Weather

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Area forecast discussion 
National Weather Service Upton New York 
254 am EDT Friday Aug 29 2008 


Synopsis... 
high pressure centered over the Canadian Maritimes will head farther 
east today. A cold front approaches from the west today and 
Saturday. The front will move through the area Saturday night. 
High pressure returns Sunday and remains over the area through middle 
week. 


&& 


Near term /through today/... 
stacked low pressure...southeast of Nova Scotia...will drift north today. 
This will allow upper flow to flatten a bit today...with surface 
high pressure slowly sliding east. Surface warm front remains well 
south of the region. Meanwhile...a cold front associated with an 
upper trough digging into southern Ontario reaches the eastern 
Great Lakes by this evening. 


Deep moisture gradually increases today as deep layer flow turns 
more to the SW as ridging surface/aloft move east. Forcing 
responsible for shower activity to the west of the region...across 
PA/central New York...weakens this morning as shortwave energy shears out. 


GFS suffering from some convective issues and overdoing precipitation early 
this morning...with NAM looking like it is initializing better. 
Forcing will mainly be from a modest zone of low level Theta-E 
advection working across the region today. Forecasting chance of 
showers this afternoon for extreme western zones...tapering to 
slight chance...mainly late this evening...as one works east due 
to moisture/lift axis eroding as it works further east. 


Plenty of high based cumulus and middle deck increase from west to east today 
with Theta-E-advection. With 850 hpa temperatures only around 12c...this 
should keep temperatures in the middle to upper 70s today. 


&& 


Short term /tonight through Sunday/... 
with forcing vanishing...expecting any isolated rain shower 
activity to dissipate tonight. Temperatures running near seasonable with 
plenty of low and middle deck remaining...and with dewpoints climbing 
into the lower 60s. 


Amplifying shortwave slides from Ontario into northern New England 
Sat into Sat night. This will push a weak cold front from the 
eastern Great Lakes...to western portions of the County Warning Area by late in the 
day...and then offshore Sat night. 


With partial sunshine and 900 hpa temperatures around 16-17c...expecting 
highs in the upper 70s/lower 80s across the region. Moisture 
pooling ahead of the cold front...and S/southeast flow should have 
dewpoints rising into the middle 60s...making for muggy conditions. 


With marginal instability developing and some right rear upper jet 
lift...expecting scattered rain showers/thunderstorms and rain to develop along pre-frontal 
trough Sat afternoon across western and northern 
zones...translating east to coast Sat evening with cold front. Best 
chance of convection to sustain late in the day/evening along cold 
front will be across northern zones with southern fringe of 
shortwave forcing. 


Severe threat looks limited with deep layer shear increasing late 
in the day when instability is waning...and only marginal 
instability to start with. 


Models in good agreement with cold front sliding offshore by early 
evening...with weak cold air advection on gusty northwest flow as Canadian high builds southeast 
from eastern Great Lakes. Skies clearing after midnight. 


High pressure continues to build southeast from the eastern Great Lakes 
on Sunday. Deep northwest flow will bring plenty of sunshine. 850 mb temperatures 
forecast to be 12 to 13c...and with mixing to around 825 hpa on 
offshore flow...expecting highs in the lower to middle 80s...warmest 
New York/New Jersey metropolitan and coast. 


&& 


Long term /Sunday night through Thursday/... 
a large middle and upper level ridge will develop and remain in 
control over most of the eastern half of the country Sunday night 
through Wednesday. This ridge will then start to flatten out on 
Thursday. Meanwhile...at the surface...strong high pressure will 
slowly drift from the Great Lakes to the middle Atlantic coast by 
Thursday. As a result...expect no threat of precipitation with 
little or no clouds until Wednesday night or Thursday as the ridge aloft 
begins to weaken. 


Temperatures will run above normal between the strong ridge aloft 
and full sunshine each day. Expect the typical end of Summer trend 
of warm days and cool nights as the days get shorter and nights 
longer. 


&& 


Aviation /07z Friday through Tuesday/... 
latest 00z model guidance seems to back off on the development of 
a stratus deck between 09z-13z. There is still the potential for 
some low clouds to develop...so will leave a sct015 group in the 
06z taf package...but will remove the tempo for the broken deck. 


Light winds today turning S to southeast at 5-10 knots. L/v winds then in 
place once again tonight after 02z. 


Middle-deck will be lowering to 5-8 kft at most terminals. 


Outlook for 06z Saturday through Tuesday... 
as high pressure moves slowly east and further offshore...a weak cold 
front will approach and pass across the region Sat night. This 
will be followed by high pressure Sunday through Monday. MVFR ceilings are 
possible with the approach of this front Friday night into Sat along 
with scattered showers and a few thunderstorms. Otherwise...VFR weather 
conditions are forecast. 


&& 


Marine... 
winds and seas expected to remain below advisory levels through the 
period. 


Weak surface high over the waters will move offshore as the day 
progresses. East winds will be turning southeast later today at 5-10 knots...and 
with a southeast swell on the on the ocean...seas will range from 2 to 3 
feet. On the sound/Harbor/bays...seas will average 1 feet or less. 


A cold front will move across the waters Sat night with winds 
becoming northerly by sun. Expect gusts 15 to 20 knots on the waters 
behind the front on Sunday as high pressure builds into the 
northeast. An offshore northerly wind expected for the start of the 
new week. For now kept seas below Small Craft Advisory...but will have to watch the 
progress of Tropical Storm Hanna which is forecast to be a hurricane 
northeast of the Bahamas early next week. Swells from this system 
will have the potential to affect the local ocean waters. 


&& 


Hydrology... 
trace to a few hundredths of an inch today across the western 
fringe today. Generally less than a tenth of an inch quantitative precipitation forecast on 
Sat/Sat evening...with locally one half inch to an inch in convection. 
Dry again Sunday into middle week. No hydrologic problems are 
expected. 


&& 


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


&& 


$$ 
Synopsis...Nevada 
near term...Nevada 
short term...Nevada 
long term... 
aviation...mps 
marine...mps 
hydrology...Nevada 

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