textproduct: San Diego

SYNOPSIS

Scattered light showers this evening will increase in coverage and intensity Thursday morning, with chances for thunderstorms Thursday morning and afternoon. Showers taper off late Thursday. A period of drier weather will occur on Friday. A series of weak but colder weather systems will bring more chances for light to moderate showers over the region for this weekend into the middle of next week.

DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE

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

Today through tomorrow...

An upper level low continues to propagate up from the south, which is currently located around 750 miles to the northwest of San Diego. This will continue to produce more showers moving onshore from the southwest throughout a good portion of the day. An associated cold frontal boundary will also push through by later in the afternoon, and will help to provide some additional instability, so there will likely be a line of more moderate to heavy showers along the leading edge, with even the slight chance of a thunderstorm. As this feature continues to transition up towards the north, with the a major shortwave trough advancing in towards California, which will help to force the cut off to move northward and become absorbed into the ridge downstream. More moisture being advected up ahead of the approaching trough will keep the chance of showers going into Friday, although there will be somewhat of a break in between the two systems, and therefore a lesser chance. Temperatures with the southerly flow will remain on the more mild side for this time of year, although highs will be notably cooler today as compared to yesterday. Through tomorrow morning, additional rainfall rates are expected to be from around 0.5 to 1 inch for the coastal and inland areas, with an inch to 2.5 inches possible for the mountains, and around 0.10-0.25 inches for the lower deserts, to 0.25 to 0.5 for the high deserts. Some of these areas have already been inundated with copious amounts of rain from last week, and given expected rainfall rates, this might lead to some areas having a risk of flooding. Please see the Flood Watches currently active, which further highlights these details.

Saturday through Wednesday...

The major shortwave trough upstream will continue to move in across the region throughout the weekend, with a steady band of rain pushing through by later in the evening on Saturday and into Sunday morning. The positively tilted axis with this trough will allow for a secondary wave to deepen in its wake going into the early part of next week with yet another trough moving in. This is where deterministic models begin to diverge more with the progression of the secondary trough. Some of the models (such as the ECMWF) have this system transitioning through much quicker, with a drier solution, whereas the GFS have the low deepening right over southern California, with a much better chance of precipitation occurring. The will continue to be evaluated in the upcoming days to see which model is resolving this feature the best, but it is safe to say the the overall active weather pattern will continue through at least the mid part of next week, as ensemble members suggest.

AVIATION

011000Z...BKN-OVC clouds based 1000-2000ft MSL for most locations. -RA continues to move in from the southwest, spreading over the region and bringing brief VIS drops to 1-3SM in RA. Southerly winds increase this morning with gusts 20-30 kt for the coast and valleys and 30-50 kt along the northern slopes of the mtns, weakening after 20z Thur. Precipitation may form into organized bands of +RA which would move across the region from west to east beginning 15-18z Thur and prevailing through 01z Fri, bringing IFR CIGs/VIS. There is a 40% chance for TSRA for areas mountains westward (~10% chance vcnty KPSP) from 12z through 00z Fri, highest chances 14-22z Thur. RA should generally end by 02z Fri, with only -SHRA lingering in San Diego County beyond this point. CIGs should return VFR after 04z Fri everywhere outside of localized SHRA.

MARINE

Southeasterly winds with gusts 20 to 25 knots peak this morning and steep mixed seas 4 to 7 feet through the coastal waters. In addition, the incoming storm system will bring a chance for thunderstorms this morning and early afternoon. Any thunderstorm that develops will bring strong gusty winds, lightning, and brief heavy rain that will lead to poor visibility. There is also a slight chance for waterspouts.

Winds diminish this afternoon and evening. Then, no hazardous marine weather conditions expected through Sunday, though there will be periods of breezy south winds through the weekend.

BEACHES

There is a slight chance for thunderstorms and associated lightning risk today, highest chances in the morning and early afternoon. If you see lightning or hear thunder, seek a sturdy, enclosed shelter. Additionally, starting Thursday morning and continuing through the weekend, high tides of 6.5 to 7 feet could lead to minor coastal overflow/flooding for beaches and flood-prone beach lots and walkways.

SKYWARN

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

SGX WATCHES/WARNINGS/ADVISORIES

CA...Beach Hazards Statement through Sunday morning for Orange County Coastal Areas-San Diego County Coastal Areas.

Flood Watch through this evening for Orange County Coastal Areas- Orange County Inland Areas-San Bernardino County Mountains- San Bernardino and Riverside County Valleys-The Inland Empire-Santa Ana Mountains and Foothills.

PZ...Small Craft Advisory until 3 PM PST this afternoon for Coastal Waters from San Mateo Point to the Mexican Border and out to 10 nm-Waters from San Mateo Point to the Mexican Border Extending 10 to 60 nm out including San Clemente Island.