Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 141623

Area Forecast Discussion
National Weather Service Buffalo NY
1123 AM EST Thu Dec 14 2017

Today will be another chilly day as high pressure moves into the
Ohio Valley. Another system will bring more lake effect snow to
some areas Friday and Saturday. Then high pressure returns
Saturday night and Sunday.


There are some lingering lake effect snow showers in the
northwest flow behind departing low pressure. These will be hit
and miss snow showers with any accumulations rather localized
depending on upstream lake feeder bands. These will diminish
through early afternoon with the arrival of drier air.

High pressure will move into the Ohio Valley tonight and weak
warm air advection will occur aloft causing lapse rates to
weaken some. The mean wind will continue to back more and allow
a convergent flow to develop on the lakes. As a result lake
effect snow will redevelop early this evening. This should
result in light to moderate accumulations east of Lake Erie,
but given the longer fetch down Lake Ontario expect localized
snowfall amounts of 3 to 6 inches. Mesoscale guidance suggests
this will most likely be in Oswego county, probably along the
immediate lakeshore due to diminishing winds. This is a
challenging forecast due to the light winds and localized
nature of the snow.

The cold will continue today through tonight with temperatures well
below normal.


A sharp mid-level trough with embedded shortwave will be found over
the Great Lakes Friday morning with a clipper over the Michigan U.P.
Through the day Friday the trough axis will cross the eastern Great
Lakes with the clipper tracking east of Georgian Bay. Boundary layer
flow will quickly back to the southwest ahead of the clipper. This
will shift weak lake effect snow bands northward with crossing
Buffalo and Watertown metro areas during the morning commute. The
bands should park across Grand Island to Niagara county off Lake
Erie and the Saint Lawrence River Valley off Lake Ontario by midday.
The transient nature of the snow bands will keep significant
accumulations from occuring with perhaps Advisory level snowfall
totals at best.

Incoming colder air aloft behind the clipper and mid-level trough
will help to strengthen lake snow bands Friday afternoon into Friday
night as lake-induced equilibrium levels rise to about 15K feet. As
winds veer behind the clipper expect the snow bands to sweep rather
quickly south across Buffalo and into the western Southern Tier off
Lake Erie and south across Watertown to the Tug Hill off Lake
Ontario Friday evening perhaps impacting the evening commute. The
bands look to be quite strong they move south with high snowfall
rates greater than an inch per hour possible. This event may
eventually need headlines and a watch was considered, but the
relatively fast band motion leaves some uncertainty to possible snow
totals locking in on any particular location. Will continue to
mention in the Hazardous Weather Outlook. Outside of the lake bands,
the clipper and passing mid-level trough axis will likely bring a
light synoptic snow of an inch or less. Will not as cold as
Thursdays temps, we will remain below normal on Friday with highs in
the low to mid 20s although gusty winds associated with the pressure
gradient will create wind chills in the teens during the day. Lows
will run in the teens to around 20 Friday night with wind chills in
the single digits.

On Saturday, arctic high pressure will build south into the Great
Lakes which will weaken lake effect snow bands east of the lakes.
00z GFS/EC models both show a channeled area of moisture along the
850mb temp gradient stretching from Wisconsin to western PA. Weak
isentropic lift may bring the potential for a narrow band of
synoptic snow which has led to adding in chance POPs through the day
mainly toward the western Southern Tier. Mid-level ridging and lower
level warm advection over the eastern Great Lakes will promote a dry
forecast Saturday night. Temps Saturday look to reach again into the
mid 20s then dipping down into the teens to single digits Saturday
night. Winds will be lighter Saturday with wind chills running in
the teens.


As we move through the weekend and into the early part of next week,
all indications are that the upstream blocking that has led to the
longwave troughing and cold weather across our region will break
down, allowing for a mild Pacific airmass to wash across the
northern tier of the country. In addition, by Sunday, high pressure
sliding across the southeastern U.S. will allow for southerly return
flow to develop across the East, pushing a warm front towards the
lower Great Lakes by Sunday night.

While Sunday should remain largely dry and still on the cool side,
with highs ranging from the 20s in the North Country to the mid 30s
along the PA border, we will see a chance for some light snow Sunday
night as the warm front lifts towards the forecast area.
Temperatures will climb above freezing, into the mid to upper 30s
Monday as warm air surges northwards into the Great Lakes. We will
see a chance for rain and snow showers as a wave riding along the
warm frontal boundary crosses the region Monday or Monday night,
depending on model timing. The warmth lasts into Tuesday, with
temperatures approaching the 40 degree mark before a stronger
clipper brings at least a temporary return to colder temperatures
with a potential for lake effect snows by Tuesday night.


Light snow will taper off through early afternoon with
lingering MVFR and localized IFR conditions in lake enhanced
bands. Impacts will be brief and difficult to forecast in the
northwest flow.

More lake effect snow will develop late this afternoon and
tonight, but will be localized. This may briefly impact JHW
through tonight, but is unlikely to impact other TAF sites.


Friday through Saturday...Mainly VFR except lake effect snow showers
will briefly impact terminal locations with IFR or lower conditions

Saturday night through Monday...Mainly VFR. A chance of snow showers


A clipper low will move away from the lakes this morning. N-NW winds
will increase and small craft conditions are expected today. Winds
and waves may briefly drop off early Friday but winds will increase
with another system late Friday into Saturday with more small craft
headlines likely.


NY...Winter Weather Advisory from 4 PM this afternoon to 7 AM EST
     Friday for NYZ006.
MARINE...Small Craft Advisory until 7 AM EST Friday for LOZ043>045.
         Small Craft Advisory until 1 AM EST Friday for LOZ042.



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