NWS San Diego, CA wrote its last area forecast discussion before the first event at Jan 9, 1:23 PM PST, 4 hours 37 minutes earlier.
Area forecast discussion, Jan 9, 1:23 PM PST, 4 hours 37 minutes before
Area Forecast Discussion
National Weather Service San Diego CA
123 PM PST Mon Jan 9 2023
.SYNOPSIS...
Light rain is spreading into portions of Orange and southwestern San
Bernardino Counties today, along with stronger and gusty south to
southeast winds. The rain will intensify, and spread southward
tonight, and could become locally heavy at times into Tuesday, with
the heaviest rainfall on south-facing mountain slopes. A period of
fair and warmer weather returns for Wednesday through Friday, ahead
of another storm system slated for arrival some time over the
weekend.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
We continue to see significant breaks in our cloud cover here in
SoCal so a bit of sun for this afternoon ahead of the main cloud
shield tonight. The sfc pressure gradient to SW NV continues to
increase this afternoon. South winds are gusting to 50 MPH or more
over the San Bernardino County Mts, and 45 MPH in some of the high
desert areas this afternoon. They will increase further this
evening. The High Wind Warning remains in effect through Tuesday,
and a Wind Advisory for Orange County begins later this afternoon.
Intermittent, light rain has been falling over portions SW San
Bernardino, and Orange Counties this morning. Radar shows the
stronger echoes have been moving ashore farther to the north, in
Ventura and Santa Barbara Counties. Latest rainfall totals for our
area since last night, are headlined on our web page, and will be
updated periodically. The more significant rainfall is expected over
northern portions of our forecast areas after dark.
A weakening AR, which has tapped some subtropical moisture, is
moving slowly south along the CA Coast today, It will help to
increase rainfall rates into Orange and far SW San Bernardino
Counties tonight. The heaviest rainfall will be aided by strong,
southerly, upslope flow onto the south-facing slopes of the San
Bernardino County Mountains. Rainfall rates will be more moderate
into the valleys and Orange County overnight. As the AR weakens
further and moves south of the region on Tuesday, forcing will be
handed off to the eastbound shortwave, currently near 140W
Longitude. It will move onshore near Pt. Conception late tomorrow,
trailing a cold front, destined to sweep through SoCal during the
day. Convergent flow from south winds turning westerly, will force
the development of more showers and isolated thunderstorms, as the
the front sweeps SE across the region by evening. Please see
Hydrology section below for further detail on rainfall and potential
flooding. The Flood Watch remain in effect late tonight through
Tuesday.
Precipitation could linger over the mountains Tuesday night, but
should end by Wednesday morning. As another storm deepens over the
EastPac, a warm ridge builds over the West later this week. This
will set us up for some weak offshore flow and warming. Temperatures
should be back above average for the latter half of the week under
fair skies.
We could start feeling the effects of that next Pacific storm system
as early as Saturday, but timing and intensity this far south is
uncertain. Based on ensemble guidance, the probability of
precipitation becomes likely as we move through the weekend but
detail consensus is lacking. So expect some, but don't rely on
timing or amounts at this juncture.
&&
.AVIATION...
092130Z...Coast/Valleys...Areas of BKN-OVC clouds 2000-5000 feet MSL
will gradually spread from Orange County/Inland Empire this
afternoon south to San Diego County tonight along with SHRA and
higher terrain obscurations. Most vis will remain 6+ miles through
04Z Tue but lower at times to 2-4 miles in SHRA along with local
CIGS below 1000 feet MSL after 04Z, continuing at times through Tue.
Mountains/Deserts...SCT-BKN high clouds at/above 20,000 feet MSL
will continue through tonight. Areas of mid level clouds with bases
3000-6000 feet will continue on the coastal and upper slopes of the
mountains this afternoon. SHRA will increase in San Bernardino
mountains this afternoon spreading south through Riverside/San Diego
County mountains tonight, along with south winds over ridges and
into high desert. Gusts 30 to 40 kt this afternoon will increase
after 23Z with local peak gusts to 50-60 kt tonight. Areas of LLWS
and moderate to strong up/downdrafts will occur over and north/east
of the mountains. Widespread terrain obscurations will spread from
north to south this afternoon and evening, continuing through Tue.
&&
.MARINE...
