Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
148 PM PST sun Jan 25 2015
high pressure aloft over northern and central California will
continue warmer weather today. Surface high pressure over the Great
Basin will bring locally strong and gusty northeast to east winds
this afternoon...gradually diminishing this evening. For Monday and
early Tuesday...a weak low pressure system from the southwest will
bring showers to the region...with best shower activity occurring
over the mountains...lower deserts and valleys. A second weak low
pressure system from the southwest could bring periods of showers
for Thursday into the weekend.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
A now mostly stationary cut-off upper level low is evident off the
coast of central Baja California on water vapor satellite imagery this
afternoon. Offshore pressure gradients are weakening
currently...with 14.9 mb from San Diego to Salt Lake City and 5.8 mb
from San Diego to Las Vegas...compared to 17.2 mb and 8.0 mb
respectively 24 hours ago. However...the WRF was showing an increase
in 850 mb winds to 40-45 knots in association with the burst of
offshore winds this afternoon...so that is likely what is resulting
in the current burst of Santa Ana winds in the mountain
passes...canyons...coastal slopes and foothills. This was also
predicted well by the cansac WRF. Thus...Sill Hill is now gusting to
66 miles per hour...with Big Black mountain at 54 miles per hour and alpine at 52 miles per hour.
Highland Springs also continues to be gusty...with 50 miles per hour gusts at
the moment. High-res models indicate these winds continuing this
afternoon before dissipating early in the evening. Thus...have
extended the High Wind Warning for the San Diego and Riverside
County mountains...and San Diego County valleys through 4 PM...and
have also extended the Wind Advisory for the inland Empire through 4
PM. Winds over the other areas have weakened below 40 miles per hour...and so
the Wind Advisory was allowed to expire at noon.
The continued offshore flow and an upper level ridge over the region
will bring continued warming today...as day-time highs reach 5 to 15
degrees above normal. However...skies are becoming cloudy as upper
level moisture from upper level moisture wrapping around the cut-off
low is bringing increasing high clouds across the area. It will only
get cloudier as we go into tonight and Monday morning.
Models are in good agreement with bringing the aforementioned low
off the coast of Baja California north on Monday and into southern and central
California by early Tuesday. Models are also in good agreement with
associated deep moisture moving in from southeasterly flow aloft
Monday into early Tuesday...resulting in widespread showers/rain.
Showers may start as early as Monday morning...but the low levels
look to remain dry at that point so most of the rain may evaporate
before reaching the ground at low elevations. The mountains will
have a better chance of measurable precipitation reaching the ground at
that time. The whole column becomes moist by late Monday afternoon
and into late Monday night...which is when the models show the most
active time of precipitation occurring. GFS and NAM show near an
inch of precipitable water being advected into the area at that
time. 850 mb flow will be pretty weak...so orographic enhancement of
rainfall should not too significant. Nevertheless...high-res models
still show best precipitation occurring in the mountains...with
storm-total of 0.50 to 0.80 inches...and local 1-1.25
inches...currently forecast. Cansac WRF and nam4 actually show some
spots in the mountains getting 1.5 to 2 inches total...so quantitative precipitation forecast was
adjusted upward a bit for this reason. Models bring decent rainfall
to the lower deserts compared to normal due to the axis of best
moisture in the southeasterly flow aloft hitting those areas...so
0.25 inches to locally 0.5 inches in some locations will be
possible. Thus...quantitative precipitation forecast was also bumped upward a bit in the lower
deserts. Meanwhile...the valleys look to get similar amounts to the
lower deserts...while the coast may only see a 0.10 to locally 0.25
inches...and the high deserts 0.10-0.25 inches and locally 0.40
inches. The warm nature of the system will keep snow levels
high...at around 7500-8500 feet during the time of heaviest
precipitation. A few to several inches of snow may fall above those
elevations. A Winter Weather Advisory may need to be issued if
confidence increases in these snowfall totals. Instability does not
look significant at the moment...but with the nam12 showing a vorticity
maximum moving through the area Monday night...would not be surprised to
see a few lightning strikes and locally heavier downpours.
By Tuesday morning...most of the moisture will have moved north of
the area as the trough moves inland into central California. A
transitory ridge and dry weather is expected for Wednesday...and
then another trough will approach the coast on Thursday...move into
Southern California and strengthen into a closed low on Friday...and
then move south into central Baja California Saturday and Sunday. Models differ
on the amount of precipitation and track...but as of right
now...looks like we will have chances for showers at times over the
region Thursday into next weekend.
252100z...VFR with scattered-broken clouds between 10000-25000 feet through
tonight. Gusty northeast to east winds will continue along the
western slopes of the mountains...below the passes and canyons...and
over portions of the inland Empire. Strongest winds will occur below
the Banning pass and over the San Diego County mountains and coastal
foothills. Moderate to strong uddfs and low level wind shear are likely with these
winds over and SW/west of the mountains...including vicinity
kont...kcno...kajo...kriv...and ksna. Winds will weaken somewhat
through this evening...but remain offshore through Monday.
Low pressure off the coast of Baja California will bring light to moderate
showers with high elevation snow for Monday and Monday night...with
the highest precipitation chances/totals over the mountains and
deserts Monday afternoon and evening. Mountain obscurations in low
clouds are possible after 26/12z.
100 PM...no hazardous marine weather is expected through Thursday.
100 PM...a long-period west-northwest swell will generate surf of
3-6 feet with strong rip currents through Monday. Highest surf will
be along west-facing beaches north of Newport Beach...between Laguna
Beach and San Clemente...and south of del Mar. Swell and surf will
gradually lower on Tuesday. A beach hazard statement is in effect
through this evening.
surface high pressure over the Great Basin will continue to bring
locally strong and gusty northeast to east winds this
afternoon...with winds strongest in San Diego County. Winds will
diminish late this afternoon into this evening. Day-time minimum
humidities in the middle teens will continue for the inland areas
today. The low humidities combined with the gusty winds will bring
near critical fire weather conditions through the afternoon.
Humidities will start to increase tonight into Monday as a low
pressure system from the south brings moisture and rainfall to the
area...with wetting rains likely in the mountains...deserts and
valleys into early Tuesday morning.
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
California...High Wind Warning until 4 PM PST this afternoon for the
Riverside County mountains...San Diego County mountains...
San Diego County valleys.
Wind Advisory until 4 PM PST this afternoon for the San
Bernardino and Riverside County valleys-the inland Empire.
Beach hazards statement until 6 PM PST this evening for the
beaches in the Orange County coastal areas...San Diego
County coastal areas.