Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

000 
FXUS61 KBUF 110909
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
409 AM EST Wed Dec 11 2019

.SYNOPSIS...
Moving bands of lake effect snow will bring a few brief rounds of 
heavy snow and blowing snow today through this evening east of Lakes 
Erie and Ontario. Lake effect snow will end tonight east of Lake 
Erie, and continue through Thursday morning southeast of Lake 
Ontario. High pressure will then bring a return to dry weather later 
Thursday through Friday. Low pressure moving northward along the 
east coast will then bring rain and warmer temperatures to the 
region Friday night through Saturday, with rain changing back to 
snow Sunday as colder air moves back into the area.

&&

.NEAR TERM /THROUGH TONIGHT/...
Lake effect snow continues to be the main concern through tonight. A 
clipper will pass by well north of the region across Quebec today, 
with the trailing cold front crossing the eastern Great Lakes during 
the early to mid afternoon. The clipper cold front itself will do 
little, with very limited moisture and forcing to work with. It will 
introduce a more favorable lake effect environment however, with 
lake induced equilibrium levels rising to around 12K feet around the 
time of the cold frontal passage. A favorably deep mixed phase layer 
will be found within the boundary layer, yielding dendritic growth. 
Convergence along the clipper cold front will merge with pre-
existing bands of lake effect convergence, maximizing low level 
forcing. This should result in strong, but short lived bands moving 
onshore from both lakes. The one limiting factor will be a relative 
lack of synoptic scale moisture compared to some events. This may 
limit the maximum intensity of the bands, but the very favorable 
thermodynamics and low level forcing should overcome this.

Off Lake Erie...

A fairly healthy band of snow is moving slowly north along the 
Lakeshore from Dunkirk to Angola early this morning. The heaviest 
snow is close to the lake, with lighter snow extending inland across 
the higher terrain. This band of snow will begin to accelerate 
northward through daybreak as boundary layer flow quickly backs to 
the SSW. The snow will cross the Buffalo Metro area during the early 
to mid morning, just in time for the morning commute. As is often 
the case with northward moving bands in a somewhat dry environment, 
the heaviest snow will be confined to near the lakeshore, with 
lighter snow inland from the lake.

The band of snow will make it all the way north to Grand island and 
central Niagara/western Orleans counties for a few hours late 
morning and midday. The clipper cold front will then capture the 
band, and force it to move quickly back to the southeast and across 
the Buffalo Metro area through mid afternoon. The entire band will 
move onshore from Buffalo all the way down to the Chautauqua County 
shoreline, moving quickly inland across the higher terrain east of 
the lake. This south/east moving band will be more intense than the 
morning band, given the stronger thermodynamics and added boost of 
convergence from the cold front. It will be moving fast however, 
only lasting an hour or two at most for any one location. 

Total accumulations from last night through this evening still look 
to be in the 3-5 inch range from the Buffalo Metro area north and 
east, and 4-7 inches from southern Erie County down the Chautauqua 
County lakeshore and inland across the higher terrain. Much of this 
snow will fall in a few quick bursts.

The east end of the afternoon band will extend quite far inland. It 
is possible a few segments of the band may detach and be carried 
eastward by the cold front across the Genesee Valley and western 
Finger Lakes, producing brief, heavy snow squalls. 

The Lake Erie snow will quickly weaken during the early to mid 
evening across the western Southern Tier, with snow showers then 
ending completely overnight.

Off Lake Ontario...

Expect a similar trend a few hours later. Most of the snow this 
morning will be over the lake with weak, disorganized flow in place. 
By midday lake snow will be carried onshore near Kingston Ontario 
and Cape Vincent. This area of snow will consolidate and intensify 
into a more focused band by early to mid afternoon. The band will 
then be captured by the cold front and carried south and east across 
the eastern Lake Ontario region. 

This initial band may move inland, followed by a brief lull. A band 
of lake effect snow should then re-develop near the southeast corner 
of the lake this evening. This band will settle south across Oswego 
County as boundary layer flow becomes WNW. Unlike Lake Erie, this 
band will last longer with a more favorable environment over Lake 
Ontario through early Thursday morning. High resolution model 
guidance differs on how far south the band will get, with some 
models moving it into northern Cayuga and northeast Wayne counties 
for a few hours in the middle of the night. If this occurs, 
advisories may need to be extended into this area. Late tonight and 
early Thursday morning the band will then move back north across 
Oswego County.

Total accumulations east of Lake Ontario will generally be 3-5 
inches in most locations. The Tug Hill may see up to 6 inches as the 
strongest forcing late this afternoon interacts with upslope flow. 
Oswego County may also see up to 6 inches if the overnight band 
remains in one location long enough. 

