895 
fxus61 kokx 200533 
afdokx 


Area forecast discussion 
National Weather Service Upton New York 
1233 am EST Thursday Nov 20 2008 


Synopsis... 
an unseasonably cold airmass will remain in place through the 
weekend as a series of disturbances push across the northeast. These 
cold air surges will be preceded by a couple of weak areas of low 
pressure...also known as Alberta clippers. The first of which moves 
through late tonight and Thursday...and then another on Friday. A 
strong polar high over the Mississippi Valley then builds eastward 
through the weekend. 


&& 


Near term /until 6 am this morning/... 
the weakening shortwave/clipper system is fast approaching. Middle 
and high clouds are on the increase...and these clouds will 
prevent temperatures from plummeting further. 


Just enough moisture and forcing from shortwave could trigger a 
few snow showers...particularly north and west.As such...cannot 
rule out a quick dusting across some of the higher elevations that 
receive a bit steadier snowfall. Temperature trends look to be on 
track with current database. Updated with new lav numbers. 


&& 


Short term /6 am this morning through Saturday/... 
a chance of scattered snow snow showers will continue into 
Thursday...with some flurries expected closer to the coast. No 
accumulations are expected. Temperatures will once again be 8 to 12 
degrees below normal. 


Another shortwave/clipper system digs through the Great Lakes to the 
East Coast Thursday night into Friday. There is no real defined surface 
low associated with this second shortwave however a deep-layered 
cyclonic flow and the upper trough moving overhead will pose another 
chance of scattered snow showers across the higher elevations north 
and west...with some possible snow flurries elsewhere. 


Other than these snow showers...it will be cold and dry. 
Temperatures will be a good 5 to 10 degrees below normal. 


&& 


Long term /Saturday night through Wednesday/... 
cold air advection with northwest winds will keep temperatures well below 
normal on Sunday. Temperatures will moderate somewhat on Monday as 
surface high pressure drifts off the coast and winds shift to the 
west-southwest. 


A low pressure system is forecast to develop across the central U.S. And 
impact the region late Monday into Wednesday. There remains model 
uncertainty about the timing and intensity of this system. European model (ecmwf) 
continues to be slower and more aggressive...intensifying a low just 
off the coast on Tuesday and Wednesday. GFS is more progressive with 
precipitation starting overnight Monday and winding down on Tuesday. 
Subsequent model runs have been trending warmer...though precipitation may 
still start as light snow or a mix in interior locations Monday 
night. Have kept low probability of precipitation for Wednesday to reflect uncertainty in 
model solutions. 


&& 


Aviation /06z Thursday through Monday/... 
increasing middle and high clouds overnight ahead of next clipper 
system. Northwest winds remain generally under 5 knots...except 5 to 10 kts 
across NYC metropolitan terminals. 


A few snow showers/flurries possible late tonight through the 
morning...mainly for kswf as clipper approaches. Possible sub VFR 
conditions in light snow at kswf...but confidence remains low at this time. 
Low end VFR elsewhere through the morning. 


Mainly VFR ceilings expected across area terminals through the 
afternoon hours. Light west winds turn to the northwest as the day progresses. 
Scattered...then broken ac clouds possible Thursday night as next middle 
and upper level disturbance approaches. Light northwest flow persists. 


Outlook for 06z Friday through Monday... 
generally VFR Friday through Sunday. Brief sub VFR conditions are 
possible Friday. More flurries possible Friday night into Sat. May 
observe sub VFR conds developing on Monday...depending on timing of 
next frontal system. 


&& 


Marine... 
will allow Small Craft Advisory to expire as winds diminish and seas subside. 


Sub Small Craft Advisory conds through Thursday night as weak clipper works across the 
area. Small Craft Advisory conds are likely to develop across all waters late 
Friday and Friday night with strong cold air advection as the pressure gradient 
tightens between a strengthening offshore low pressure system and 
strong Canadian high pressure building in from the west. There is 
a low chance for gale force wind gusts across the open waters Friday 
night/early Sat with strong cold air advection burst. 


Then Small Craft Advisory winds will likely continue through Sat...gradually 
subsiding Sat night into sun as high pressure builds towards the 
area. 


&& 


Hydrology... 
no significant precipitation (0.5 inches or more in a 12 hour 
period) is expected over the next 7 days. 


&& 


Okx watches/warnings/advisories... 
CT...none. 
New York...none. 
New Jersey...none. 
Marine...none. 


&& 


$$