Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 181840
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
240 PM 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 THURSDAY/...
Clear, mild and dry conditions expected tonight. Should be just
enough of a gradient flow and dry boundary layer to greatly
limit fog potenial overnight. If winds decouple there could be
some limited fog in the deepest river/creek valleys of the
Southern Tier. Overnight temperatures in the mid 40s to lower
50a.

Thursday, The strength of the mid level ridge will steer the next
upper level wave well north of the Great Lakes through northern
Ontario and James Bay. The weakening cold frontal trough extending
southward from this system will sweep across western New York during
the afternoon. There will be little fanfare with this through as the
airmass is so dry and surface ridge still remains in place. Looks
like at best we`ll see a period of enhanced cloud cover with the
trough, but that should be about it. Highs will fall back into
the mid to upper 60s in response to the associated weak thermal
trough.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/...
A large upper level ridge and corresponding area of surface high
pressure will slowly move over (and then east) of the Great Lakes
region and Northeast US Thursday Night through Saturday Night.  The
result for Western and Central NY will be continued dry weather with
above normal temperatures.  With the high directly overhead Saturday
Night, some valley fog will be possible in deep river valleys
despite the overall dry airmass.  But, with the growing season
essentially over, there will be less available moisture from
transpiration. So, the typical valley fog season is nearing its end.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
It will be absolutely gorgeous across western and north central New
York end 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 /19Z WEDNESDAY THROUGH MONDAY/...
Unlimited VFR flight conditions will prevail through the TAF period.
Southwest winds will continue to gust to around 20 knots until sunset
across the lake plains. Winds will probably drop off just enough
later tonight to warrant the mention of low level wind shear from
around 04z to 12z as a strengthen 40 knot low level jet crosses
the region. Drier air and some gradient will prevent the formation
of any widespread late night valley fog.

Outlook...

Thursday through Sunday...VFR except for local IFR in river valley
fog each late night and early morning.
Monday...VFR/MVFR with a chance of showers.

&&

.MARINE...
A period of moderate southwesterlies is expected on the lower Great
lakes into this evening. Winds will increase Thursday as the
pressure gradient over the eastern Great Lakes increases. This will
bring a round of small craft advisory conditions to the eastern ends
of the Lakes Erie and Ontario on a southwest wind for Thursday and
Thursday night, then to most of Lake Ontario on a westerly wind
as we move into Friday.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Small Craft Advisory from 8 AM Thursday to 2 AM EDT Friday for
         LEZ040-041.
         Small Craft Advisory from 8 AM Thursday to 11 AM EDT
         Friday for LOZ045.

&&

$$

SYNOPSIS...THOMAS/TMA
NEAR TERM...TMA
SHORT TERM...ZAFF
LONG TERM...RSH
AVIATION...TMA
MARINE...TMA


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