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Area forecast discussion 
National Weather Service Buffalo New York 
946 PM EST Friday Nov 21 2008 


Synopsis... 
a northwest flow of very cold air will allow localized heavy lake 
effect snow to continue southeast of lakes Erie and Ontario through 
Saturday night while the rest of the area will just see scattered 
flurries and snow showers. The lake snows will finally taper off on 
Sunday as slightly warmer air arrives and the winds shift to the 
south. Another storm system will approach the region early next week 
with rain or snow changing to all snow. 


&& 


Near term /through Saturday/... 
regional radars showing a temporary lull in lake effect activity... 
especially off of Lake Erie as winds realign more northwesterly as 
upper short wave approaches the area. 


Very cold northwest flow will become realigned later tonight and 
through at least the first half of Saturday. Mesoscale models 
continuing to insist there will be some contribution from the upper 
Great Lakes tonight and Saturday morning...which will help to 
enhance lake effect potential off of both Lake Erie and Lake 
Ontario. Very difficult call to where the heaviest and steadiest 
lake plumes will set up tonight and Saturday in the northwest flow 
regime...but feel a continuation of the warnings to the southeast of 
the lakes look reasonable...with the potential for an additional 
foot of snow particularly along the Chautauqua ridge and across 
Oswego County. Localized accumulations of at least 6 inches are 
likely across a good portion of the area...especially in the 
vicinity of the warning areas. With this in mind...feel it is best 
to issue lake effect snow advisories for the entire area...with the 
exception of northern Erie...Jefferson and Lewis counties. 


We expect the lake effect activity will continue Saturday... 
especially during the morning hours as lake parameters remain very 
favorable. There will be a gradual diminishing trend to the lake 
effect activity during the afternoon hours as low to middle level 
warm advection begins and increasing anticyclonic flow helps bring 
lake equilibrium levels down...and drier air begins to work into 
the area as upstream ridging starts to influence the area. 


&& 


Short term /Saturday night through Monday night/... 
our attention will continue to focus on the ongoing lake effect snow 
event early in the period. 


Off Lake Erie...expect multiple bands to be ongoing across the 
western southern tier during the evening on northwest flow. There 
may still be a dynamic upstream connection to Lake Huron during the 
first half of the night which may bring enhanced banding to portions 
of Chautauqua County. After 06z boundary layer flow will begin to 
quickly back to west and cutoff the Lake Huron connection. At the 
same time however the effective fetch on Lake Erie will increase 
dramatically...which may allow for a band to consolidate across 
northern chau/catt and southern Erie counties. The movement of the 
lake bands overnight should prevent any big totals...but still a few 
places may pick up 2-4 more inches Saturday night. Will not extend 
the flags at this point given the uncertainty in placement and exact 
amounts...but this may need to be considered eventually. 


On Sunday the forecast becomes very tricky. Winds will back to the 
southwest during the day...which will carry any remaining lake 
effect north through the Buffalo metropolitan area. At the same time the 
winds back...temperatures will warm aloft which will reduce lake 
induced instability and may also push the favorable Crystal growth 
zone too high to be tapped into by the lake band. The past few runs 
of the NCEP operational NAM and the new 12z suny Stony Brook MM5 
continue to suggest the potential for a band to lift north through 
the city. It appears the quick motion of the band will limit any 
potential accumulations...but a quick inch or two is not out of the 
question. Given uncertainties with respect to available instability 
by the time the winds go southwest...will just use chance probability of precipitation for 
now but will continue to monitor closely. 


Off Lake Ontario...deeper instability will last longer into Saturday 
night and Sunday morning. An upstream connection to Lake Huron and 
Georgian Bay may become re-established during the night...and the 
operational NAM shows an intensifying band over Wayne/northern 
Cayuga and western Oswego counties. For now will leave the end time 
of the lake effect snow warning the same...but it is likely that the 
warning will need to be extended through Sunday morning on later 
shifts. Additional amounts Saturday night through Sunday morning may 
exceed 7 inches in the most persistent bands. The lake snows may 
also brush the shoreline in the Rochester area as well with some 
local minor accums north and east of the city. 


On Sunday the lake snow will lift north across the east end of the 
lake reaching Watertown by afternoon. Similar to the Lake Erie 
activity...the snow will weaken with time as instability diminishes. 
Just expect weak remnant snow showers by evening from Watertown up 
through the Thousand Islands. 


Our attention then turns back to the synoptic scale. A very strong 
Pacific system...now evident in water vapor imagery off the West 
Coast...will make landfall tonight in British Columbia. This system 
and its associated surface low will dive southeast into the Great 
Lakes on Monday then cross western New York Monday night. As seen in water 
vapor imagery...this is a very dynamic system with lots of energy to 
work with. Strong warm air advection and upper level diffluence 
ahead of the system will support widespread precipitation developing from 
west to east during the day Monday. A surge of warm air ahead of 
this system will bring temperatures above freezing on Monday and warm 
enough for a rain/wet snow mix or even all rain across the lower 
elevations at the onset. Cooler air then filters back in Monday 
night changing a mix or rain back to all snow with some minor 
accumulations possible. See the long term for the rest of the story 
on this system. 


&& 


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/21 and 12z/21 GFS 
runs are the most impressive...parking the middle level cyclone over 
New England for much of next week with a strong surface low sitting 
over eastern New York. If this were to verify...it would produce a 
significant synoptic snowstorm for all of the County Warning Area. The 00z/21 European model (ecmwf) 
closes the middle level low off farther west...with a surface low 
lifting north across western New York on Tuesday then looping back towards 
James Bay by Thursday morning. This scenario would produce much less 
synoptic snowfall...but would bring a much more favorable lake 
effect setup in its wake. The 00z/21 Canadian Gem has a track more 
like the GFS...but is weaker and much more progressive with the 
system. The ensembles 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 far as precipitation type GOES...both the GFS/European model (ecmwf) are cold enough to 
support all snow from Tuesday right through Friday...as are most of 
the ensemble members. Have thus kept precipitation type all snow. Gmos 
temperatures look too warm through the period given the forecast 
temperatures aloft and the persistently cold pattern that we are now 
in. 


&& 


Aviation /03z Saturday through Wednesday/... 
general VFR conditions will predominate for kiag and kbuf tonight 
with occasional MVFR to IFR conditions in snow showers from Buffalo to 
Rochester. Lake effect snows will bring occasional LIFR ceilings and 
visibility southeast of the lakes...northwest of Syracuse, and from 
Jamestown north to Lake Erie. Watertown will be mainly VFR. 


Outlook... 
Saturday...local IFR in lake effect snow southeast of the lakes. 
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 of the upcoming 
weekend over 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. On Lake 
Ontario...expect a brief period of stronger winds and larger waves 
to develop later tonight and last through midday Saturday before 
diminishing. Small craft advisories will remain in place for Lake 
Erie during this period...with the biggest waves expected south of 
Sturgeon Point where fetch will be greater. 


&& 


Buf watches/warnings/advisories... 
New York...Lake effect snow warning until 6 PM EST Saturday for 
nyz004>006-019-020. 
Lake effect Snow Advisory until 6 PM EST Saturday for 
nyz001>003-011>014-021-085. 
Marine...Small Craft Advisory until 3 PM EST Saturday for lez040-041. 
Small Craft Advisory until 7 am EST Sunday for loz043- 
044. 
Small Craft Advisory until 3 PM EST Saturday for loz042. 


&& 


$$ 


Synopsis...Hitchcock 
near term...tma/wch 
short term...Hitchcock 
long term...Hitchcock 
aviation...tma/wch 
marine...Hitchcock 

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