Weather

612 
fxus61 kokx 060946 
afdokx 


Area forecast discussion 
National Weather Service Upton New York 
446 am EST Tuesday Jan 6 2009 


Synopsis... 
high pressure will slowly retreat to our northeast and strengthen 
into Wednesday. Meanwhile a storm system will lift northeast out 
of the Tennessee River valley today...up The Spine of the 
Appalachians into upstate New York by Thursday morning. This 
system will develop a secondary coastal low near the Delaware-Maryland-Virginia 
peninsula tonight...with this low tracking just south of Long 
Island on Wednesday. The trailing cold front associated with the 
main low will push through the tri-state Thursday. High pressure 
then builds in from the plains into Friday night. An Alberta 
clipper will track just to our north Saturday and Saturday night. 
High pressure then builds in from the plains Sunday. 


&& 


Near term /until 6 PM this evening/... 
increasing clouds today as storm system begins to approach the 
area. With sub-tropical moisture feed evident on water 
vapor...could see light precipitation begin over mainly southeast 1/2 of 
the County Warning Area by this afternoon (only chance pops). Atmosphere too cold 
aloft and too dry at the surface to support any precipitation type 
but snow. Little if any accumulation expected through this 
afternoon. For highs blended nam12 2 meter temperatures and cooler 
mav/FWC guidance. 


&& 


Short term /6 PM this evening through Thursday night/... 
preferred a NAM/GFS blend for 2 reasons with system into Thursday. 1) 
NAM/GFS have not been consistent on exact placement of coastal low 
and how far/fast the warm front pushes north...so blend helps 
smooth differences. 2) while NAM thermal profiles are clearly too 
cold...the GFS so far this winter has been too fast to bring in 
warmer air in the lowest levels and change things to 
rain...especially across the interior. So to address the apparent 
biases in both...opted for a blend. 


Retreating...but strengthening damming high (thanks to confluence 
over northern New England...then exiting to far southeast Canada Wednesday 
am...coupled with developing coastal low will keep the surface 
flow north to NE over a snow pack into the overnight keeping cold air 
over much of the region...the only exception is across Suffolk 
County where lack of snow pack plus air mass modification by the 
sound should allow temperatures to rise above freezing there 
overnight. Temperatures should then rise above freezing across NYC 
metropolitan/southern parts of the lower Hudson Valley/southeast and most of SW 
CT and NE New Jersey Wednesday morning. However with snow pack and best 
damming expect northern lower Hudson Valley locations and 
northern Fairfield County (mainly north of I-84)...along with western 
Passaic County to have temperatures stay at or below freezing all 
day Wednesday. 


Based on this expect a period of snow this 
evening...transitioning to a freezing rain/snow/sleet mix 
(rain/snow/sleet mix Suffolk county) by around midnight...then 
transition to mainly freezing rain with possible sleet (rain with 
possible sleet Suffolk county) overnight. Expect temperatures to 
mainly be above freezing across coastal CT/NYC metropolitan (except northwest 
portion) around sunrise...so mainly rain there during the day on 
Wednesday. Expect transition to rain across northwest NYC metropolitan and 
interior southern CT (except northern fairfield) Wednesday morning. 
Expect freezing rain for most of the day across western 
Passaic...northern lower Hudson Valley and northern Fairfield (mainly north 
of I-84) through the day on Wednesday. 


As a result have upgraded the Winter Storm Watch to a Winter Storm 
Warning in those locations for the entire day...for northern New 
Haven County through midday...and gone with a Winter Weather 
Advisory elsewhere for all but Suffolk County with end times 
staggered based on expected warm up to above freezing. 
Across the warning area expect 1-3 inches of snow followed by 1/4 
to 2/3 of an inch of ice (highest totals across all day warning 
area. Across the advisory area expect 1-2 inches snow and 1/4 to 
1/2 inch of ice across interior southeast CT and Bergen/eastern Passaic 
counties...and up to an inch of snow followed by up to a quarter 
inch of ice across the remainder of the advisory area including NYC. 


With colder air working in behind the system Wednesday 
evening...could see up to an inch of snow/sleet before precipitation 
tapers off. 


Passing Arctic front could bring some scattered snow showers on 
Thursday...with Thursday night dry with ridging building in. 




&& 


Long term /Friday through Monday/... 
mean trough remains established from central Canada southeastward into the 
Middle Atlantic States during this time. Short waves in the mean flow 
will result periodic amplification in the flow with areas of low 
pressure sending reinforcing shots of polar air into the region. The 
period will be marked by unseasonably cold weather and a chance of 
wintry precipitation on Sat. Global models continue to point to a positive 
pna and negative nao next week...suggesting cold and stormy weather. 


Strong cold advection is forecast Thursday night into Friday on the backside 
of low pressure tracking NE across the Canadian Maritimes. Strong northwest 
winds will diminish Friday night into Sat morning as a surface ridge axis 
moves off the eastern Seaboard. 


