A low pressure system off the West Coast will draw moisture from Tropical Storm Priscilla northward into the area for today through Saturday morning, with chances for showers and a chance for thunderstorms at times. Cooler with drying and a return of the marine layer for Saturday through Monday. For Tuesday and Wednesday of next week, a low pressure system moving southward along the West Coast will bring a chance of showers along with stronger westerly winds.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Update: Priscilla continues to weaken at this hour, and the remnants are beginning to stream up over the region this morning, which has allowed for some showers and a few very high-based embedded thunderstorms. The moisture plume appears as if it is going to be located mostly over the southeastern half of the CWA throughout the day. Although, given the upper level difluence over the region, as there is a trough located to the northwest, and this could allow for enough instability to initiate some convection by later this afternoon over the mountains, even outside of the moisture plume. Given the "dry slot" the is being produced by the troughing upstream, there is a very sharp moisture gradient, which may translate to the southeastern potion of San Diego County having a much better chance of seeing storms later today, while the northwestern portion may remain mostly dry. By tomorrow, the area of low pressure associated with this weakening tropical system will become absorbed into the trough to our south and increasing southerly flow with more instability will give way to a better chance of showers and thunderstorms for tomorrow, especially over the mountains and deserts. The forecast still appears to be on track with the system becoming sheered off towards the east by early Saturday morning, with chances of precipitation diminishing as it does. An isolated storm over the mountains can't be ruled out during the afternoon on Saturday, otherwise conditions will become much drier and cooler, with much more influence from the trough upstream, and the will carry into next week, as a series of deepening troughs bring bouts of light rain and cooler temperatures to southern California.
(Previous discussion submitted at 259 AM):
Patches of low clouds persist in the San Diego County coastal areas and valleys this morning but are not showing signs of increasing in coverage while mid and high clouds are moving in from the south on the edge of a plume of deep-layer moisture from Tropical Storm Priscilla. The bulk of the moisture from Priscilla will stay to the south and east of San Diego County but enough moisture should make it into the region for a chance of showers and potentially isolated tstms from the deserts to the coast and from San Diego County north to southwestern San Bernardino County, beginning later this morning. Showers will be mostly light but heavier showers could develop this afternoon into this evening. Scattered light showers could continue tonight into Friday morning. More widespread and heavier showers/tstms are likely Fri afternoon/evening, and light showers could persist into Saturday morning. Due to the showery nature, rainfall amounts will vary greatly but will range from a few hundredths in the coastal areas and valleys to nearly an inch in some mountain locations between today and Saturday. Heavier showers or tstms could produce locally heavy rainfall, as much as 0.60 inch per hour. By Friday night, Priscilla will become absorbed into the southwesterly flow between the low pressure system to our northwest and the high pressure centered near the TX/MX border. As this process continues, available moisture will be transported to the northeast.
Sunday and Monday will see a return to dry and more typical conditions as the low pressure system moves inland and the upper closed low becomes an open wave over the Rockies, leaving an area of broad troughing over the western US. Temperatures will remain below seasonal averages and the marine layer low clouds will return for Sat and Sun nights.
For next Tue and Wed, another low pressure system moving south over the west coast will bring cooler and windy conditions along with more chances for precipitation. At this time, the spread among model solutions makes the forecast more uncertain but a plurality of ensemble solutions across model platforms indicate precipitation moving in from the northwest as early as Tuesday morning and lasting through Wed morning.
091530z. Clouds at or above 10000 feet will thicken and lower at times to 6000-9000 feet. Isolated -SHRA and sprinkles through tonight. Isolated TSRA after 21Z Thu, most likely over mountains and deserts. Any TSRA could lower cloud bases to 4000 feet MSL briefly, and could bring gusty winds and reduced vis in +RA.
Northwest winds occasionally exceeding 20 knots around San Clemente Island during the afternoons and evenings Friday and Saturday. There is a slight chance of thunderstorms today through Friday, most likely during the afternoons. Lightning, erratic winds, choppy seas, and/or reduced visibility in heavy rain is probable in the vicinity of any thunderstorm.
There is a 5-15% chance of thunderstorms producing lightning today and Friday, most likely during the afternoons.
Ca, None. PZ, None.
