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Area forecast discussion
National Weather Service Buffalo New York
423 PM EDT Wed Sep 18 2019

Synopsis...
an area of strong high pressure will provide US with a prolonged
stretch of magnificent late Summer weather for the rest of the week,
with temperatures climbing to well above normal by late in the week.
The next chance of rain will not arrive until Sunday night.

&&

Near term /through Thursday night/...
a 1028mb high pressure is located from the Canadian Maritimes
to northern New England late this afternoon. This airmass
extends southwest into western and north central New York. Besides
some high/thin cirrus and a few diurnal cumulus of little
vertical extent across western NY, sunshine and dry conditions
will persist across the region into the early evening hours.

A building mid-level ridge will track overhead tonight and while
little change will occur at the surface, warmer temperatures will
filter into the region aloft. Clear skies and dry air will result in
another night of radiational cooling. Valley fog is likely again
across the southern tier and lower Genesee Valley. Low temperatures
will again drop to the low to mid 40's away from the lakes and low
50's near the Lake Shores. A few places in eastern Jefferson and
Lewis counties may drop into the upper 30's.

After valley fog dissipates Thursday morning, the warmer
temperatures aloft and sunshine will result in temperatures reaching
the low to mid 70's Thursday afternoon. Low temperatures will be a
few degrees warmer than previous nights. Valley fog is likely again
across the southern tier and lower Genesee Valley.

&&

Short term /Friday through Sunday night/...
well advertised upper ridge from the south central Continental U.S. Toward
Hudson Bay expands across the Great Lakes and into the northeast
Continental U.S. By this weekend. Sfc high pressure from Atlantic Canada to the
lower Great Lakes reorients by Friday, with high pressure center
settling along the East Coast with secondary ridge from Hudson Bay
to the lower Great Lakes. Overall this pattern brings warmer air
aloft into New York by the weekend with 850 mb temps rising to 13-15c by
Saturday and into the mid teens by Sunday. Initially as the high
pressure ridge is close by, forecast soundings indicate we will not
tap into these very warm temps aloft due to subsidence inversion
around 900mb/3kft above ground level. However, later Saturday afternoon and into
Sunday, mixing increases where high temps should reach into at least
the lower if not mid 80s in some locations.

Main question on Sunday is how quick will a pre-frontal trough ahead
of main cold front, and the associated showers, arrive from the
west? GFS remains quickest as edge of stronger moisture transport
and entrance region of upper jet would support some showers into
western New York mid to late afternoon. European model (ecmwf) shows similar features
driving the showers, but is overall 6-12 hours slower. Canadian
is a compromise solution. Forecast soundings indicate mid clouds
invading as early as Sunday morning, but more significant deeper
moisture with precipitable waters over 1.75 inches not arriving until Sunday
evening. Prefer to lean toward slower ideas since the pre-frontal
trough and main cold front will be parallel to the upper flow and
since the mid-level winds through Sunday are SW instead of W which
would drive showers into western New York. For now, brought low-end
chances to western New York after 21z, ramping up to likely pops across
the board by later Sunday evening as axis of deep moisture arrives.
After a warm start for temps on Sunday morning, kept highs into the
lower 80s western New York toward mid 80s southeast of Lake Ontario and
toward Finger Lakes. If cloud cover is thicker, then highs could be
held back into the upper 70s to lower 80s from west to east.

Looks like there will be a couple periods of showers work through
Sunday night on into Monday. All models trending toward better
chance for rainfall all areas on Monday with stronger shortwave
working through in overall troughing aloft. Went for likely pops all
areas on Monday. Though guidance doesn't explicitly show it, could
be some thunder especially western New York as edge of plume of elevated
instability tries to advect in. Probably just a few rumbles and
certainly not enough of a signal to put in the forecast attm.
Lastly, as previous shift mentioned, remnant deeper moisture from
what once was briefly ts Imelda may be around on Monday as the main
front moves through which would only help enhance heavy rain
chances. Even without that though, given precipitable waters above 1.5 inches, may
see some heavy rain at times later Sunday night through Monday.
Though with the rain and cloud cover it will be cooler compared to
the Friday - Sunday time frame, readings on Monday even in the lower
to middle 70s will be above normal as normal highs are in the upper
60s to near 70f.

No choice but to hang on to at least lower chance pops through much
of Monday night due to slower trend in exiting the system. Best
chances for showers, especially overnight, should remain south and
east of our area.

&&

Long term /Monday through Wednesday/...
gradual improvement Tuesday into Wednesday in the wake of mid level
shortwave trough moving offshore over the Atlantic. 850 mb temps by
Tuesday afternoon will be in the vcnty of 6c, so it will certainly
be cooler. Afternoon highs Tuesday should be in the upper 60s to
near 70, which will still be a couple ticks above normal. Dry
weather extends into Wednesday with temperatures reaching back into
the lower to middle 70s.

&&

Aviation /21z Wednesday through Monday/...
VFR conditions will continue into the evening hours with
nothing more than some high/thin cirrus and a few cumulus across
western New York with little vertical extent. Valley fog is likely
across the western southern tier and may extend into kjhw late
tonight into Thursday morning. VFR conditions expected Thursday
as high pressure remains across the region.

Outlook...
Thursday through Sunday...mainly VFR...with localized IFR in
southern tier valley fog possible each night/early morning.

&&

Marine...
high pressure will provide our region with light winds and minimal
wave action for the rest of the week. The one minor exception will
be on Lake Erie and Western Lake Ontario, where a brief period of 10-
15 knot northeast winds will develop this afternoon, bringing waves
up to around 2 feet briefly.

&&

Buf watches/warnings/advisories...
New York...none.
Marine...none.

&&

$$

Synopsis...Hitchcock/Thomas

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