Weather

141 
fxus61 kokx 060258 
afdokx 


Area forecast discussion 
National Weather Service Upton New York 
958 PM EST Monday Jan 5 2009 


Synopsis... 
high pressure will build over the area from the Ohio Valley 
tonight...then slide east and weaken on Tuesday. Low pressure taking 
shape over the lower Mississippi and Tennessee valleys tonight and 
Tuesday will head northeast along The Spine of the Appalachians 
Tuesday night into Wednesday...while its leading warm front lifts 
north to the middle Atlantic coast. A secondary low is expected to form 
along the warm front along the middle Atlantic coast...and then pass 
just southeast of Long Island by Wednesday evening. This combination 
of these systems will bring wintry weather to the area from Tuesday 
night into Wednesday evening. 


&& 


Near term /through Tuesday/... 
updated for hourly temperature trends and lowered winds a couple 
of knots. Otherwise forecast remains on track. 


High pressure will build over the area from the Ohio Valley 
tonight...with diminishing northwest flow. Latest satellite trend shows 
clearing skies moving mainly into northern sections of the County Warning Area...so 
will end up mostly clear there overnight...while NYC metropolitan and Long 
Island transition to partly cloudy. Min temperatures should range from near 
30 in NYC...to the 20s most elsewhere...to some upper teens well 
inland and in the Long Island Pine barrens. 


&& 


Short term /Tuesday night through Wednesday night/... 
the high will remain over the area on Tuesday and weaken slightly... 
while a leading warm front associated with developing low pressure 
over the lower Mississippi and Tennessee valleys lifts to the 
southern middle Atlantic coast. Precipitation should move in a little faster 
than previously forecast...with likely pop arriving at the doorstep 
of NYC by late afternoon or early evening and beginning primarily as 
snow...perhaps mixing with rain at the onset. 


As the primary low rides The Spine of the Appalachians Tuesday night...a 
secondary low should develop along the warm front along the Delaware-Maryland-Virginia 
coast....with precipitation continuing to spread northward into the rest of 
the County Warning Area on deep layer SW flow aloft. NAM appears too cold aloft and 
preferred a warmer GFS/European model (ecmwf) compromise...with warm air surging in 
aloft after about 06z-08z. With the warmer air moving in atop a deep 
cold surface-based layer initially...expect precipitation to transition first 
to sleet late Tuesday night...and then freezing rain/rain toward 
daybreak Wednesday as low level easterly flow increases. Could see 2-4 
inches snow/sleet accumulation Tuesday night across the interior roughly 
north of I-80 and I-95...also nearby portions of the Long Island 
North Shore...with amounts 1-3 inches elsewhere in the NYC metropolitan 
area...and generally an inch or less across central/eastern Long 
Island and far southeast CT. 


During Wednesday...expect rain across Long Island/far southeast CT...and 
freezing rain/sleet elsewhere...changing to rain in NYC metropolitan in the 
morning and interior CT during the afternoon as temperatures gradually rise 
via strengthening east flow as secondary low pressure passes just southeast of 
Long Island. The lower Hudson Valley should maintain cold air longer 
via channeled north-NE flow...and hold onto freezing rain for most of 
the day. All in all...much of the interior should see 2-4 tenths of 
an inch of ice accumulation on top of the earlier moderate 
sleet/snow accumulation...so have raised a Winter Storm Watch for 
most of the interior zones except for New London County CT. 
Advisories will likely be needed farther south for much of the rest 
of the County Warning Area...with the exception of Suffolk and coastal New London CT 
where initial snowfall should be light and freezing rain is not 
expected. 


Precipitation then tapers off from west-east during Wednesday evening...but with a deep 
upper trough and several shortwaves rotating through...will continue 
to carry chance pop over the area Wednesday night into Thursday. 


&& 


Long term /Thursday 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 
ptype. 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 /03z Tuesday through Saturday/... 
high pressure over the terminals will move to the northeast 
Tuesday as a storm system over the southern states moves off the 
middle Atlantic coast. Conditions start off VFR at all the 
terminals...then ceilings and visibilities lower as precipitation 
begins after 20z Tuesday. Precipitation is expected to be rain and 
snow along the coast with all snow inland. Ceilings and 
visibilities continue to lower and may become IFR toward 00z. 
Timing of the onset...and uncertainty of the precipitation 
type...will have an impact at the terminals Tuesday afternoon. 


Outlook for 00z 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... 
seas running about 1 foot below forecast heights on the ocean and 
winds a few knots lower. Updated winds and seas tonight. 


Light northerly winds turn to the east Tuesday and increase in 
speed Tuesday night. This ahead of warm front and associated coastal low. 
Small Craft Advisory this time frame. 


Winds changeable Wednesday as the low passes nearby. Some locations could 
observe gusts to 30 or 35 kts...but feel gale winds not likely Wednesday. 


Then strong westerly flow behind the front and deepening low 
pressure Wednesday night and Thursday. Gales likely this time frame. 


Followed wavewatch forecasts closely. 


Long term /Thursday night through Saturday night/... 


This period will be marked by near gale force conditions Friday and 
again Sat night into sun with strong cold advection on the backside 
of low pressure. Surface ridge axis builds across the waters Friday night 
into Sat with a brief lull in the seas and winds. 


&& 


Hydrology... 
between 1 and 2 inches of liquid quantitative precipitation forecast will be possible Tuesday night 
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 Watch from Tuesday evening through Wednesday 
afternoon for ctz005>007. 
New York...Winter Storm Watch from Tuesday evening through Wednesday 
evening for nyz067>070. 
New Jersey...Winter Storm Watch from Tuesday evening through Wednesday 
evening for njz002. 
Marine...Small Craft Advisory from 10 PM Tuesday to 6 PM EST Wednesday 
for anz330-335-338-340-345. 
Small Craft Advisory from 6 PM Tuesday to 6 PM EST Wednesday 
for anz350-353-355. 


&& 


$$ 
Synopsis...bg 
near term...bg 
short term...bg 
long term...dw 
aviation...met 
marine...dw/pw 
hydrology...bg 

National Weather Service Glossary of Abbreviations

Non-Expanded Version (with abbreviations)