141 
fxus61 kokx 220045 
afdokx 


Area forecast discussion 
National Weather Service New York New York 
845 PM EDT sun Mar 21 2010 


Synopsis... 
low pressure over Tennessee Sunday night will very slowly move 
toward the region...passing over the area early Tuesday. This low 
will intensify over the Gulf of Maine Tuesday night into Wednesday 
as high pressure starts building into our region. A cold front 
will cross the region Thursday night...followed by Canadian high 
pressure building down from Canada for Friday into the weekend. 


&& 


Near term /until 6 am Monday morning/... 
clouds thicken through morning. Since moon is dimly visible...have 
gone with a mostly cloudy becoming overcast. 


Expect precipitation to hold off until sunrise...thus have dropped probability of precipitation 
for the overnight period. This based on 18z runs of NAM/GFS and 
hrrr (through 06z). 


Before clouds get too thick...should have some radiational cooling 
for lows to get down to around 40 (some 30s) eastern CT and Li. 
Then temperatures rise. 


Low level moisture is fairly high on the 00z sounding and think 
warm advection over the water will start to form stratus my 
morning. 


&& 


Short term /6 am Monday morning through Wednesday/... 
the various models appear in fairly good agreement through the 
short term as cut off slowly low lifts east northeast. 


Expect on and off light precipitation in the morning due to isentropic 
lift/warm air advection forcing. Added drizzle to the forecast. 
Fog will likely not be dense enough to mention during the day. 


Rand becomes moderate to occasionally heavy in the afternoon as 
cutoff's upper difluent pattern moves in for western sections. NAM 
precipitation appears convective in its pattern...but it being generated 
mainly by grid scale forcing and not the convective 
parameterization scheme. 


Expect moderate rain to continue...possibly heavy at times into 
Tuesday morning...before gradually tapering off by Tuesday night 
as the storm pulls off to the northeast. 


With potential for heavy rainfall and rivers across western 
portions of the tri-state at relatively high levels already have 
issued a Flood Watch from late Monday afternoon through 
Tuesday...see hydrology section of the afd for more details. 


For temperatures Monday through Tuesday night...followed generally 
followed a mav/met blend with mainly above normal values expected. 


Strong northwest flow on the backside of the departing storm will push 
through a dry cold front on Wednesday with highs generally from 
the middle 50s to around 60 (consistent with a mex/mex ensemble mean 
blend). 


&& 


Long term /Wednesday night through Sunday/... 
high pressure builds through the region Wednesday night and Thursday...bringing dry 
weather and temperatures slightly above normal with highs in the middle to upper 
50s on Thursday. Two systems then approach Thursday night/Fri...low pressure ahead 
of a cold front sliding through southern Canada and the northern 
states and low pressure over the MS valley. Currently...models are not 
indicating that these systems will phase...though European model (ecmwf) is hinting 
at a possible coastal low to develop over the Delaware-Maryland-Virginia area. Given 
how far out this is and uncertainty among the models...will carry 
chance probability of precipitation for Thursday night/Fri...mainly in the form of rain...but a 
rain/snow mix is possible at night across the lower Hudson Valley 
and possibly eastern Long Island. 


Cold front then clears the region Friday night...and an Arctic air mass 
looks to build into the region for the weekend. 800 mb temperatures generally 
-8 to -10 c will result in highs in the low to middle 40s Sat with lows 
in the 20s to lower 30s...and these temperatures would be about 10 degrees 
below normal. Temperatures rebound back closer to normal on sun as high 
pressure moves offshore and winds become more west to southwest. 


&& 


Aviation /00z Monday through Friday/... 
slow moving low pressure over Tennessee approaching with light onshore 
southeast flow next 24 hours plus. 


Expect Monday is mainly IFR...though confidence in timing and 
development of stratus for the morning is low. Precipitation may tapper of 
and end with improved conditions for a few hours (not in tafs) 
during the middle day. Higher confidence in IFR for afternoon. 


Winds: high confidence in light east-southeast < 10 knots then some increase 
for afternoon - still around 10 knots. 


Outlook 00z Monday through Friday... 
Monday night...IFR rain br/fg. 
Tuesday...IFR early lifting to VFR late. -Ra ending. 
Tuesday night-Wed...VFR west-northwest wind gusting 25-30 knots. 
Thursday...VFR west wind 10-15kt. 
Friday ... 


&& 


Marine... 
relatively tranquil conditions expected on the waters through 
Monday with winds 10 knots or less and seas 4 feet or less on the ocean 
(higher monday) and 1 feet or less on the remainder of the waters. 


Fog tomorrow in th 1-3 range...though could be lower. 


Increasing (but sub sca) east-southeast winds Monday night should build seas 
on the coastal ocean waters to Small Craft Advisory levels. Not quite confident 
enough at this time to issue the advisory. Small Craft Advisory seas on the ocean 
with sub-advisory winds continues through Tuesday. 


Wind gusts should increase to Small Craft Advisory levels Tuesday night in response 
to deepening storm system over the Gulf of Maine. Small Craft Advisory conditions 
continue Wednesday...with gusts to gale force possible in cold 
advection behind a cold front Wednesday. 


Wind gusts of 25-30 knots will remain on most waters Wednesday night as 
low pressure continue to depart. Seas on the ocean...especially 
eastern ocean waters...will gradually subside below 5 feet by Thursday 
evening. Another storm system on Friday may bring a period of 5 feet 
seas on the ocean...but wind gusts look to remain below 25 knots. 
Tranquil conditions expected next weekend. 


&& 


Hydrology... 
currently expecting 1 to 1.5 inches of rain...with locally higher 
amounts across the tri-state from late tonight through Tuesday 
night...with the bulk of the rain expected to fall from late 
Monday afternoon into Tuesday. With river levels over NE New Jersey and western 
portions of the tri-state already running relatively high and 12 
hour flash flood guidance over NE New Jersey less than 1.5 inches...have 
issued a Flood Watch for northeast New Jersey and the western 
lower Hudson Valley from late Monday through Tuesday in 
collaboration with surrounding offices. It is possible that this 
advisory could be expanded further east into Connecticut...but was 
not confident enough to do so at this time. For New York City/Long 
Island...mainly minor urban flooding is possible. 


&& 


Okx watches/warnings/advisories... 
CT...none. 
New York...Flood Watch from Monday afternoon through Tuesday afternoon 
for nyz067-069. 
New Jersey...Flood Watch from Monday afternoon through Tuesday afternoon 
for njz002>006-011. 
Marine...none. 


&& 


$$ 
Synopsis...jst 
near term...jst 
short term...jst/pfm 
long term...mps 
aviation...jst 
marine...mps/pfm 
hydrology...pfm 

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