Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Southwest California area forecast discussion 
National Weather Service Los Angeles/Oxnard California
350 am PST sun Mar 1 2015

Synopsis...

A cold upper low will slowly move over Southern California bringing
periods of showers and a slight chance of thunderstorms. Snow will
fall as low as 4000 feet. This low will persist over the area
through early Monday before exiting. A weaker storm system will
follow on its heels later Monday allowing for lingering showers into
early Tuesday. Dry and warmer weather is expected late Tuesday
through Friday.

&&

Short term (today-tue)...
the upper low is currently Over Point Conception. It is swinging a
nice vorticity lobe through the area from Santa Barbara to Los Angeles.
This vorticity lobe is spawning heavy showers and some thunderstorms. A
few heavy showers are now over The Springs fire and a Flash Flood
Warning was issued due to the heavy rainfall. The upper low will
move very slowly to the east-southeast and will not exit the area until Monday
morning. This upper low will spin lobes of positive vorticity advection and negative vorticity advection over the area
through Monday morning. This will make for a very variable forecast
at times of positive vorticity advection there will be plenty of clouds and showers but when
the negative vorticity advection is moving through there will no rain and breaks in the
clouds. Most of the action will be south of Point Conception but slo
and sba County will still see some bands of showers moving through
at times. The 500 mb temperatures at the core of the upper low are about
-28 degrees c which is cool enough to destabilize things enough to
allow for a slight chance of thunderstorms. Any thunderstorm that does
form could produce some small hail.

The cold air will also lower snow levels to 4000 feet and locally
down to 3500 feet.

Rain and snowfall amounts with this first system will be highly
variable due to the showery nature. An areal average of 0.10-0.25"
can be expected for the coastal and valley areas through Monday
morning. There will be locally heavier amounts up to an inch under
heavier showers or thunderstorms. In the mountains 0.50-1.00" of
liquid equivalent is likely over many areas. This will likely
translate to 8-12" of snow is above 6500 feet...with 2-4" possible
between 4000 and 5000 feet.

Hot on the heals of the current storm a secondary system will move
into the area. This storm is now forecast to take more westerly
track over the Pacific and further away from land. This will reduce
the amount of rainfall over the land. This system now looks like it
will not produce much rainfall for the area. Like todays system the
rainfall will be showery and rainfall will vary considerably form
location to location.

The second system will scoot out fairly quickly Monday and night and
skies will clear for Tuesday.

Maximum temperatures will be 4 to 8 degrees below normal today and Monday with
about 3 degrees of warming on Tuesday.

Long term (wed-sat)...
high pressure will set up Wednesday along with weak offshore flow.
This will kick off a round of dry weather with clear skies and a
warming trend. Maximum temperatures will reach normals Wednesday and then will
be above normal for the rest of the period. Right now Friday looks
like it will be the warmest day with plenty of upper 70s and a
smattering of lower 80s forecast.

&&

Aviation...

01/1115z

At 1100z...there was no marine inversion at klax.

Overall...low confidence in 12z taf package. Unstable air mass will
continue to generate scattered showers and even the possibility of
an isolated thunderstorm just about at any taf site through this
evening. In terms of ceiling/visibility restrictions...conds will likely vary
between VFR and MVFR...with a good chance of MVFR ceilings being
predominate this afternoon/evening.

Klax...low confidence in 12z taf. Confidence in timing of any MVFR
ceilings through the period is low. There is a slight chance of thunderstorms
through this evening.

Kbur...low confidence in 12z taf. Confidence in timing of any MVFR
ceilings through the period is low. There is a slight chance of thunderstorms
through this evening.

&&

Marine...01/200 am...

High confidence in winds remaining below Small Craft Advisory levels
through Monday night. On Tuesday...there is a chance of northwest
winds increasing to Small Craft Advisory levels across the outer
waters.

Main issue in the short term will be the continued threat of
thunderstorms through Monday evening. With any thunderstorms that
develop...there will be the potential for brief gusty winds...small
hail and even a waterspout.

&&

Lox watches/warnings/advisories...
Winter Weather Advisory (see laxwswlox).
Marine weather statement (see laxmwslox).

&&

$$

Public...rorke
aviation/marine...rat
synopsis...ck

Www.Weather.Gov/losangeles

National Weather Service Glossary of Abbreviations