Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 220743
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
243 AM EST Mon Jan 22 2018

.SYNOPSIS...
A warm front will continue across the area today with some light
rain and drizzle. More significant rainfall is expected later today
and tonight, as a large storm system tracks through the Great Lakes,
with temperatures warming well into the 40s ahead of this system. A
cold front will then bring back more typical winter weather late
Tuesday into Thursday. Another warm up is forecast Friday into next
weekend.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A Dense Fog Advisory has been issued across western NY as
observations sites are reporting visibilities down to a quarter mile.
This will make for hazardous driving during the morning commute. Ran
this through 10am where incoming rain may help lift visibilities.

A warm front has lifted across much of Western NY early this morning
with its eastern end yet to move across central New York. Dewpoints
have risen into the upper 30s to low 40s behind the warm front while
dewpoints stay in the low 30s east of Lake Ontario. Warm air
advection aloft will parallel the front overnight continuing
chances for hit and miss rain showers and areas of drizzle and fog.
Boundary layer winds are light so warm front will likely be slow to
lift across central NY overnight. A stationary front along the Saint
Lawrence River will stay across far Northern NY and southern Canada
as warm air/moisture advection continues across the eastern Great
Lakes. Overnight temperatures will stay mild, in the low 30s across
the North Country and mid to upper 30s across Western NY.

A several hour period of warm frontal precipitation will push
through the region during the day today. For most areas, this
precipitation will fall as rain, however persistent northeasterly
flow up the Saint Lawrence Valley will likely keep sub-freezing air
locked in across that area. This should result in precipitation
falling as freezing rain in that area this afternoon and evening
before temperatures climb above freezing tonight. A winter weather
advisory remains in place for Jefferson county to account for about
two to three tenths of an inch ice accretion.

The precipitation will wane with the warm frontal passage, as most
of the area south of Lake Ontario emerges into the warm sector by
this afternoon. Temperatures will climb into the 40s south of Lake
Ontario, possibly near 50 degrees closer to the Pennsylvania state
line.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY NIGHT/...
Monday night and Tuesday a slowly deepening surface low will track
northeastward across the central Great Lakes and into southern Quebec.
As it does so...it will finish pushing its warm front across our area
Monday night...followed by its trailing cold front later Monday night/
Tuesday morning. Plentiful lift and moisture accompanying the warm and
cold frontal passages will translate into a certainty of widespread
precipitation Monday night and early Tuesday...for which 100 PoPs will
be in play. With a mild airmass in place...the vast majority of the
frontally-driven precipitation will fall in the form of plain rain.
The one exception to this will be across the Saint Lawrence Valley
and northern portions of Jefferson county...where a lingering
northeasterly low level flow of colder air will likely lead to some
additional light freezing rain and ice accumulations of up to a tenth
of an inch Monday evening...before the warm front passes through and
forces a changeover to all rain by Tuesday morning. With this in mind...
a Winter Weather Advisory is in effect through 06Z Tuesday for
Jefferson county. As for temperatures...continued warm advection will
result in early evening lows ranging from the upper 20s to lower 30s
near the Saint Lawrence River to the lower to mid 40s south of Lake
Ontario...with readings then holding steady or rising through most
of the rest of the night.

Following the passage of the cold front...there will probably be
a brief relative lull in the precipitation late Monday night and
Tuesday morning...before the main upper level low/trailing area of
attendant wraparound moisture works across the region and leads to
another round of fairly numerous showers...which will also become
enhanced downwind of the lakes as increasing amounts of upsloping
come into play. Owing to the rather mild start to the day and only
a modest cold air advection regime found behind the front (850 mb
temps likely only dropping to the -4C to -6C range by early Tuesday
evening)...temps on Tuesday will likely remain mild enough to support
all rain through midday areawide...before cooling of the column
allows for a mix/with changeover to wet snow to develop across the
higher terrain of the Southern Tier Tuesday afternoon. Speaking more
specifically with respect to temperatures...daytime highs on Tuesday
will range from the low-mid 40s across the far west to the mid-upper
40s elsewhere...before giving way to falling readings during the
afternoon.

