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Area forecast discussion 
National Weather Service Upton New York 
1237 am EST Sat Nov 22 2008 


Synopsis... 
Canadian high pressure builds in from the plains through Saturday 
night...then slowly sinks to the south of the region into Monday 
morning. A complex low pressure system will approach from the west 
on Monday...then slowly lift northeast across the northeastern 
states into Thursday. High pressure then builds in from Canada to 
close the work week. 


&& 


Near term /until 6 am Saturday morning/... 
any clouds over western areas will dissipate around 
sunrise...clouds over the eastern tip of Long Island will pull of 
to the east with the developing low. The result will be a mainly 
clear night...with gusty northwest winds...due to the pressure 
gradient between the departing low and the high building in. 
Strong low level cold advection will bring colder air into the 
region. However with mixing have upped the low a couple of 
degrees. Temperatures will still run 15 to 20 degrees below 
normal. The north winds of 10-20 gusting to 25 to 30 miles per hour along 
with these lows will produce wind chills into the single digits 
north of Long Island Sound and in the Long Island Pine 
barrens...and 10-15 elsewhere. 


The strong northwest flow in the low levels over the lakes should produce 
sufficiently Strong Lake effect bands that scattered flurries 
warrant mentioning across far northwest portions of the County Warning Area tonight as well. 


&& 


Short term /6 am Saturday morning through Monday/... 
gradual increasing heights aloft and high pressure building in at 
the surface will keep things dry into Monday...with slowly 
moderating temperatures once the low level ridge axis moves to the 
east of the region on Sunday. 


Saturday will be very cold with 850 temperatures of -14 to -16c 
limiting highs to within a couple of degrees on either side of the 
freezing mark (consistent with a blend of NAM 2m temperatures with a 
FWC/NAM MOS blend). However if mixing is limited to beneath 850 mb 
(models sometimes under do subsidence in these sort of 
events)...then highs could end up struggling to reach the 30 
degree mark. Saturday night will be about as cold as tonight...but 
with lighter winds will not feel as cold (wind chills in the teens 
(except 5-10 Li Pine barrens). Highs on Sunday should recover to 
the middle to upper 30s (bringing temperatures above the freezing 
mark for the first time in about 36 hours at many non 
urban/coastal locations). 


Lows will only be in the single digits below normal across the 
tri-state Sunday night...but still below freezing at all but in 
The Heart of the NYC metropolitan heat island...and far eastern portions 
of the South Fork of Long Island. 


Some timing difference in the models in terms of when 
precipitation begins on Monday (nam is driest...European model (ecmwf) the 
wettest...went with a CMC global/GFS/sref blend as a compromise). 
This results in a forecast of delaying probability of precipitation until late in the 
afternoon across western (chance) and central (slight chance) 
portions of the County Warning Area. Increasing cloud cover and low level warm 
advection should yield highs in the lower to middle 40s (but still 
4-8 degrees below normal). 


&& 


Long term /Monday night through Friday/... 
a warm front associated with low pressure digging into the Great Lakes 
will lift north through the region Monday night. The low itself will 
track over western New York state...then a persistent northwest flow will 
establish itself over the region as it slowly tracks towards eastern 
Canada through the week. 


The best chances for precipitation over the area will be Monday night/early 
Tuesday as a weak secondary low develops just over the Delaware-Maryland-Virginia area 
before tracking north over the local area. Will increase probability of precipitation to 
likely over the eastern two-thirds of the County Warning Area...as that is where 
best forcing is expected. Temperature profiles could become a bit 
problematic...but much of the southern portion of the County Warning Area can expect 
rain...while inland locations will be cold enough to support snow. 
Several weak shortwaves will rotate through the base of the trough 
for the first half of the week...keeping chance probability of precipitation in the forecast. 
Unseasonably cold temperatures remain over the area as highs will generally 
be in the upper 30s to low 40s. 


&& 


Aviation /06z Saturday through Wednesday/... 
VFR...with winds the main concern. Deepening low pressure well east 
and north of the terminals will move north into the Canadian 
Maritimes Saturday...while high pressure builds from the west. A 
large pressure gradient between the two along with colder air moving 
into the area will produce strong northwest winds/gusts through the 06z taf 
period. Kewr taf especially tricky overnight into the morning push 
as wind direction straddles 310...have started off with an initial 
320 so terminal can maintain dual operational runway 
configuration...but this will have to be closely watched...with 
amendments if winds shift to the left of 310. 


Winds will increase during the day on Sat via mixing of higher winds 
from aloft. As the low moves well to the north late in the period... 
winds will very gradually diminish. 


Outlook for 06z Sunday through Wednesday...winds will continue to 
gradually diminish through Sunday. Sub-VFR conditions may develop 
late Monday or Monday night into Tuesday...as next storm system approaches 
from the west...and then lingers nearby through Wednesday. 


&& 


Marine... 
with deepening low pressure east of the forecast waters late 
Friday night...winds and seas have increased earlier and higher 
than in the grids. So have adjusted grids for current conditions 
and trends. Keeping the small craft on all the waters with 
occasional gusts to 35 knots at buoy 44017. 


A tight pressure gradient will persist through the weekend as the 
local waters remain between the strong low to the northeast...and 
high pressure to our west. Strongest winds expected to be 
Saturday...where an occasional gust to 35 kts cannot be ruled out. 


Winds eventually back to the west Sunday...then southwest by Monday 
as high pressure passes to the south...and next storm system 
approaches from the west. 


Seas will remain rather rough through Sunday. Seas subside a bit 
Sunday night and early Monday...then increase again in strengthening 
southerly flow. Wave watch iii guidance looks good and will be 
generally accepted. 


The strong southerly flow continues on the waters Monday night as 
warm front associated with deep low pressure over the Great Lakes 
lifts north across the waters. Winds turn west on Tuesday...then a 
persistent west to northwest flow at 15-20 knots on the ocean and 
10-15 knots elsewhere will be in place through the period. Small 
craft advisories will most likely be needed on the ocean waters 
through the period...as seas will also build to 6-9 feet. Li 
sound/New York Harbor/back bays will experience rough and choppy 
conditions which may fall just below advisory criteria. 


&& 


Hydrology... 
dry through late Monday afternoon...then there is the potential 
for moderate rainfall Monday night and Tuesday...with spotty 
precipitation into the middle of next week as a slow moving storm 
system impacts the area. It is too soon due to differing model 
solutions to offer any meaningful predictions on quantitative precipitation forecast amounts. 


&& 


Okx watches/warnings/advisories... 
CT...none. 
New York...none. 
New Jersey...none. 
Marine...Small Craft Advisory until 6 am EST Sunday for anz330-335-338- 
340-345-350-353-355. 


&& 


$$ 


Aviation...bg 

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