textproduct: San Diego

SYNOPSIS

Warm and dry today, then cooler with periods of showers tonight through at least the middle of next week. The first round of precipiation is expected late tonight into Friday morning. 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 at times Monday through Wednesday.

DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE

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

A few patches of low clouds are developing over the coastal waters this morning, otherwise skies are clear. One last warm and dry day is in store before the weather takes a turn for the next week. Highs today will be anywhere from about 5-10 degrees above normal: upper 70s to mid 80s for the coastal areas to the inland valleys, upper 50s to upper 60s in the mountains, low to mid 70s in the high desert, and low to mid 80s in the low desert.

Cloud cover begins to increase later today as an upper level trough approaches the West Coast. A closed low forms in the southern stream of the jet, moving over the California Bight and becoming an open wave again as the vort max passes through northern Baja Friday morning. Given the trajectory of this low, the highest rainfall amounts are expected near the coast late tonight into Friday morning, with showers becoming isolated and lighter during the afternoon as the trough moves out but we remain under weakly cyclonic flow. For this first round of precipitation, chances of at least 0.25" range from 45-65% along the coast, 25-55% in the valleys and mountains, and less than 5% in the deserts. Snow levels will be anywhere from 8000-8700 ft on Friday.

Another weak short wave trough moves through Friday night into Saturday morning, providing a round of more widespread light to moderate showers. Chances of at least 0.25" from 4 PM Fri-4 PM Sat range from 65-85% for the coast to the mountains, 5-10% in the high desert, and less than 5% in the low deserts. Chances of 0.50" or more range from around 45-70% for the coasts to the mountains and less than 5% in the deserts. The snow level remains upwards of 8500 ft with less than an inch expected above that elevation. Gusty west winds will also develop across the mountains and deserts Friday night into Saturday morning as the trough moves through. Gusts 30-40 mph are expected across the ridges, desert mountain slopes, high desert, and below the passes with isolated gusts 45-55 mph on the wind-prone passes and desert slopes.

Transient ridging moves over on Sunday for dry weather and minor warming. This is short-lived as yet another upper level trough amplifies along the West Coast and moves inland Monday afternoon into Tuesday. Ensembles are in generally good agreement with the timing of this trough, though there is some spread in the depth of the trough, resulting in differences in rainfall amounts and snow levels. In general this looks to be another light to moderate event providing widespread beneficial rainfall with a 50-70% chance of at least 0.25" for the coast to the mountains and a 35-60% of at least 0.50" for the coast to the mountains. NBM snow levels fall to around 7000-7500 ft Tuesday morning with generally a inch or less at that elevation, but up to 2-4 inches on the highest peaks of the San Bernardino and San Jacinto Mountains. Gusty onshore winds are anticipated again during this period. Weak cyclonic flow may maintain light precipitation behind this trough on Wednesday, followed by yet another long wave trough moving across the state sometime Thu-Fri, though ensemble solutions really begin to diverge on the timing and amplitude of that trough. Otherwise high temperatures will remain roughly 5-10 degrees below normal next week, a stark change from our stretch of well above normal temperatures this past week.

AVIATION

120600Z...Mostly SKC and VFR conditions through tomorrow. Increasing confidence for clear skies to prevail near the coastline through the night. Increasing low/mid-level cloud cover across the coastal basin after 22z Thu.

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 Saturday afternoon with seas diminishing 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.