Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 171957
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
257 PM EST Sat Feb 17 2018

.SYNOPSIS...
A pair of weak systems will split our region tonight while
generating some nuisance light snow. Fair weather will return
on Sunday as high pressure will pass to our south...then a
dramatic warm up will being for the first half of the work week
when temperatures will soar well into the 60s and possibly to
70. This will be the warmest weather since last October.

&&

.NEAR TERM /THROUGH SUNDAY/...
Conditions will quickly deteriorate tonight as a pair of weak
systems will split our region. A shortwave...seen in WV imagery
cruising across northern Illinois at 19z...will advance across the
Lower Great Lakes tonight while driving a surface trough through our
forecast area. The actual frontal boundary will never really make it
through our region though...as it will stall out across Lake Ontario
before being lifting back north on Sunday. To our south though...a
wave will track along a frontal boundary that will be found over
Virginia.

Isentropic lift on the north side of the passing system will combine
with the forcing from being under the left front exit region of a
cyclonically curved 110kt H25 jet to produce deep lift through a 5-
8k ft thick dendritic growth zone. This lift will be greatest
between 00-06z. This should result in very efficient snow making
over a narrow 3-6 hour window...so have raised pops over the entire
region...particularly south and east of a line from Jamestown to
Canandaigua to the Tug Hill. Snowfall totals have been bumped as
well...with nighttime accumulations now forecast to range from an
inch or less in the more populated areas near the lakes to an
average of 2 inches across the Southern Tier...portions of the
Finger Lakes region and the Tug Hill plateau.

As the sfc wave and overlying jet dynamics push east from
Pennsylvania after 06z...the snow will quickly taper off across the
region. By daybreak...the synoptic supported snow should be largely
done with more locally driven snow showers east of both lakes.

The lake snow Sunday morning will be focused on Oswego county and
the southern slopes of the Tug Hill...although with a cap under 5k
ft... am not impressed for anything more than nuisance snow showers
with morning accumulations under an inch. East of Lake Erie...any
leftover snow showers or flurries will be largely supported by
orographics. No accumulations are forecast for this particular area.
Otherwise...a large area of high pressure passing to our south will
provide fair weather across the region.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/...
Surface high pressure will shift off the East Coast south of New
England Sunday night. Expect this high to continue to influence our
region with mainly clear skies and southerly winds promoting a non-
diurnal temp trend. Low temperatures will occur during the evening
with readings near freezing in WNY and mid 20s east of Lake Ontario,
then warming above freezing across WNY by daybreak Monday and
pushing to near freezing east of Lake Ontario. Consensus of 12z
guidance holds off any precipitation from entering NY until after
12z Monday.

A warm and wet period is then expected Monday into Wednesday. Low
pressure will cross the Central Plains Sunday night then push to
Michigan by Tuesday. Warm air advection supported by a 50+ kt low
level jet ahead of this low will draw anomalously moist air tied to
the Gulf of Mexico north over New York with widespread rainfall
expected across Western and North-Central NY by Monday afternoon.
Surface temperatures should be above freezing across the forecast
area before rain arrives. A +3/+4 standardized anomaly is associated
with PWATs in excess of one inch. This is near or above the daily
max moving average. The surface warm front will be lagging behind
the rain not forecast to reach NY until closer to 12z Tuesday.

The latest models indicate the warm front should shift the
widespread rainfall north Tuesday but still likely allowing for
additional rain across Western and North-Central NY. Perhaps a
portion of the forecast area sees some dry time with likely a tight
gradient between rain and no rain. The axis or heaviest rain south
remain north and west of the forecast area along the northern edge
of the strong 50-60kt low level jet and tightest gradient of 850mb
temps aloft. Tuesday night the band of rainfall looks to push even
further north and west with again perhaps all or at least a portion
of the forecast area seeing some dry time. Using WPC QPF guidance
yields closer to one half an inch of rainfall over the Finger Lakes
Monday through daytime Tuesday increasing toward an inch or more
further north and west to near a Buffalo to Watertown line.

Temperatures are expected to run well above average Monday and
Tuesday. Highs Monday should reach into the 50s then hold steady or
slow rise higher Monday night with Highs Tuesday in the 60s across
most locations with 70 in the Genesee Valley not our of the
question.

Concern arises across the North Country where snow pack still
exists. The combination of snow melt and rainfall may cause flooding
issues on area creeks and rivers including the Black River. This
will continue to be highlighted in the HWO.

&&

.LONG TERM /WEDNESDAY THROUGH FRIDAY/...
Medium range model consensus shows the surface low will shift
northeast across Quebec through Wednesday. This should drag an
associated cold front across Western and North-central Wednesday or
Wednesday night. Widespread rain should again shifting east across
our region with likely mixing with and changing to some snow
showers.

Strong dry high pressure should then build over the Great Lakes
Thursday/ Thursday night. There is a low chance of some rain and
snow showers on Thursday depending on the speed of the front but
mainly dry weather should be expected. Model consensus then shows
another warm front or surface low crossing our region Friday night
into Saturday likely leading some rain and/or snow showers Friday
night and chance or rain showers Saturday.

Temperatures Wednesday will be highly dependent on the timing of the
cold front but should likely remain above normal. Temperatures will
fall back toward normal Thursday through Saturday but likely
remaining 5-10 degrees above mid-late Feb normals.

&&

.AVIATION /20Z SATURDAY THROUGH THURSDAY/...
While high and mid level clouds will continue to thicken across our
region during the rest of the afternoon...VFR conditions will remain
in place.

Tonight...a weak low passing by to our south will help to generate
some light snow while cigs will lower to MVFR levels. Vsbys across
the Southern Tier and portions of the Finger Lakes region could also
briefly lower to IFR levels.

On Sunday...conditions will quickly improve to VFR. The exception
will be in the vicinity of the Tug Hill where MVFR cigs/vsbys will
accompany some weak lake effect activity.

Outlook...

Monday...Deteriorating to MVFR to IFR in rain.
Monday night and Tuesday...Generally VFR to MVFR in showers but IFR
across the North Country in more widespread rain.
Wednesday...MVFR in moderately heavy showers.
Thursday...VFR.

&&

.MARINE...
While generally light winds will be in place across the Lower Great
Lakes through this evening...they will freshen in the wake of a
passing trough later tonight. The higher winds and waves on portions
of Lake Ontario will reach small craft advisory criteria after
daybreak...so have raised a small craft advisory from Hamlin Beach
to Mexico Bay for the bulk of Sunday.

Winds and waves will subside Sunday night and Monday...as the next
area of high pressure will pass to the south.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Small Craft Advisory from 7 AM to 4 PM EST Sunday for LOZ043-
         044.

&&

$$

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



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