760 
fxus61 kaly 041800 
afdaly 


Area forecast discussion 
National Weather Service Albany New York 
100 PM EST Thursday Dec 4 2008 


Synopsis... 
over the next few days a series of fast moving systems will 
influence our weather. A cold front will slide offshore this 
evening. High pressure will build into the Ohio Valley Friday and 
drift offshore Saturday...but produce a cold flow of air across 
the Great Lakes. Saturday night and Sunday a clipper type low pressure 
area will race across southeast Canada...dragging yet another cold 
cold front through the region...and bring some light snow. Sunday night 
into Monday an Arctic high pressure area will move east from the 
Great Lakes across our region. Midweek a rather complex storm 
system will head our way from the Tennessee Valley. 


&& 


Near term /until 10 PM this evening/... 
cold front should be be along coast during the evening...there will be 
some Anna type -shra/shsn in southeast sections...otherwise fca will spend 
the evening hours in weak surface ridging...accompanied by cold air advection...as 
cold layer deepens...preparing the environment for a lake effect 
event to come later. May be scattered --shsn early in west Adirondacks/Mohawk 
Valley....but otherwise breezy and turning colder. 


&& 


Short term /10 PM this evening through Sunday/... 
overnight niziol instability class becomes moderate...and east/west single band 
across Lake Ontario organizes...as cap rises quickly. Meanwhile 
series of 500hpa short waves pass across region with cva. Initially 
there may some -shsn into mhwk valley and mainly along South Shore of 
the lake...but in time secondary east/west cold front drops south into 
fca...and main band sets up along 280 to 270 vector by late at 
night. Friday and Friday night the band fluctuates between 280 and 250 
degree...putting much of north Herkimer and West Hamilton cos in periods of 
lake effect snow. This fire house effect will keep the event from 
reaching warning criteria as the snow is spread over a wider 
area. 


Plan to issue a lake effect Snow Advisory for north Herkimer/Hamilton 
counties with the forecast package. Away from the lakes under high 
pressure and subsidence fair weather expected...but moisture and clouds 
off the lakes will keep it more partly cloudy than clear. 


Friday night surface ridge sets up from Maine to West Virginia. Lake effect diminishes 
as upper support ends...and the whats left is turned toward Saint 
Lawrence valley as h850 flow becomes SW. Just about ideal radiation 
conditions Friday nt and will take mins several degrees below model 
blend. 


Sat will start fair...but clouds associated with warm air advection ahead of approaching 
clipper system will move into region later in the day. The NAM is 
slower with this by 3-6 hours...but both models hold precipitation off till 
evening. 


The clipper surface low moves through the east Great Lakes as a series of 
500hpa short waves carve out a negatively tiled trough at that level 
from the Great Lakes to middle Atlantic. Fca is in warm air advection area between surface low over 
east Great Lakes and developing offshore coastal low Sat nt into Sunday. 
The main occluded axis is east of fca Sunday morning. However the 
GFS/NAM shows continuing widespread -shsn in cold air advection mainly north & west of 
alb. While conds in lower levels are not indicative of lake 
response into our area...(n-NNW flow)...this precipitation is mainly 
driven by the strength of the 500 hpa trough. NAM is still a tad 
faster ending this event. Much of area will see -sn...with an inch 
or so possible valleys and a few inches in higher elevations...particularly 
Adirondacks. The ensembles have two outliers that would indicate a 
6 inch snow storm...but they are outliers. 


&& 


Long term /Sunday night through Thursday/... 
the sharp upper level trough will induce strong cyclogenesis over 
the Atlantic...but too far out to sea to affect our region 
directly. However...this ocean storm will increase the gradient 
over the region Sunday night into early Monday when it will be 
quite windy. 


A brief period of dry weather expected Monday and early Monday night 
as a surface high builds into the region. As it exits to our 
east...a southerly flow of increasing moisture will follow as a sharp 
long wave trough develops/deepens over the middle of the County. A 
strong surface low will form in response to this developing long 
wave trough...but there is substantial model disagreement as to what 
will occur during the Tuesday through Thursday period. Operational 
GFS shows a 964 mb surface low moving into eastern Canada by 
Wednesday evening with a frigid push of Arctic air into the region. 
The European model (ecmwf) holds off strong surface low development until Thursday. 
With so much uncertainty...but models suggesting a significant 
weather event will occur sometime during the late Tuesday into 
Thursday time frame...will forecast a long period of 50 percent probability of precipitation 
with snow and/or rain forecast. 


&& 


Aviation /18z Thursday through Tuesday/... 
cold front still progressing through New York...creating precipitation 
and low clouds. Most of the precipitation has moved through the kgfl 
terminal with scattered light rain showers possible into the 
evening...MVFR visibilities and IFR ceilings possible in these showers for 
the afternoon. Kalb affected by precipitation through afternoon with 
showers creating MVFR conditions through 20z. Kpou will that main 
line of showers move through this afternoon through the evening. 
Only light rain is expected. Overnight...VFR conditions expected 
as subsidence occurs behind the front. Friday...Lake effect snow 
showers expected to affect the Adirondacks with possible flurries 
reaching kgfl. 


Low level wind shear expected through afternoon at kalb...before winds mix down 
creating gusts to 20kts. Kgfl and kpou winds not expected to mix 
down...therefore have low level wind shear out of the west at 25-30kts to 2000 
feet. Wind shifting west at the surface expected late this afternoon 
into early evening behind the front. Wind speeds will remain 
4-8kts through the overnight and increase in the late morning 
Friday. 


Outlook... 
Friday...VFR/MVFR...wdly scattered/scattered -shsn in the north. 
Sat...VFR...no sig weather. 
Sat nt-sun...MVFR/IFR...chc -sn. 
Monday...VFR...no sig weather. 
Tuesday...MVFR...chc -shsn/-shra. 


&& 


Hydrology... 
no Hydro problems are expected over the next 5 days. It will turn 
much colder starting later today with precipitation changing from 
rain to snow. 


Starting tonight temperatures over the region will average well below 
freezing into early next week with highs from the middle twenties to 
the middle thirties and lows from the middle singles to the middle twenties. 
This will be favorable for ice to form and thicken on rivers and 
lakes. 


For details on the rivers...please visit the advanced hydrologic 
prediction service /ahps/ graphs on our website. 


&& 


Aly watches/warnings/advisories... 
CT...none. 
New York...none. 
Massachusetts...none. 
Vermont...none. 


&& 


$$ 
Synopsis...Snyder 
near term...Snyder 
short term...Snyder 
long term...maglaras 
aviation...kgs 
hydrology...rck 

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