textproduct: San Diego

SYNOPSIS

Low pressure systems will impact the region through Monday. These are going to be accompanied by cooler, wetter. amd windier weather. A chance for light showers will occur tonight into Saturday morning. These weather systems will also bring the chance of light to moderate rainfall and high elevation snow. The heaviest rainfall and mountain snowfall is expected on Sunday, where there is 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.

DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE

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

Today through tomorrow night...

Onshore flow out of the southwest is becoming enhanced by troughing upstream which is advancing towards the region. This has allowed for the marine layer to become more elevated and somewhat dispersed this night, with best coverage along the coastal-facing slopes. As the first associated shortwave with this trough propagates over SoCal today, there is a slight chance of a few showers developing, especially against the foothills and coastal-facing slopes. Any measurable precip that falls will likely be generally less than a tenth of an inch, and possibly only up to a quarter of an inch locally for some of the mountains. However, the only real notable impact from this today will be much cooler temperatures and gusty winds.

It will be the secondary low deepening and pushing through by later this evening into Sunday that will provide a better chance of showers. There will also be enough instability with the U/L low feature associated with this that it may allow for there to be a few thunderstorms. Better precipitation amounts are expected tomorrow, with amounts of generally a quarter to a half an inch for the coastal to inland areas, and higher to around three quarters of an inch for the coastal slopes and foothills. Amounts will typically be from a half to an inch for the mountains, although the coastal- facing slopes of the San Bernardino Mountains may receive locally higher amounts up to 1.5 inches. For elevations above 5000 ft, there may also be snow accumulations ranging from a dusting, up to 2 inches around the vicinity of Big Bear Lake. Winds will also be rather strong and gusty, especially across the higher terrain and within the wind-proned areas, although strongest gusts for the most impacted areas will generally be between 45 to 50 mph, and should primarily be below Wind Advisory criteria. A mountaintop inversion, coupled with a weak mountain wave setup, will help to enhance winds slightly more during the early morning hours on Sunday, and winds may peak over criteria on the leeward side within the lower deserts for a few hours during this timeframe until the winds better mix by later in the morning. Again, this will likely be short-lived, but may produce some blowing dust as a result across some of the lower desert locations downwind of these stronger gap flow winds through the passes. Sunday will also have much stronger cold air advection behind this system, with rapidly dropping snow levels by later in the evening, and highs being the coldest of the week.

Monday through Friday...

By Monday, the secondary major shortwave trough is going to continue to exit the region, with lingering showers tapering off throughout the day, mainly for the coastal-facing slopes. Drier conditions will return by later in the evening on Monday and going into Tuesday as weak ridging aloft propagates overhead, which will follow into Wednesday with drier conditions remaining in place through then. Temperatures will still be quite chilly on Monday, with some of the mountain locations being as much as 15 degrees below average, but then rebound quite nicely with notably warmer high temps for Tuesday and Wednesday. Deterministic models do reflect general agreement with another trough deepening over the Great Basin region Thursday into Friday, which will likely just influence us with more winds in SoCal, although this could allow for there to be some showers west of the mountains, as well as a reinforcement of cooler temperatures on Thursday. This will translate to a persistence of the marine layer and onshore flow predominantly throughout the work week, with temperatures primarily being below the seasonal average for this time of year.

Mountains/Deserts

West to southwest winds pick up after 19Z today, with gusts 35-50 kt through passes, along deserts slopes and locally into the deserts. Local areas BLDU (vis 3-5SM) expected. Moderate up/downdrafts in lee of mtns. Winds gradually calming after 05Z.

MARINE

There is a slight chance of thunderstorms Sunday afternoon. Additionally there will be periods of increased northwest winds with gusts 15 to 20 kt and choppy seas through the day Sunday.

SKYWARN

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

SGX WATCHES/WARNINGS/ADVISORIES

CA...None. PZ...None.