Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 230911

Area Forecast Discussion
National Weather Service Buffalo NY
511 AM EDT Tue May 23 2017

A weak ridge of high pressure will bring dry weather today through
most of Wednesday with temperatures above normal. Low pressure will
then bring more rain to the region Wednesday night and Thursday with
temperatures closer to normal.


Surface high pressure spans from the upper Ohio Valley northeast
across PA and NY this morning. Subsidence brought on by convergent
flow aloft will continue to support mainly clear skies across
western and central NY. Low temperatures will run in the upper 40s
to around 50 on the lake plains, with low to mid 40s in the cooler
sections of the interior Southern Tier and Lewis County.

The surface high will slowly shift northeast through today and
tonight. Further north a weak mid level shortwave will move
northeast across southern Ontario with little direct impact on our
area although it will bring scattered showers and thunderstorms
north of the Canadian border. While we will remain dry today, the
shortwave will bring some increase in moisture and cloud cover, with
both mid level clouds and diurnal cumulus expected across the
region. Stable lake shadows will allow more sunshine northeast of
Lakes Erie and Ontario. Temperatures will rebound to around 5
degrees above normal with the southerly flow. Highs expected to run
in the lower to mid 70s away from lake influences. Weak synoptic
scale flow and strong differential heating will allow local lake
breezes to develop with winds becoming onshore along all the
shorelines in the afternoon, keeping temperatures cooler within a
few miles of the lakes.

Tonight, the surface high will weaken over New England while a mid-
level ridge axis shifts over the eastern Great Lakes region. This
will continue fair weather while warm advection aloft and a bit more
cloud coverages holds overnight temps above normal. Lows should only
slip back into the low to mid 50s with some mid-upper 40s possible
in the colder valleys of the western Southern Tier.


The main feature of note during this period will be an upper level
low that will track from the central Mississippi valley Wednesday
morning to the Gulf of Maine by Friday afternoon. Initially, the
location of the low near the confluence of the Ohio and Mississippi
rivers will force ridging downstream across the lower Great Lakes,
resulting in what should be a dry day across western and north-
central New York. Showers will move into the forecast area from west
to east Wednesday night however, as the upper low center moves east
across the Ohio valley and a corresponding surface low moves into
the lower Great Lakes region.

Rainfall should be widespread Thursday into Thursday evening, as the
increasingly vertically stacked low drifts across the lower Great
Lakes and the Mid-Atlantic states. Strong DPVA, favorable jet
dynamics, and a east-southeasterly low and mid-level flow will serve
to advect Atlantic moisture into the region, resulting in 6-12 hours
of soaking rain for the whole forecast area, with most areas
receiving half an inch to an inch of rain on average during the
period. Precipitation will transition to showers Thursday night into
Friday, as the low moves overhead and past the forecast area, though
scattered to numerous showers should linger thorugh much of the day
on Friday, thanks to continued troughing across the area, coupled
with wrap-around moisture. Shortwave ridging moving into the region
in the wake of the departing low pressure system Friday night should
put an end to the showers.

Regarding temperatures, a decent amount of sunshine in addition to
warm advection ahead of the approaching low should allow for
temperatures to climb into the mid 70s across most areas, though
northeasterly flow will keep temperatures cooler along the Lake
Ontario shore. Cloudy and rainy conditions Thursday will depress
temperatures, with highs in the 60s, and cooler air advecting into
the area behind the departing low pressure system will result in
cooler readings in the low to mid 60s Friday. The cloudy skies will
dampen diurnal swings in temperatures, with lows in the 50s during
the nights.


Upper level ridging crossing the region should result in generally
dry conditions on Saturday, though moisture moving through the top
of the low-amplitude ridge just might generate a shower or two, so
have low slight chance pops in place for now. A northern stream wave
diving across the upper Midwest and Great Lakes out of Canada will
bring the next likely round of showers to the forecast area on

The location and timing of the various vorticity maxima
rotating around the upper low, in addition to additional upper level
energy moving thorugh the longwave trough that will be re-
established across the east will determine the specific timing of
rounds of showers as we move into next week, and it is too far out
to pinpoint these kinds of details. However, given aforementioned
longwave troughing becoming re-established across the Great Lakes
and Northeast, suffice it to say that the coming week will trend
towards the cool and showery.


A weak ridge of high pressure slowly shift over the eastern Great
Lakes region through tonight with VFR cigs/vis expected. Weak warm
advection and diurnal cumulus will bring some increase in cloud
cover as a disturbance moves north of Lake Ontario but CIGS will
remain VFR with light southwest winds. The high pressure will
continue to bring VFR and fair weather through tonight.


Wednesday night...VFR/MVFR with a chance of showers.
Thursday...VFR/MVFR with showers likely.
Friday...VFR/MVFR with a chance of showers.
Saturday...Mainly VFR.


Weak high pressure shifting over the Lower Great Lakes today through
Wednesday will provide light winds and little wave action through
the middle of the week. A storm system will pass over our region
Wednesday night through Friday but winds and waves will remain below
advisory levels.





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