173 
fxus66 ksgx 052034 
afdsgx 


Area forecast discussion 
National Weather Service San Diego California 
130 PM PDT Sat Jul 5 2008 


Synopsis...a shallow marine layer will continue areas of coastal 
low clouds and fog during the nights and mornings...otherwise fair 
with warm days inland through Tuesday. By midweek...building high 
pressure over central California will force easterly flow over the 
southern portions of the state...possibly increasing monsoonal 
moisture. This would bring an increase in clouds...humidity...and a 
chance of showers and thunderstorms...especially in the mountains. 


&& 


Discussion...for southwest California including San Diego... 
Orange...southwest San Bernardino and West Riverside counties. 


Areas of marine stratus/fog continued all day along the coast and 
beaches in San Diego County. There were a few cumulus in the mountains 
and some haze along the coast and in the valleys. Weak onshore 
surface pressure gradients have increased slightly over yesterday. 
Satellite imagery showed some cumulus building over the mountains...and a 
thunderstorm south of the border on the Baja California spine at 20z. The water 
vapor loop shows upper-level troughing becoming more pronounced 
along the West Coast which should be bringing in dryer air aloft. 
Temperatures at 20z were 95 to 100 in the valleys and deserts and in 
the 70s to lower 80s closer to the coast where the sea breeze and a 
shallow marine layer have a greater influence. 


Model guidance indicates slight cooling sun and Monday with minor 
500 mb height falls. This could help add a couple hundred feet to 
the marine layer and help to cool the coastal strip by a few 
degrees...otherwise no significant changes. Increased dry...westerly 
flow aloft will diminish any chance for monsoon activity through Monday 
as well. Dewpoints have dropped a bit in the lower deserts...but are 
still high enough to keep maximum temperatures in check. Hard to determine the 
depth of the moisture there...so if the surface dew points do not 
mix out...heat index values will again be near 110 in the late 
afternoons while actual temperature runs closer to 100. In either case... 
hot. 


Tuesday and Wednesday are transition days as the upper-level flow over socal 
shifts from the west...to the East. Heights rebuild over central California 
on for Tuesday and Wednesday...setting up an easterly flow aloft and 
increasing monsoonal moisture over socal for the second half of the 
week. The European model (ecmwf) and the latest GFS runs seem to be more consistent 
with this pattern...so a slight chance of thunder has been added for 
the mountains and deserts beginning late on Wednesday...and continuing 
through Friday. Model cross sections show moderate easterly flow in the 
middle levels and considerable moisture...which suggest any convection 
that develops over the mountains will have a chance at making it 
into the valleys and even coastal areas. However...since this is 
several days out...probability of precipitation over the valleys and coasts will be more 
conservative for those later periods until confidence increases in 
the strength of the easterly flow. 


Both relative humidity and temperatures will be climbing again by midweek...so it will 
continue quite warm inland...while the marine layer and sea breeze 
keep the coastal strip more comfortable. 


By next weekend...it appears we will be transitioning again to a dry 
SW flow aloft...and slight cooling as heights/thickness fall. 


&& 


Aviation... 
052000z...shallow marine layer around 800-1100 feet. Low clouds and 
patchy fog lingered early this afternoon near the immediate coast 
and beaches of San Diego Colorado...but should mainly clear out by 23z. 
The stratus was well organized further offshore. 


Areas of stratus and patchy fog will start to reform this evening 
near the immediate coast from 03-07z. The stratus should develop 
earlier than recent nights with coverage becoming more widespread 
and extending further inland tonight. Bases mainly 400-800 feet mean sea level. 
Expect IFR-LIFR ceilings at ksan/kcrq/ksna from approx 09-16z sun 
with 3-5sm visibilities across the coastal areas and local visibility 1sm 
or less near The Mesas. 


Above the marine layer...unrestricted visibilities will continue 
through tonight except for some local 3-5sm MVFR haze. A few cumulus 
over the mountains until 02z with bases around fl100. 


&& 


Sgx watches/warnings/advisories...none. 


&& 


$$ 


Public...jad 
aviation...lavis