Another round of widespread and heavier rain is expected Friday. Highest precipitation favored in the northern mountains, with lighter totals closer to San Diego. Shower activity weakens late Friday night, fully tapering off Saturday morning. Drier and warmer weather early next week with a Santa Ana event peaking Monday. Showers could return from the south some time the latter half of next week centered around New Year's Day.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Today provided a break in precipitation with most model guidance indicating scattered light showers will begin to develop for some locations by midnight. A more defined band of rainfall is expected to move northwest to southeast across the area tomorrow. There still remains some model differences in timing, but latest guidance is indicating the timing of the rain band entering Orange and western San Bernardino counties around mid-morning Friday. Rain will be moderate to locally heavy with rainfall rates of 0.30-0.60"/hour. More information on rainfall totals and expected snow amounts (for elevations 6500-7000 ft and above)can be found in the hydrology section below. In the wake of the main rain band scattered mostly light showers will develop. Showers will eventually taper off by late Saturday morning.
From previous discussion issued at 2 PM 12/25,
Sunday through Late Week,
Much drier conditions expected come the beginning of next week after this weekend's system departs. However, a potent inside slider upper trough helps to strengthen the offshore gradient, with a Santa Ana Wind event looking more likely for Sunday into Tuesday. Cw3e WRF ensemble means suggest this could be a moderate strength event with a ~60% chance of a moderate to strong event. Given the recent rainfall, there is not as high of a fire concern, but the potential for strong wind gusts through and below mountain passes is worth noting. Weak upper level ridging coinciding with the downsloping offshore winds will trend temperatures up to 5 to 10 degrees above normal.
Attention quickly turns to cut-off low out in the south-central Pacific that could bring the next shot of rain to southern California. Global ensembles diverge significantly on the resolution of this storm system, so uncertainty for this event is quite high. Keep an eye on the forecast to see how this pans out, but early indications hint that this will be a much less intense event than yesterday's atmospheric river.
More widespread showers and a more defined band of rainfall is expected to push through the region Friday. Maximum rainfall rates with this band of 0.3-0.6"/hr expected. Total additional rainfall of 1-3 inches (and locally up to 4") for the San Bernardino Mountains, 1-1.5 inches for Orange County and portions of the Inland Empire adjacent to the San Bernardino Mountains, with about 0.25-0.75" for San Diego County coasts/valleys and the remainder of the Inland Empire. Given the 4-8" (locally up to 12") that fell in the San Bernardino Mountains, resulting in widespread flash flooding and numerous instances of debris flow in the mountains and surrounding drainages, a Flood Watch is now in effect for the San Bernardino Mountains, High Desert, and portions of the northern Inland Empire adjacent to the mountains from midnight tonight through 4PM Friday afternoon.
Rainfall will trend down in intensity Friday afternoon, but additional light precipitation remains possible into Saturday morning before clearing out completely late Saturday morning. Snow levels fell below 7000 feet briefly today, but rise back to 7500- 8000 feet for most of the duration of the precipitation before falling back to near 5000 feet by Saturday morning. 2-3 inches of snow is possible near 7000 ft with 8-12 inches possible near mountain peaks.
260430z. Coasts/Valleys, A few low clouds around 1000 ft MSL over San Diego County with Orange County seeing a few around 6000-8000 ft MSL. Low clouds are expected to increase in coverage and lower beginning over Orange County after 07Z and in San Diego County after 10Z to around 2500-6000 ft MSL. Gusty southerly winds up to 20kt are possible as this next surge of moisture moves through the area. Moderate up/downdrafts downwind of the Santa Anas into the Inland Empire through Friday morning.
.Mountains/Deserts, Low clouds around 7000 ft MSL are expected to slowly lower to around 1000-3000 ft MSL after 10Z. Winds are still a bit breezy over KONT with winds out of the west around 7-10kts and are expected to stay around those values through the TAF period.
.Region-wide, A band of moderate to locally heavy rain moves into the region from the northwest starting around 12-14Z, though exact timing is still a bit uncertain, and will move across the area through the daytime. A few hours of MVFR to locally IFR cigs/vis are expected as the rain moves through. SCT -SHRA in the wake of the main band will create intermittent cig/vis reductions into Saturday night.
South to southwest winds strengthen slightly again late tonight into Friday, with gusts intermittently exceeding 20 kts. Winds will then turn northwest and gradually decrease late Friday into Saturday.
Westerly swells will lead to surf building 5 to 8 feet Friday- Saturday. Highest surf is expected for west-facing beaches. A Surf Advisory is in effect now through Saturday afternoon.
Ca, High Surf Advisory until 11 AM PST Saturday for Orange County Coastal Areas-San Diego County Coastal Areas.
Flood Watch from midnight PST tonight through Friday afternoon for Apple and Lucerne Valleys-San Bernardino County Mountains-San Bernardino and Riverside County Valleys-The Inland Empire.
PZ, None.