Finally, winds will become quite gusty today as the pressure 
gradient tightens across the eastern Great Lakes. Expect gusts of 
around 40 mph on the lake plains northeast and east of the lakes, 
and up to 30 mph farther inland. Where lake effect snow develops, 
the strong winds will produce blowing and drifting snow and very 
poor visibility for short periods of time. The combination of brief 
bursts of heavy snow and blowing snow will be the greatest impact 
from this event.

&&

.SHORT TERM /THURSDAY THROUGH SATURDAY NIGHT/...
Thursday, winds will back as surface high pressure passes just to 
our south, with this feature also sending a wealth of mid level dry 
air across the eastern Great Lakes. A few flurries are possible 
early Thursday near Buffalo on a southwest flow, while east of Lake 
Ontario a weakening band of lake effect snow will likely continue to 
add to modest accumulations. Another inch or so of snow is possible, 
generally along and to the west of I-81. The backing winds will send 
a weakening band of snow from near Oswego County in the morning, to 
near the Thousand Islands by Thursday afternoon...where it will be 
in a much weaker state. 

Fair weather will then occur Thursday night through Friday as this 
surface high pressure slides to the east. Behind the surface high a 
southerly flow will develop, and aid in sending Friday's 
temperatures into the 40s, with mid 40s likely through the Genesee 
Valley.

While our region is under fair weather, two upstream shortwave 
troughs will be advancing towards our region...and develop a surface 
low that will be our next weekend weather system. 

The first wave, within the southern branch of the jet will be 
streaming across the Central Plains Friday, while a second shortwave 
will be dropping southward across Manitoba. These two waves will 
carve a deep trough over the eastern US, with this trough replacing 
a downstream ridge (which help to give us fair weather Friday).

Friday night a surface low will be forming just off the Carolina 
coastline. A deep southerly and southeasterly flow will transport 
both Gulf of Mexico and Atlantic moisture northward...with the core 
of the moisture along a LLJ that will remain well to our east across 
eastern NY and New England. Still we will have PWAT values rising to 
three-quarters of an inch Friday night and Saturday, with initial 
warm air advection, and isentropic lift rain moving across our 
region Friday night and Saturday. There may be enough initial cold 
air on the onset of precipitation that a little snow may fall over 
the Tug Hill region early Friday night. Overall rainfall with this 
system again looks to be manageable for our region, with minor rises 
in creeks and streams. 

Later Saturday and into Saturday evening a deformation axis rain 
shield will cross the region, that should primarily fall as plain 
rain across WNY before the cold air deepens and precipitation type 
changes to snow. There is still uncertainty with the timing of the 
colder air and change to snow..but we could see several inches of 
synoptic snow east of Lake Ontario if the colder air before the 
deformation band of precipitation ends.  

Under the onset of cold air advection Saturday night (850 hPa 
temperatures falling to around -6 to -8C, and still under moist 
cyclonic flow aloft, and the passage of the upper level trough axis 
rain showers will transition to light accumulating snow for our 
region. Highlighted will be the colder, higher terrain where 
orographic lift maintains light snow through the night with a 
coating of snow across the hills of SW NYS, and additional snow on 
top of the deformation band of snow for areas east of Lake Ontario.

&&

.LONG TERM /SUNDAY THROUGH TUESDAY/...
Sunday, cold northwesterly flow will continue across our region as a 
now phased upper level trough, and deepening surface low are across 
Atlantic Canada. A few wind gusts could near 40 mph along the 
southern and eastern shoreline of Lake Ontario with this departing 
surface low. Continued cold air advection, with 850 hPa temperatures 
dropping down towards the negative teens range through the day will 
limit any surface warming. Highs Sunday will only be a few degrees 
warmer than the early Sunday morning lows. There will still be 
enough moisture around to continue now lake effect snow showers, 
highlighting areas to the south and southeast of the Lakes. There 
will also be some blowing snow within these stronger wind 
gusts...and will add this to the forecast for Sunday. As a ridge of 
high pressure draws towards the region Sunday night, drier air will 
end snow showers...while also inducing some clearing. East of Lake 
Ontario clearing skies will help bring a chilly night with lows 
dropping down into the lower teens, and possibly into the single 
digits in the coldest of spots.

Monday a surface ridge will pass across our region, ending any 
lingering lake effect snow early, and bring a quiet December weather 
day across the region with temperatures in the afternoon around the 
freezing mark. 

Tuesday there becomes considerable model spread with the track of 
the next storm system. The 00Z GFS takes a classic high wind profile 
track of a deepening low pressure to our west and north, while the 00Z 
ECMWF and Canadian maintain this low to our south, keeping a colder 
airmass over our region and possible snow.

