Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 241148
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
648 AM EST Thu Jan 24 2019

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

&&

.NEAR TERM /THROUGH TONIGHT/...
A cold front is crossing into Western New York this morning, with
rain changing to snow across these areas as colder air infiltrates
behind the front. The cold front will continue to track east through
the morning, changing all precipitation to snow by the late morning
across the eastern most portion of the area. This front associated
with a surface low just northeast of James Bay, will cross the area
this morning, bringing an end to milder temperatures experienced
across the area over the last 24 hours. This area of low pressure
and cold front associated with a broad mid and upper level trough
over the eastern half of the U.S. will push through as the axis of a
shortwave trough embedded within the larger trough, tracks east from
near the Appalachians early this morning to the eastern seaboard by
this afternoon and evening.

Out ahead of the cold front an area of rain has been persistent as a
plume of moisture ahead of this system treks north along the front
half of the trough, with sources from the Gulf of Mexico and the
Atlantic. After the cold front passes through the area, temperatures
will drop from west to east, with the warmest temperatures of the
day already having occurred across far Western NY. As temperatures
cool through the morning, any areas of rain will start to transition
to a mix of rain and snow, and then change to all snow. With the
cooling temperatures changing precipitation over to snow, and
moisture still over the area, light snow will persist until the
shortwave trough axis pushes the synoptic moisture east of the area.
Light snow will be likely through the middle of the morning across
Western NY and the mid afternoon time for the North Country. Light
snow will taper off to snow showers through the afternoon. Snow
accumulations for areas closer to the lakes will be around 1 to 2
inches, and areas of higher terrain can expect 2 to 4 inches of
snowfall today.

Weak cold air advection behind the front will continue though the
day. As the synoptic moisture moves east of the area, cooling
temperatures aloft will help support some lake enhanced snow showers
downwind of the lakes. Early high temperatures today will be in the
low to mid 30s across the area before cooling through the day to the
upper 20s by mid afternoon.

Tonight, lake enhanced snow showers from the afternoon will
transition to lake effect snow showers downwind of the lakes. As the
night progresses, a weak area of low pressure will cross the Great
Lakes and center between James Bay and Lake Ontario Friday morning.
As this area of low pressure approaches, winds will shift from a
west-northwest direction to a southwest direction, briefly
suppressing the cold air advection over the area ahead of an
approaching cold front associated with the area of low pressure. Out
ahead of the area of low pressure, a weak warm frontal boundary and
increasing synoptic moisture will help spread light snow showers
across the areas, especially across the western part of the area.
850 temperatures will stay cooler than -10C, resulting in marginal
conditions for lake enhancement early in the night with the light
synoptic snow showers over the area.

As the cold front crosses the area, 850 temperatures will drop to
around -15C downwind of Lake Erie behind the front and to around -
13C downwind of Lake Ontario as the front is passing around 12Z
Friday morning. Equilibrium heights off of Lake Erie tonight will
start out around 7kft, and increase to near 10kft as cold air
advection increases early in the morning. Off of Lake Ontario early
morning equilibrium heights of around 7kft will continue to rise
through the morning with cold air advection. Through though the
early morning on Friday, with a southwest wind still over western
NY, a band of lake effect snow will develop northeast of Lake Erie
over the Buffalo Northtowns before slowly shifting south to the
Southtowns and the Boston Hills through daybreak. Lake effect off of
Lake Ontario will start to northeast of the lake as well, and
continue northeast of the lake over the Watertown and Fort Drum area
through the morning. Snow accumulations through daybreak on Friday
morning will be 2 to 4 inches northeast of Lake Erie, and 1 to 3
inches north of Lake Ontario, where the lake snows will start a bit
later. Temperatures tonight will be in the low 20s across the lake
plains of Western NY and in the teens for all other areas.
Temperatures will continue to cool behind the cold front through the
morning on Friday.

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY/...
...Significant lake snows possible Friday through Saturday morning...

Much colder air will pour back into the eastern Great Lakes late
tonight through the first part of the weekend, bringing the
potential for significant lake effect snow. While the large scale
pattern appears favorable, there is still a good deal of uncertainty
with respect to band placement and intensity with relatively poor
agreement so far in mesoscale guidance.

On the synoptic scale, a deep longwave trough will move from
northwest Ontario early Friday morning to western Quebec by early
Saturday morning. A shortwave embedded in the base of the trough
will cross the eastern Great Lakes early Friday morning, with a weak
clipper low passing just north of Lake Ontario. A few snow showers
will occur areawide with the passage of this shortwave and
associated cold front early Friday morning, with another round of
widespread snow showers possible Friday afternoon as another period
of ascent and deep moisture crosses the region. Outside of lake
effect areas accumulation will be light.

Lake effect parameters become quite favorable Friday and Friday
night, with equilibrium levels rising to about 10K feet with strong
instability. Moisture is not overly deep, but should be sufficient
to support a strong lake response at times. A deep dendritic crystal
growth layer will be found in the cloud bearing layer. Shear may be
an issue at times, especially over Lake Ontario by Friday night as a
weak ridge axis builds over the northern portion of the lake.

Off Lake Erie...

