Winter Storm Watch 1, NWS San Diego, CA

Area Forecast Discussion
National Weather Service San Diego CA
342 PM PST Tue Jan 17 2017

.SYNOPSIS...
The focus of the forecast remains on the series of storms
expected to impact California Thursday into Tuesday of next week.
For our region, heavy mountain snowfall and heavy rain leading to
urban and possible river flooding look to be the main impacts.
However there could be periods of gusty winds and thunderstorms as
well. As the event progresses flooding will become and increasing
concern as soils in the region saturate. A break in the stormy
pattern is expected by the middle of next week.

&&

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

The focus of the forecast remains the upcoming series of storms,
slated to impact our region between Thursday and Tuesday of next
week. Prior to these systems, weather will remain quiet in
SoCal.

The first storm system is slated to arrive on Thursday, bringing
moderate to heavy rainfall, with snow at elevations above 5000
ft. With this system, light showers will be possible early
Thursday morning, however the bulk of the rain/snow should arrive
between 6 AM and 3 PM. Instability appears sufficient with this
system for scattered thunderstorms Thursday morning and
afternoon. The primary impacts should be mountain snowfall and
locally heavy rain leading to urban flooding. The river flood
threat with this first storm appears to be low. Activity should
become more showery in nature Thursday night, with the best
precipitation potential focused over the mountains and valleys.

Storm two will impact the region Friday, with the best rainfall
chances being Friday morning and afternoon. The primary threats
with this system look to be winds, mountain snow and heavy rain.
The strongest winds are expected in SD County, with gusty
southerly winds along the coast in the morning transitioning to
gusty northwesterly winds for all areas by Friday evening. There
is some potential for thunderstorms friday afternoon, and this
will have to be watched closely over the coming days with current
model projections suggesting 35-50 kt 900-700 mb winds that could
be easily be mixed to the surface resulting in strong gusts over the
over the coast and valleys. Snow levels with this system may be as
low as 4500 ft in the San Bernardino County Mountains, with levels
closer to 5500 ft in the SD County Mountains. Therefore the most
significant snow accumulations are expected at elevations above
6000 ft in the San Bernardino and Riverside County Mountains.
Urban flooding will also be a concern with high rainfalls rates
possible during the day on Friday. With the ground increasing in
saturation, flash flooding and debris flows near burn scars will be
a concern. Some River flooding, particularly involving the San
Diego River, is possible during this period.

A relative lull in activity is expected Saturday in Sunday, with
scattered light to moderate rain/mountain snow showers Saturday
and mostly cloudy conditions for most areas during the day on
Sunday. Strong winds will remain a concern in the mountains and
along the desert slopes, with mountain wave activity continuing
through the day in Saturday.

The third storm system is expected to arrive Sunday night and
Monday. Currently the intensity of this system looks similar to
Friday's forecast storm. Thus heavy rain/mountain snow, winds and
flooding may again be concerns with this system. At this time
however, global models continue to show inconsistencies with the
timing and evolution of the system.

&&

.AVIATION...
172130Z...Mostly clear through this evening. Patchy low clouds along
the coast tonight, with bases 800-1000 ft MSL and tops near 1200 ft
MSL. VIS could lower to 1-3 SM BR where low clouds develop along the
coast, or where fog forms in the valleys due to radiational cooling.
Conditions will improve by late Wed morning.

&&

.MARINE...
A series of Pacific storms will create strong winds, rain and rough
seas Thursday through Tuesday. Conditions hazardous to small craft
are likely Thursday, then gale force wind gusts to 35 kt and very
large combined seas of 14-18 ft are likely Friday and Saturday.
Winds and seas will diminish Sunday, then gale force conditions
developing again late Sunday through Monday as another system moves
across the area.

&&

.BEACHES...
Swell will gradually increase Thursday into Saturday with high surf
resulting. The highest surf will occur Saturday when surf could be
large enough to cause coastal damage, coastal flooding and beach
erosion. Swell and surf will decrease Sunday before increasing again
Monday. A High Surf advisory will likely be needed through the
period.

&&

.HYDROLOGY...
A Hydrologic Outlook has been issued to discuss precipitation
potential, flooding issues, and runoff, including potential river
flooding issues. Please see the Hydrologic Outlook, located on our
home page: weather.gov/SanDiego.

&&

.SKYWARN...
Skywarn activation will not be needed today.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&

PUBLIC...BA
AVIATION/MARINE/BEACHES...JJT