&&

.AVIATION /09Z WEDNESDAY THROUGH SUNDAY/...
The lake effect snow off Lake Erie will move quickly north early 
this morning, before moving quickly back south during the afternoon. 
The band will produce IFR and VLIFR conditions with moderate to 
heavy snow as it migrates across the region. The fast movement will 
make for very changeable conditions, with the low VSBY not lasting 
for more than an hour or two at any one location. The same will 
occur off Lake Ontario, with lake effect snow developing over Canada 
at the northeast end of the lake late this morning, then moving 
quickly south and east across the east end of the lake during the 
afternoon and evening. This band will also produce IFR and VLIFR 
conditions with brief periods of moderate to heavy snow.

Outside of lake effect areas VFR will prevail most of today, 
although a few very brief snow showers and IFR are likely this 
afternoon with a cold frontal passage. Winds will gust up to 35 
knots northeast of Lakes Erie and Ontario, and around 25 knots 
farther inland.

The lake effect snow off Lake Erie will quickly diminish this 
evening across the western Southern Tier and end overnight. The Lake 
Ontario band will last longer, and center on Oswego County overnight 
with areas of IFR. Outside of lake effect areas VFR will prevail 
tonight.

KBUF Airport...Lake effect snow will move north across the airfield 
during the early to mid morning. This first batch will produce IFR, 
but VSBY below airfield minimums is not expected. The band of snow 
will then be north of the airport for a few hours before moving back 
south across KBUF during the early to mid afternoon. This second 
round of snow is likely to be heavier and accompanied by more 
blowing snow, with VSBY below airfield minimums possible for a brief 
(around 1 hour) period. Conditions will improve rapidly by 21Z as 
the band moves south of the airport.

Outlook... 

Thursday...Lake effect snow southeast of Lake Ontario with local IFR 
in the morning, ending in the afternoon. Otherwise VFR. 
Friday...VFR. 
Saturday...MVFR. Rain likely.
Sunday...Areas of MVFR/IFR in snow showers, especially southeast of 
the lakes.

&&

.MARINE...
A clipper low will pass by well north of the region today, with its 
trailing cold front crossing the eastern Great Lakes during the 
early to mid afternoon. A brief period of marginal gales will 
accompany the cold front on both lakes, with a few hours of 
sustained winds near 35 knots. Winds will quickly diminish tonight 
as the pressure gradient relaxes across the eastern Great Lakes.

&&

.TIDES/COASTAL FLOODING...
A period of low end gale force winds will develop this afternoon
and evening on Lake Ontario. The strong onshore winds, high 
wave action, and high lake levels will bring an increased risk 
of lakeshore flooding along the Lake Ontario shore at the east 
end of the lake. The Lakeshore Flood Watch was upgraded to a 
Warning for Jefferson, Oswego, and northern Cayuga counties 
this afternoon through tonight. This event will not be as 
significant as the Halloween night lakeshore flooding, but still
may be high enough to result in some flooding in flood prone 
areas and more shoreline erosion.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Winter Weather Advisory until 10 PM EST this evening for 
     NYZ012-085.
     Lakeshore Flood Warning from 3 PM this afternoon to 4 AM EST 
     Thursday for NYZ005>007.
     Winter Weather Advisory from 11 AM this morning to 1 AM EST 
     Thursday for NYZ007-008.
     Winter Weather Advisory from 4 PM this afternoon to 4 AM EST 
     Thursday for NYZ006.
     Winter Weather Advisory from 8 AM this morning to 3 PM EST 
     this afternoon for NYZ001-002.
     Winter Weather Advisory until 1 AM EST Thursday for NYZ019-020.
     Winter Weather Advisory until 7 PM EST this evening for NYZ010-
     011.
MARINE...Small Craft Advisory until 10 PM EST this evening for LEZ020.
         Gale Warning from 9 AM this morning to 7 PM EST this 
         evening for LEZ040-041.
         Small Craft Advisory until 10 PM EST this evening for 
         LOZ030.
         Small Craft Advisory until 7 AM EST Thursday for LOZ042-
         043.
         Gale Warning from 3 PM this afternoon to 1 AM EST Thursday 
         for LOZ044-045-063>065.
         Gale Warning from 1 PM this afternoon to 10 PM EST this 
         evening for LOZ062.
         Small Craft Advisory from 2 PM this afternoon to 10 
        PM EST this evening for SLZ022-024.

&&

$$

SYNOPSIS...Hitchcock
NEAR TERM...Hitchcock

National Weather Service Glossary of Abbreviations