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fxus66 ksgx 200523 

Area forecast discussion
National Weather Service San Diego California
923 PM PST Tue Nov 19 2019

moderate to heavy rain will taper off this evening with mostly
light precipitation overnight. Precipitation will increase again
Wednesday morning as the next storm approaches. Mountain snowfall
is expected with the snow level lowering to about 5000 feet
Wednesday morning. Scattered mostly light showers will prevail
late Wednesday into early Friday. Mostly dry weather will prevail
for the upcoming weekend into early next week.


Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino

tropical moisture continues to wrap around the upper low currently
moving over the northern Gulf of California. Widespread moderate
showers have continually developed in the deformation zone between
the low to our southwest and the approach upper level low
currently centered along the northern California coast. This
training cells have produced rainfall totals in excess of 2 inches
over portions of San Diego County this afternoon. Areas further
north have received far less rainfall. This axis of instability
will gradually shift east over the next few hours. Latest hrrr
runs, which seem to have an okay handle on things, suggest heavier
rainfall will move east of our forecast area by midnight. Mainly
light showers will continue overnight ahead of the next system.
Main updates this evening were to adjust pops and precipitation
amounts based on latest hi-res guidance. Models have all backed
off on the idea of more precipitation for late Friday into
Saturday, keeping a third upper low well to the west as opposed to
over US. So for now, that part of the forecast is dry.

Previous discussion...
a cold core upper low moving south from norcal will move directly
over socal Wednesday morning through afternoon. 700 mb temps will
lower to -7c. This is cold with snow levels dropping easily to
5000 ft, so snow levels have been lowered. The most widespread
rainfall likely will occur over San Diego County (except the
deserts), where a favored off- the-water trajectory/instability
lasts the longest.

Flash flooding could occur as heavier cells develop when the cold
core moves overhead. The flash flood risk is highest between dawn
on Wednesday through Wednesday evening. This period is when it is
most unstable as MUCAPE increases into the 400-800 j/kg range,
highest closest to the coast, but isolated tstorms Wednesday could
occur anywhere west of the and along the mountains. Precipitation
will become less widespread and lighter Wednesday evening, with
showers lingering into early Friday.

Snow will accumulate down to about 5000 feet and significant
snowfall above 6000 ft. Storm total snowfall will be around 4-8"
5000-6000 ft, 6-10" 6000-7000 ft, and 10"+ above 7000 feet. Maximum
rainfall rates of 0.50-0.60" per hour are forecast. Many areas
along and west of the mountains are forecast to receive an
additional 1-2" of rain.

The lower deserts will mostly be rain-shadowed, though some
showers are expected there but amounts will average less than 0.25

Forecast has trended drier for Friday and Saturday as the GFS has
taken on more of an ec solution, keeping a third upper low well to
the west. However, if this ends up closer to the coast we could
see additional showers. Warmer and drier this weekend under weak
ridging and possibly some weak offshore flow. Another trough digs
through the Great Basin early next week, but for now looks too far
inland to give US any precipitation and trend is towards more
offshore flow.


200450z...bkn-ovc bases 010-015 with -shra/-tsra slowly moving
out of the area from west to east through the evening. Some cigs
as low as 008 early. Areas of oc/inland Empire higher bases near
050-060. All cigs expected to lower again tonight after 12z with
next part of the storm coming into the area.

12z Wednesday and onward: winds picking up with widespread rain showers.
Isolated -tsra with ceilings 020-040 and west winds 15-25 kt with local
vis 2-4 sm at the coastal taf sites. Ksan may gust 30-35 knots 12z-20z.
Mountains obscured in clouds and pcpn with west winds 20-30 kt
gusting to 50 kts and moderate uddfs east of the ridges and into the
lower deserts.


a Small Craft Advisory is in effect from 6 PM this evening to 10 PM
Wednesday. South-southwest winds 10-20 kt this evening will shift
west 15-25 kt tonight with the passage of a cold front and remain
strong through Wednesday. Showers with isolated thunderstorms. On
Thursday and Friday scattered, lighter showers and lighter northwest
winds from 10-15 kt.


a beach hazard statement is in effect through noon Thursday for
above average surf and a high rip current risk. A short period wind
swell will generate surf of 3-6 ft. There is also a chance for
isolated thunderstorms.


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


Sgx watches/warnings/advisories...
California...Flash Flood Watch through late Wednesday night for Riverside
County mountains-San Bernardino County mountains-San
Bernardino and Riverside County valleys-the inland Empire-
San Diego County coastal areas-San Diego County mountains-
San Diego County valleys-Santa Ana Mountains and foothills.

Winter Storm Warning from 7 am Wednesday to 7 PM PST Thursday
for Riverside County mountains-San Bernardino County

Beach hazards statement through Thursday morning for Orange
County coastal areas-San Diego County coastal areas.

Pz...Small Craft Advisory until 10 PM PST Wednesday 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.


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