Given expected snowmelt from the milder temperatures/dewpoints and
the expected rainfall...there will be a continued risk of ice jam
flooding through early Tuesday evening...for which a Flood Watch
remains in effect for far western New York and portions of the
Finger Lakes Region.

Tuesday night the core of the upper low and the surface low will
slide northeastward into the Canadian Maritimes and become vertically
stacked. In the wake of this system...a continued westerly to west-
northwesterly low level flow will continue to drag progressively colder
air into our region...resulting in lingering synoptically/orographically-
driven precipitation mixing with and changing to snow areawide as it
winds down...while also allowing for some modest lake enhancement
to come into play east and then east-southeast of the lakes. As it
has appeared for the past couple of days...the latter will be best
east of Lake Ontario where deeper moisture and a longer fetch across
the lake will be in place...while any enhancement from Lake Erie will
likely be hampered at least somewhat by lingering ice cover. At this
point snowfall amounts for Tuesday night do not look to be overly
noteworthy...with nighttime totals likely ranging from an inch or
two in the areas of most favorable enhancement to well under an inch
elsewhere. Otherwise...ongoing cold air advection will send our
temperatures back down into lower half of the the 20s.

Wednesday and Wednesday night the surface low will quickly eject
northeastward across Labrador and out to sea...while expansive surface-
based ridging and drier air will ridge eastward into our region.
While our airmass will remain cold enough to support a lake response
during this period...subsidence and drying attendant to the ridge will
otherwise result in an increasingly hostile environment for the lake
snows...which will result in the activity southeast of the lakes
steadily weakening over time. With a capping inversion of only 3-4 kft
in place along with shortening northwesterly fetch to begin with...
these will be relatively insignificant...resulting in only some
nuisance-type additional accumulations through Wednesday night.
Otherwise conditions will just be largely dry and cold...with highs
in the 20s Wednesday followed by lows Wednesday night ranging from
the single digits east of Lake Ontario to the teens elsewhere.

Thursday and Thursday night the aforementioned ridge will crest
across our region...with continued drying and subsidence squelching
whatever weak lake effect snow showers are left during the day
Thursday...with a quiet and dry night then following for Thursday
night. Otherwise it will remain on the cold side...with highs on
Thursday ranging from the upper teens across the North Country to
the lower to mid 20s elsewhere...and lows Thursday night ranging
from the teens south of Lake Ontario to near zero across portions
of the North Country.

&&

.LONG TERM /FRIDAY THROUGH SUNDAY/...
The lack of any significant mid level blocking will support a
progressive flow across the country during this period...and that
usually translates into near to above normal temperatures. In this
case...our temperatures will average WELL above normal with the
mercury averaging as much as 20 degrees above late January normals.
That warmth is coming at a good time for most people...as this is
climatologically the coldest time of the year.

Speaking of warmth...one of the driving features for the warm up
will be a fairly significant storm system that will lift northward
from the Tennessee Valley. More on this in a moment.

Fair weather will be in place across our region on Friday as an
amplifying progressive ridge will cross the Lower Great Lakes...
while its corresponding surface high will exit our region via New
England. This will strengthen an already established southerly flow
that will increase the warm advection and allow H85 temps to climb
into positive territory by the end of the day. Max temps will climb
a solid 10 deg higher than the previous day as highs will easily
eclipse freezing over the western counties.

After a fair and notably less chilly night...Saturday will feature
an increase in clouds with another 10 degrees being tacked onto the
max temperatures. A fairly strong southerly flow ahead of an
approaching wavy cold frontal boundary will encourage temperatures
in the valleys west of Seneca Lake to reach 50. While clouds will be
on the increase...the bulk of the day will be rain free...especially
for the Finger Lakes and Eastern Lake Ontario regions.

