Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
900 PM PST Thursday Jan 29 2015
a slow-moving trough will bring light rain and high elevation snow
tonight and Friday. Most of the precipitation will fall Friday and
Friday night. Decreasing showers Saturday. Next week will be dry and
warm with high pressure aloft and weak to moderate offshore flow.
Discussion...for extreme southwestern California including
Orange... San Diego...western Riverside and southwestern San
The 00z nkx sounding showed a deep saturated layer between 9000 and
30000 feet...a layer deep enough for light rain to make it all the
way to the surface despite the dry layer below 9000 feet. Rain
amounts have been light with only a few hundredths of an inch in the
mountains through 9 PM. Coastal and valley sections of San Diego
County also reported a few hundredths of an inch of rain. The
rain/snow line was around 7000 feet at 9 PM.
A long wave trough off the West Coast stretches all the way to
southern Baja California this evening and is drawing deep layer moisture into
the southwest. The 00z nkx precipitable water was 0...
increase of 0.31" since 12z...and is 200% of normal.
The center of the upper low was 100 miles west of Ensenada this
evening and will drift northeast tonight. Satellite trends show the
deepest surge of subtropical moisture is shifting east into Arizona.
Nevertheless...the low layers will continue to saturate over
Southern California through Friday as the upper low drifts northeast.
The trough will transition into a closed low over so-cal Friday
afternoon with the deep moist layer in place through Friday night.
This will bring a beneficial steady soaking light to moderate rain
to the mountains. Middle level northeasterly flow around the closed low
should enhance precipitation amounts on the northeast slopes due to
orographics. Even the deserts will see rain with this pattern. Rain
amounts will be lower west of the mountains. The coastal zones will
likely see the least amount of rain...especially Orange County...due
to the track of the upper low.
The rain will taper off Saturday and end by Saturday night as the
low is forced southeast toward the Gulf of California in response to
a strong building ridge into the Great Basin. This will result in
weak to moderate offshore winds Saturday night and Sunday in San
Bernardino and Riverside County.
Here are the forecast precipitation amounts through Saturday. Precipitation
amounts were increased slightly in the mountains.
Forecast snow amounts
above 8000 feet...6"
Dry and warm next week with ridging over the southwest bringing weak
to moderate offshore flow and above average temperatures through
300430z...coast/valleys...mid level clouds at or above 10000 feet mean sea level
producing light showers will continue through Friday morning. Visible
will decrease to 5-6 sm at in light rain showers. After
30/0900z...sct/bkn low clouds with bases between 1500-2500 feet mean sea level
will move onshore...affecting the coastal airports. These broken/overcast
low clouds...along with the middle and upper level clouds will persist
through the evening on Friday. Scattered light to moderate rain
showers may lower visible down to 3-5 sm.
Mountains...light to moderate showers continuing overnight with clouds
obscuring coastal mountain slopes. Freezing level 8000 feet
mean sea level...lowering to between 6500-7000 feet Friday. Moderate to locally
heavy precipitation may increase in coverage after 30/1800z and continue
through the evening...decreasing visible to below 3 sm at times.
Deserts...bkn/ovc ceilings near 10000 feet mean sea level will continue through the
night lowering to 5000 feet mean sea level by 30/1800z. After 30/1800z...vcsh conds
then increasing chance of precipitation and further lowering ceilings after
31/0300z. Visible may decrease to 5-6 sm in light rain showers.
800 PM....no hazardous marine weather is expected through Tuesday.
Skywarn activation is not requested...but reports of rain and snow
totals are greatly appreciated!