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Area forecast discussion 
National Weather Service Upton New York 
353 am EDT Sat Aug 30 2008 


Synopsis... 
a weak surface wave passes south of the region this morning...then 
a cold front approaches from the west this afternoon...and will 
move through the area late in the day into the evening hours. High 
pressure returns Sunday and remains over the area through middle 
week. 


&& 


Near term /until 6 PM this evening/... 
rain shower activity will slide east of NYC and through 
Li/southern Conn this morning. This activity is being forced by 
weak shortwave energy tracking east through the region and focused by 
surface wave sliding south of the region along a warm front. Rain 
showers may be locally heavy with precipitable waters  around 1.75 inches. Will 
forecast likely probability of precipitation to deal with this batch this morning. 


Meanwhile amplifying shortwave slides from Ontario into northern New 
York today...pushing a weak cold front from the eastern Great Lakes 
early this morning...to western portions of the County Warning Area by late in the 
day...and then offshore after midnight. 


With morning rain showers...plenty of cloud cover and 900 hpa temperatures 
around 15c...expecting highs in the upper 70s...around 80 across the 
region. Moisture pooling ahead of the cold front...and S/southeast flow 
should have dewpoints rising into the middle to upper 60s...making for 
muggy conditions. 


With marginal destabilization this afternoon...and increasing right 
rear upper jet lift...expecting scattered rain showers/thunderstorms and rain to develop 
ahead/along approaching cold front this afternoon across western 
and northwest zones. This activity should translate east this evening with cold 
front. Best chance of afternoon/evening convection will likely be 
across northern zones with better shortwave/upper jet forcing. 


Cloud cover is expected to keep instability levels marginal. Severe 
threat looks limited with deep layer shear increasing late in the 
day/this evening when instability is waning. 


&& 


Short term /6 PM this evening through Monday/... 
dry and above seasonable temperatures expected through the period. 
Amplifying shortwave slides into northern New England tonight...with 
cold front sliding offshore this evening. Weak cold air advection on gusty northwest flow 
expected in its wake as Canadian high pressure builds southeast from eastern 
Great Lakes. Skies clearing after midnight. Temperatures will remain near 
or slight above seasonable tonight with delayed cold air advection and mixed 
atmosphere. 


Surface high pressure continues to build southeast from the eastern Great 
Lakes on Sunday as upper ridging builds into Ohio Valley. Deep northwest 
flow will bring plenty of sunshine. 850 mb temperatures forecast to be 
around 12 c...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. Weakening flow late in the day may allow for 
late day seabreeze development along immediate coast. 


High pressure surface/aloft continues to build east towards the 
region Sunday night. Temperatures near or slightly above seasonable. 


Sunny skies continue on Monday with high pressure surface/aloft 
continuing to build in. Mixing will be limited to around 875 hpa on 
Monday with strengthening subsidence inversion...but a modifying 
airmass should have temperatures in the lower to middle 80s once again. 
Weakening north flow late in the day should allow for late day seabreeze 
development along immediate coast. 


&& 


Long term /Monday night through Friday/... 
very quiet conditions expected through the long term period as high 
pressure...both aloft and at the surface...will keep conditions dry. 
Each day though the period...expect sunny/mostly sunny skies with 
temperatures above normal. Highs will climb into the upper 80s to 
near 90 each day. The only exception will be along the coast where 
temperatures will only reach the lower and middle 80s. 


&& 


Aviation /08z Saturday through Wednesday/... 
scattered showers associated with a weak shortwave aloft/surface low pressure will 
move across the area from SW to NE into the morning daylight 
hours. All terminals are VFR...but upstream observation indicating MVFR 
ceilings not too far off. Also have been experiencing a drop to MVFR 
visibilities in moderate to heavy showers the last few hours...so have 
continued with tempos to account for this. Showers should taper 
off at all terminals by late morning early afternoon. Winds will be 
light (less than 10 kt) and generally be southerly...but the weak 
surface low may cause them to back more to the east at coastal 
locations for a few hours this morning. Otherwise...MVFR ceilings are 
expected to lift to low VFR with daytime heating and mixing as a 
cold front approaches from the west. Models close in timing of 
frontal passage (between 18z and 00z) and there could be some thunderstorms with 
it...but amount of instability will depend on how much sun we get. 
Have left the cumulonimbus in the prob30 group for the 06z tafs...but will 
reevaluate for the 12z package. VFR conditions return behind front. 


Outlook for 06z Sunday through Wednesday... 
MVFR visibilities possible tonight outside of NYC terminals with light 
winds and low dewpoint depressions. Drier air filters in towards 
morning with VFR conditions returning from west to east and 
remaining through midweek as high pressure settles into the northeast. 


&& 


Marine... 
winds/seas are expected to remain below Small Craft Advisory levels through the 
period. 


A cold front will approach this afternoon and move across the waters 
tonight with gusts up to 20 knots possible for a few hours during the 
morning on sun. Otherwise...tranquil conditions as high pressure 
builds into the northeast. 2 feet swells out of the east/southeast are forecast 
to continue into early next week. However...will have to watch the 
progress of 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... 
generally less than a quarter of an inch quantitative precipitation forecast today/this 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...Alabama 
marine...Alabama 
hydrology...Nevada 

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