Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 240324
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
1024 PM EST Wed Jan 23 2019

.SYNOPSIS...
An area of low pressure will track from the Great Lakes into
southern Quebec tonight with rain this evening changing over to
snow before ending Thursday morning. Cold air will build in
behind this system, with lake effect snow developing east and
southeast of the lakes Thursday night through Saturday.

&&

.NEAR TERM /THROUGH THURSDAY/...
An elongated mid-level trough extending down the Mississippi valley
this evening will gradually move east tonight. Meanwhile,
surface low pressure will track from Lake Huron into southern
Quebec with a surface trough and cold front extending south from
the surface low. A 65kt LLJ will be ahead of this trough and
across our region this evening will move slowly east overnight.

A cold front across western Lake Erie this evening will move
slowly across western and north central NY late tonight. Steady
rain will move across the region with the front and trough axis.
There will be locally higher rainfall amounts due to upsloping along
the south- face of the Tug Hill where the LLJ will result in
upsloping. This will produce a soaking rain with a total of 1.5
to 2 inches through Thursday morning. There also will be some
fog along and ahead of this front. This will be most widespread
northeast of the lakes, potentially resulting in a few hours
with visibility below a half mile in Buffalo late tonight.

Cold air advection will drop temperatures and result in rain
transitioning to snow late tonight and Thursday morning. Unlike
most cases, where dry air rushes in behind the cold front, a
mid- level shortwave trough will ride along the front into
Thursday morning. This coupled with deep layer moisture will
result in widespread light snow to continue through the morning
hours across western NY. The cold front will cross the North
Country around 12z Thursday so rain will have just transitioned
to snow. Temperatures will fall below freezing around daybreak
across western New York, which may freeze up slush or wet spots
on untreated roadways.

Light snow will end from west to east across western NY by afternoon
and persist into the afternoon across the North Country. Minor
accumulations are expected from late tonight through Thursday
afternoon with 2-3 inches across the higher terrain of the western
Southern Tier and east of Lake Ontario. Expect a dusting to 2
inches most everywhere else, including the Buffalo and
Rochester Metros.

Temperatures will fall back to "winter-like" temperatures tonight
and Thursday. Temperatures will drop into the upper 20s across
the higher terrain to the low 30s around daybreak Thursday. The
high temperature will likely be met Thursday morning as temperatures
fall into the 20`s through the day.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/...
...Significant lake snows possible Thursday night through
Saturday morning...

Conditions favorable for lake effect snow set up ENE of Lake Erie
Thursday night, and later Friday/Friday night east of Lake Ontario.
The event can be broken up into two distinct periods - one before an
arctic boundary that will blast through the region on Friday, and
one following the boundary.

East of Lake Erie...A lake band should begin to organize Thursday
Night.  This one will be tricky, with a WSW flow focused on the
Southtowns to near the Buffalo Metro region near the Friday morning
rush hour.  Snow rates may reach 1-2"/hr with this band, but models
have yet to fully lock into this idea.  The atmospheric profile is
favorable though, with a cap above 7500` along with a saturated and
cold airmass together with a full lake fetch.  This band may drop
several inches of snow until the above mentioned arctic boundary
forces the band inland with eventual reorganization over the higher
terrain to the east in the afternoon and evening.   Later Friday
evening, the band or multiple bands will probably keep going east of
the lake, peaking at roughly 1"/hr and then weaken rapidly on
Saturday as flow quickly backs to the south during the morning.
Current forecasts have storm totals reaching 8-16" under the
heaviest snows, with of course much less outside of lake bands.

East of Lake Ontario...There are some models that try to generate a
lake band SE of Lake Ontario (ex the Canadian), but most models have
primarily a WSW flow without much of a response until Friday.  With
borderline temperatures aloft together with backing winds with time
as the arctic boundary approaches, will hold off on any watches and
higher snow rates until Friday.  Some lake enhancement or general
upslope flow should generate at least some snow accumulations across
the Tug Hill Plateau during the morning, but a full fledged band may
in fact have a hard time getting going until the frontal passage.
After this point though, expect a band to blossom over and then move
to the south of the Tug Hill.

A band may then become quite intense Friday night along the Southern
Lake Ontario shore from about Wayne County to Oswego County with
snow rates in excess of 2"/hr as is often the case with increased
convergence at night.  There is the possibility that the band may
hug Monroe County as well. These types of bands however typically
remain just north of the Rochester Metro area and sometimes even
have a slight concave appearance on radar. Regardless, this will
probably be the most intense and interesting part of this particular
lake effect event.  The band should begin to weaken and move to the
north on Saturday as winds back with time.

For other areas,  the main event will likely be a short-lived burst
of snow with the arctic front on Friday.  This may drop a quick inch
or two of snow in the afternoon, probably before the evening
commute. The boundary will disrupt or interact with the lake bands,
and may evolve into a squall line as it moves ESE across the state.
But otherwise most areas outside of lake effect regions will only
see a chance of snow showers.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
Throughout this period a classic coupled +PNA/-NAO pattern will
remain firmly anchored in place...with a strong upper level ridge
entrenched off the west coast of North America...and a second upper
ridge extending from the central Atlantic northward to Greenland.
These two ridges will help to lock a huge closed low and its
associated deep pool of bitterly cold air in place over central and
eastern Canada...with a large-scale cross-polar flow also helping to
continually recharge this cold air supply. For our region...all of
this will ensure that temperatures will average out decidedly below
normal right through this period and into the beginning of February.

