Widely scattered, mostly light showers will continue today into this evening with the next Pacific low pressure system from the northwest bringing another round of more widespread showers for Thursday night and Friday with decreasing chances for showers into the weekend. Drier and warmer for next week.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Today through Wednesday,
Current satellite and mesoscale analysis depicts the upper level low pressure system responsible for the continued unsettled weather positioned near Point Conception. While this system will be relatively progressive in its departure for a cut-off low, the core of the low is set to pass overhead Wednesday afternoon and depart Wednesday night. Until then, isolated to scattered showers remain possible. The focus for shower activity today will generally be for the coastal basin from the waters through the coastal slopes of the mountains, while Wednesday's shower activity should be limited to the mountains. Rainfall rates from any of these showers will be largely light, with additional accumulations of less than a quarter of an inch through Wednesday evening. With the passage of the cold core upper low, snow levels stay low through Wednesday evening, near 5500-6000ft, with any shower activity above these elevations falling as snow. Additional snowfall accumulations through Wednesday are about an inch or less, with locally higher totals on the highest mountain peaks. Temperatures stay notably below average as this system passes through, with afternoon high temperatures 10 to 15 degrees below normal and low temperatures dipping into the 40s for inland valleys.
Thursday through Saturday,
Attention then quickly turns to the next weather system in the form of yet another cut-off low that is currently progged to drop southward from northern California on Thursday into Friday. As with most cut-off lows, volatility in their forecast track/timing and uncertainty is quite high, though ensemble guidance is coalescing towards a scenario where the center of this low drops considerably far south, over northern Baja by Saturday morning. The effect of a low tracking as such brings a cold front through the region some time early on Friday. High resolution guidance now in range suggests the chance for light pre-frontal showers on Thursday, primarily for the coastal areas. The main band of precipitation will accompany the cold front overnight Thursday into Friday though several ensemble members are depicting the potential for wrap around precipitation on the northern side of the low. Given the inherent uncertainty in the track of the cut- off low, a fairly wide spread in the forecast total rainfall remains for this event. The most likely outcome is to see 0.75-1 inch on the coasts/valleys, with 1-1.5 inches in the mountains, however, should the intensity of the wrap around banding come to fruition as seen a higher-end clustering of ensemble members, localized rainfall totals off the mountains could be closer to 1.5-2 inches. Given the displacement of the center of the low to the south, snow levels will be a touch higher than seen today/tomorrow, closer to 6500-7000ft.
In addition to the precipitation, wind will also be a notable impact from this second system. Initially, elevated southerly winds ahead of the cold front could bring wind gusts of 20-25 mph to the coasts and coastal waters Friday morning. Then, depending on the track of the upper level low, easterly winds on the north side of the parent storm system could bring easterly offshore winds to the region Friday afternoon, brining strong wind gusts to mountains, mountain passes, the high deserts, and portions of the Inland Empire.
Early next week,
The late week storm system eventually slides eastward into Arizona/New Mexico on Sunday, though uncertainty in the upper level pattern increases dramatically come early next week. Zonal flow to a weak ridging looks to be the dominant solution, though the timing/intensity of the ridge is in question. Ultimately, temperatures will gradually warm back to near normal for Sunday/Monday. Conditions look to stay dry as well, bringing an end to the wet pattern we've been in as of late.
182100z, Widely scattered showers expected through 07z Wednesday with scattered snow in the higher mountains. Precipitation will generally be light in nature. Slight chances for precipitation will return after 20Z Wednesday for over the mountains. BKN cloud deck is expected to stay between 5,000 to 10,000 ft MSL for most of the period with areas along the coast dipping down to 3,500 ft MSL around 01-02Z before lifting/scattering around 07Z.
No hazardous marine conditions are expected through Thursday, but the next storm system has the potential to bring hazardous winds and seas Thursday night and Friday.
Ca, Winter Weather Advisory until 10 PM PST this evening for San Bernardino County Mountains.
PZ, None.