A clipper low drops southeast across the Great Lakes and NE states Sat into 
Sat night. A progressive system with a track just to the north 
should limit probability of precipitation to the chance category...with snow the predominant 
p-type. Should a farther south track develop in subsequent model 
runs...these chances would likely increase. 


Strong cold advection ensues Sat night into sun with high pressure 
returning to the area late sun into Monday. 


&& 


Aviation /09z Tuesday through Saturday/... 
weak high pressure will move through the area overnight and to the 
northeast Tuesday. VFR conditions until about 22z with mainly a high 
and middle level ceiling. As low pressure over the Gulf Coast states 
moves to off the middle Atlantic by late Tuesday there is a chance of 
mixed precipitation at the terminals. Mainly snow is expected at the 
start...then as warmer air moves in aloft the snow will transition 
to sleet and possibly some freezing rain away from the coast. The 
precipitation type will depend on how quickly and far the warmer air 
gets Tuesday night. Conditions after 00z Wednesday are expected to 
lower to MVFR and then to IFR. 


Outlook for 06z Wednesday through Saturday... 
the storm continues to deepen and move through the terminals 
through Wednesday night. IFR conditions will be likely with a 
mixture of precipitation type at the terminals. Toward Wednesday 
morning coastal terminals should switch over to all rain. The 
warmer air will be slow to push inland and freezing rain and 
sleet will be likely at the inland terminals into Wednesday. As the 
low pulls to the northeast late Wednesday night into Thursday the 
precipitation will taper off and end. 


Gusty westerly winds develop Wednesday night into Thursday. Areas 
of MVFR to IFR conditions are possible Thursday in snow showers. 


High pressure builds toward the terminals late Thursday into 
Friday with VFR conditions. 


A clipper system will bring MVFR to IFR conditions in rain and 
snow Saturday. 


&& 


Marine... 
at 8z...seas 2ft or less with winds blw 20 knots all buoys. This 
downward trend will continue through the day as surface high centered over 
eastern PA builds over the coastal waters today. 


East winds will increase ahead of a slowly approaching warm front Tuesday 
night as low pressure tracks into the Ohio Valley. Small Craft Advisory conditions to 
develop by midnight. Starting times were pushed back slightly due to 
a later trend. 


Coastal low develops S of Li Wednesday. In the vicinity of the low winds will 
become vrb and blw Small Craft Advisory levels for a time. North of the warm front...as 
the low deepens there is a small window for an occasional gust to 
35 knots late morning early afternoon. As the low tracks northeastward Wednesday night 
into Thursday...gales are possible...especially across the eastern ocean and 
sound. A gale watch will be issued. 


Gales are possible through Thursday with seas to finally fall to blw Small Craft Advisory 
levels Friday night. Latest guidance forecasts a clipper for the weekend 
which would bring gusty winds and snow. 


&& 


Hydrology... 
between 3/4 and 1 1/2 inches of liquid quantitative precipitation forecast will be possible into 
Wednesday night...with the highest amounts across NYC...Long 
Island and southeast CT. Interior areas should see a good portion 
of this as snow/sleet/freezing rain...while coastal areas see the 
bulk as rain. There is a potential for minor urban flooding...especially 
across Long Island. 


&& 


Okx watches/warnings/advisories... 
CT...Winter Storm Warning from 6 PM this evening to 6 PM EST 
Wednesday for ctz005-006. 
Winter Weather Advisory from 6 PM this evening to noon EST 
Wednesday for ctz007-008. 
Winter Weather Advisory from 6 PM this evening to 6 am EST 
Wednesday for ctz009>012. 
New York...Winter Storm Warning from 6 PM this evening to 6 PM EST 
Wednesday for nyz067>070. 
Winter Weather Advisory from 6 PM this evening to 6 am EST 
Wednesday for nyz071>077. 
New Jersey...Winter Storm Warning from 6 PM this evening to 6 PM EST 
Wednesday for njz002. 
Winter Weather Advisory from 6 PM this evening to noon EST 
Wednesday for njz003-004. 
Winter Weather Advisory from 6 PM this evening to 6 am EST 
Wednesday for njz005-006-011. 
Marine...gale watch from Wednesday evening through Thursday afternoon 
for anz330-335-340-345-350-353-355. 
Small Craft Advisory from 10 PM this evening to 6 PM EST 
Wednesday for anz345-350-353-355. 
Small Craft Advisory from midnight tonight to 6 PM EST 
Wednesday for anz330-335-340. 
Small Craft Advisory from 10 PM this evening to 6 am EST 
Thursday for anz338. 


&& 


$$ 


Synopsis...pfm 
near term...pfm 
short term...pfm 
long term...dw 
aviation...jmc 
marine...jmc 
hydrology...pfm 

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