A storm system will bring increasing south winds late this afternoon
and tonight, with southerly winds 15-25 knots and local gusts to 30
knots, shifting to the west late Tuesday with speeds decreasing
Tuesday evening. Seas will be sloppy with a developing west swell 6-
7 feet at 12 seconds and the 5-7 second wind waves from mostly the
south. Isolated thunderstorms are expected late tonight through
Tuesday. An additional west swell will occur Tuesday night through
Wednesday night, up to 11 feet at 15 seconds in the outer waters. A
Small Craft Advisory is in effect late this afternoon through
Wednesday night. Winds and seas could increase again this weekend
due to another storm system.
&&
.BEACHES...
Isolated lightning strikes will be possible at or near the beaches
late tonight and Tuesday due to the low pressure system.
A series of west swells will bring elevated to high surf Tuesday and
Wednesday. The first swell will arrive at the inner coastal waters
by 6 AM Tuesday at 6 feet/12 seconds/265 degrees which should
produce mostly 5-8 foot surf. The second swell will arrive at the
inner coastal waters Tuesday night and continue Wednesday at 7
feet/15 seconds/275 degrees which should produce mostly 7-10 foot
surf, highest in San Diego County. A High Surf Advisory for Tuesday
and Wednesday is in effect. Another storm system could bring more
high surf this weekend.
&&
.HYDROLOGY...
Areas of light rain will move across Orange County, and the San
Bernardino Mountains today, becoming more widespread in the
mountains this afternoon, then expand southward tonight. The rain
will be most widespread and heaviest on Tuesday with the heavier
precipitation spreading southward during the day. Showers are
expected to end Tuesday evening with the passage of a cold front.
Through Tuesday evening, rainfall for Orange and southwestern San
Bernardino Counties is expected to range from around 1.5 inch
near the coast to 3 to 5 inches in the mountains with local totals
of 6 to 8 inches on south-facing slopes of the San Gabriel
Mountains.
For San Diego and western Riverside Counties, rainfall for northern
areas is expected to range from around 1 inch in the I.E., to 1.5 to
2.5 inches in the mountains, while around one-half inch is expected
for southern portions of San Diego County.
High desert areas can expected from one-third to two-thirds of an
inch, except near the mountain foothills where an inch or more is
possible. One-quarter inch or less is forecast in the lower deserts.
There is also a chance for thunderstorms on Tuesday. Peak rainfall
rates of 0.75 inch per hour are likely along the south-facing slopes
of the mountains, and possible locally, in the heaviest showers and
thunderstorms ahead of and along the cold front.
Snow levels will initially be quite high, but will lower Tuesday
afternoon and evening with 1 to 2 feet of snowfall possible,
mostly above 7500 feet.
Urban and small stream flooding, and ponding of water will be most
likely on Tuesday, especially in northern parts of the forecast
area. The flood potential will be elevated in and below burn scars
as well. Nearly saturated soils and high snow levels initially, will
lead to enhanced runoff potential near the mountains. There should
be some flow in the Whitewater River as well, which could make it to
northern parts of the Coachella Canal, but flow is currently not
forecast to make it to Indio.
The CNRFC maintains the Santa Margarita and San Diego Rivers
reaching Monitor stage late Tuesday. They also have flow in the
Santa Ana River channel near Riverside, at least equaling what was
measured at the Municipal Water District Crossing on New Years Day.
Prado Dam operators will release water through the Santa Ana Channel
in preparation for inflows tonight and Tuesday.
&&
.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory from 6 AM Tuesday to 10 PM PST Wednesday for
Orange County Coastal Areas-San Diego County Coastal Areas.
Flood Watch from late tonight through Tuesday evening for Orange
County Coastal Areas-Orange County Inland Areas-Riverside
County Mountains-San Bernardino County Mountains-San
Bernardino and Riverside County Valleys-The Inland Empire-
San Gorgonio Pass Near Banning-Santa Ana Mountains and
Foothills.
High Wind Warning until 8 PM PST Tuesday for Apple and Lucerne
Valleys-San Bernardino County Mountains.
Wind Advisory until 4 PM PST Tuesday for Orange County Coastal
Areas-Orange County Inland Areas.
PZ...Small Craft Advisory until 2 AM PST Thursday 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...10
AVIATION/MARINE/BEACHES...Maxwell