Santa Ana winds expected today through Saturday, with the strongest and most widespread winds on Friday. Additionally, moderate to major HeatRisk is expected for coastal areas. Cooler conditions will spread inland Sunday as Santa Anas weaken, with greater cooling and chance of showers next Tuesday through next Thursday.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
, Today through Saturday, Oct 17, Mid-level low pressure has settled into western AZ and southeastern CA, with a strong surface high pressure in the northern Intermountain West. This has resulted in moderately to locally quite strong Santa Ana winds from the northeast. Fairly widespread offshore winds are broadly gusting 15 to 30 mph even towards some of the coastal areas (especially in Orange County), with gusts towards 25 to 40 mph along the foothills into the inland valleys, including the Inland Empire. Our typically gusty canyons and mountain passes are, as per usual, winning the gust- off with peak gusts 45 to 60 mph.
The strong downward motion of these winds has lead to much warmer temperatures than yesterday from the foothills to the coast. In terms of change in temperature from yesterday, temperatures this afternoon are anywhere from 5 to 20 degrees warmer in this area, with highs from 80 to just above 90 degrees. While temperatures in the valleys and coastal regions are 5 to 15 degrees above average, temperatures in the mountains and deserts are actually below average thanks to the colder air mass moving into the region. This has also lead to lower humidity, with values generally 20-25% in the valleys/non-immediate coast and localized areas around 15-20%.
Surface high pressure gradually moves southward into the Great Plains tonight into Friday as the mid-level low moves southwest. This will turn offshore winds from northeast to more due easterly, which will lead to stronger and more widespread winds for the east Inland Empire and San Diego and Orange counties Friday, while winds in the San Bernardino Mtn foothills into the northern IE will weaken slightly, though remain gusty. Winds will be in the 20 to 30 mph range with gusts 45 to 60 mph for foothills and inland valleys, while coastal areas will see gusts closer to 15 to up to about 30 mph. This will drive temperatures even warmer for Friday, especially for coastal regions. Low temperatures in this region will struggle to dip far below 70 degrees, with highs in the mid 80s to mid 90s.
This flow pattern will actually help to drag some moisture from the south/southeast into the region Friday, so unlike the typical Santa Ana pattern where stronger winds = drier conditions, humidity will actually increase slightly for Friday. This, along with recent substantial rainfall, will help temper the danger for fire weather, though conditions will be elevated to locally near critical for fire weather through Saturday. This moisture will also lead to increased cloud cover for Friday into Saturday, and even lead to the possibility of elevated storms late Friday into Saturday. The majority of precipitation will evaporate in the dry layer beneath the cloud, but there's about a 10% chance for some very light precipitation during this time period, mostly for the mountains/deserts and perhaps for far south-central/southeastern San Diego Co. There will be a little bit of elevated instability (MUCAPE ~100-300 J/kg) that could result in an isolated thunderstorm, but chances look pretty small (around 5%).
Saturday, the central U.S. ridge and associated surface high weakens and shifts eastwards, and offshore winds will weaken, though they'll be breezy. Temperatures will decrease a few degrees.
..Sunday, Oct 18 through Friday, Oct 23, As the highcontinues its eastward shuffle, winds continue to weaken late Saturday into Sunday, so while winds will be offshore Sunday morning, they will be much weaker. Winds will switch to onshore Sunday afternoon, bring additional cooling, a trend that will continue into Monday as weak low pressure hangs out in southern California. At least patchy marine layer low clouds will likely return Monday morning, resulting in patchy coastal fog.
A large- scale, stronger mid- level low pressure system starts moving down from the Gulf of Alaska late Monday into Tuesday, bringing breezier onshore flow and even cooler temperatures for Tuesday, along with a chance for showers that will increase from north to south later Tuesday into Wednesday morning. Global weather models already have pretty good agreement on timing of the trough, with the large majority of ensemble members agreeing on widespread rain showers. There are some location differences in the trough placement which is leading to differences in how much precipitation exactly, but at this range precipitation is looking light to locally moderate. Temperatures will continue to decrease through Wed-Thu, with highs in the 60s-70s for the coastal basin/high deserts, 40-55 for the mountains, and mid 70s in the low deserts. Breezy onshore winds are likely for Tuesday into Wednesday in the usual areas (coastal waters, mountains and desert foothills). Keep your eye on the forecast this upcoming week.
Models diverge Friday into next weekend, but general agreement is in some strength of large-scale mid-level troughing continuing, so while any precip will likely taper off by late next Thursday, temperatures look to remain in the cool to average zone through next week.
151830z, SKC and VFR through Fri. Northeast winds will remain elevated into Fri, when the strongest and most widespread winds are expected. For the mountain foothills peak gusts of 45 to 55 kt are expected. For the valleys, gusts 30 to 45 kt, locally higher near mountain foothills are likely. Coast and Coachella Valley will also see elevated winds with gusts 20 to 30 kt. There is a potential for gusts of 50 kt to occur at KONT early Fri AM. Winds may decrease briefly after 00Z Fri, increasing around 10Z Fri. Winds Fri will weaken from north to south 18-22Z. Areas of MOD-STG up/downdrafts in lee of (south and west of) mountains along with areas of LLWS where strong winds do not surface. East winds continue into Sat.
Isolated northeast gusts could exceed 20 knots Friday into early Saturday. Otherwise, no hazardous marine conditions are expected through Monday.
A south swell from 190 to 200 degrees at 3 to 4 feet with a 15-17 second period will generate elevated surf of 3 to 6 feet, with local sets to 7 feet. There is an increased risk of strong rip currents.
Ca, Beach Hazards Statement until 2 PM PDT this afternoon for Orange County Coastal Areas-San Diego County Coastal Areas.
Heat Advisory until 8 PM PDT Saturday for Orange County Coastal Areas-Orange County Inland Areas-San Diego County Coastal Areas.
High Wind Warning until 8 PM PDT Saturday for San Bernardino and Riverside County Valleys-The Inland Empire.
High Wind Warning from 8 PM this evening to 8 PM PDT Saturday for San Diego County Valleys.
High Wind Warning until 8 PM PDT Friday for San Bernardino County Mountains.
High Wind Warning until midnight PDT Saturday night for Riverside County Mountains-San Diego County Mountains-San Gorgonio Pass near Banning.
High Wind Warning until noon PDT Saturday for Santa Ana Mountains and Foothills.
Wind Advisory until noon PDT Saturday for Orange County Inland Areas.
PZ, None.
