Weather Service Report


248 
FXUS66 KSGX 210526
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
926 PM PST Fri Jan 20 2017

.SYNOPSIS...
A storm system will continue to gradually taper off tonight and
Saturday, but a few heavy showers will continue especially tonight.
A brief dry period will occur late Saturday through early Sunday
before the next storm brings more heavy rain, strong winds,
mountain snow with another chance of thunderstorms and flooding.
Showers will linger Tuesday, with fair weather likely starting
Wednesday. Temperatures will average below normal through the
middle of next week, then increase some the second half of next
week.

&&

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

...Update - One Storm Departing While Another is Poised to Arrive
on Sunday...

Southern California saw significant precipitation with today's
storm system. It brought localized flash flooding and high winds
downing trees across the area. The brunt of the storm is over.
However, scattered showers will continue to move onshore
overnight...and a few could be briefly heavy, especially San Diego
County. 

Updated precipitation amounts and local storm reports can be found
on our webpage weather.gov/sandiego

The San Diego River at Fashion Valley is above flood stage and a
Flood Warning is in effect there. The stage peaked this evening at
11.9 feet (flood stage is 11.3 feet), but scattered heavy showers
could possibly lead to another peak overnight. 

The next big storm with widespread, heavy precipitation arrives on
Sunday. Excessive rainfall is likely over the San Bernardino
County mountains as strong low level, moist SSW wind associated
with an Atmospheric River generates tremendous upslope. Precip
amounts locally to 8"+ are possible Sun-Mon there. Metro areas
looks to receive 1-3". Wind again will accompany the next storm,
though is looking slightly less than we saw with today's storm. 
More details on the next storm below from the previous discussion.
/Gregoria

...Previous Discussion (200 PM PST Fri Jan 20 2017)...

A lot of moisture lingers overnight, so the showers likely will
be numerous most of tonight before tapering off Saturday morning.

The break in the precipitation should occur late Saturday through
very early Sunday morning, though a lot of clouds will likely linger
due to moisture both below 850 MB, helped by the wet ground, and
some moisture above 600 MB. The next storm will move from northwest
to southeast Sunday through Monday and bring substantial rainfall
again along with strong winds and a possibility of thunderstorms.
Strong warm air advection in the 850-700 MB layer will bring the
snow levels up to 7000 feet or higher Sunday, so this will cut back
on snowfall amounts, and high humidity in the mountains will cause
some snowmelt to occur, in addition to the rain. There will
definitely be a flash flood threat Sunday through Monday, especially
as soils will be saturated. Cold air comes in behind a front Sunday
night, so snow levels will fall to 3500-4000 feet Monday and
continue Tuesday under a broad cold low pressure system. This could
result in substantial snow accumulations as saturation reaches 500-
600 MB at times. Fair weather will not return until at least
Wednesday, but models are consistent at showing a high pressure
ridge late next week for fair warmer weather.

&&

.AVIATION... 
210500Z...BKN020-030 TOPS 200 with -SHRA through 15Z, with local
CIGS 010-020 in +SHRA and VIS AOB 3 miles. Mtns obscd in clouds
and pcpn. Sustained winds 15-25 kt tonight west of the mountains
with higher winds 20-30 kt gust to 50 kt in the mountains. 

After 15Z...SCT-BKN025-035 with showers tapering off through 20Z.

&&

.MARINE...
Strong winds and showers tonight with showers ending Saturday
morning. A third and final storm Sunday through Tuesday will
bring more strong winds, heavy rain and very large seas greater
than 10 feet. A Gale Warning continues through Saturday afternoon.  

&&

.BEACHES...
A High Surf Warning is in effect through Tuesday. Very large
west swells will produce wave heights of 13-17 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 continue into Tuesday. It is not until Wednesday
that surf and swell conditions will lower below high surf
thresholds. 

&&

.HYDROLOGY...
Showers will gradually taper off tonight and Saturday, but a few
could be briefly heavy especially in San Diego County. Heavy
rainfall will return late Sunday and continue at times through
Monday with occasional showers lingering through at least Tuesday.
Snow levels will mostly be around 5000 feet today. Snow levels
will rise up to 7500 feet Sunday before dropping to as low as 3500
feet by Monday afternoon. Grand totals for this wet period from
today through Tuesday:

Coast and Valleys: 2-5 inches
Mountains: 3-6 inches, locally 8"+
Deserts: 0.50-1 inch

The San Diego River at Fashion Valley is above flood stage and a
Flood Warning is in effect there. The stage peaked this evening at
11.9 feet (flood stage is 11.3 feet), but scattered heavy showers
could possibly lead to another peak overnight. 

&&

.SKYWARN... 
Skywarn will likely be activated Sunday through Monday. The main
threats are flooding, damaging winds, heavy snow, and high surf.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Winter Storm Warning until 6 AM PST Saturday for Riverside 
     County Mountains-San Bernardino County Mountains-San Diego 
     County Mountains.

     High Wind Warning until 10 PM PST Saturday for San Diego County 
     Deserts.

     Wind Advisory until 10 PM PST Saturday for Apple and Lucerne 
     Valleys-Coachella Valley-San Gorgonio Pass Near Banning.

     High Wind Warning until 10 PM PST this evening for Orange County 
     Coastal Areas-Orange County Inland Areas-San Bernardino and 
     Riverside County Valleys-The Inland Empire-San Diego County 
     Coastal Areas-San Diego County Valleys-Santa Ana Mountains 
     and Foothills.

     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 Saturday 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...Gregoria (Update)/Maxwell (Previous Discussion)
AVIATION/MARINE...Moede

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