textproduct: San Diego

SYNOPSIS

Cooler conditions with increased cloud coverage is expected for Thursday through early next week. Periods of rain are expected Friday through early next week. The first round is expected Friday morning, with chances of isolated thunderstorms over the coastal waters locally into the beaches. The next chance will be Friday evening into Saturday, with more widespread light to locally moderate showers. In addition to periods of rain, winds are expected to increase over the mountains and deserts. Sunday could see mostly dry conditions with our next chances of precipitation and increased winds Monday and Tuesday.

DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE

SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES...

Another day of high temperatures 10 to 15 degrees above average for coastal areas and 5 to 7 degrees above average elsewhere. An incoming upper level low will push the ridge over the Southwest US further east by Thursday, bringing cooler conditions and increased onshore flow. Highs on Thursday are expected to be 3 to 5 degrees cooler than today for areas west of the mountains with more noticeable cooling for Friday. Below average temperatures are expected for Saturday through next Wednesday.

The aforementioned upper level low will dig south and move east into Northern Baja on Friday. This will bring periods of rain to the area by early Friday morning. The highest chances of rain for this first period of rain are along the coast. Additionally, there is potential for isolated thunderstorms to develop over the waters, locally into some coastal communities. The thunderstorm chances are largely focused to coastal waters and the coast due to the temperature difference between sea surface temperatures (running well above average for this time of year) and the cold temperatures associated with the passing low pressure system. High resolution guidance is picking up on an increase in instability with CAPE values increasing to 500-1000 J/kg early Friday morning. There is some potential for thunderstorms to locally reach coastal communities but atmospheric instability drops drastically the further inland you go, which will limit thunderstorm potential. Where thunderstorms develop, expect erratic winds and locally heavy rain that may lead to localized flooding. Rainfall Friday morning is generally expected to be on the lighter side for inland areas. Isolated rainfall rates of 0.40- 0.60 inches per hour are most likely to develop along the coast where thunderstorms or heavier rain develops.

Chances of rain decrease during the day Friday, but isolated light showers at times cannot be ruled out. Rainfall chances increase again later in the day Friday as another upper level low moves east through Central California. This will bring another round of rain Friday evening into Saturday, which is expected to be more widespread across the coast, valleys, and mountains. Peak rainfall rates of 0.20-0.30 inches per hour are expected during this time. Rainfall is expected to taper off from north to south late Saturday morning through the early afternoon. Dry conditions look likely for Saturday evening into Sunday.

Another low pressure system is expected to dig south along the West Coast sometime around Monday and Tuesday. Ensemble guidance is in good agreement that precipitation will develop but there is low confidence in exact timing of rainfall and amounts. This system also looks like it has enough cold air associated with it to drop the snow levels below 8000 ft, although there are model differences in just how low the snow level will get.

Winds are expected to increase over the mountains and deserts with each passing system. Expect a slight increase in winds late Thursday, with a more noticeable increases Friday evening into Saturday. Peak gusts Friday evening into Saturday will be mainly 35 to 45 mph, with gusts up to 55 mph through wind prone passes. Winds are expected to increase again early next week with the next trough passage, with the track of the low the main determining factor in expected wind speeds.

Additional precipitation and winds are possible for the latter half of next week, but there is low confidence in details. Continue to monitor the forecast for more information.

AVIATION

111800Z...Mostly SKC and VFR conditions through tomorrow. Localized patchy FG near the coastline (15-25% chance) between 10z-16z.

MARINE

Isolated thunderstorms possible over the marine waters early Friday morning, beginning before sunrise with decreasing chances by Friday afternoon. Onshore winds increase late Friday and seas build Saturday, which are likely to generate hazardous boating conditions. Winds diminish late Saturday and seas diminish late Sunday.

BEACHES

A series of swells (14-15 seconds) from the west-northwest (270-280 degrees) will generate elevated surf starting Friday, with higher surf and sets to 7-8 feet by Saturday. Surf begins to wane on Sunday but may remain elevated for west-facing beaches into Monday. Additionally, isolated thunderstorms will be possible at the beaches early Friday to late Friday morning.

SKYWARN

Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions.

SGX WATCHES/WARNINGS/ADVISORIES

CA...None. PZ...None.