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Area forecast discussion 
National Weather Service Buffalo New York 
354 am EST Sat Nov 22 2008 


Synopsis... 
a northwest flow of very cold air will allow localized heavy lake 
effect snows to continue southeast of lakes Erie and Ontario today 
and tonight...with just scattered flurries and snow showers across 
the remainder of the area. The lake snows are expected to taper off 
during Sunday and Sunday evening...then another storm system will 
approach the region early next week with a mix of rain and snow 
developing Monday...then changing to all snow Monday night. 


&& 


Near term /through tonight/... 
lake snows on the radar are marginal in intensity for warnings and 
advisories, but the models show strengthening during the morning, 
then weakening during the afternoon as subsidence brings drying. 


Off Lake Erie both the NAM and GFS show a strong band with a Lake 
Huron connection. The NAM shows the band continues into the evening 
and then spreads out across the Chautauqua ridge after midnight. The 
warning may have to be extended by the day shift if the band 
develops as prognosticated. 


Off Lake Ontario light lake snows over Oswego County in the 
early morning should intensify with the NAM showing strong 925 mb 
Omega during the morning, then weakening during the afternoon. It is 
a question how far west the stronger lake snows will get, but we 
don't have enough confidence to drop the warning from Wayne or 
Cayuga counties at this time. The NAM shows the lake snows 
redeveloping after midnight tonight, but moving northward in Oswego 
County, so the day shift will need to consider extending or 
reissuing the warning for late tonight into Sunday. 


Elsewhere accumulations should be well below the 4 inch advisory 
criterion today, so we have dropped the lake snow advisories except 
for southern Erie County where it is likely that the band will 
spread in the afternoon south of Angola and Colden. 


Elsewhere only scattered flurries are expected tonight. 


&& 


Short term /Sunday through Monday night/... 
during the first half of the period...our main forecast concern will 
continue to be the present lake effect snow event...which should be 
gradually winding down during the course of Sunday and Sunday night. 


Off Lake Erie...expect only very weak activity at best to be present 
east of the lake by Sunday morning...as warming/subsidence aloft 
associated with continued low level ridging will have lowered the 
capping inversion to only 3-5 kft above the lake surface... 
effectively removing the lake snows from the favorable snow growth 
region. The negative effects of this will also be augmented by 
increasing shear below the inversion...which will act to further 
limit organization. 


The resulting remnant weak lake effect should have a tendency to 
slowly shift northward and dissipate during the day on Sunday as 
winds back...temperatures aloft continue to warm...and shear below the 
inversion continues to increase. For this reason...have dropped probability of precipitation 
back to low chance downwind of the lake Sunday morning...then to 
slight chance and below Sunday afternoon and evening as the activity 
moves north and falls apart. Expect this to be gone by no later than 
Sunday evening...which will set the stage for a dry and quiet Sunday 
night across the western end of New York state. 


Off of Lake Ontario...generally expect to have a Single Lake band 
ongoing southeast of the lake early Sunday morning...given lake 
equilibrium levels still around 7-8 kft along with a relatively 
well-aligned west-northwest flow...decent moisture...and favorable snow growth 
region remaining in place below the capping inversion. Expect this 
environment to generally remain in place through the morning...which 
would keep the activity focused across the Wayne-northern Cayuga-Oswego 
County corridor through midday. As such...have continued to indicate 
a mix of categorical to likely probability of precipitation in this area during this time 
frame...along with some additional accumulations. Should the current 
les headlines for areas southeast of the lake eventually be extended 
in time...any such extension may also need to encompass Sunday 
morning given the still-relatively favorable environment expected at 
that time. 


Thereafter...expect the same general weakening trend and northward 
shift to occur during Sunday afternoon and evening...as the 
thermodynamic environment becomes increasingly unfavorable...and the 
steering flow backs to more of a southwesterly orientation and 
becomes increasingly sheared. Given that the band should still have 
a decent amount of organization as it begins to lift northward late 
Sunday morning and early Sunday afternoon...have held onto likely 
probability of precipitation while lifting the band north during the afternoon and 
evening...before dropping these into the chance/scattered range 
Sunday evening as the flow becomes increasingly sheared. Could still 
see some remnant snow showers lingering from the Watertown area 
northward to the Saint Lawrence River during the early overnight 
hours Sunday night...before finally falling apart by Monday morning. 


