Area Forecast Discussion
Issued by NWS Buffalo, NY

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046
FXUS61 KBUF 240255
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
1055 PM EDT Sun Sep 23 2018

.SYNOPSIS...
An area of high pressure over the area tonight will move east
Monday. Temperatures will climb back above normal Monday and through
mid-week. A storm system will bring the next chance for showers
Monday night, with unsettled weather remaining through Wednesday
night.

&&

.NEAR TERM /THROUGH MONDAY/...
High pressure centered over the eastern Great Lakes will continue to
influence conditions across Western and North-Central New York
through Monday, as it gradually exits to the east. Mid-high level
clouds will stay confined to the North Country tonight.

Some increase in the easterly gradient tonight will tend to limit
the potential for greater decoupling relative to this morning.
Therefore, a more modest radiational cooling response will result
under a mostly clear sky. Lows Monday morning arriving near
seasonable values, generally settling in the mid to 40s, perhaps
down to near 40 for interior sections of the North Country.

Surface warm front will begin to lift toward the region Monday as
the area of high pressure shifts to the east. Moisture begins to
return northward, but with plenty of dry air in place we should only
see a steady increase in high cloud and gradually veering southeast
flow. Temperatures look to get just a bit above normal with most
highs on Monday in the upper 60s to lower 70s.

&&

.SHORT TERM /MONDAY NIGHT THROUGH THURSDAY/...
Monday night a broad warm air advection pattern will be in place
across our region...in between strong surface-based ridging over the
Canadian Maritimes...and low pressure and its trailing cold front...
which will be draped from northern Ontario Province to the Upper
Mississippi Valley. Within this broader pattern...a mid-level
shortwave and associated warm front pushing northeastward from the
Ohio Valley will help to enhance available moisture and isentropic
lift...resulting in fairly numerous showers overspreading the area
from southwest to northeast through the course of the night. As for
temps...it will be a notably warmer than average night for late
September...with lows ranging from the lower to mid 50s across the
North Country to the lower 60s across the lake plains of far western
New York...where a stiffening southeasterly to southerly downslope
flow will be in place. The flow will be the strongest along the Lake
Erie shoreline...where winds gusts of 30-40 mph will be possible.

On Tuesday the broad warm advection pattern will continue across
our region...while aforementioned shortwave and surface warm frontal
boundary finish their northeastward trek across our region. Numerous
to widespread showers out ahead of the front/shortwave should become
much more scattered following their passage...with a substantial amount
of rain free time looking to be very possible from the Finger Lakes
westward during the afternoon...particularly in areas where a continued
good southerly low level flow leads to downsloping and attendant low
level drying. With 850 mb temps pushing to around +14C...daytime highs
on Tuesday should at least range from the mid/upper 60s to lower 70s
across the North Country and higher terrain of the Southern Tier to
the mid to upper 70s across the lake plains south of Lake Ontario
thanks to the aforementioned downslope flow...with warmer readings
than this possible if sufficient breaks in the cloud cover manage to
materialize.

Tuesday night and Wednesday the aforementioned cold front should slowly
push eastward and across our region along with fairly widespread showers...
for which categorical PoPs remain in play. In terms of thunder potential...
available instability still looks to be relatively limited in nature
through Tuesday night...so have restricted thunder probabilities to
the slight chance range through that time. After that...there may be a
little better chance for a few scattered storms on Wednesday as the cold
front crosses our region and at least some diurnal instability comes into
play...however this will probably only be modest at best given the expected
widespread cloud and shower coverage. While about 45-50 knots of deep
layer shear will be in place out ahead of the front...the relatively tame
projected instability levels do not currently inspire much excitement
regarding severe weather potential across our region...with the best
chances for this appearing to lie from interior portions of the Southern
Tier/Finger Lakes southeastward across the remainder of New York State
and Pennsylvania. Put another way...the environmental setup does not look
to be anywhere near as impressive as that which led to our severe weather
episode late last Friday afternoon and Friday evening.

