484 
fxus61 kaly 231128 
afdaly 


Area forecast discussion 
National Weather Service Albany New York 
630 am EST Monday Nov 23 2009 


Synopsis... 
high pressure off the Canadian Maritimes will continue to drift 
northeast today...as a low pressure system along the Carolina 
coast continues to move northeastward. This low pressure system will 
pass far east of Cape Cod on Tuesday... resulting in mainly light 
rain across especially areas south and east of Albany tonight into 
early Tuesday. 


&& 


Near term /until 6 PM this evening/... 
as of 630 am...stratus clouds have pretty much covered the entire 
County Warning Area. The only exceptions are Washington County and 
portion of Herkimer. With time...these areas should fill in as 
well. 


Temperatures generally have rises a little with the clouds moving 
in...and in some cases...coupled with a breeze...a bit more. 
However...now that the clouds are here...we doubt they will rise 
much at all during the day. Already have factored that into our 
forecast but did issue an update to increase the cloud cover in our 
dacks. No other changes other than to update hourly grids. 


****************Previous near term forecast*************** 




Despite a fairly "benign" system...tricky forecast. First problem is 
how far west the incoming stratus will get today? The second and 
potentially bigger problem...will these clouds linger all day? 


The second question will have a huge impact on how high temperatures 
would get today. Temperatures had tumbled into the 20s in the Hudson 
west. Once the stratus made into the middle Hudson 
Valley....temperatures jumped as much as 20 degrees! But...suspect 
temperatures will not rise much more as long as clouds linger. 


Prior to the clouds moving in...temperatures remained in the 
20s...with lots of very low level moisture...areas of fog...dense in 
spots...have formed. 


Unfortunately...the model guidance from the NAM and GFS differ a 
bit...but both do indicate (or at least imply) the clouds could hang 
touch across much of our region today as an easterly flow moistens 
the column from the bottom up. It looks as if the stratus will at 
the very least...make across most if not all of our County Warning 
Area. 


Meanwhile...the water vapor loop also indicated a baroclinic Leaf 
off the Carolina coast. Closely examining it along with surface 
temperatures supports a track that would take the main storm out to 
sea....while the upper air low tracks along the coast. 


The combination of the upper air low and good low level inflow off 
the Atlantic Ocean looks to not only keep US in clouds today...but 
expect some light drizzle or very light rain likely to develop 
south and east of Albany...possibly making it into the capital 
region and points north and northwest (where probability of precipitation lower to slight/no 
chance). 


With the clouds in place...we will generally undercut the mavs (and 
in some cases even the mets) across the board. Generally look for 
highs topping out in the 40s today. 


&& 


Short term /6 PM this evening through Wednesday night/... 
while the main surface low should track well to our east and 
south...inflow off the Atlantic Ocean ... "hints" of an inverted 
trough...inducing low level isentropic lift...will keep the threat 
of some rain tonight into early Tuesday. We have seen this setup a 
few times this past fall...and in some cases...was enough to bring a 
significant rainstorm even when the main system stayed well south 
and east. 


The difference in this case is that precipitable water values don't get all that 
high...(1/2-3/4 inches). Also...and probably more 
importantly...model soundings indicate that the clouds might remain 
mainly ice-free...which would limit the size of the water droplets 
and consequence accumulation of water (since this is of course a 
non-Tropic environment). Therefore...we expect mainly light rain 
with this system. Also...removed any mention of snow since h850 hpa 
and h925 hpa temperatures remain well above freezing with this 
system. Went higher than all guidance for overnight lows...generally 
bottoming out in the 35-40 degree range. 


The isentropic lift will shift east on Tuesday...but then the 
problem is how long does it take for the clouds to go away? The GFS 
would dictate sunshine much of the day...but we do not buy this 
solution. The slower clearing NAM has climatology on its side. After 
all...Nov is Albany/S cloudiest month and thus far...this month as 
not been all that cloudy. However...the past few days have seen 
clouds stubbornly hanging on underneath an inversion. With a very 
low sun angle...it is hard to break up clouds this time of 
year...and with no good downward motion or drying behind the 
system...expect it will take much of the day for the clouds to 
become scattered. For that reason...went lower than even the 
normally cooler met nos...undercutting them by a degree or so. Since 
drying looks to begin across our northwest zones...temperatures over the 
dacks will probably get as high (if not a touch higher) than temperatures 
say over the middle Hudson Valley...and northwest Connecticut. Overall 
look for temperatures to top out in the 45 to 50 degree range. 


