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Area forecast discussion 
National Weather Service Upton New York 
743 am EDT Sat Jul 5 2008 


Synopsis... 
a stationary front will remain in the vicinity through the 
weekend. Waves of low pressure will develop and move northeast 
along this front causing periods of showers and thunderstorms 
through the Holiday weekend. Unsettled weather will prevail into 
the early portion of the upcoming week. 


&& 


Near term /through tonight/... 
deep SW flow across the region as upper trough digs into the Ohio 
Valley. Series of low pressure wave will track NE along stalled 
front wavering across the region...as impulses race in SW middle-level 
flow. At the same time...a deep SW flow will have a tropical airmass 
entrenched over the region. 


Heavy rains associated with one vorticity lobe early this morning will 
move into southern New England...while a second vorticity lobe across 
southeast PA will have rain showers/thunderstorms and rain likely through the morning/early 
afternoon from SW to NE as it rides NE through the region. Mostly 
cloudy conditions and scattered rain showers/thunderstorms and rain expected in its wake. 
Weak instability should inhibit severe convection. Thin but deep 
cape evident of precipitation efficient storms...and points towards heavy 
downpours. Potential for flash flooding in tropical airmass. Will 
highlight potential in severe weather potential statement. 


Temperatures will run a few degrees below seasonable...upper 70s to around 
80 with abundant cloud cover. 


Vorticity impulses continuing to track through aloft should be enough for 
scattered rain showers/thunderstorms and rain in this tropical airmass. Patchy fog likely with 
light onshore flow and moist low-levels. Temperatures running a few degrees 
above seasonable in tropical airmass(mid 60s to near 70). 


&& 


Short term /Sunday through Monday/... 
upper trough over Ohio Valley shears east across the Appalachians on 
Sunday and weakens further Monday...as subtropical ridging gradually 
builds west and maintains a tropical airmass over the region. 


On Sunday...the stationary front dissipates or moves north of the 
region as region comes under the influence of periphery of Atlantic 
ridging. Believe this should allow for a few breaks of sun on 
Sunday with temperatures warming into the lower 80s interior...upper 70s 
to around 80 coast with southerly flow. Steepening middle-level lapse 
rates and vorticity energy still tracking NE across the area ahead of 
weakening upper trough should enhance convective strength on 
sun...particularly across the interior where surface instability 
will be greater. Amount of surface heating will dictate severe 
convection possibilities. Appears the best chance of convection 
will be during the afternoon/early evening with best heating. 


Similar scenario on Monday as region remains on northwest periphery of 
subtropical ridging. 850 hpa temperatures warm to around 16c...and with 
breaks of sun once again...temperatures across city interior should be able 
to get into the middle 80s. Upper 70s to around 80 coast with southerly 
flow. Expect another round of diurnal convection as remnants of 
upper trough appear to track through the region. With marginal to 
moderate instability and modest deep layer shear...isolated severe 
convection possible. 


&& 


Long term /Monday night through Friday/... 
Bermuda high remains in place over the Atlantic...and persistent SW 
flow will allow a very warm and humid airmass to overspread the 
region. Highs will be in the upper 80s to around 90 with dewpoints 
in the upper 60s. Diurnally driven convection will result in 
scattered evening showers and thunderstorms Monday night...then again 
on Tuesday afternoon/evening. A cold front will push into the region on 
Wednesday...moving south of the area Wednesday night and becoming nearly 
stationary as high pressure builds from the north. Another round of 
showers and thunderstorms will develop Wednesday and Wednesday night...then Thursday 
is expected to be dry with cooler and less humid conditions. 


&& 


Aviation /12z Saturday through Wednesday/... 
frontal boundary south of Long Island will remain through the 
forecast period as waves of low pressure track along the boundary. 
With the next wave is currently tracking just south of Long Island. 
This has resulted in scattered rain showers and isolated thunderstorms and rain tracking generally 
along and south of I-95 corridor. 


Expect that ceilings and visibilities will improve 12-14z as low levels 
begin to warm ever so slightly. The next middle level short wave 
will spark an increase in coverage and intensity of precipitation across 
the region 16-20z. Have included vcsh for this with a cumulonimbus cloud 
group. Thereafter...we may get a break from organized areas of 
precipitation and may be looking at widely scattered rain showers and isolated thunderstorms and rain. 
As typical for trying to time and place waves along a stalled 
frontal boundary...forecast timing is low. 


Light northeast flow will slowly shift to more easterly direction 
as the morning progresses...and then to southeast or S in the afternoon. 
Expect a light southerly component to the wind this evening and 
into the overnight Sat night. 


Outlook for 12z Sunday through Wednesday...very unsettled weather 
pattern continues. Showers and thunderstorms trek from west to east 
through most of Sunday. As such...multiple chances for sub VFR 
ceilings and visibilities in showers and thunderstorms. Front 
likely moves north as a warm front sometime Sunday with VFR 
conditions. High pressure remains across the terminals into 
Wednesday. Monday through Wednesday there will be a chance of 
showers and thunderstorms as a surface trough develops during the 
day...and daytime heating increases instability. 


&& 


Marine... 
with frontal boundary nearby through Sunday...winds and seas will 
remain rather tranquil. 


Main concern for mariners through the weekend will be the presence 
of showers and thunderstorms. The threat remains through the weekend. Any 
shower or thunderstorm will have the potential to produce heavy downpours 
with plenty of moisture to work with. Looks like we will have to 
deal with waves moving across the waters early this morning (pre and 
around daybreak) and then again late morning into early afternoon. 
Both waves will result in a period of widespread rain with isolated 
embedded thunderstorms. At other times...generally just isolated to 
widely scattered showers and thunderstorms. 


The front will begin to move north of the waters by Sunday 
afternoon. This will result in a developing southerly flow. By 
Monday...the gradient tightens...and southwesterly winds will 
increase. Seas will respond...likely to marginal Small Craft Advisory thresholds over 
the ocean by Monday. 


Monday night through Wednesday...persistent south to southwest flow will 
dominate area waters through the period. Seas will gradually build 
during the period...approaching Small Craft Advisory criteria on the ocean waters 
late Monday night before subsiding Tuesday morning. As a southerly swell 
develops by mid-week...seas on the ocean will build up to 4-6 feet 
late Tuesday night and Wednesday. 


&& 


Hydrology... 
band of rain showers/thunderstorms and rain across lower Hudson Valley produced between 2 
and 4 inches of rain in about 2 hours...with wider radius of up to 
an inch across SW Conn and NE New Jersey. Rain showers/thunderstorms and rain likely today...with 
scattered showers and thunderstorms tonight through Monday. 


Heavy rain potential will be there for entire County Warning Area as any of the 
vorticity lobes work across the region and ignite rain showers/thunderstorms and rain activity. 
Confidence not high enough on pinpointing exact location of 
these lobes...so will not put up Flash Flood Watch at this 
time...but will highlight flash flood threat in severe weather potential statement for entire 
area. 


&& 


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


&& 


$$ 

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