textproduct: Los Angeles

SYNOPSIS

04/1053 PM.

It will be a little cooler today across the coasts and lower valleys. Today's highs, however, will remain 10 to 12 degrees over normal. A cooling trend will begin Monday with temperatures back to near normal around mid week. Rain is likely sometime between Thursday and Saturday.

LONG TERM (THU-SUN)

05/143 PM.

For the extended, 12Z models continue to exhibit decent synoptic agreement, indicating a wet and unsettled pattern as an upper low moves across the region. Given the nature of upper lows in Spring, confidence in the details of the storm (timing, precipitation amounts, etc.), but there is high confidence in measurable rainfall for the area.

The upper low, and its associated rainfall, will begin to impact the area Thursday night/Friday with the rain chances continuing through Saturday. On Sunday, the upper low will be south and east of the area, but there still could be a chance of some additional wrap-around showers (mainly across LA county). Based on WPC QPF guidance, best forecast for now remains rainfall totals between 0.25 and 0.75 inches with local amounts around 1.00 inch. This matches up well with GFS/ECMWF ensembles indicating a 50-70% chance of totals between 0.50 and 1.00 inches. For amounts over 1.00 inch, ensembles indicate a 10-20% chance of that occurrence.

Along with the rainfall, there will definitely be a convective element with this system. With any upper low in April, there is always a concern about thunderstorms. Looking at ensemble MUCAPE, there is a noticeable increase Friday through Saturday. Additionally, 500 MB temperatures drop to around -23 degrees Celsius. So, that is enough to warrant a 10-20% chance of thunderstorms for all areas in the Friday through Saturday time frame. Of course, the exact track of the upper low will determine which areas will be most at risk for thunderstorms, but cannot get that detailed this far out. If thunderstorms do develop, there will be the potential for heavy showers, strong outflow winds and hail.

AVIATION

05/1758Z.

At 1714Z at KLAX, the marine layer was 300 ft deep. The top of the inversion was at 1500 ft with a temperature of 22 C.

High confidence in all TAFs through 06/06Z. Moderate confidence in timing of CIG arrival and heights (+/- 200 ft) for coastal sites.

Low confidence in KOXR & KCMA with a 25% chance of LIFR CIGs developing between 06/10-16Z. There is also 40% chance of LIFR CIGs at KSMO through the aforementioned timeframe.

KLAX...High confidence in TAF through 08Z. Moderate confidence after 06/08Z. Arrival and clearing times of CIGs may be off +/- 2 hours. CIG heights could range from: 002-008. No significant east wind component is expected.

KBUR...High confidence in VFR TAF.

MARINE

05/1059 AM.

High confidence in winds and seas remaining below Small Craft Advisory (SCA) levels through this afternoon. SCA level winds will develop overnight south of Point Conception and will become widespread by Monday afternoon to include all Outer Waters, nearshore along the Central Coast, and the Santa Barbara Channel.

SCA winds will continue across all Outer Waters through Wednesday. Winds will diminish later in the week with moderate chances for SCA winds lingering south of Point Conception on Thursday and Friday. The Inner Waters will reach SCA levels at times mainly during the afternoon and evening hours - lower chances along the Central Coast later in the week.

There is a 30% chance of GALE force winds Wednesday night across the Santa Barbara Channel and near the Channel Islands.

A storm system is expected to impact the coastal waters sometime Thursday into the weekend bringing rainfall and the potential for thunderstorms. Confidence is low on exact timing and details for now.

LOX WATCHES/WARNINGS/ADVISORIES

CA...NONE. PZ...Small Craft Advisory in effect from 3 PM Monday to 3 AM PDT Tuesday for zone 645. (See LAXMWWLOX). Small Craft Advisory in effect from 3 PM Monday to 3 AM PDT Wednesday for zones 650-670. (See LAXMWWLOX). Small Craft Advisory in effect from 3 AM Monday to 3 AM PDT Wednesday for zones 673-676. (See LAXMWWLOX).