Expect a band of snow to intensify late tonight over or even a
little north of Buffalo just ahead of the clipper low and associated
cold front. This band of snow will then move south across the
Buffalo Metro area and Genesee County by early Friday morning,
likely intensifying further. This band will then move into the
northern portions of the Southern Tier by mid or late morning as
boundary layer flow veers westerly behind the clipper. The band may
temporarily weaken for a few hours during this time as moisture
depth decreases. The moisture will improve again later Friday
afternoon, and boundary layer flow is now forecast by most guidance
to back again to the WSW by late in the day Friday. This will carry
the band back north at least into Southern Erie and Wyoming
counties, and possibly into the Buffalo Southtowns and southern
Genesee County by late afternoon. The band of snow will continue in
this area through the first half of Friday night. Late Friday night
and Saturday morning boundary layer flow steadily weakens, which
will force the band to tea kettle and shrink back towards the
lakeshore.

The amount of snow this band produces is not a high confidence
forecast yet, given the frequently moving band. The band will likely
be most stationary from late Friday afternoon through the first half
of Friday night, when it will likely be focused across Central Erie
County to northern Wyoming/far southern Genesee counties. If the
band can remain in one place long enough, accumulations of over a
foot are likely in the most persistent snows. Given the northward
trend in model guidance, have expanded the Winter Storm Watch to
include northern Erie, Genesee, and Wyoming counties as well.
Specifically for the Buffalo Metro area, there will likely be a
sharp gradient in snow amounts with the heavier amounts in the
Southtowns, and much less north of the city. If the northward trend
in model guidance continues, Chautauqua and Cattaraugus counties may
miss the heavier snow amounts.

Off Lake Ontario...

Lake effect snow will increase across northern Jefferson County by
Friday morning in the southwest flow just ahead of the clipper cold
front. This band will then increase in intensity as it drifts into
central Jefferson and northern Lewis counties during the morning.
Most of the mesoscale guidance then suggests the lake band will
merge with the clipper cold front and push onshore and cross Lewis
County and into the western Adirondacks Friday afternoon. Following
this, most mesoscale guidance re-develops a lake band along the
south shore of the lake, with a possible upstream connection to Lake
Huron Friday afternoon. This band is then forecast to focus on areas
southeast of Lake Ontario Friday night, most likely Oswego County
but possibly northern Cayuga and NE Wayne counties as well. The
major exception to this is the Canadian GEM guidance, which keeps
the boundary layer flow WSW or SW through the entire event, which
would keep all the snow focused on Jefferson County and the northern
Tug Hill.

Given this uncertainty in the model guidance, confidence is low on
band placement and amounts off Lake Ontario. The early portion of
the event may drop 6-10 inches on portions of Jefferson and Lewis
counties if the band becomes strong enough just ahead of and along
the cold front. The late Friday afternoon through early Saturday
morning portion of the event is where uncertainty increases. For now
went with the consensus of NAM and GFS wind fields, suggesting the
band will focus on the southeast corner of the lake. If this band
becomes stationary over one area, snowfall amounts in excess of a
foot are possible.

On Saturday the boundary layer flow will become weaker and more
sheared, forcing the lake effect snow to weaken. What remains will
move north as weak boundary layer flow backs to the southwest,
carrying light snow into the Niagara Frontier off Lake Erie, and
Jefferson County off Lake Ontario. Any additional accumulations
after mid morning should be light.

Saturday night and Sunday another mid level shortwave and
associated cold front will cross the area. This will produce another
round of snow showers areawide. Another round of lake effect will
develop behind this cold front on Sunday, although model guidance
shows a good deal of uncertainty with respect to moisture depth and
degree of shear.

Temperatures will turn quite cold again, with temperatures dropping
into the teens on Friday behind the clipper. Lows Friday night will
be in the single numbers away from the lakeshores, and highs
Saturday will be in the teens. Temperatures will recover slightly on
Sunday just ahead of the next cold front, with highs in the 20s.

&&

.LONG TERM /SUNDAY NIGHT 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.

Looking at the details, Sunday night cold westerly flow in the wake
of the Sunday cold front will produce at least some lake response
east of the lakes, although the degree of shear and moisture depth
is uncertain in model guidance.

Another synoptic system will cross the area late Monday through
Tuesday. Model guidance continues to show a variety of track
solutions with this system. Some runs, including the 00Z GFS and GEM
take the low center to the north and west of our region, which would
bring a brief warm-up and possible mixed precipitation or even rain
to our region. The ECMWF on the other hand takes a more southern
track, which would keep our area all snow. If the more southern
track verifies this system could be a respectable snow producer for
our region.

Regardless of the eventual track of this system, model guidance
remains in good agreement in bringing another strong push of true
arctic air into the Great Lakes and New England for the second half
of next week. 850mb temps may bottom out at -30C, which would
support near record cold across our region.

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
A cold front will approach and move across the region this morning.
High confidence in cigs lowering to IFR or lower with this boundary,
with locally dense fog a concern northeast of Lake Ontario early
affecting KART. Expect widespread IFR conditions with some LIFR
conditions possible into this morning before a modest improvement to
MVFR mid to late afternoon. Colder air will transition rain to snow
from west to east this morning.

Snow will taper off this evening, but then increase in coverage late
tonight as lake effect snow develops. This will result in mainly
MVFR conditions this 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 this morning.
Winds will briefly diminish along this boundary, but then shift to
the west and increase behind this front today. Small Craft
Advisories were extended, with a brisk flow expected tonight 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 tonight through Saturday morning
     for NYZ010>012-019-020-085.
MARINE...Small Craft Advisory from 10 AM this morning 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 this morning to 7 PM EST
         Friday for LOZ042.

&&

$$

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


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