Quiet weather with a mix of Sun and clouds will continue through this weekend. An area of low pressure with an associated atmospheric river will move through the region on Monday, bringing moderate to locally heavy rain and mountain snow. The troughing pattern will remain over the area through much of the week, bringing a chance for light showers, a mix of Sun and clouds, along with breezy and cool conditions.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Update:
Clear skies over Southern California this evening will not last long. Forecast remains largely unchanged with high clouds moving in late Saturday into early Sunday ahead of the coldest storm system of the year so far. A robust shortwave is still expected to round the base of an amplified trough early Monday. The resultant precip band should produce rainfall rates at least high enough for minor flooding concerns as it passes through Monday afternoon and evening. Additionally, the environment looks marginal for isolated thunderstorm development, which could boost rainfall rates and totals locally. On the other hand, current QPF appears relatively high for Tuesday's shower activity, considering latest model runs are more in agreement on a lull in upper level features.
As mentioned in the previous discussion, another wave of energy is expected to cross the area on Wednesday, bringing another round of enhanced precipitation. However, a more northerly track than currently forecast could exclude San Diego County from any significant additional precipitation. Overall, inclined to hold the line with the previous discussion and forecast rain/snow totals. If anything, San Diego County QPF may be slightly overdone at the moment.
Previous discussion submitted at 126PM:
A currently over the region continues to move eastward with clouds and showers moving into Arizona. This has left mostly clear skies across region with some moisture still available across the mountains in form of cumulus clouds. The trough will be replaced by weak and short-lived ridge by Saturday. A "lovely" day is in store with highs near to slightly above average with mostly sunny conditions. Temperatures will max out into the 70s for western valleys and the lower deserts, 60s toward the coast and high desert, with 50s for areas above 4,500 feet.
We hope you enjoy the sunny and warmer weather because a change is on the way. A large area of low pressure will move southward down the coast toward our region by Sunday. This will lead to increasing clouds across the area throughout the day. Most areas will remain dry. The storm system moves closer to Southern California, with increasing chances for rain and high elevation snow from north to south Monday morning and afternoon. This will lead to areas of moderate to locally heavy rain/mountain snow. Current hi-res model guidance shows the heaviest rainfall moving through the region in the afternoon hours in northern areas and early evening in southern areas. Showers will become more isolated on Monday night. Confidence decreases in how heavy rainfall becomes on Tuesday as the exact track of the trough is still uncertain, where showers may become significantly lighter. Another wave of energy moves through the trough on Wednesday, where chances for rain and mountain snow increase yet again.
Flood risk will be highest on Monday for areas near recent burn scars, lesser chance for areas west of the mountains. Mountain snow looks to be the greatest impact of this winter storm. Potentially significant snowfall will create hazardous travel and possible power outages. This includes along Interstate 15 through the Cajon Pass where light snow may fall and cause travel disruptions.
Models show a fairly agreeable consensus in the troughing pattern lingering into the end of the week. There is still some uncertainty on precipitation, but ensembles have consistently become drier by Thursday and Friday. Nbm precip chances go down to around 10-20% during this time. This would lead to mostly dry weather with a mix of clouds and Sun, along with cooler weather sticking around.
In terms of precipitation amounts, for the 48 hr period from 4 AM Monday - 4 AM Wednesday, the NBM chances for at least 0.50" are around 80-100% for the mountains westward, 50-80% over the high desert, and 20-45% over the low deserts. Chances of at least 1" are around 40-75% for the coasts and valleys, 75-100% for the mountains, 10-25% for the high desert, and less than 20% for the low desert. Highest amounts will be along the coastal slopes of the mountains with 3-6"+ of rain in total. Hourly rain rates will be near 0.40-0.70"/hr as the system on Monday moves through. Rates will be much lower on Tuesday and Wednesday.
Significant snowfall is possible with this storm system next week. At the 6500 ft level in the San Bernardino and Riverside County mountains, there is around a 75% chance of at least 12" of snow during this same 48 hr period, and around a 15-25% chance down at the 5000 ft level. Given the higher snow levels in San Diego County, chances of at least 12" at Palomar and Mount Laguna are around 10-15%.
Additional light rain and mountain snowfall may occur later in the week with low confidence on exact totals.
140400z, Low clouds near 2000ft MSL look to increase a bit in coverage across San Diego County tonight, though remaining mostly SCT. 30-40% chance of CIGs intermittently BKN at KSAN or KCRQ between 03-10z Saturday. Low clouds tomorrow evening will begin to fill back in towards the end of the forecast period with increasing coverage initially around the coastal areas from around 02Z Sunday, and then expanding into the inland areas by 06Z Sunday.
No hazardous marine conditions are expected through Sunday night. A storm system will generate strong winds and high and choppy seas likely hazardous to small craft Monday, continuing through Wednesday. Seas expected to be around 9-12 feet with wind gusts 25- 35 knots. There is also a slight chance of thunderstorms over the waters Monday afternoon/evening.
Combined elevated swell (about 9-11 feet with an average period of about 10-12 seconds) from the west and southwest (240-280 degrees) will likely provide large breaking waves of 8-12 feet on most beaches across Orange and San Diego Counties from Monday afternoon through Wednesday. Widespread, strong rip currents are also likely with these waves and dangerous swimming conditions are expected.
Ca, None. PZ, None.