The guidance packages diverge in their solutions Saturday night and
Sunday...as one camp is stubborn at phasing the sub tropical and
polar jets...while another camp phases the jets and generates a
slower and deeper surface low. So in lies the problem with the
forecast confidence for Saturday night and Sunday. While there is no
doubt that the second half of the weekend will be stormier...the
start and end times for the steadiest rain are as much as 18 hours
apart given the guidance. Stay tuned.

&&

.AVIATION /08Z MONDAY THROUGH FRIDAY/...
A saturated airmass is in place across the terminals early this
morning with a warm front lifting across WNY. Most terminals with the
exception of KROC/KART are seeing sub-IFR/IFR cigs and vsbys as warm
air moves over the snowpack along with areas of drizzle and fog.
KROC/KART are running MVFR but only KROC should dip to IFR by
sunrise. KJHW will hold in VLIFR/LIFR CIGs and VIS through this
morning. Terminals look to then lift to MVFR/VFR for a short
time between this afternoon and this evening behind the warm front.

A cold front will push into WNY tonight with an area of widespread
rain. There could be potentially some fog as well. Additionally, Low
Level Wind Shear looks likely as a strong low level jet shifts over
our region just ahead of the front. This should bring a return of
MVFR/IFR cigs.

Outlook...

Tuesday...MVFR/IFR with rain showers changing to snow showers before
ending...then areas of lake effect snow also developing east of the
lakes Tuesday night.
Wednesday...VFR/MVFR with a chance of snow showers.
Thursday and Friday...Mainly VFR.

&&

.MARINE...
East winds will freshen on today on Lake Ontario with a warm front
running along the south shore of the lake. This front will be
associated with an area of low pressure tracking into the mid-
Mississippi Valley then towards the Great Lakes tonight. Conditions
may approach small craft advisory conditions on the western half of
Lake Ontario this afternoon into this evening.

The low will sweep a cold front across the lower Great Lakes late
Tuesday into Tuesday night, bringing solid small craft advisory
conditions and possible gales to Lake Ontario behind the front
Tuesday night into Wednesday morning.

&&

.HYDROLOGY...
A flood watch for ice jam flooding is in effect for all of
western New York from this afternoon into Tuesday evening.

Temperatures climbed into the lower 40s across much of western
New York on Saturday...and while freezing temperatures returned
Saturday night...this allowed the snowpack across the region to
partially `ripen`. This process continued yesterday as the
mercury returned to the 40s from the Finger Lakes region
westward. Temperatures will remain above freezing into Tuesday
evening...with daytime readings peaking between 45 and 50 and
widespread rain coming tonight. This will allow a true melt
down of the snowpack over the western counties with the runoff
flowing into creeks...many of which are ice covered/clogged.

Using research proven over several decades...the melting degrees
experienced from the above described temperature forecast
suggests that ice jam flooding could prove to be a problem as
early as this afternoon. This potential problem will be
exacerbated by a general quarter to as much as three quarters
inch of rain later today through tonight.

While there will be a risk for ice jam flooding...a less
impressive snowpack...lower temperatures and less rainfall
compared to last weeks flooding should translate into more
localized flooding. In other words...flooding should not be as
widespread as the last event. In any case...those living in
areas prone to ice jam flooding should pay attention to water
levels and subsequent statements and warnings issued by the
Buffalo National Weather Service office.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Winter Weather Advisory from 1 PM this afternoon to 1 AM EST
     Tuesday for NYZ007.
     Flood Watch from 1 PM EST this afternoon through Tuesday
     evening for NYZ001>005-010>014-019>021-085.
     Dense Fog Advisory until 10 AM EST this morning for NYZ001>003-
     010>013-019>021-085.
MARINE...None.

&&

$$

SYNOPSIS...SMITH
NEAR TERM...HSK/SMITH
SHORT TERM...JJR
LONG TERM...RSH
AVIATION...SMITH
MARINE...SMITH
HYDROLOGY...RSH/SMITH



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