Tropical moisture will increase over the region through this evening. Showers and scattered thunderstorms will be expected, where some may be locally heavy with localized flooding across the mountains and the deserts. Moisture will decrease by Friday into the weekend, with drier weather across the area with a lower chance across the mountains and deserts. There will be a subtle warming trend for this weekend into next week with drier weather.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Update: Latest radar imagery displays a large swath of precipitation currently over the outer waters of the SoCal bight. There is also a generally broad band of rain south of San Diego, which will continue to move northward and fill into the inland areas by later this evening. Most of this will be on the lighter side, although there could be some embedded heavier cells and possibly even a thunderstorm or two overnight. Most of the total rainfall amounts will amount to less than a tenth overnight, although there could be some areas which could pick up more with some of the heavier embedded showers. This will be possible through late tomorrow morning for the coastal and inland areas, and then most of the inclement weather will shift to the mountains and deserts by later in the afternoon. Given the parameters, based off forecasted soundings for Palm Springs for tomorrow afternoon, with CAPE of 3500- 4000 J/kg and mid-level shear at around the 700-500 mb level of roughly 30 kts, the possibility exists of a few storms to become strong and possibly severe over the mountains, and especially the deserts as they move northeast after moving off the mountains. With DCAPE of around 1000 J/kg, the main threat with any strong/severe storms will be strong gusty outflow winds, which may surpass criteria and prompt an AWW at PSP. There could also be some hail of possibly an inch or greater if storms become severe, with the most likely area over the mountains and deserts adjacent to the east- facing slopes. The extended forecast still appears to be on track with a slight chance of storms over the mountains and deserts going into the upcoming weekend, and then a gradual warmup early next week.
(Previous discussion submitted at 148 PM):
Increasing clouds and moisture have overspread the area this afternoon as post tropical storm Mario continues to weaken. Radar shows weak thunderstorms beginning to form over the mountains, with greater coverage in rain across northern Baja. The chance for showers and storms will increase from south to north through this afternoon and evening across Southern California. Latest model data shows storms dissipating overnight, where a brief lull in activity is expected as an expansive mid level cloud deck moves over the region. Another rather humid night will occur again tonight with lows near 70 degrees west of the mountains into the high desert. The humidity will stick around through Friday.
The tropical moisture will continue to move northward on Thursday, bringing the greatest chance for the heaviest showers and thunderstorms across the region. Hi-res models indicated heavier downpours possible as daytime heating and higher instability will foster an environment for growing thunderstorm activity. Some models indicate hourly rain rates near 3/4" to 1" across these regions, so a Flood Watch has been issued for early Thursday morning through night, with heaviest rainfall expected on Thursday afternoon and evening. Be on the lookout for flooded roadways and areas near recent burn scars to impact communities and travel. Storm activity will calm by Friday morning, with best chances for showers to spring up across the mountains and deserts.
The weekend will look much drier as a trough offshore moves closer to the area. There may be enough instability and moisture leftover for a shower or two across the mountains and the deserts each afternoon. Models indicate the trough forming into a closed low by early next week, which makes for a fickle weather forecast. While precip is not out of the question, most areas are expected to remain dry with near average temperatures and a deeper marine layer.
180330z, As daytime storms dissipate over the mtns, another round of SCT -SHRA/TSRA will move over the area from south to north overnight, primarily west of the mtns. Some cloud bases to lower to around 5000 ft MSL tonight into early Thursday, intermittently obscuring some of the higher terrain.
By midday Thursday, SHRA/TSRA start to shift eastwards toward inland valleys/mountains/deserts, with lingering but decreasing chances for ISO -SHRA/TSRA for coastal areas through Thursday evening. Daytime heating may allow for a few stronger storms over mtns and deserts Thursday evening with strong UDDFS, frequent lightning, and CB tops to 35 kft.
Patchy low clouds based above 2000 ft MSL may return to coasts and valleys after 03Z Friday, but confidence in CIGs is low at this time.
The remnants of Mario will continue to bring a slight chance of thunderstorms through Friday morning, greatest chances Thursday morning. Any storm could briefly produce lightning, gusty variable winds, and choppy seas. Additionally, gusts around 20 kt possible in the vicinity of San Clemente Island this evening through early Thursday morning.
No hazardous marine conditions are expected Friday through Monday.
There is a slight chance of lightning today through Friday morning, greatest chances early on Thursday.
Ca, Flood Watch from 5 AM PDT Thursday through late Thursday night for Apple and Lucerne Valleys-Coachella Valley-Riverside County Mountains-San Bernardino County Mountains-San Diego County Deserts-San Diego County Mountains-San Gorgonio Pass near Banning.
PZ, None.