Digging further into the day-to-day details...on Sunday a
potent shortwave trough will dig across the Upper Great
Lakes...with its attendant surface reflection rippling across
Quebec Province and pushing its trailing cold front through our
region in the process. At this juncture it appears that this
boundary will be accompanied by enough moisture and lift to
bring a period of fairly numerous snow showers and minor snow
accumulations to the region...for which PoPs have been bumped up
to likely.

In the wake of this front...a fresh shot of bitterly cold air
(850 mb temps ranging from the lower negative teens across the
Southern Tier to negative mid twenties across the North Country)
will pour across our region Sunday night. While this will guarantee
at least some some form of a lake response...this may turn out to be
fairly muted given the increasingly dry nature of the incoming
airmass...building low level ridging...and a commensurate increase
in shear. Otherwise the incoming colder airmass will easily drive
temps back down into the single digits...which have been knocked
back significantly from continuity.

On Monday the axis of the surface ridge will quickly push from
our region into New England...while the next mid level trough
and its attendant organizing surface low push into the western
Great Lakes. This will result in any lingering lake effect snow
showers giving way to increasing chances for some light snow across
far western New York into the afternoon...as warm air advection
begins to take shape aloft out ahead of the next surface wave.
Otherwise...it will be a cold day with afternoon highs mostly
running between 15 and 20.

After that...the medium range guidance packages remain in rather
good agreement on the aforementioned trough/surface low becoming
increasingly better organized and tracking across our region between
Monday night and Tuesday. Given all this...have bumped PoPs up a bit
further into the high likely range for this period. Depending upon
the exact track of this system (which currently ranges from directly
over to a little west of our region in the various guidance packages)...
it is possible that enough warm air could get drawn northward into
our region to result in a period of mixed precipitation or even
rain during Tuesday...though for now have kept the forecast ptype all
snow out of consideration for the overall pattern and our forecast
continuity.

Following the passage of this second system...it still appears all
but certain that a pronounced surge of arctic air will then pour
across our region for not only the end of this period but right
through the end of next week. This will result in temperatures
returning to bitterly cold levels once again...along with another
possible round of lake effect snow.

&&

.AVIATION /03Z THURSDAY THROUGH MONDAY/...
The axis of a LLJ will move east of the area between 03-06Z
with wind shear diminishing from W-E.

Meanwhile, a cold front will approach and move across the
region late tonight. High confidence in cigs lowering to IFR or
lower with this boundary, with locally dense fog a concern
northeast of the lakes at KBUF and KART. Expect widespread IFR
conditions late tonight and into Thursday morning before a
modest improvement to MVFR mid to late afternoon. Colder air
will transition rain to snow from west to east late tonight and
Thursday morning.

Snow will taper off Thursday evening, but then increase in
coverage Thursday night as lake effect snow develops. This will
result in mainly MVFR conditions Thursday evening, lowering to
IFR in heavier lake snows east of the lakes.

Outlook...

Friday and Saturday...VFR to MVFR in scattered to numerous snow
showers, with IFR possible in more numerous snow showers east of the
lakes.

Sunday and Monday...A chance of snow showers. MVFR likely.

&&

.MARINE...
A cold front will track across the eastern Great Lakes tonight
into Thursday. Winds will briefly diminish along this boundary,
bu then shift to the west and increase behind this front on
Thursday. Small Craft Advisories were extended, with a brisk
flow expected Thursday night and Friday.

&&

.HYDROLOGY...
The combination of rain and snow melt will cause creeks to rise
overnight into Thursday, with some likely to reach action stage.
The Buffalo creeks will have to be monitored overnight, with
downsloping resulting in significant snow melt in these basins.
There was only a half inch to an inch of rain in these basins,
with crests likely to be near action stage.

The other area of concern is the Black River basin where basin
average rainfall amounts may push 1.5 inches. This combined with
snow melt will likely push Boonville to near action stage.

Although these will need to be monitored, the overall risk for
flooding is relatively low with RFC forecasts and ensembles
suggesting it is unlikely that any forecast point will reach
flood stage. This said, the combination of rain and snow melt
will result in minor ponding in areas with poor drainage.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Winter Storm Watch from Friday morning through late Friday
     night for NYZ007-008.
     Winter Storm Watch from Friday morning through Saturday
     morning for NYZ006.
     Winter Storm Watch from Friday evening through Saturday
     morning for NYZ004-005.
     Winter Storm Watch from late Thursday night through Saturday
     morning for NYZ019-020-085.
MARINE...Small Craft Advisory from 10 AM Thursday to 7 PM EST Friday
         for LEZ040-041.
         Small Craft Advisory until 7 PM EST Friday for
         LOZ043>045.
         Small Craft Advisory from 10 AM Thursday to 7 PM EST
         Friday for LOZ042.

&&

$$

SYNOPSIS...Apffel
NEAR TERM...Apffel/HSK
SHORT TERM...Zaff
LONG TERM...JJR
AVIATION...Apffel/HSK
MARINE...Apffel/HSK
HYDROLOGY...Apffel


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