659 
fxus61 kokx 212116 
afdokx 


Area forecast discussion 
National Weather Service New York New York 
416 PM EST Sat Nov 21 2009 


Synopsis... 
high pressure builds across eastern Canada...and into the 
Maritimes thorough Monday. An area of low pressure will develop 
off the southeast US coast Sunday...then move up coast 
Monday...passing south and east of Long Island through Tuesday. Weak high 
pressure builds in from the north Wednesday. Another storm system 
may impact the tri- state to close the upcoming work week. 


&& 


Near term /until 6 am Sunday morning/... 
mostly sunny this afternoon. Solid SC/St west of the County Warning Area is drying 
sharply due to downsloping off higher terrain. Decent radiational 
cooling for at least a few hours tonight. Forecast lows...and 
dewpoints approach the middle 30s in spots...so early morning fog is 
a possibility. This is not in the grids at this point given that 
decoupling should only last a few hours as NE winds pick up a bit. 


Undercut MOS in general in the normally cooler spots across 
Orange/Putnam County and The Pine Barrens of Li. Persistence and 
MOS very close elsewhere. 


&& 


Short term /6 am Sunday morning through Tuesday/... deep layer 
ridge passes north of the County Warning Area Sunday...allowing easterly flow on 
the south side to increase. All in all a decent day with highs 
near or slightly below climatological norms with east winds. 


Tricky temperature forecast Sunday night...as cold air damming and low 
level cold air advection continue from the north and east. There 
may again be a period of decoupling...thus forecast low temperatures are 
expected to end up close to tonight's. This period is perhaps the 
lowest confidence temperature forecast of the short term. If surface 
winds stay up...and increasing moisture from a developing surface 
low get here earlier than expected...lows will be much warmer than 
forecast. 


Model solutions still diverge on the track and intensity of a 
diffuse coastal low...but the wind fields are bit more aligned. 


Precipitation expected to hold off until Monday night...although a brief 
period of light overrunning rain possible Monday afternoon. 
Increased pop to likely for about the eastern two thirds of the 
County Warning Area Tuesday morning...but this ultimately depends on if the low 
center passes close enough to put the area in the best lift. The 
NAM continues to be the most robust in terms of quantitative precipitation forecast...but the 18z 
run has backed off from its 1 to 1.5 inch forecast earlier today. 
Light rain...primarily wrap around...possible into Tuesday night. 


Not a whole lot of temperature variation Monday night through Tuesday 
night...especially near the coast. 


&& 


Long term /Tuesday night through Saturday/... low pressure departs 
the region Tuesday night with chance probability of precipitation for -ra ending. SW flow aloft 
develops Wednesday as 500 mb low drops into the Ohio Valley. 300 mb jet produces 
some lift...but forcing otherwise is weak as evidenced by the time 
heights. With marginal moisture...only light precipitation expected at this time. A lull 
settles in Wednesday night into Thursday...then the focus shifts to late Thursday 
and Friday. Another 500 mb low drops into the Ohio Valley with a complex 
reflection at the surface. Models hint at low pressure developing along 
the northern Gulf Coast and tracking northeastward off the Atlantic coast...with 
a second low developing over the eastern Great Lakes. Although there is a 
spread in the model solutions...it appears a shot of rain on track 
during the period. Main issue may turn out to be the wind if the 
12z GFS/European model (ecmwf) solutions are close and a 980s low occludes over northern New 
England Sat morning. 




&& 


Aviation /21z Saturday through Thursday/... 
northwest flow under 10 knots should veer north tonight...and then NE with speeds 
increasing to around 10 knots...higher at NYC/coastal terminals... 
toward or just after daybreak Sunday morning as high pressure over 
the the Ohio Valley builds NE into New England. Radiation fog with 
MVFR conditions may is likely late tonight at kswf and kgon...and 
will have to monitor other terminals outside the NYC urban heat 
island for this possibility close to/just after sunrise. 


Outlook 18z Sunday through Thursday... 
Sunday afternoon/night...VFR. 
Monday...sub-VFR possible. 
Monday night-Tue...sub-VFR likely. 
Tuesday night-Wed...becoming VFR. 
Thursday...sub-VFR possible. 


&& 


Marine... 
light northerly flow becomes northeast overnight...as high 
pressure settles into eastern Canada. The pressure gradient 
strengthens through Sunday evening with lowering pressure to the 
south. Small craft conditions expected to begin on ocean waters 
Sunday evening. Expect winds to increase from south to north...and 
it is possible the the waters right along the coast of Long Island 
will not see 25 kts until Monday morning. 


Small craft wind conditions...with a few gusts possibly 
approaching gale force Monday through Tuesday. 


Small Craft Advisory seas on the ocean linger Tuesday night into Wednesday...then begin to 
subside as low pressure weakens north of the coastal waters. A complex low 
pressure system will then impact the waters late Thursday into Friday. Depending 
on the exact track and intensity of the system...gales may be 
possible during the period. 


&& 


Hydrology... 
dry through Monday morning. A quarter to a half an inch of 
rainfall is possible Monday afternoon through Wednesday. More 
precipitation is expected towards the end of next week. 


&& 


Okx watches/warnings/advisories... 
CT...none. 
New York...none. 
New Jersey...none. 
Marine...Small Craft Advisory from 6 PM Sunday to 6 PM EST Monday for 
anz350-353-355. 


&& 


$$ 
Synopsis...bs 
near term...bs 
short term...bs 
long term...jmc 
aviation...bg 
marine...bg/jmc 
hydrology...bs