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Area forecast discussion 
National Weather Service Upton New York 
1215 PM EDT Friday Jul 18 2008 


Synopsis... 
high pressure remains entrenched over the middle-Atlantic before 
slowly drifting offshore late Saturday. A slow-moving cold front 
will approach from the northwest on Sunday...becoming nearly 
stationary over the area and resulting in unsettled weather for 
the first part of the new week. 


&& 


Near term /through tonight/... 
area remains just to the south of zonal flow. Weak embedded short 
wave and vorticity maximum moves to the north this afternoon. Much of the 
area capped and not expecting any showers or thunderstorms to 
develop. However...across the northern tier with the short wave 
may be able to develop cumulus and break the cap late in the day. 
Visible satellite showing cumulus across northeastern PA into northern 
New Jersey...with some in far western Orange County. Any storms that 
develop could produce some gusty winds as lower levels are 
relatively dry. So have introduced a slight chance across the 
northern tier from 20z to 00z. 


Otherwise just some modifications to hourly temperatures. Heat 
advisories remain. May not quite make the 100 heat index across 
northeastern New Jersey as mix out dewpoints into the lower 60s 
from current readings in the upper 60s. 




Hot and humid weather on tap for the region today as SW winds 
usher an airmass with 850 mb temperatures near +19c resulting in maximum 
temperatures in the middle to upper 90s for the NYC metropolitan area...and in the 
low to middle 90s most elsewhere. As a result...the heat index will 
be in the middle to upper 90s for NYC and in the upper 90s to near 
100 for highly urbanized areas of northeast New Jersey. 


Tonight will be quite warm and muggy with lows in the upper 70s 
across the NYC metropolitan...and in the upper 60s to lower 70s most 
elsewhere. Outlying locales will drop into the middle 60s...but with 
temperatures approaching the dewpoint...will see patchy fog developing in 
these locations. 


&& 


Short term /Saturday through Sunday/... 
hot and humid weather continues on Sat with a deep southwest flow 
and 850 mb temperatures once again near +19c and surface dewpoints perhaps a 
degree or two higher than Friday. As such...will continue heat 
advisory for NYC as heat index will be in the upper 90s once 
again...possibly approaching 100 at klga. Will also go ahead and 
add heat advisory for same locations in New Jersey as the heat 
index will be around 100 during the afternoon. 


Cold front sags closer to the area Sat afternoon...and with 
unstable airmass in place...cannot rule out afternoon and evening 
convection. Will carry slight chance probability of precipitation for the region from 
about noon through about midnight. Any thunderstorms that develop will 
diminish Sat night with loss of diurnal heating. Low pressure passes 
north of the region as well...keeping most of the precipitation to the 
north. 


Sunday should feature better chances for thunderstorms as an upper trough 
digs into the upper Great Lakes region...and leading shortwave 
energy moves across central PA/New York toward the County Warning Area. Cooler temperatures and 
more expected cloud cover ahead of the front should break the 
string of 90+ degree days...with middle/upper 80s forecast. 


&& 


Long term /Sunday night through Thursday/... 
Ely storm motion of 15-20kt from any Sun afternoon convection will 
bring the threat of thunderstorms and rain Sun night across the County Warning Area. Lljet develops 
and should sustain and perhaps enhance convection. The exact setup 
is still uncertain. At this time...nose of the lljet sets up north of the County Warning Area 
so best lift may be north. 


12z GFS/GFS ensembles depict a fairly uniform scenario at 500 mb 
bringing an upper level trough into the northestern Continental U.S. Monday. Trend is 
faster. Latest 12z European model (ecmwf) trending faster as well. With previous GFS 
runs and 00z European model (ecmwf) slower...did not completely go with the faster 
solution at this time. 


