Area Forecast Discussion
Issued by NWS San Diego, CA

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947
FXUS66 KSGX 211354
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
554 AM PST Sat Jan 21 2017

.SYNOPSIS...
Decreasing showers and winds through this evening as the second in
a series of storms to impact Southern California moves east today.
The third and strongest storm is expected for late Sunday and Monday
with showers continuing through Tuesday. Strong winds...heavy
rainfall with flooding...and heavy mountain snowfall is expected.
Dry with warming for Wednesday into next weekend with moderate to
strong offshore winds possible late in the week.

&&

.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...

Showers will continue this morning...decreasing later today into
this evening with greatest coverage and amounts across San Diego
County. Strong gusty west winds continue early this morning in the
mountains and deserts with strong gusts...between 50 and 60
mph...in the mountains of San Diego County. Winds are expected to
decrease late this afternoon into this evening.

The strongest in this series of storms is expected for late Sunday
into Monday with showers continuing into Tuesday. A subtropical
plume of moisture will feed into this system increasing the
precipitation potential with precipitable water values increasing
to around 1.35 inch Sunday afternoon and evening...around 300
percent of normal. A strong pre-frontal low level jet will lift
this moisture along the south slopes of the San Gabriel Mountains
Sunday afternoon and early evening with higher resolution models
showing peak rainfall exceeding 3 inches in 3 hours. Given the
strength of this south flow...this could spread the heavy rainfall
into areas of the upper deserts adjacent to the mountains
increasing the flooding potential for the Mojave River Sunday
night and Monday.

The heavy precipitation will spread southward across far Southern
California Sunday evening with showers continuing at times through
Tuesday. Very strong south to southwest prefrontal winds could
cause damage late Sunday afternoon and evening. Strongest winds
are expected near the mountain ridge tops of the San Bernardino
County mountains into adjacent areas of the upper deserts. For
coastal areas...the strong winds combined with the saturated soils
increases the possibility of tree damage.

Very cold air aloft...around -30 C at 500 mb...will spread into
far Southern California for Monday afternoon and persist through
Tuesday. This will continue the showery pattern and bring a slight
chance of thunderstorms. Snow levels could fall to 2500 to 3000
feet Monday night and early Tuesday.

Dry with warming for Wednesday into next weekend with
moderate to strong offshore winds possible late in the week.

&&

.AVIATION...
211100Z...Scattered showers continuing through mid afternoon across
the area with occasional CIGS BKN025-035 TOPS to 200 with the
heavier precipitation as well as VIS to 2-3 SM. Mtns obscd at times
in clouds and pcpn. Precipitation tapering off after 21Z this
afternoon. Westerly wind gusts will continue through about 00Z this
evening...with gusts to 30 kt west of the mountains and gusts to 50
kt over and east of the mountains. Widespread moderate to heavy rain
and mountain snow developing Sunday after 12Z and spreading from NW
to SE during the day with IFR conditions likely under the heavier
precipitation and mountain obscurations.

&&

.MARINE...
Showers tapering off this morning. A third and final storm arrives
Sunday and continues through Monday night...bringing more strong
winds, heavy rain and very large seas up to 18 feet. Another Gale
Warning has been issued for Sunday, in effect through Monday night.


&&

.BEACHES...
A High Surf Warning remains in effect through Tuesday. Very large
west swells will produce wave heights of 13-18 feet through
Saturday, resulting in very large surf to 15 feet. Surf this large
could damage structures and produce beach erosion. Early morning
high tides will be around 5 ft, so the coastal flooding magnitude
will likely be minor.

The swells will diminish a little on Sunday but high surf conditions
are still likely to persist into Tuesday. It is not until Wednesday
that surf and swell conditions will lower below high surf
thresholds.

&&

.HYDROLOGY...
The San Diego River has now fallen to near flood stage of 11.3
feet at Fashion Valley. It peaked at 11.99 feet at 7:15 PM
Saturday with a secondary lower peak at 11.81 feet at 2:15 AM.
This is the highest level since 14.01 feet in December of 2010.
That crest in 2010 was the third highest on record and the crest
Saturday evening was the ninth highest on record. The rainfall for
Sunday night and Monday could bring additional flooding.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...High Wind Warning until 10 PM PST this evening for Riverside
     County Mountains-San Diego County Deserts-San Diego County
     Mountains.

     Winter Storm Warning from 4 PM Sunday to 6 PM PST Monday for
     Riverside County Mountains-San Diego County Mountains.

     Wind Advisory from 6 AM to 6 PM PST Monday for San Diego County
     Deserts-San Gorgonio Pass Near Banning.

     High Wind Warning from noon Sunday to 6 PM PST Monday for Apple
     and Lucerne Valleys.

     Wind Advisory until 6 PM PST this evening for Apple and Lucerne
     Valleys-San Gorgonio Pass Near Banning.

     High Wind Warning from 4 PM Sunday to 6 PM PST Monday for San
     Diego County Coastal Areas-San Diego County Valleys.

     Winter Storm Warning from noon Sunday to 6 PM PST Monday for San
     Bernardino County Mountains.

     High Wind Warning from noon Sunday to noon PST Monday for Orange
     County Coastal Areas-Orange County Inland Areas-Santa Ana
     Mountains and Foothills.

     High Wind Warning from 4 PM Sunday to noon PST Monday for San
     Bernardino and Riverside County Valleys-The Inland Empire.

     High Surf Warning until 10 PM PST Tuesday for Orange County
     Coastal Areas-San Diego County Coastal Areas.

PZ...Gale Warning until 4 PM PST this afternoon for Coastal Waters
     from San Mateo Point to the Mexican Border and out to 30 nm-
     Waters from San Mateo point to the Mexican Border Extending
     30 to 60 nm out including San Clemente Island.

     Gale Warning from 10 AM Sunday to 4 AM PST Tuesday for Coastal
     Waters from San Mateo Point to the Mexican Border and out
     to 30 nm-Waters from San Mateo point to the Mexican Border
     Extending 30 to 60 nm out including San Clemente Island.

&&

$$

PUBLIC/HYDROLOGY...17
AVIATION/MARINE/BEACHES...JMB



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