458 
fxus61 kaly 030848 
afdaly 


Area forecast discussion 
National Weather Service Albany New York 
348 am EST Wednesday Dec 3 2008 


Synopsis... 
high pressure near the middle Atlantic coast will produce dry 
and seasonable weather today. A strong cold front will 
approach from southeastern Canada and the Great Lakes region 
tonight. This front will quickly move across the region on 
Thursday... with scattered rain and snow showers...as a much colder 
air mass...and lake effect snow for the western Adirondacks...will 
return Thursday night into Friday. 


&& 


Near term /until 6 PM today/... 
the ruc13 analysis shows low and middle level heights rising with 
weak ridging settling over the northeast and Atlantic Coastal 
Plain. At the surface...high pressure will be south of the region 
today...and then drifts off the middle Atlantic coast in the late 
afternoon. A warm advection pattern will continue to unfold...with a 
strengthening low level S/SW flow. Model soundings do show a 
pronounced low level inversion from h925-800 today...which will 
inhibit temperatures from soaring above normal. However...h925 temperatures of 
-2 to -3c with mixing to about h900...should allow highs to reach 
the upper 30s to lower 40s in the valleys...and middle to upper 30s 
across the hills/mountains with partly to mostly sunny skies. We went a 
shade colder than the gfsmos maximum temperatures. 


&& 


Short term /6 PM Wednesday through Friday/... 
tonight...the water vapor/infrared satellite loop this morning 
shows a cold front and its associated short wave trough pivoting 
around the polar vortex near Hudson Bay. The front will be 
approaching from Great Lakes region...southern Ontario...and Quebec. 
The GFS is a little faster on the timing of the showers ahead of 
the boundary compared to the NAM/Canadian regional. Some very light 
precipitation with the warm advection on the leading edge of the front will 
likely reach the Adirondacks/western Mohawk Valley prior to 12z/Thu. We 
placed some chances of snow showers there. We also tried to 
account for rising temperatures overnight...with a brief shot of 
radiational cooling early in the evening...before the boundary 
layer winds increase from the southwest...as well as some middle and high 
level cloudiness. 


Thursday...the cold front will make swift progress across the forecast 
area between 15z-21z. We increased the probability of precipitation to likely values from 
the Mohawk Valley...capital region...and northern Berkshires northward 
in the late morning into the early PM. We did place some 
categorical values over the southern Adirondacks. The 850 hpa low 
level jet intensifies to 45-50 kts between 12z-18z...with good low 
level convergence along the boundary. The thermal gradient 
tightens with the 1000-850hpa 2-d frontogenesis strengthening. Low 
and middle level lapse rates steepen...but not enough for deep 
convection with rumbles of thunder. The best upper level jet 
dynamics are over northern-western New York by 18z...with those locations in the 
right rear quadrant of an h250 jet streak. Again...we leaned a 
little closer to the GFS with the timing of front here. Best snow 
accumulations will be over the higher terrain north and west of 
the capital region...where an inch or two is possible. Compressional 
warming effects in the wake of the front with the cold air 
advection will allow some warming in the valleys...however...we 
only went a few degrees warmer than the gfsmos with highs in the 
upper 30s to lower 40s in the valleys...and 30s elsewhere. The 
winds will be blustery from the west in the afternoon at 10-20 miles per hour...with 
some gusts in the 25-35 miles per hour range. 


Thursday night into Friday...the synoptic subsidence in the wake 
of the strong cold front will take control early in the evening. 
However...with h850 temperatures of -10c to -13c over the region in the 
blustery west/northwest flow...we are expecting a lake effect snow band to 
form downwind of Lake Ontario towards 06z. We are not confident 
for a 4th period watch right now for northern Herkimer/Hamilton 
counties. The biggest negative factors for the lake band 
extension into our area will be the amount of dry air in the 
boundary layer and some directional shear in the surface-h850 layer 
early on. Despite that...in the 270-280 degree mean low/middle level 
flow...with moderate lake induced instability /Lake Ontario temperatures 
in the 45-48f range/...and the inversion heights off the kuca/ksyr 
soundings around 10-12 kft...we could see several inches of snow 
in northern Herkimer and Hamilton counties along the band. We will 
mention possible advisory level snow amounts for Friday /06z Friday 
to 06z Sat/ for the western Adirondacks. In time...the low level flow 
backs to the southwest...and the band lifts north. 


The rest of the forecast area should be mainly dry and cold Thursday night 
through Friday with the exception being the northern tier of the forecast 
area...and the westerly upslope region of the southern Green Mountains with 
snow showers and flurries persisting. Low temperatures Friday morning will be 
in the teens to middle 20s...and highs Friday will be a solid 5-10 
degrees below normal...with highs in the middle and upper 20s over the 
hills and mountains...and 30s in the valleys. 


&& 


Long term /Friday night through Tuesday/... 
coming soon 


&& 


Aviation /07z Wednesday through Sunday/... 
VFR conditions will continue through the entire taf period. Stratocu 
clouds over kalb/kgfl will continue to diminish by around sunrise as 
the last remains of an upper level trough lifts to the northeast and 
as a weak upper level ridge builds into the region. This should 
allow for skies to go mainly sky clear or scattered middle/high clouds during the 
day on Wednesday. The middle/high clouds will get thicker Wednesday 
night...especially across kgfl/kalb. Surface winds will remain light 
through sunrise...then become south or southwest at 10 kts or less 
through the rest of the taf period. 


Outlook... 
Thursday...VFR/MVFR. Scattered -shra/-shsn. Windy. 
Friday...VFR/MVFR. Widely scattered/scattered -shsn in the north. 
Sat...VFR. No sig weather. 
Sun...MVFR/IFR. Chance -sn. 


&& 


Hydrology... 
no Hydro problems are expected over the next several days. It 
will turn colder this week and any precipitation should then come 
as snow which will not have any immediate effect on the rivers. 


Starting Thursday night temperatures over the region will 
average well below freezing into the middle of next week with 
highs from the middle 20s to the middle 30s and lows from the middle 
singles to the middle teens. This will be favorable for ice to 
form and thicken on rivers and lakes...especially in the 
Adirondacks and valleys in the Catskills and southern Vermont. 


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...wasula 
near term...wasula 
short term...wasula 
long term... 
aviation...gjm 
hydrology...NAS 

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