07/205 AM.
Moderate to strong Santa Ana winds will continue through Sunday, with widespread gusty conditions expected across much of Los Angeles and Ventura Counties today. Temperatures will warm through the weekend, with widespread highs in the 80s. Briefly cooler conditions are likely early next week, with another warm and dry spell expected to start on Wednesday.
(tdy-Mon), 07/858 AM.
A 555 dam upper low is retrograding to the SW and by late afternoon it will be a couple hundred miles SSW of San Diego. This system is bringing strong northeast wind flow aloft from 850 mb to 500 mb level today. This upper level support is combining with 4 mb offshore sfc flow from both the N and E to continue the moderate to locally strong Santa Ana wind event. Today is the strongest and most widespread for the offshore winds. The strongest winds will continue to be across the San Gabriel and Santa Susana Mountains, with damaging gusts from 60 to 70 mph. In addition to the typical Santa Ana wind corridor areas, also seeing gusty north to northeast winds in areas that typically do not see much offshore winds such as the LA basin (especially west LA) and the San Gabriel Valley (especially foothills near Highway 210 corridor), due to the strong upper level wind support and associated mountain wave wind activity. As of 830 am, already seeing a number of observing stations seeing wind gusts between 35 and 45 mph across the LA Basin and San Gabriel Valley, with higher gusts of 45 to 60 mph across the San Gabriel valley foothills and Santa Monica mountains. We are still on track for the strongest winds to continue in these areas through early afternoon, then slowly diminish by late afternoon. Current High Wind Warnings and Wind Advisories remain on track. The potential impacts today associated with the gusty winds include downed trees and powerlines as well as isolated power outages and blowing dust, including the populated urban areas of the LA Basin and San Gabriel Valley.
On Sunday, the upper level wind support will not be as strong, and will become more easterly. The surface pressure gradients actually become more offshore and will be about 6 mb offshore from both the N and E. The weaker upper level wind support, however, will overshadow the increasing offshore surface flow, keeping most of the offshore winds focused in the more typical Santa Ana wind prone corridors of LA/Ventura counties, and overall wind speeds not as strong in most areas. No high wind warning level winds anticipated on Sunday, but will likely continue to see many wind advisories in effect, with gusts mostly in the 35 to 50 mph range.
The offshore winds will bring significant downslope warming and drying to the region today, and especially tomorrow. With this type of event, coastal areas will likely see the most significant compressional heating, with temperatures likely climbing into the lower 80s today, and around 90 on Sunday (about 15-20 degrees warmer than normal), which could approach record levels in a few locations. With the afternoon forecast package, will be considering the potential for a heat advisory for portions of the LA Basin valid for Sunday, especially considering how early in the year this heat is occurring, and the large LA Marathon race which could now see temperatures peak around 90 degrees by the end of the event. While Red Flag Warnings have not been issued for this event due to the continued moist vegetation levels, the hot, dry (humidities falling into single digits), and windy conditions will bring the possibility of small fire activity through the weekend.
*** From previous discussion ***
The great basin high weakens considerably early Monday. So much so that gradients turn weakly onshore in the morning. Sometimes such a fast reversal allows marine layer clouds to form but right now it looks like any low cloud formation will hold off until Tuesday. The lack of offshore flow will bring a cooling seabreeze to the csts and vlys and max temps will collapse - cooling 10 to 15 degrees and ending up in the 70s with mid and upper 60s at the beaches.
(Tue-Fri), 07/205 AM.
A weak ridge begins to move into the state from the west on Tuesday. Onshore flow will peak at this time and morning low clouds will likely develop and should cover most of the csts and some of the vlys. Look for an additional 3 to 6 degree of cooling making Tuesday the coolest of the next 7 with cst/vly highs mostly in the upper 60s and lower 70s.
Look for temperature whiplash on Wednesday as the ridge pushes further into the state and the onshore push rapidly weakens and even becomes slightly onshore in the morning. There is a chc that some areas such as the LA south coast and the western SBA county coast could see some morning low clouds but odds are skies will be clear everywhere. Max temps will likely rebound by 5 to 10 degrees.
Thursday and Friday look very warm. The east Pac ridge will peak and hgts will rise to ~588 dam. There will be 2 to 4 mb of offshore flow in the morning, which will bring some non advisory level gusts to the NE passes and canyons. Skies will be clear. Max temps will jump 5 to 10 degrees on Thursday and then change little on Friday. Look for cst/vly highs to reach the 80s and lower 90s each day. These max temps are 15 to 20 degrees over normal.
Both the AI-EC and the AI-GFS show no rainfall through the 21st.
07/0905z.
At 0900Z at KLAX, there was no marine layer. There was a surface based inversion. The top of the inversion was 1000 feet with a temperature of 19 degrees Celsius.
For 12Z TAF package, high confidence in CAVU conditions for all sites through the period. However, only moderate confidence in wind forecasts for sites across Ventura and Los Angeles counties with timing of wind shifts could be +/- 2 hours of current forecast and gusts could be off 5-10 knots from forecast.
Moderate offshore winds will generate light to occasionally moderate turbulence across the mountains and foothills of Ventura and Los Angeles counties.
KLAX, High confidence in CAVU conditions through the period. Moderate confidence in wind forecast. There is a 30% chance of an easterly wind component 10-14 knots between 14Z and 20Z.
KBUR, High confidence in CAVU conditions through the period. There is moderate confidence in wind forecast as direction could be +/- 30 degrees of current forecast and gusts could be +/- 10 knots.
07/758 AM.
***UPDATE***
Will be extending all current Small Craft Advisories likely through early Sunday afternoon. This will be updated with the afternoon forecast package. Zones: PZZ676/650/655.
***MAIN DISCUSSION***
For the Outer Waters, moderate to high confidence in current forecast. Today through Sunday, there is a 60-70% chance of Small Craft Advisory (SCA) level northeast winds across PZZ676 with high confidence in winds and seas remaining below SCA levels across PZZ670/673. For Monday through Wednesday, high confidence in a combination of SCA level winds and seas for all the Outer Waters with a 20-30% chance of GALE FORCE winds across PZZ670 on Tuesday.
For the Inner Waters north of Point Sal, moderate to high confidence in current forecast. Today through Sunday, high confidence in winds and seas remaining below SCA levels. For Monday through Wednesday, there is a 30-40% chance of SCA level winds in the afternoon and evening hours.
For the Inner Waters south of Point Conception, high confidence in current forecast. Today through Sunday, SCA level northeast winds are expected from Ventura south to Santa Monica and across the San Pedro Channel, with winds and seas remaining below SCA levels elsewhere. For Monday through Wednesday, high confidence in winds and seas remaining below SCA levels for all of the southern Inner Waters.
There is a 40-50 percent of winds up to 15 knots with gusts to 25 knots reaching Avalon this morning, with wind driven waves up to 3 feet possible.
Ca, Wind Advisory remains in effect until 6 PM PST this evening for zones 87-366>368-381-548. (See LAXNPWLOX). Wind Advisory remains in effect until 3 PM PST Sunday for zones 88-354-355-358-362-369>374-376>378. (See LAXNPWLOX). High Wind Warning remains in effect until 3 PM PST this afternoon for zones 375-379-380. (See LAXNPWLOX). Wind Advisory remains in effect from 3 PM this afternoon to 3 PM PST Sunday for zones 375-379-380. (See LAXNPWLOX). PZ, Small Craft Advisory in effect until 3 PM PST this afternoon for zones 650-655-676. (See LAXMWWLOX).
