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Area forecast discussion 
National Weather Service Upton New York 
757 PM EDT Wednesday Jul 23 2008 


Synopsis... 
a slow moving cold front continues to approach the tri-state area 
this evening with the potential for severe weather in advance of 
it. The front will then slowly push across the region on Thursday 
with heavy..potentially flooding...rainfall. Dry weather returns as 
the front will be east of the region by Friday. 


&& 


Near term /until midnight tonight/... 
have to be short today due to diverse weather event. 


Despite the cloud cover...atmosphere very unstable with 1000-1500 
j/kg of ml cape. The most unstable area is over central New Jersey where 
temperatures are now approaching 90. 


Shear is very impressive and the threat for tornadic storms is 
high as 0-1 km helicity is near 150 m2/s2. Local height is 
low...which is another classic tornado indicator. 


Severe watch out until 02z for entire area. Storms over eastern Li 
and southeast CT were pulse in nature with elevated cores with weak 
rotation. Expect storms coming out of New Jersey to have better rotation. 


&& 


Short term /midnight tonight through Thursday night/... 
followed GFS solution here based on recommendation from HPC. 


Looks like heaviest precipitation focus in on the am in the NYC metropolitan as 
front presses a little fast to the east than previously 
anticipated. 


Have added all areas to the Flood Watch and split up the end 
times. 


See Hydro section below. 


Have gone with cooler Eta model/FWC MOS for temperatures on Thursday. 


Probably a little slow in ending the precipitation Thursday night. 


&& 


Long term /Friday through Wednesday/... 
unsettled weather pattern will continue through the long term. Continental U.S. 
Pattern will consist of troughing in the northwest and NE with ridging in 
the center part of the country. 


Closed upper low will lift into southeastern Canada with cold front 
expected to be just east of the area by Friday morning. Dry conditions 
return on Friday...but medium range models are forecasting the upper 
system to become absorbed into another long wave trough dropping out 
of central Canada this weekend. This too is forecast to close off 
aloft with a cold front slowly approaching Sat night and sun. Front 
will clear the area on Monday...but upper trough with vorticity maxes 
swinging through from time to time will remain across the NE into 
the early part of next week. This will keep the chance of showers and 
thunderstorms in the forecast (although Tuesday looks capped) through much of 
the period. European model (ecmwf) is flatter and slower than the GFS which is 
preferred by HPC...so leaned more towards HPC guidance/ECMWF. 


&& 


Aviation /00z Thursday through Monday/... 
terminals mostly at MVFR to IFR at this time with thunderstorms in the vicinity of 
the westernmost terminals. Expecting a continuation of MVFR to IFR 
conditions as axis of steadiest precipitation slowly shifts eastward as 
showers and storms within move in a general north-north-northeast direction. 


Gusty winds possible in thunderstorms...with sustained winds southeast-S to 
start...shifting more towards the south later this evening...and 
generally 15kt or less. Threat of thunderstorms continue through Thursday 
morning...so have added cumulonimbus attachments through this time. Precipitation and 
thunderstorm threat expected to end altogether across the terminals 
by late afternoon. VFR conditions to follow. 


Outlook for 00z Friday through Sunday...vrf likely Thursday 
night...and continuing into Saturday. A cold front approaches late 
Saturday into Sunday with local MVFR ceilings and visibilities in 
showers and thunderstorms. 


&& 


Marine... 
winds and seas will build rapidly overnight as winds increase from 
the south. Small Craft Advisory will be expanded to other areas as a result. 


Wavewatch iii guidance was under cut significantly. 


High pressure builds in on Friday resulting in tranquil 
conditions. 


(Friday through monday)... 
wind gusts on the ocean may reach marginal Small Craft Advisory levels ahead of the 
cold frontal passage Sat night...otherwise...seas will likely remain 
above Small Craft Advisory levels in anz350 and anz353 through the weekend. Tranquil 
conditions should return on Monday. No problems expected on the 
remainder of the marine zones. 


&& 


Hydrology... 
flash flooding watch up through Thursday. 


Expecting overall averages of 3 to 4 inches. Training of echoes is 
the concern and where this occurs...will not be surprised to see 
6+ inches. 


Rates in the storms will easily exceed 4-6 inches instantaneously...with 
hourly totals likely in the 1.5-3 inch range. Thus...urban 
flooding likelihood is very high. 


NYC and west should see the heaviest in the overnight into the 
early morning...with rain tapering off or ending by afternoon. 


&& 


Equipment... 
on July 28th...marine observations from Ambrose light tower will 
be decommissioned. 


&& 


Okx watches/warnings/advisories... 
CT...Flash Flood Watch through Thursday evening for ctz005>012. 
New York...Flash Flood Watch through Thursday evening for nyz077>081. 
Flash Flood Watch through Thursday afternoon for nyz067>076. 
New Jersey...Flash Flood Watch through Thursday afternoon for njz002>006- 
011. 
Marine...Small Craft Advisory from midnight tonight to 6 PM EDT 
Thursday for anz330-335-338-340-345. 
Small Craft Advisory until 6 am EDT Friday for anz350-353-355. 


&& 


$$