After that...our attention will then shift back to the synoptic 
scale...as another potent upper low drops from Manitoba to the 
western Great Lakes on Monday...then to New York state Monday 
night...with its associated surface low reaching southern Ontario by 
late Monday...and New York state by Tuesday morning. A strong warm 
air advection pattern developing out ahead of this system will send 
temperatures surging to around 40f during the day on Monday...with 
an impressive swath of warm advective/jet-induced precipitation spreading 
across the area from west to east Monday afternoon and early Monday 
evening. Expect temperatures to be warm enough to support mostly rain 
initially...before cooling enough to allow for a gradual mix 
with/changeover back to snow during the course of Monday 
night...along with some minor accumulations. Then...things get 
trickier for the long term portion of the forecast...more on that 
below. 


&& 


Long term /Tuesday through Friday/... 
long term models continue to be in reasonably good agreement in a 
very large scale sense with a seasonably deep longwave trough 
remaining centered over the eastern half of noam with ridging along 
the West Coast. This will keep temperatures below average through 
the period. There are considerable differences with the handling of 
smaller scale shortwaves however...which makes the forecast of day 
to day sensible weather very uncertain for much of next week. 
Overall forecast confidence is well below average. 


Looking at the details...the most significant feature through the 
period will be the development and handling of a closed middle level 
low during the Tuesday-Thursday period next week. Just about all of the long 
range models and their various ensemble members develop this 
feature...however the placement...amplitude...and timing are 
considerably different from run to run. The 00z/22 GFS continues to 
be the most impressive model with this system...parking the middle 
level cyclone over eastern New York/western New England for much of next 
week...with a corresponding surface low sitting over eastern New York. If 
this were to verify...it would produce a significant synoptic snow 
event for all of the County Warning Area...with the precipitation coming in two distinct 
shots...one Tuesday into early Wednesday and another later Wednesday 
into Thursday. Meanwhile...the 00z/22 European model (ecmwf) continues to close off the 
middle level low off farther west...with a surface low lifting north 
across the lower lakes on Tuesday...then looping back towards James 
Bay by Thursday morning. This scenario would produce much less 
synoptic snowfall...but could also potentially result in More Lake 
effect problems in its wake. As for the ensembles...those offer 
little clustering as to where this system will close off and 
eventually track...as they place the upper low anywhere from off the 
New England coast to over the lower Great Lakes. 


Given such model variability...it is impossible to offer any 
predictive insight as to where the heavier snowfall may occur with 
this storm. A majority of the possible tracks offered by the 
ensemble guidance would bring at least some snow to most of the 
region...lending enough confidence to go with likely probability of precipitation for 
Tuesday and Tuesday night. After that...the amount and placement of 
lake effect following the storm will be tied to the eventual 
verifying track. Given such high uncertainty...will just carry 
chance probability of precipitation everywhere for Wednesday through Friday next week for 
now until we have a better idea of what the boundary layer wind 
direction may be. As for ptype...temperatures look to be cold enough for a 
predominant ptype of snow Tuesday and Wednesday...then may moderate 
just enough late in the week to allow a possible mix with rain 
during the daytime hours Thursday/Friday. 


&& 


Aviation /09z Saturday through Wednesday/... 
cold air will continue to produce areas of lake effect snow to the 
south and southeast of lakes Erie and Ontario. Snow over the Niagara 
Frontier will continue into the morning hours with occasional IFR 
conditions at both Buffalo and Niagara Falls. IFR conditions are 
also likely at Jamestown now and then through tonight. Rochester 
should remain VFR until the afternoon when lake snows will bring 
occasional IFR visibility and MVFR ceilings through the late 
afternoon. 


Outlook... 
Sunday...VFR. 
Monday...MVFR/IFR in rain or wet snow. 
Tuesday and Wednesday...MVFR in snow showers. 


&& 


Marine... 
a brisk northwest flow will continue through much today and tonight 
across the lower Great Lakes. On Lake Ontario...the northwest flow 
will bring small craft criteria waves to the south and southeast 
shoreline from about Hamlin beach to Mexico Bay...mainly early this 
morning and then again this afternoon and tonight. Meanwhile on Lake 
Erie...expect a brief period of stronger winds and larger waves to 
persist from Sturgeon Point southward through midday today...before 
diminishing during the course of the afternoon. 


&& 


Buf watches/warnings/advisories... 
New York...Lake effect snow warning until 6 PM EST this afternoon for 
nyz004>006-019-020. 
Lake effect Snow Advisory until 6 PM EST this afternoon for 
nyz085. 
Marine...Small Craft Advisory until 4 PM EST this afternoon for lez040- 
041. 
Small Craft Advisory until 7 am EST Sunday for loz043- 
044. 


&& 


$$ 


Synopsis...jjr 
near term...apb 
short term...jjr 
long term...Hitchcock/jjr 
aviation...apb 
marine...Hitchcock/jjr 

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