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Area forecast discussion 
National Weather Service New York New York 
631 PM EST Wednesday Mar 10 2010 


Synopsis... 
high pressure over coastal New England and eastern Canada will be 
remain nearly stationary through the upcoming weekend...while a 
large storm system over the middle section of the country slowly 
works eastward. High pressure will then build back into the 
region on Tuesday. 


&& 


Near term /until 6 am Thursday morning/... 
gradually strengthening easterly flow the next few days with Small Craft Advisory 
conditions expected by Sat and a potential gale by late Sat. 


Ridging both aloft and across New England this afternoon putting 
a squash on any precipitation working up from the SW with just some sprinkles 
being reported across eastern PA. Weak middle level warm advection 
this evening and overnight will allow for some middle level clouds to 
work into the area. However...with a dry sub cloud layer...will 
only mention sprinkles overnight with measurable precipitation not 
forecast. 


The cloud cover and onshore flow will keep temperatures in check with 
lows several degrees above normal....ranging from the low to middle 
30s north and west...to around 40 in urban areas. 


&& 


Short term /6 am Thursday morning through Saturday/... 
springtime blocking pattern in the southern branch will feature a 
large upper low spinning across the nations middle section...while 
ridging builds downstream across the eastern Seaboard. At the 
surface...high pressure will remain nearly anchored across the 
eastern Canada and coastal New England into Sat. This will place 
the forecast area in an onshore flow...initially light...but then 
strengthening Thursday night through Sat as low pressure works slowly 
eastward. While middle level clouds will be on the increase Thursday...any 
precipitation will be limited to sprinkles with dry air holding on in the 
low levels. 


Moisture deepens Thursday night into Friday with low-level warm advection 
strengthening in the onshore flow. Strong hi pressure to the north will 
provide an ideal overrunning surface. Expect precipitation to initially be 
light with rain and drizzle...but to then pick up intensity Friday 
after and night. The heaviest rain looks to be during the day Sat 
into Sat night with the potential for several inches of rainfall. 
Flooding will be a concern during this time. Refer to the hydrology 
section for additional details. 


Easterly winds on Sat may approach Wind Advisory criteria with 
boundary layers winds near 60 knots by Sat evening. There should be 
enough mixing for gusts in the 40-50 miles per hour range...but this looks to 
be late Sat. 


There is one caveat here...the 12z NAM while an outlier...is 
slower with bringing in the precipitation on Sat due to it maintaining 
stronger low-level ridging. This is where the NAM can outperform 
the global models. So a trend toward pushing the heavier precipitation back 
would not be surprising. Either way...there will be a significant 
pressure gradient and strong winds. 


&& 


Long term /Saturday night through Wednesday/... 
low pressure moving up the coast will run into strong high pressure 
situated over Maine and the Canadian Maritimes. Medium range models 
are in relatively close agreement initially on the strong pressure 
gradient flow between these two systems delivering a windswept heavy 
rain Sat night as deep layer east-southeast flow from just off the deck to 800 
mb increases to 70-80 knots...but then differ on how quickly the system 
pulls away from the area Sunday night and beyond. Operational GFS 
appears to be a fast outlier compared to its own ensemble mean and 
also the ECMWF/ggem...so think light rain/drizzle should linger into 
Monday over most of the area...and into Monday night mainly across eastern 
CT/Long Island...as winds gradually turn NE and then north. Fair weather 
should follow for the middle week period especially by Wednesday...with temperatures 
a few degrees above normal courtesy of building high pressure of 
Pacific origin and downslope northwest flow. 


&& 


Aviation /00z Thursday through Monday/... 
VFR through tonight with low end VFR ceilings through Thursday. 


Light easterly flow at 5 knots or less tonight...increasing to 5-7 knots 
on Thursday morning. East-southeast winds at 5-7 knots then expected through the taf 
period. 


Middle clouds will overspread the terminals tonight...then a stratus 
deck around 4 kft will spread into the terminals Thursday afternoon. 


Outlook 00z Friday through Monday... 
Thursday night...sub-VFR conditions with light rain becoming likely 
late. 
Friday through Saturday night...MVFR with periods of IFR 
with rain. Increasing easterly flow. Heavy rain possible Friday 
night through Sat night. Potential for gusty winds Saturday 
afternoon through Sat night. Gusts in excess of 30kt at times for 
Saturday night. 
Sun through Monday...sub-VFR likely Sunday morning and possible 
thereafter with any leftover rain. Gusts diminishing and winds 
decreasing through Sunday night and Monday. 


&& 


Marine... 
tranquil conditions with a persistent easterly flow developing on 
Thursday. Seas on the ocean waters will build to 4-6 feet by Friday 
afternoon...then wind gusts at 25 knots and greater will develop Friday 
night. Small Craft Advisory winds will then develop on all waters Friday night through 
Sat. 


Easterly gales are expected Sat night via a very tight pressure 
gradient between low pressure approaching from the south...and 
strong high pressure over northern New England and the Canadian 
Maritimes. Storm force wind gusts may even be possible for a time 
especially on the western ocean waters...but this remains 
uncertain as a low level inversion may limit mixing potential of a 
70-80 knots low level jet just off the deck. The strong onshore flow 
is also likely to build seas close to 20 feet on the ocean...and 4 
to 7 feet on central and western Long Island Sound...during Sat 
night. 


As the low slowly drifts east Sunday into Monday...the flow will weaken 
and gradually back northerly by Sunday night-Mon. Conditions should 
ramp down fairly quickly by Sunday afternoon on The 
Harbor/sound/bays...but lingering swell should keep ocean seas well 
above Small Craft Advisory thresholds through at least Monday. 


&& 


Hydrology... 
potential for several inches of rainfall in the Friday night into sun 
time frame. Snow water equivalent values in the lower Hudson Valley 
of several inches in the higher elevations...but much of this 
will be melted by the onset of the storm. Still though high soil 
moisture content and low ffg...especially in northern New Jersey raises the 
concern for flooding problems Sat and Sat night. River flooding 
very well likely could be a problem on sun for the slow responders. 
A Flash Flood Watch will likely be issued the next 24 48 hours. 
This though will depend on strength of the ridge to the north. 


&& 


Tides/coastal flooding... 
strong and persistent east winds will result in the potential for coastal 
flooding Sat and Sat night. Tidal departures of 2 feet needed for 
minor and 3 to 4 feet for moderate. Widespread minor coastal 
flooding is appearing more likely at this time with localized 
moderate. The details though at this time are difficult to 
resolve. In addition...beach erosion is another potential problem 
for the South Shore beaches with high surf from easterly swells. 
Seas on the ocean forecast just shy of 20 feet Sat night. 


&& 


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


&& 


$$ 
Synopsis...dw 
near term...dw 
short term...dw 
long term...bg 
aviation...mps 
marine...bg/dw 
hydrology...dw 
tides/coastal flooding... 

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