Swell Matrix

Area Forecast Discussion

National Weather Service Los Angeles/Oxnard Ca

459 pm PDT Wed Mar 22 2017

Synopsis

Possible precipitation with isolated thunderstorms will occur into tonight. A dry and breezy northerly flow may bring a warming trend from Thursday into Friday. But from Friday night through Saturday precipitation is again possible with cooler temperatures. Then early next week decreasing clouds will occur as high pressure moves in.

Short Term

(tdy-Sat)

The latest radar imagery showed the cold front stretched across the southeastern portion of San Luis Obispo (SLO) County and across Santa Barbara County, just to the east of Gaviota. There were good build ups along the front and a few behind it in SLO County with the strongest cell near Buttonwillow along the front and another east of Paso Robles near Shandon. Rainfall rates have been about a tenth of an inch per hour with the frontal passage and just a bit more with the stronger storms. There was a funnel cloud reported with the Buttonwillow storm earlier in the day near Santa Maria and small hail and gusty winds are also possible.

Widespread instability continues across the region and across the coastal waters through this evening. LIs are negative 2-3 with CAPE values 300-500 J/KG in many areas, but they become negative LIs of 5-7 with CAPE values of 500-800 J/KG in the Ventura County mountains this afternoon and evening with values just a little less favorable in the Los Angeles County mountains. Moisture is a bit limited but with breaks in the clouds providing a little extra heating there should be increased enhancement of the storms as the front moves across through Ventura and Los Angeles Counties. The vertical wind profile does not favor deep rotation but terrain may provide enough curvature to the profile to have another funnel develop.

Rainfall totals will be a tenth to a quarter inch with up to a half inch or so near thunderstorms. As the colder airmass comes in behind the front the higher elevations will get a dusting of snow. The snow level will begin near 6000 feet and drop to near 5000 feet overnight with one to three inches of snow possible above 6000 feet.

As the wind shifts to the northwest-north direction winds will become gusty in Santa Barbara County in the traditional sundowner canyons and locations. The winds will generally remain below advisory criteria but there may be periods when they approach those levels.

Skies will clear and temperatures will warm on Thursday and Friday as a weak ridge of higher pressure builds into the region. Increasing onshore flow may keep coastal areas a few degrees cooler on Friday though the flow will likely boost the temperature a few degrees in the Antelope Valley due to downslope flow. Thursday will likely be the warmest day north of Point Conception due to the increasing clouds ahead of the next weather system blocking the Friday afternoon sunshine.

The next chance of precipitation comes to the region by late Friday. The models are not in sync regarding the exact timing of the system, with a possibility of the precip coming Friday afternoon north of Point Conception versus late on Friday. However the trend is for less rainfall overall with this next system and to bring it in earlier rather than later. So areas to the north will have the best chance of rain by the Friday evening commute and those to the south of Point Conception will have the best chance of rain Friday night into Saturday morning.

Skies will slowly clear on Saturday and some precipitation may linger in the Los Angeles County mountains.

Long Term

(Sun-Wed)

Conditions will be warmer and drier on Sunday as a weak ridge moves into the region, which is followed by a weak trough on Monday and a slight chance of light showers. There continue to be significant differences in the models beyond Monday however, with the possibility of a stronger ridge over the region or a low pressure center that drops down to the east of the region. The second solution provides a possibility of unsettled weather for Tuesday and Wednesday. Have kept the forecast on the warm and dry side but this discrepancy will bear watching.

Aviation

23/0000z

At 2303Z, there was no marine inversion present at KLAX.

Generally hi confidence in the 00Z TAFs. VFR conditions are expected at all the airfields thru Thu afternoon. There is a slight chance of thunderstorms around KWJF and KPMD thru about 02Z this evening, with a 20 percent chance of MVFR conditions. Gusty w to NW winds will affect several airfields thru this evening, and some airfields Thu afternoon, including KSBA, KOXR, KCMA, KSMO, KLAX and KLGB. Gusty w to NW winds will affect KWJF and KPMD thru Thu.

KLAX, Generally hi confidence in the 00Z TAF. VFR conditions are expected thru Thu evening. Gusty w winds will affect the airfield thru this evening, and again Thu afternoon and early evening.

KBUR, High confidence in the 00Z TAF with VFR conditions expected through Thu afternoon.

Marine

22/200 PM

Isolated thunderstorms are possible early today across the northern waters initially, then across all coastal waters late morning through the early evening hours. Any thunderstorm that forms will be capable of producing locally gusty winds and rough seas, dangerous lightning, heavy rainfall with reduced visibility, and waterspouts.

Gusty NW winds will reach SCA levels tonight through Thursday. There will be a few gale force gusts between San Nicolas Island and Santa Rosa Island during this time. The winds will weaken late Thursday night into Friday.

Watches, Warnings, Advisories

Ca, Beach Hazards Statement in effect through Thursday afternoon for zones 39>41-87. (See LAXCFWLOX). PZ, Small Craft Advisory in effect until 3 AM PDT Thursday for zones 645-650-670. (See LAXMWWLOX). Small Craft Advisory in effect until 4 PM PDT Thursday for zone 655. (See LAXMWWLOX). Small Craft Advisory in effect until 9 PM PDT Thursday for zones 673-676. (See LAXMWWLOX).

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