Area Forecast Discussion

SYNOPSIS

20/307 AM.

Light to moderate rain is expected late today through Tuesday, will the highest rain amounts expected for San Luis Obispo County and minimal impacts overall. Temperatures will be mild today, followed by much cooler weather Tuesday and Wednesday. Gusty southwest winds are expected through Tuesday, followed by west to northwest winds Wednesday through Friday.

SHORT TERM (TDY-THU)

20/1250 PM.

No significant changes in forecast thinking.

We are on track for a moderate (for April) storm targeting the Central Coast and points north, although lesser impacts anticipated for the rest of the area.

A cold front with moist southwest to west flow will march through the region early Tuesday morning through the afternoon or evening hours. It will become weak as it moves through Ventura and Los Angeles Counties. Gusty southwest to west winds generally 20 to 40 mph and just shy of advisory levels is anticipated along and ahead of the front save for interior LA County where winds will likely be a bit stronger. Generally one quarter of an in to locally an inch is anticipated for San Louis Obispo and Santa Barbara Counties with less than a quarter of an inch elsewhere. Steep mid level lapse rates will support the slight chance of a thunderstorm for San Luis Obispo County focused mainly behind the front mid morning to mid afternoon Tuesday. Brief heavy downpours, gusty winds up to 40 mph, and cloud-to- ground lightning are the most likely hazards with any thunderstorms. Peak rainfall rates will generally be around a quarter of an inch per hour or less, although may locally peak near 0.5 inches per hour in any thunderstorms or along the frontal boundary in Santa Barbara to far western Ventura County (in the mountains). Minor flooding is possible if these rates occur, especially in urban areas or near recent burn scars.

Moist west to northwest flow behind the storm may support occasional showers or drizzle Tuesday night into Wednesday for west and north facing mountain slopes focused from San Luis Obispo to northern Ventura County.

Gusty northwest to west advisory level winds of 30 to 50 mph is late Tuesday through early Thursday focused across the mountains to interior, but likely extending into coastal areas at times.

LONG TERM (FRI-MON)

20/1222 PM.

Near normal temperatures are expected Friday when most highs will be in the low to mid 70s. Then temperatures will fall to several degrees below normal over the weekend, with highs in the 60s common. There is a 30-50 percent chance of mainly light rain focused across the foothills to interior sometime this weekend thanks to moist upslope flow over the mountains and limited instability. The storm energy is coming from the southwest to west and is weak so significant wind concerns are unlikely, but it does lend itself to below normal forecast confidence.

An active pattern (for April) may continue into early next week as another weak storm is possible.

AVIATION

20/1724Z.

At 1630Z at KLAX, the marine layer was 1500 feet deep. The top of the inversion was 2000 feet with a temperature of 14 degrees Celsius.

For 18Z TAF package, moderate to high confidence in current forecast. Through 05Z, high confidence in VFR conditions for all sites. After 05Z, a front will begin to move into the area, bringing CIG/VSBY restrictions as well as rain. Timing of rain and flight category changes tonight and Tuesday morning could be +/- 3 hours of current forecasts.

There will be a 10-15% chance of thunderstorms Tuesday morning at KPRB and KSBP.

KLAX...Overall, moderate confidence in 18Z TAF. High confidence in CAVU conditions through this evening. Overnight, high confidence in return of CIG/VSBY restrictions, but timing of flight category changes could be +/- 3 hours of current forecasts. Timing of light rain could also be +/- 3 hours of current forecast. No significant easterly wind component is expected.

KBUR...Overall, moderate confidence in 18Z TAF. High confidence in CAVU conditions through this evening. Overnight, high confidence in return of CIG/VSBY restrictions, but timing of flight category changes could be +/- 3 hours of current forecasts.

MARINE

20/1203 PM.

For the Outer Waters, moderate to high confidence in current forecast. Today through Tuesday, there is a 20-30% chance of Small Craft Advisory (SCA) level southerly winds. For Wednesday through Friday, high confidence in combination of SCA level northwesterly winds and seas with a 20-30% chance of GALE force winds south of Point Conception Wednesday night. For Saturday, high confidence in winds and seas remaining below SCA levels.

For the Inner Waters north of Point Sal, moderate to high confidence in current forecast. Today through Tuesday, there is a 20% chance of SCA level southerly winds. For Wednesday through Friday, there is a 60-80% chance of SCA level northwesterly winds, mainly in the afternoon and evening hours. On Saturday, high confidence in winds and seas remaining below SCA levels.

For the Inner Waters south of Point Conception, moderate to high confidence in current forecast. Today through Tuesday, high confidence in winds and seas remaining below SCA levels. On Wednesday, high confidence in SCA level northwesterly across all the southern Inner Waters with a 20% chance of GALE force winds. For Thursday through Friday, winds and seas are expected to remain below SCA levels for most areas. The only exception will be the western half of the Santa Barbara Channel with a 60-80% chance of SCA level winds. On Saturday, high confidence in winds and seas remaining below SCA levels for all of the southern Inner Waters.

A cold front will sweep across the coastal waters tonight and Tuesday. With this frontal passage, there will be a 20% chance of thunderstorms across the coastal waters north of Point Conception. Any thunderstorms that develop may produce brief heavy rain, gusty winds and locally rough seas.

LOX WATCHES / WARNINGS / ADVISORIES

CA...Wind Advisory in effect from 10 AM to 10 PM PDT Tuesday for zones 378>383. (See LAXNPWLOX). PZ...NONE.