Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 220524

Area Forecast Discussion
National Weather Service Buffalo NY
124 AM EDT Tue Aug 22 2017

The return flow between a surface high off the mid-Atlantic and low
pressure approaching the region will build heat and humidity through
Tuesday. A strong cold front will cross the region late Tuesday, and
may be accompanied by strong to severe thunderstorms. The end of the
week into the weekend will have a touch of fall in the air as a
sprawling Canadian high pressure builds in cooler and drier air.


A strengthening low-level jet will feed warmer, moisture rich air
into the area on the deep southwesterly flow ahead of a low pressure
system approaching from the upper midwest. Despite patchy model
QPF, suspect the leading edge of this jet will provide ample lift
for a few scattered thunderstorms to develop late tonight across far
western portions of the cwa. The increasing SSW winds will also keep
overnight temperatures quite warm with most locations not falling
out of the 70s overnight, and also quite muggy as dew points rise
into the upper 60s to the near the 70 degree mark by early Tuesday

The primary forecast concern continues to be the potential for
severe weather on Tuesday. SPC continues to have the area in a
slight risk for severe thunderstorms with damaging winds the primary

Model consensus has been fairly consistent with this system, with
12Z guidance trending perhaps a tad faster. The leading edge of a 50
kt 850mb LLJ will continue to lift from SW-NE across the region
Tuesday morning. This will leave robust wind profiles across the
entire region by late Tuesday morning, with more than ample speed
and directional shear to support well organized convective
development. The critical factor appears to be how much
sunshine there is before clouds associated with the shortwave
overspreads the area and limits daytime heating. Forecast
profiles show modest mid- level lapse rates with a long and thin
CAPE very sensitive to small differences in surface temperature
and dew point. If there is significant morning sunshine, then
the risk for severe weather will increase with damaging winds
the primary threat.

Although model guidance is in good agreement on the general pattern,
there is lower confidence in the specifics with model guidance
presenting a wide array of QPF solutions. In general expect
scattered thunderstorms during the morning hours with a limited
contribution from daytime instability but with some large scale
forcing and moisture. Areal coverage will expand during the
afternoon hours with the approach of the shortwave and with
increasing diurnal instability. High resolution guidance tends to
focus this across inland of the lake plains with lake shadowing
diminishing coverage some during the afternoon hours. Forecast
maintains categorical PoPs in these area, though specific timing
varies by a few hours by model.

There is also a potenial for heavy rain with thunderstorms on
Tuesday. PWAT values are forecast to approach 2 inches, with very
heavy rainfall possible. However, the strong flow will result in
fast storm motion which somewhat mitigates this threat, though it
still remains a concern if training were to occur.

Expect high temperatures on Tuesday to be in the 80s, but these may
need to be adjusted a few degrees in either direction depending on
cloud cover.


The cold front will finally cross the area during the late
evening/early overnight on Tuesday Night. This will be accompanied
by a few more showers and thunderstorms...ending from west to east.
In the wake of the front skies will clear from northwest to
southeast. As the night wears on however expect some lake
clouds to begin to form by morning.

On Wednesday a broad longwave trough will become established from
the Great Lakes to New England, with a secondary weak cold front
crossing the area during the late afternoon and evening. Any morning
sunshine will fade during the afternoon with the approach of the
secondary cold front and continued increase in lake effect and
upslope clouds. Increasing moisture and convergence over the lakes
may allow for a few lake enhanced showers during the afternoon and
evening. A few lake enhanced showers may continue into Wednesday
night east and southeast of the lakes, however short fetch NW flow
and a fairly dry synoptic scale background will keep this limited.

Temperature-wise the period will be dominated by much cooler and
less humid air.  Highs on Wednesday in the upper 60s to low 70s.


A long wave trough will remain over the region through the end of
the week. A shortwave will deepen the trough Thursday, bringing
cloudy skies and a chance for a shower. Cool temperatures Thursday
in the 60s, will only improve a degree or two for Friday and
Saturday. Fair weather Friday and Saturday with abundant sunshine
as surface high pressure passes through.

Sunday a weak back door cold front will drop down from Canada,
though limited moisture suggest nothing more than just a few clouds
with this feature. Dry weather is expected to continue into the
start of next week with high pressure again entrenched across the
Northeast. As the upper level trough exits to the east Sunday,
temperatures will be a bit closer to normal in the mid 70s across
the region.


VFR conditions will prevail overnight with a west to east increase
in mid level clouds. A few isolated showers will spread from
southwest to northeast across the area as a weak warm front crosses
the region. These showers and possibly a few thunderstorms may
become a little more widespread east of Lake Ontario for a few hours
around daybreak as the warm front strengthens.

The showers along the warm front will exit the eastern Lake Ontario
region by mid morning, leaving VFR to prevail through midday with
areas of mid level clouds crossing the area. Expect one or more
lines of strong to severe thunderstorms to develop across Western NY
around midday or early afternoon, then spread very rapidly northeast
across the rest of the area through late afternoon. These storms
will produce a brief period of heavy rain, gusty winds, and local
IFR as they sweep across the area. A few storms may be severe with
surface wind gusts exceeding 50 knots.

In the wake of the line of storms, a few more widely scattered
showers and thunderstorms will develop from late afternoon through
evening, with VFR prevailing most of the time. These will end
overnight from west to east as a cold front crosses the area.

It will become quite windy today even away from the thunderstorms,
especially northeast of Lake Erie where gusts may peak at 35-40
knots during the afternoon and early evening near KBUF and KIAG.

Wednesday and Thursday...VFR/MVFR with a chance of showers.
Friday and Saturday...VFR.


Light southerly flow tonight will direct any waves mainly toward
Canadian waters. A strong cold front will cross the region Tuesday
prompting small craft headlines as outlined below. A few strong to
possibly severe thunderstorms are also possible Tuesday ahead of the
cold front.


NY...Lakeshore Flood Watch from this afternoon through Wednesday
     evening for NYZ007.
     Lakeshore Flood Watch from this evening through Wednesday
     evening for NYZ004>006.
     Beach Hazards Statement from 1 PM EDT this afternoon through
     Wednesday morning for NYZ010-019-085.
MARINE...Small Craft Advisory from 10 AM this morning to 8 PM EDT this
         evening for LEZ020.
         Small Craft Advisory from 10 AM this morning to 5 AM EDT
         Wednesday for LEZ040-041.
         Small Craft Advisory from 10 AM this morning to 8 PM
         EDT this evening for LOZ030.
         Small Craft Advisory from 2 PM this afternoon to 11 PM EDT
         Wednesday for LOZ043>045.
         Small Craft Advisory from 2 PM this afternoon to 2 PM EDT
         Wednesday for LOZ042.



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