A low pressure system will impact the region through Monday, bringing moderate rainfall, high elevation snow and a slight chance of thunderstorms west of the mountains. This low pressure system may linger over the area into Monday, bringing additional light showers. Drier and slightly warmer weather is expected by the middle and end of next week.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Today through tomorrow night,
At this hour, there are some very isolated pre-frontal showers beginning to develop within the inner SoCal bight, and some of these may make it on shore for just a few light showers this morning through early afternoon before arrival of the associated cold frontal boundary with this secondary low pressure system propagating overhead through tomorrow. This will allow for there to be some light to moderate showers to develop along the leading edge of this boundary as it makes its way through the area by later this afternoon, which high res models put the timing of the front to begin moving through Orange County by around 11 to Noon. There is also just enough instability that there could be a heavier showers/thunderstorms embedded within this line of showers as it moves through the CWA during the afternoon hours. The tightening of the surface pressure gradient is also going to allow for some strong and gusty winds by later this afternoon across the higher terrain, and especially within the areas prone to gap flow, and across the ridges and slopes. There may be some gusts that peak over criteria on occasion, although the majority of peak winds for higher elevations should remain closer to the 45 to 50 mph range, which is why a Wind Advisory has not been issued. Nonetheless, it is going to be gusty and chilly, with highs today generally running around 5 to 15 degrees below the seasonal average for this time of year, for most locations.
This low will continue to track through the area going into tomorrow, with also a weak perturbation at the 700-500 mb level moving over the region during the early morning hours, which may allow for there to be some persistent light showers remaining through the morning hours tomorrow before tapering off towards the afternoon. Highs for tomorrow will be similar to today, and still quite chilly, perhaps even a few degrees cooler for a few locations as there will be much stronger cold air advection moving in behind this exiting trough. Snow levels will also drop down to around 5000- 5500 feet by later tonight into early tomorrow, and there could be some of the urbanized areas above 5000 feet picking up several inches of new snow as a result. Strong and gusty westerly winds will continue into tomorrow after weak decoupling overnight, although not be as strong and will continue to diminish throughout the day. By the time this low has exited, there could be some of the coastal areas picking up around three quarters of an inch, to over a half an inch for the inland areas, and some of the coastal slopes of the mountains may receive up to around one to one and one half inches of rainfall, with locally up to 2 inches possible for the southern- facing slopes of the San Bernardino Mountains.
Tuesday through next weekend,
High pressure will be building in back over the region from Tuesday into Wednesday as some weak ridging aloft is ushered in behind the exiting trough, which will help to allow temperatures to rebound quite nicely for both days, and back to near average temperatures, especially by Wednesday. The overall ensemble pattern looks has had little change to previous runs, showing solutions of more troughing by later in the work week, which could influence the area with some precipitation, increased winds again, along with a reinforcement of cooler air on Thursday. Depending on the track of the deepening major shortwave trough, and moreover if it takes a more "inside slider" track will determine whether or not this will be more of just a wind producer, with possible offshore winds. A return of weak ridging over the region for this upcoming weekend will help to dry things out and warm things up considerably by Saturday.
121100z, Coasts/Valleys, Increasing clouds based 3-6 kft MSL to this morning throughout the coastal and inland basin. ISO -SHRA this morning will become more numerous overnight into early Monday. Mostly VFR vis/cigs overnight until main frontal band pushes into the region from the northwest, reaching Orange County around 16-18z. This band is expected to bring a few hours of SHRA/RA and periods of MVFR vis/cigs (1-3 kft bases, 4-6SM) with the occasional +SHRA/+RA, yielding brief IFR cigs/vis. The front reaches SD Co. around 19z, sweeping through the county during the afternoon and yielding similar conditions. After FROPA, winds switch from SW to W.
Forecast window for RA/+RA and IFR cigs/vis:
KSNA, 17-20z Sun KONT, 17-21z Sun KSBD, 17-22z Sun KCRQ, 20-23z Sun KSAN, 20-24z Sun
.Mountains/Deserts, West to southwest winds gusts 35-50 kt to persist throughout the TAF period in mountain passes, along deserts slopes and locally into the deserts. Local areas BLDU (vis 3-5SM) expected. Moderate up/downdrafts in lee of mtns. VIS down to 0-5SM in mtns with FG where clouds and terrain meet; SHSN may reduce vis locally above 6500 ft MSL.
There is a slight (~10%) chance of thunderstorms later this afternoon. Additionally there will be periods of increased northwest winds with gusts 15 to 20 kt and choppy seas throughout the day.
Ca, None. PZ, None.