Appears there will be at least one day in the Monday-Wednesday period with 
a good chance of severe thunderstorms. 12z GFS forecasts Monday as moisture streams 
northward...heights lower and 0-6km shear increases to 30-40kt. A slower 
solution would favor Tuesday or later. With the slow progression of the 
upper trough...could have 2 days of numerous thunderstorms and rain with the potential for 
moderate/heavy rain accums. Faster 12z GFS does introduce ample dry at the 
middle levels by Tuesday. If this forecast is correct...convection on Tuesday/Wednesday 
isolated-scattered and diurnal in nature. 


Temperatures cooler but humid on Monday with clouds and thunderstorms and rain. GFS forecast 
would be warmer on Tuesday/Wednesday with pcloudy skies and better mixing. 
Slower solution humid with more clouds. Temperatures will warm for Thursday as the 
500 mb trough will be in northern Canada. 


GFS/European model (ecmwf) deepen the broad area of low pressure currently over northestern 
Florida...tracking it NE up the coast and out to sea next week. Will 
follow the trends with this system. 


&& 


Aviation /08z Friday through Tuesday/... 
VFR conditions to prevail across the terminals next 24h. A light 
and variable flow early this morning will become SW after daybreak 
at around 10 knots. Low pressure bypassing the area to the north this 
after/evening will allow for a tightening of the pressure gradient. This 
may limit seabreeze circulations to kjfk...kisp...kbdr...and kgon. 


Outlook for 06z Saturday through Tuesday... 
VFR through Sat night as a cold front drifts south and becomes 
stationary in the area Sunday morning. The front moves back north 
as a warm front Sunday. Scattered showers and thunderstorms 
possible Sunday afternoon and evening with local MVFR conditions. 
VFR Monday...then there is a chance of showers and thunderstorms 
Monday night into Tuesday as a cold front moves through...with 
MVFR to local IFR conditions possible 


&& 


Marine... 
no changes at this time. 


Easterly swells from distant T.S. Bertha continue to impact the 
ocean waters with seas around 4 feet at buoys 44025 and 44017. 
Elsewhere...seas are a foot or less with a west/SW wind generally 10 
knots or less. 


A SW flow will persist across the waters through this weekend 
with wind speeds of 10 to 15 knots...but a period of slightly 
stronger winds are forecast on the ocean waters tonight. Low pressure 
bypassing the area well to the north late today into tonight will 
allow for a tightening pressure gradient. The stronger SW flow 
will likely push seas up to around 5 feet on the easternmost ocean 
zone...anz350...necessitating a Small Craft Advisory for hazardous seas tonight. 
Beyond that time...confidence is not high enough to extend further 
in time. 


As low pressure tracks across the Canadian Maritimes on Sat...its 
trailing cold front will drop southward across New England. The front 
looks to stall just to the north of the waters Sun morning before 
returning north as a warm front later in the day. Winds will 
become southerly sun into Monday. Seas on the ocean will remain close 
to Small Craft Advisory criteria during this time...especially across the 
easternmost ocean zone. 


Low pressure from the Great Lakes will move across the waters late Monday 
and Monday night with a series of waves to follow closely on its 
heels Tuesday into Wednesday. Winds and seas look to stay below Small Craft Advisory criteria 
during this time. 


&& 


Hydrology... 
mainly dry through Saturday. Isolated thunderstorms possible 
across the norther tier late this afternoon into this evening with 
local quarter to one half inch amounts. The next chance of any 
significant rainfall later sun through Wednesday with convection ahead 
of a slow moving front. Any convection that develops Sat 
afternoon/evening would be capable of locally heavy rain with 
localized flooding possible. 


&& 


Okx watches/warnings/advisories... 
CT...none. 
New York...heat advisory until 6 PM EDT Saturday for nyz072>076. 
New Jersey...heat advisory until 6 PM EDT this afternoon for njz003>006-011. 
Heat advisory from 12 PM to 6 PM EDT Saturday for njz003>006- 
011. 
Marine...Small Craft Advisory for hazardous seas from 6 PM this evening 
to 6 am EDT Saturday for anz350. 


&& 


$$ 

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