Following the passage of the trailing cold front...any showers and storms
will quickly wind down from west to east Wednesday afternoon and evening...
with high pressure and cooler/drier air then bringing a return to fair
and dry weather for the balance of this period...along with a return to
near normal temperatures.

&&

.LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/...
Generally benign weather can be expected across our region during
this period...as a deamplifying longwave trough over the center of
the country will evolve into a pseudo zonal flow with the main H25
jet aligned from the high plains to the St Lawrence Valley. This
will support temperatures that will average close to normal
throughout the period.

A stacked storm system tracking just northwest of Lake Superior
looks to push an occluding frontal system across the lower Great
Lakes Thursday night. A triple point along this occlusion will be
found in the vcnty of Georgian Bay or southern Ontario. This feature
will serve as the pivot for an advancing weak warm front that will
do little more than to increase some high and mid level clouds over
our forecast area.

As the parent storm system moves to near James Bay on Friday...its
negatively tilted mid level support will push a cold front across
our region. Given the minimal lift (incl absence of upper level
support) and general lack of moisture...will only carry low chc pops
for the majority of the region. It should go without saying that the
vast majority of the day will be rain free.

Colder air in the wake of the front will overspread the Lower Great
Lakes Friday night...while a very broad...low amplitude trough will
become situated across the eastern half of Canada. Most of the
guidance packages are not as `impressed` with the amount of cold air
as previous model runs...as average H85 temps are targeted to be in
the vcnty of 4 to 6c. While this should be chilly enough to support
some instability over the lakes...it still appears that low and mid
level moisture will be limited. Will maintain slgt (LK Erie) to low
chc (Lk Ontario) pops east of both lakes for now while the remainder
of the forecast area will be fair and dry.

On Saturday...high pressure stretching from the oil fields of
western Canada to the Mid Atlantic region should encourage fair dry
weather over our region. There has been an increasing spread though
in the solutions between some of the ensemble packages...with the
main issue being the placement of a baroclinic zone. One camp parks
a tightening baroclinic zone directly over the Lower Great Lakes
while the other envelope places this mid level boundary well to our
north. Given the disparity of the solutions...will simply maintain
continuity (dry wx) to avoid possible flip flopping between future
guidance packages.

As we close out this period on Sunday...there is a fair amount of
agreement that a cold front will be close to our region. Again...
placement of this boundary varies by as much as 300 miles between
the individual medium range ensemble members...so will broad brush
with low chc pops until greater clarification becomes available.

&&

.AVIATION /03Z MONDAY THROUGH FRIDAY/...
Widespread VFR conditions are expected through early tonight. Winds
will remain light as surface high pressure remains near the region.

High clouds will begin to increase late tonight and will likely
restrict any fog to the immediate river valleys of southern New
York, with KJHW likely to remain VFR through the night.

Outlook...

Monday...VFR. Showers likely late Monday night.
Tuesday and Wednesday...Areas of MVFR (IFR possible in So. Tier)
with showers likely.
Thursday and Friday...Mainly VFR.

&&

.MARINE...
Area of high pressure over the eastern Great Lakes will move east
late tonight and into Monday. Light winds and minimal waves will
continue on the lakes through the first half of tonight, before an
easterly flow increases on the lakes, with small craft conditions
developing late tonight into Monday for the western nearshores of
Lake Ontario. Small Craft Advisories are in effect from Niagara
River to Sodus bay beginning late tonight.

Ahead of a cold front slowly marching eastward towards the eastern
Great Lakes a southerly flow will begin to increase later Monday
through Wednesday, likely bringing another round of small craft
conditions on the lakes.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Beach Hazards Statement from 6 AM EDT Monday through Monday
     afternoon for NYZ001>003.
MARINE...Small Craft Advisory from 2 AM to 4 PM EDT Monday for LOZ043.
         Small Craft Advisory from 2 AM to 6 PM EDT Monday for
         LOZ042.

&&

$$

SYNOPSIS...TMA
NEAR TERM...HSK/TMA
SHORT TERM...JJR
LONG TERM...RSH
AVIATION...TMA
MARINE...HSK/TMA



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