wind direction
will keep the greater wave action in Canadian waters tonight and
Saturday. East winds Saturday night will become northeast by early
Sunday. This will produce choppy conditions along the south shore of
Lake Ontario and also portions of Lake Erie, but winds and waves are
expected to remain below Small Craft Advisory criteria.

&&

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

&&

$$

SYNOPSIS...Hitchcock
NEAR TERM...Hitchcock
SHORT TERM...JM
LONG TERM...SW
AVIATION...Hitchcock
MARINE...Hitchcock

NWS BUF Office Area Forecast Discussion