Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 221642

Area Forecast Discussion
National Weather Service San Diego CA
930 AM PDT Tue May 22 2018

A deep upper level trough will move northeast out of the area this
afternoon and tonight, resulting in a gradual decrease in cloud
cover through Wednesday. Another area of low pressure will through
the region Friday through Sunday, so the below normal daytime
temperatures will continue through the weekend with periodic low
clouds west of the mountains. More marine layer low clouds are
likely early next week as well.



Marine layer depth ranged from 4000 feet above sea level in San
Diego County to 5000 feet farther north this morning, with a lot of
breaks in the clouds over southern San Diego County. A few light
showers occurred earlier this morning, but less than on Monday. With
the thinner cloud cover (due mostly to higher cloud bases) and
a slightly weaker inversion, by about 1 deg C, we should have
somewhat better clearing this afternoon, especially San Diego
County. It`s less unstable in San Bernardino County, so we should
not have a repeat of the Monday afternoon showers there.

The upper low will move to the northeast mainly tonight and weaken
while some ridging forms over the interior southwestern US. Some
lowering of the marine layer will occur, with better afternoon
clearing Wednesday, especially inland. With onshore flow continuing
as well as the peak stratus season, we will still have a lot of
stratus around, especially nights and mornings, most of the week. An
upper level low will move into California Friday night, and this
will bring more cooling to inland areas, though the marine layer
effects here will depend partly on if we have a coastal eddy.  Right
now, the GFS is saying no to the eddy, so we may end up with a
decrease in stratus Friday/Saturday, especially with cooling above
the marine inversion. Models are inconsistent for early next week,
except for one thing--no significant ridging, and yes to continued
onshore flow. Thus, coastal low clouds are likely to occur then,
with temperatures at or a little below normal.


221530Z...Coast/Valleys/Coastal Mountain Slopes...Stratus deck will
prevail west of the mountains and along some mountain slopes with
bases 1500-3000 feet MSL and tops 4000-5000 feet. Patchy -DZ could
impact the northern areas. Expect at least partial clearing to take
place beginning 17-19Z at the terminals, with KSBD/KONT the latest
to see the clearing. Expect a few hours of SKC/SCT conditions this
afternoon and early evening. The marine layer will be much shallower
tonight/Wednesday morning. Expect low clouds to fill in again
beginning 03-05Z coastal terminals and 06-10Z inland terminals with
BKN IFR/MVFR conditions at the terminals thereafter. Will see bases
900-1300 feet MSL and tops 1500-2500 feet late tonight/Wednesday

Mountain Crests/Desert Mountain Slopes/Deserts...VFR conditions with
clear skies. Local west winds 15-25 kt with gusts 25-35 kt will
occur on the desert mountain slopes and through San Gorgonio Pass,
with the strongest gusts late this afternoon and evening.


No hazardous marine conditions are expected through Saturday,
although some gusts over 20 kt are forecast in the outer waters
Friday and Saturday.


A long-period swell from 200 degrees and resulting surf on south
facing beaches will peak today through Wednesday before subsiding
slowly Thursday and Friday. Check the beach hazard statement for all
the details.


Skywarn activation is not requested. However weather spotters are
 encouraged to report significant weather conditions.


CA...Beach Hazards Statement through Thursday afternoon for Orange
     County Coastal Areas.



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