Weather

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Area forecast discussion 
National Weather Service Upton New York 
802 PM EDT Friday Aug 29 2008 


Synopsis... 
high pressure centered over the Canadian Maritimes will head farther 
east tonight. A cold front approaches from the west on 
Saturday...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 am Saturday morning/... 
ridge over the area continues to slowly break down tonight as low 
near Nova Scotia heads northeast and trough to the west continues its 
approach. Actual precipitation reaching ground just to our west probably 
won't be as widespread as radar indicates when it drifts here. 
Slight chance probability of precipitation for showers look good through the evening hours as 
weak lift moves through the County Warning Area...then dry overnight. Mostly cloudy 
with lows ranging from the middle-upper 60s in the city...to near 60 
across the outlying suburbs. 


&& 


Short term /6 am Saturday morning through Monday/... 
cold front approaches...with a chance of showers mainly for the northwest 
half of the city by noon...then chance probability of precipitation for showers and 
thunderstorms for the entire County Warning Area during the afternoon. Should be 
enough cloud cover to hold high temperatures in the upper 70s/lower 80s. 
Best chance of convection will be late in the day / early evening 
with cold front passage...with slightly higher overall chances 
across the northern zones where jet dynamics will be better. 
Severe threat looks still looks limited at this time. Chance probability of precipitation in the 
evening for the southeast 2/3 of the SW...and slight chance elsewhere. 


Weak cold air advection on gusty northwest flow during the overnight hours of Saturday as 
Canadian high builds southeast from eastern Great Lakes. Skies will clear 
out as well. 


High pressure continues to build in from the eastern Great Lakes on 
Sunday. Deep northwest flow will bring plenty of sunshine. 850 hpa temperatures 
forecast to be 12 to 13c...and with mixing to around 825 hpa on 
offshore flow...expecting highs generally in the middle 80s...with the 
warmest spots in the city and adjacent suburbs. Sunny skies continue 
on Monday with high pressure continuing to build in. Although winds 
will be from a less favorable down sloping direction...and mixing 
will be limited to around 875 hpa...ridging aloft will modify our 
airmass...so expecting highs on Monday to be a degree or two warmer 
than on Sunday for most spots. 


&& 


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 /00z Saturday through Wednesday/... 
scattered showers working there way across terminals around Long 
Island Sound this evening...with ceilings occasionally down to 
low end VFR. Ceilings slowly diminish overnight becoming low end 
VFR with occasional MVFR during the morning push (along with some 
MVFR fog possible then as well). Solid push of low level moisture 
will continue to lower ceilings to solid MVFR levels by late 
morning...while IFR ceilings cannot be ruled out (and are 
suggested by some guidance) not enough evidence to go with at this 
time...so only tempo down to low end of MVFR scale. Appears best 
bet for any showers with possible embedded thunderstorms is 15-19z 
for western terminals/17-21z eastern terminals...with the best 
chance for thunder a couple of hours after that...for now suggest 
that with a prob30 group...as not quite convinced what coverage 
will be due to low level cloud cover will help limit available low 
level energy typically needed for widespread convection. Western 
terminals should return to VFR conditions very late in the taf 
period (22z or so). 


Winds will be generally light out of the south to light and 
variable overnight...then come out of the south to southwest at 
4-8kt until late afternoon at western terminals...when winds will 
become SW-west behind the front at around 5 knots (the exception to this 
likely will be LGA...where appears low level flow will be light 
enough for winds to swing around to the east-northeast to NE out of the sound 
during the day tomorrow...and not become SW until after the front 
passes in late afternoon). 


Outlook for 00z Sunday through Wednesday... 
MVFR conditions will be possible Sat evening over eastern 
terminals ahead of cold front with scattered showers/tstms...otherwise 
VFR. 


&& 


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


Weak surface high will move farther offshore tonight. Light southeast to S 
winds will have seas at only 2 to 3 feet along with a little swell. 


A cold front will move across the waters Sat night with winds 
becoming northwest to north 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 northwest to north 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. 
Otherwise...high pressure over the area waters will keep winds below 
10kt for the rest of the forecast period. As a result...sub-sca 
conditions are expected through the period. 


&& 


Hydrology... 
trace to a few hundredths of an inch tonight. Generally less than a 
quarter 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...jc 
near term...jc 
short term...jc 
long term...British Columbia 
aviation...maloit 
marine...BC/jc 
hydrology...jc 

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