Special Marine Warning 34, NWS Buffalo, NY

Area Forecast Discussion
National Weather Service Buffalo NY
439 PM EDT Fri Jul 27 2018

.SYNOPSIS...
A mild, almost fall-like, pattern will persist through Saturday with
diurnal cumulus and isolated to scattered showers inland from the
lakes each afternoon, as an upper level low spins south of the
Hudson Bay. High pressure will build across the region Sunday
bringing completely dry conditions and seasonable temperatures to
start the week. A low pressure system will track just west of the
forecast area Tuesday into Wednesday bringing some periods of rain
for mid-week.

&&

.NEAR TERM /THROUGH SATURDAY/...
For the late afternoon and early evening hours...the bulk of our
area can expect fair and mainly dry weather...with just some
isolated to widely scattered showers and perhaps a thunderstorm or
two found along our southeastern periphery...where lake breeze
boundaries intersect lingering diurnally-driven instability.

Tonight, a weak secondary frontal boundary will move across the
lower Great Lakes, also marked by a spoke of cooler 850mb
temperatures down to around +10C. Lower Great Lakes surface
temperatures around +22C will be near the threshold for helping to
support some lake cloudiness and enhancement to the showers along
the weak frontal boundary as it crosses Lake Erie and western Lake
Ontario during the early morning through around sunrise. Thus some
isolated to widely scattered showers or even a rumble of thunder are
possible over and northeast of Lake Erie Saturday morning. In
addition, the morning timing of the surface front acting
constructively with the land breeze circulation over Lake Erie will
result in an area of enhanced surface convergence over the lakes.
Lake-induced equilibrium heights over 30kft, and steep low-level
lapse rates marked by the 12C difference between lake surface
temperature and 850mb temperatures, may help support the development
of waterspouts over Lake Erie and western Lake Ontario, and thus
have added a chance to the marine forecast.

Saturday, behind morning weak frontal passage, winds will become
more westerly and the airmass slightly drier than today. The result
will be organizing the best lake breeze convergence zone across the
Niagara Peninsula eastward toward Rochester and the Northern Finger
Lakes. Numerous cumulus will develop inland from these lake breezes
through the afternoon, with the aforementioned best convergence zone
most likely to result in some isolated to scattered showers and
thunderstorms through the afternoon. High temperatures will be
slightly cooler than today behind the weak frontal passage, with
highs in the low to upper 70s.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
After the fading of some weak convergence off the south end of
Lake Ontario to start the period, a rather dry interlude looks
to be in store for the CWA. This is mainly due to a dry column
becoming resident. While fairly cool 850 mb temperatures start
the period, which would induce some lake effect instability, a
lack of moisture in the layer should preclude much in the way of
shower activity from forming.

As the core of cool air just off the deck starts to lift
northeastward by the end of the weekend, surface high pressure will
gradually build into and linger over the area to start the new week.
This will result in rather quiescent conditions with near normal
temperatures. However, as it gradually starts to lose influence over
the area, and southerly flow returns on its western flank with and
upper trough digging into the western Great Lakes, deep moisture
will quickly start to advance northward beyond Tuesday. This will
allow for a rapid increase in layer RH, instability, and PWAT
values. As such, humidity and rain chances will skyrocket by mid-
week and a very unsettled and soggy interlude looks to be on tap.

Interestingly enough, we start out slightly below normal to end the
weekend in the temperature department, and even with surface high
pressure giving way to increasing southerly flow, our temperatures
really just modestly increase toward normal through mid-week. Thus,
the biggest differences in sensible weather will not only be from an
increase in temperatures from the southerly flow, nay, they will be
from the increase in boundary layer RH as well.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
A weak cold front will pass through the region late Wednesday
helping to drop our PWATs from near 2.00 inches down to around 1.00
inch. Southerly flow will remain mostly in place as an area of high
pressure remains anchored off the mid-Atlantic coast. With some
moisture still available there is at least a chance for some showers
Wednesday night and Thursday. Instability looks a little weak as of
right now so thunderstorm potential may be limited, but will see
with future guidance updates.

On Friday a slight increase in the PWATs and instability ahead of
the next cold front will increase the chance for some showers and
thunderstorms. The best chances for thunderstorm activity will be
inland away from of the lake breeze area.

High temps during this time period will be in the mid 70s to low 80s
for Thursday and the upper 70s to mid 80s for Friday. Low
temperatures will be in the low to upper 60s for each Wednesday,
Thursday and Friday nights.

&&

.AVIATION /21Z FRIDAY THROUGH WEDNESDAY/...
Broad cyclonic flow across the area will result in a fall-like
pattern with isolated to scattered showers and thunderstorms found
inland from the lake breezes late this afternoon and again on
Saturday afternoon. CIGS will remain VFR with scattered low cloud
bases in the 3kft-5kft range. Northeast of the lakes, CIGS may
become SKC in the lake breezes, however surface gusts of 20 to 25
knots will be common there.

Late tonight, a weak frontal boundary will move across Lake Erie and
western Lake Ontario resulting in some enhanced lake cloudiness and
isolated to widely scattered showers over and northeast of the Lake.
There is a chance of land breeze waterspouts over Lake Erie and
western Lake Ontario early Saturday morning with any showers that
develop there. A brief period of MVFR CIGS is possible at BUF/IAG
with this frontal passage, and a brief period of IFR at JHW.

Outlook...
Saturday...Mainly VFR with a slight chance of showers.
Saturday night through Monday...mainly VFR.
Monday night...Mainly VFR with MVFR in scattered showers.
Tuesday and Wednesday...MVFR in showers and thunderstorms with
a chance of IFR.

&&

.MARINE...
Broad cyclonic flow across the lower Great Lakes will supply almost
fall-like conditions through Saturday...with winds and waves likely
remaining below advisory levels through a good chunk of
Saturday.

A weak frontal boundary will drop across the lower Great Lakes early
Saturday morning. Surface convergence from the combination of the
land breeze circulation and frontal boundary, combined with steep
lapse rates over the warm lakes may support the development of
waterspouts over Lake Erie and western Lake Ontario with any showers
that develop along the boundary.

Westerly winds will then increase a bit on Saturday behind the weak
frontal passage, which may approach low-end SCA conditions on
eastern Lake Ontario by Saturday afternoon.

High pressure will build across the lower Great Lakes Sunday
supplying tranquil conditions to start the week.

&&

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

&&

SYNOPSIS...Church/JJR
NEAR TERM...Church/JJR
SHORT TERM...Fries
LONG TERM...SW
AVIATION...Church/JJR
MARINE...Church/JJR