Then Tuesday night...the dilemma is whether or not clouds will 
reform underneath a lowering subsidence inversion as weak high 
pressure builds over the region. Model soundings don't give a clear 
signal whether or not this will happen. For now...will lean slightly 
with the colder mav nos and call it partly cloudy. Did however...add 
some patchy fog as well. On Wednesday night expect lows to drop in 
the 30-35 range...except 20s up north. 


Wednesday is of course the big travel day before Thanksgiving. Right 
now...travel conditions across our County Warning Area look nearly optimal in that 
we expect little or no precipitation. (We do have a slight chance in 
the afternoon to the west of the Hudson valley). The day could start 
out at least partly sunny...with an increase of clouds later in the 
afternoon. If we can "mix" out at all...temperatures should reach 
50-55 in the valleys...45-50 over the higher terrain. These values 
are a little above normal. 


&& 


Long term /Thursday through Sunday/... 
much of the long term period will be dominated by a developing 
trough across the eastern Continental U.S. And the possibility of a phased 
storm system affecting the northeast. 


Global model consensus is becoming more clear with developing 
mid-west/Great Lakes trough toward Thanksgiving Holiday. Potent 
Pacific wave seen in the water vapor imagery this early Monday morning 
was situated between longitude 130-150w and north of latitude 40n. 
Models appear to capture this feature quite well which results in 
good model consensus. In fact...latest GFS ensemble data reveals 
too the guidance envelope is narrowing with 500mb and surface Standard 
deviations are closing with values less than 20mb. With that 
said...Thanksgiving day should remain dry yet the cloud cover will 
be increasing rather quickly. As the aforementioned trough evolves 
upstream...surface wave is expected to develop off the middle Atlantic 
coast and track northeast Thanksgiving evening into Friday. Ample 
moisture will be advecting northward with precipitable waters  forecast to climb 
above 1 inch. With these values and impressive dynamics...rainfall 
could be locally heavy as we will closely monitor trends. At this 
time...thermal profiles favor more liquid than solid and will 
continue to trend weather grids/forecast in this direction. 


On Friday...deep upper low and expected negative tilt to the upper 
flow will be sure to allow the surface low to deepening accordingly 
into a nor-Easter. As this wave tracks northeast late Friday into 
Friday night...pressure gradient increases as thicknesses fall 
quickly. This will result in any precipitation to become mixed with 
and chance to snow showers overnight. We will need to watch for the 
potential of a deformation axis which could result in the regions 
first accumulating snowfall...but much too early to get pinned down 
on specifics at this time. 


The chance for rain/snow showers continue into the first half of the 
Holiday weekend as an expected vertically stacked system moves into 
the Canadian Maritimes. With sub zero 850mb temperatures...high 
temperatures will at best be into the lower 40s in the valley...with 
mainly 30s expected. Weather improves Sunday as the nor-Easter 
lifts further away and subsidence/ridging takes hold over the 
region. Ptsunny and dry conditions expected at this time with a 
couple degree rebound expected in the afternoon. 


&& 


Aviation /12z Monday through Friday/... 
enhanced infrared satellite imagery and metars reveal MVFR to vlifr 
conditions across the Hudson River valley this early Monday 
morning. The vlifr conditions were observed for kalb-kgfl due to 
fog as these areas remained clear before the stratus deck arrived. 
Now the MVFR ceiling are in...a slow improvement to the visibility is 
expected for kalb-kgfl. This cloud deck will likely be difficult to 
dislodge and expect the MVFR ceilings to linger for most of the day. 


Upstream system across the virginias arrives late today into tonight 
with areas of drizzle/light rain expected. This will result in the 
continued MVFR category with an increased potential into IFR 
category overnight. 


Outlook... 
Tuesday am...MVFR...chc of lt rain/dz. 
Tuesday PM-Wed...VFR...no sig weather expected. 
Wednesday nt-Fri...VFR to MVFR/IFR...rain possible late Thursday through Friday. 


&& 


Hydrology... 
the next threat of precipitation will be late today into early 
Tuesday. Expect total quantitative precipitation forecast amounts to be fairly light with less than 
a tenth of an inch of quantitative precipitation forecast across northwest zones to a little over a third 
of an inch far southeast zones. This event should have very little 
impact on rivers and streams. Further out an unsettled period of 
weather late Thursday into the weekend could result in significant 
precipitation amounts. 


For details on specific area rivers and lakes...including 
observed and forecast river stages and lake elevations...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...hwjiv 
near term...hwjiv 
short term...hwjiv 
long term...bgm 
aviation...bgm 
hydrology...11/hwjiv 




Www.Weather.Gov/Albany 

National Weather Service Glossary of Abbreviations

Non-Expanded Version (with abbreviations)