Light rain/snow showers over the highest points of the mountains today before drier weather tonight into Thursday morning. The next system arrives Thursday, delivering heavy rainfall late Thursday night into Friday afternoon. Up to an inch of rainfall possible for coast/valleys, higher in the foothills and lower elevations of the mountains. Periods of heavy snowfall for the higher terrain, especially early Friday morning, with snow levels around or just above 6500ft. The slow moving system will allow precipitation to linger into Saturday. Drier weather with a very slow warming trend sets in for the end of the weekend into early next week, warming to near normal by Wednesday.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Satellite shows bubbling cu over much of the region as a cutoff low shifts eastward into Arizona this afternoon. A few lingering light rain and snow showers will be possible across the San Bernardino and Riverside mountains through this evening, with very limited additional accumulations expected due to lessening moisture in the mid levels. Outside of these locations, dry weather will prevail with chilly temperatures due to the exiting low. Highs both today and tomorrow will be well below seasonable averages by around 10-20 degrees, generally in the 50s and 60s.
The next system to arrive will be a trough over the PacNW that is pinched and becomes cutoff, rapidly advancing southward along the coast. This low, similar to the last system, will situate right off the coast of Southern California Thursday/Friday before moving inland Saturday. There will be less moisture with this upcoming low compared to the system this past weekend, but we are still looking at widespread wetting rainfall for the end of the week. Rain will begin as early as Thursday morning, increasing Thursday night and Friday morning, with an associated thunderstorm threat during this time period. Rain may continue for much of the day Friday as the low moves into position, with increasing winds over the marine waters and the higher elevations. This system looks to only produce moderate winds with limited gradient tightening and the core of the system a bit too far south. Still, gusts in the deserts, mountains, and marine waters could reach up to 30 mph at times on Friday, with even gustier and erratic winds in any thunderstorm. The thunderstorm threat lessens Friday afternoon, with only light to moderate rain showers prevailing into Saturday.
700 mb temperatures remain extremely cold, attributing to our inability to warm much in between systems. The snow level for the beginning of this event looks to hover right around 6000ft, raising a bit to 6500ft Thursday night into early Friday morning coinciding with the timing of the heaviest precipitation. With snow levels rising, elevations between 5500-6500ft will see a mixture of snow/rain, transitioning to more rain by Friday morning. Periods of rain with rates greater 0.50"/hr will fall on already highly saturated soils, which may cause moderate flooding on and around recent burn scars. Always monitor the forecast and listen to local emergency officials. Above the snow level, snowfall rates could reach 1"+/hr, primarily in the early Friday morning time frame. Snowfall totals Thursday through Saturday of 5-10 inches for elevations 6500-7500ft, with up to 16 inches for the highest peaks. A Winter Storm Watch is in effect for elevations above 6500ft for this period, and heavy snow in the early morning hours of Friday may make travel hazardous. Avoid travel during this time if possible, especially along Hwy 38 near Big Bear. If you must travel, ensure you have emergency supplies in your car and have a way to contact emergency services in low cell coverage areas.
This system will follow a similar path to the cutoff low exiting today, moving into Arizona Saturday into early Sunday. As this system moves across, wrap around moisture will result in lingering light rain and snow showers across the region, best chances in San Diego and Riverside counties. High uncertainty remains on timing and accumulations Saturday due to the model spread in the movement of the low, fairly unusual to have such limited agreement 72 hours out. Snow levels will remain around 6500ft on Saturday, rising closer to 7000ft by early Sunday. As the last of the precipitation moves out, a slow warming and drying trend will settle in for the remainder of the forecast period. Highs may return to near normal by Tuesday/Wednesday as weak ridging develops overhead, and dry weather prevails after Sunday.
192130z, Primarily VFR conditions through 18Z Thursday. SCT-BKN cumulus based 8-10 kft MSL and SHRA over the mountains through 02Z Thu. Increasing clouds around 2500-4000 feet MSL in coast and valley areas after 06Z Thu with SCT -SHRA after 12Z for San Diego/Orange County coasts and valleys ahead of the next storm system.
Increasing south to southwest winds after 18Z Thu along with widespread RA/SHRA moving in from northwest to southeast, reaching KSAN 21-00Z. Widespread MVFR cig/vis reductions expected for the coasts and valleys after onset of SHRA, with the mountains becoming shrouded in FG.
No hazardous marine conditions are expected through Thursday. Southerly winds will increase late Thursday ahead of the next storm system. Moderate confidence in winds turning westerly and strengthening by early Friday as the front passes, but exact track of the low pressure system may create large differences in both wind speed and direction Thursday evening through Friday. Gusty winds and choppy seas may create hazardous conditions for small craft. There is also a slight chance of thunderstorms late Thursday through late Friday. Any thunderstorm could bring lightning, gusty winds, choppy seas, and a waterspout.
Ca, Winter Storm Watch from Thursday morning through Saturday morning for Riverside County Mountains-San Bernardino County Mountains.
PZ, None.
