Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 180831
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
431 AM EDT Wed Oct 18 2017

.SYNOPSIS...
High pressure over the Mid-Atlantic coastline will remain anchored
there through the week, bringing dry weather, plenty of sunshine and
above normal temperatures to our region.

&&

.NEAR TERM /THROUGH TONIGHT/...
This morning an area of high pressure is found near Virginia,
stretched along the eastern coastline. IR satellite imagery displays
the region virtually cloud free. Cool and dry conditions will start
this morning...with these dry conditions and a gentle breeze
minimizing any valley fog formation.

For today and tonight clear, dry conditions will prevail. It will
not be as windy today as yesterday...though some SW gusts of 20 to
25 mph will remain possible across the lake plains. There could be
some valley fog tonight...but the dry boundary layer will likely
restrict any fog formation to over the moisture source of creeks and
rivers.

Temperatures today will be some 5 to 7 degrees warmer than Tuesday,
with highs peaking in the mid 60s to lower 70s. Tonight will feature
lows in the mid 40s to lower 50s. These temperature readings will be
around 10 degrees above normal.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
As we have promised for nearly a week now...an anomalously strong
East Asian jet racing across the North Atlantic would provide our
region with mild weather...and here it is. Temperatures will average
above normal throughout this period...and well above normal as we
push into the upcoming weekend. We can ultimately thank the
aforementioned East Asian jet for this latest bout of indian summer
weather.

Hemispheric features such as the East Asian jet not only cut off the
supply of chillier air from the higher latitudes...but they usually
encourage troughing over the western half of the country. This is
important because troughing over the western conus will typically
lead to downstream ridging and moderating temperatures over the
Great Lakes region. Take note local mets...this can be a very useful
teleconnection forecast tool...especially during the winter months
when this jet is poleward of 40N.

Getting into some details of this period...
As a burgeoning ridge takes shape over the nations mid section on
Thursday...a robust shortwave (seen in hemispheric WV imagery
crossing the Canadian prairies this morning) crossing Hudson Bay
will sweep a far reaching cold frontal boundary across our region.
Given the limited moisture that will be in place across the Lower
Great Lakes and lack of any mid-upper level forcing...this will be a
DRY frontal passage with nothing more than a 3-6 hour window of
negligible increased cloud coverage during the second half of the
afternoon into the evening. A 40-45kt low level jet will precede the
sfc frontal boundary...but with cold advection ahead underway...a
fair amount of this wind will be able to mix to the ground. This
will encourage somewhat windy conditions with gusts well into the
30s (mph) across the Niagara Frontier...parts of the North Country
and across the higher terrain. The passing of this boundary will
also temporarily stall our day to day upward trend in temperatures.
That being said...H85 temps cooling to around 7c will still easily
support afternoon temperatures in the mid to upper 60s f.

High pressure centered over the Upper Ohio Valley will then nose
back to the north and become re-established over the Lower Great
Lakes region Thursday night. While this will lead to clear starlit
skies and weakening winds...the mild airmass will preclude the
potential for any frost. While we will likely aim a couple degrees
lower than most guidance packages for overnight mins...the mercury
will remain above normal by only falling into the 40s.

Delightful weather can be expected to end the work week on Friday...
as expansive high pressure will become centered directly over our
forecast area. Generous amounts of sunshine will combine with H85
temps in the vcnty of 10c to encourage the mercury to climb well
into the 60s for the afternoon...with some of the warmer valleys
tickling 70. The mild weather...sunshine and light winds will make
this day a great one for viewing the Fall foliage throughout the
region.

As the large surface high drifts to eastern New York during the
course of Friday night...a southerly low level flow will gradually
become established over our region. This will help to keep overnight
temps at above normal levels...as mins are forecast to range from
the lower 40s across parts of the Srn Tier and North Country...to
the upper 40s across the bulk of the lake plains.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
It will be absolutely gorgeous across western and north central New
York this weekend...as a high amplitude ridge will be anchored along
the East Coast. This staunch feature will pump late summer warmth
into our region while maintaining fair skies. Temperatures will be
some 15 to 20 deg f above normal...with the greatest anomalies found
during the day when the mercury is forecast to climb well into the
70s. It will be well advised to take advantage of the nice
weather...not only because of the calendar...but because a change to
increasingly unsettled weather with significant cooling can be
anticipated by the end of the period.

As we head out of the weekend...big changes will be heading our way.
The strong latitudinal jet that had been traversing the north
Pacific in the preceding days will be making significant inroads
across the northern Rockies while broad troughiness will become
established across the center of the country. Meanwhile...guidance
has been consistent with the East Coast ridge holding its ground.
This will result in a strengthening southerly flow that will not
only increase the general moisture profile across our region for the
start of the new work week...but will also serve to weaken an
advancing frontal boundary. The cool front will push across the
Lower Great lakes late Sunday night and Monday...but will wash out
by Monday night as it will become parallel to the aforementioned
southerly flow. The resulting frontolysis (weakening of
baroclinicity) will lead to less synoptic forcing for the associated
shower activity...so have backed off on the likely pops and will
only use chc pops at this point.

A semblance of a dry slot will work in behind the dissipating front
Monday night...so have again backed off significantly on the pops
from continuity.

For Tuesday...while there is general agreement within the ensembles
of a longwave trough digging across the Upper Great Lakes and Mid
Western states...there is a fair amount of spread in the surface
solutions. Without getting into the gory details between the various
camps of solutions from this range...will boil it down by saying
that the likely pops in continuity appear reasonable so will refrain
from making any significant changes at this time.

Looking further down the road at the end of next week...a
significant pattern change will be well underway across the
continent. A phased -NAO and +PNA pattern will be found across the
northern hemisphere as ridging over Greenland will block up the flow
over North America. This will encourage a deep...longwave trough
over eastern Canada with ridging found upstream over the western
half of the continent. Given this scenario...relatively cold air
found over the Canadian Archipelago will be given the opportunity to
push well to the south towards the Great Lakes region. While the
brunt of any true cold air will not be felt until NEXT weekend...the
trend in temperatures will be lower during the week. Thus...the bulk
of next week should feature near to below normal temperatures. Can
lake effect snow be far behind? Stay tuned.

&&

.AVIATION /09Z WEDNESDAY THROUGH SUNDAY/...
VFR flight conditions for the 06Z TAFS will prevail through the TAF
period. Winds will generally be light, though a few SW gusts this
afternoon may reach 18-20 knots across the lake plain. Dry air
should prevent the formation of any widespread morning valley fog.

Outlook...

Thursday through Sunday...VFR except for local IFR in river valley
fog each late night and early morning.

&&

.MARINE...
Winds are slowly diminishing this morning, though a still
southwesterly fetch is yielding waves 4 to 6 feet on the eastern
waters of the Great Lakes. Small craft advisories will continue for
the eastern waters this morning.

A period of lighter winds this afternoon and evening will increase
tomorrow as the pressure gradient over the eastern Great Lakes
increases. This will likely bring another round of SCA on a
southwest wind for Thursday and Thursday night.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Small Craft Advisory until 8 AM EDT this morning for LEZ040-
         041.
         Small Craft Advisory until 8 AM EDT this morning for
         LOZ043>045.

&&

$$

SYNOPSIS...THOMAS
NEAR TERM...THOMAS
SHORT TERM...RSH
LONG TERM...RSH
AVIATION...THOMAS
MARINE...THOMAS



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