16/521 PM.
A moderate to strong Santa Ana Wind will bring widespread strong winds and critical fire weather conditions to much of Southwest California through Saturday. In addition, the very warm temperatures bring a high risk of heat-related illness to all coastal areas. A significant cool down is expected Sunday with a chance of widespread rain by Tuesday or Wednesday.
(Fri-Mon), 16/1019 PM.
***UPDATE***
Persistent, gusty Santa Ana NE to E winds lead to dry, hot conditions for the coasts and coastal valleys, with widespread 90s and pockets of low 100s. Temperatures were far cooler for the mountains and southern interior. Winds peaked this morning as the LAX-DAG offshore pressure gradient reached 7.4 mb and the Santa Barbara to Bakersfield offshore gradient peaked at 3.7 mb. The Santa Ana wind cooridor from the San Gabriel mountains to the Ventura County coasts saw widespread gusts in the 30 - 50 mph range including lower elevations, with more localized gusts from 50 to 81 mph at higher elevations.
This evening, winds have relaxed a bit with gusts falling in the 15 to 40 mph range from the Soledad Pass to the Ventura County coast and Santa Monica mountains. Looking into the future, offshore winds will persist overnight then peaking again Saturday morning. Offshore gradients are forecast to be about 1-1.5 mb weaker, so will still see windy conditions but not quite as strong as this morning. With winds being more easterly, areas outside the normal Santa Ana wind corridor will be affected. Temperatures will be a touch cooler Saturday, and gradients should weaken enough to allow a brief seabreeze near the coasts. Convection to the south wrapping around the upper level low south of us could also bring additional clouds to LA County Saturday, leading to cooler temperatures. The cooling trend will be more pronounced Sunday, with lingering weak offshore winds. Temperatures start to fall below normal Monday as the low approaches from the north.
***From Previous Discussion***
Overall, 12Z models in good synoptic agreement through the period. At upper levels, low to the southwest will undercut the ridge this weekend. At the surface, offshore gradients will gradually weaken with weak onshore gradients returning Sunday and Monday.
Forecast-wise for the short term, main issues remain Santa Ana winds and the heat. As mentioned, offshore gradients will continue through Sunday morning, but will exhibit a weakening trend. At the same time, the upper level support will also weaken. So, will expect the offshore winds to decrease. So, with the afternoon forecast, have extended the current WIND ADVISORIES through 200 PM Saturday. For the LA county mountains, will let the HIGH WIND WARNINGS continue through 800 PM this evening and have issued WIND ADVISORIES from 800 PM this evening through 200 PM Saturday. By Saturday night and Sunday morning, the offshore winds should diminish below advisory levels with a return of weak onshore winds Sunday afternoon through Monday.
The second concern is the heat. With the continued offshore flow, very warm conditions will persist through Saturday. Based on current Heat Risk forecasts, the coastal plain will continue at HEAT ADVISORY levels through Saturday evening. So, will continue with the HEAT ADVISORIES through 800 PM Saturday. For Sunday and Monday, a welcome cooling trend is expected with the return of onshore flow and lowering thicknesses.
(Tue-Fri), 16/112 PM.
For the extended period, models are in decent synoptic agreement through the period. Main feature of note will be an upper low, dropping south off the CA coast on Tuesday then moving inland across the area on Wednesday and Thursday. Models differ slightly in the speed of this low moving across the area, but those differences should be minimal.
So, forecast-wise, main concern in the extended period will be rain chances, associated with the upper low. Looking at the ensembles, most every member from every model indicates some amount of rain between Tuesday night and Thursday morning. However, the range of potential amounts remains quite large. At this time, ensemble means indicate totals between 0.25 and 1.00 inches which is a reasonable early estimate. There is about a 20-30% chance of totals greater than 1.00 inch. Will continue to monitor this situation closely as potential amounts are likely to change from day-to-day.
Other than the rain chances, no significant issues are expected. Temperatures will experience a noticeable cooling trend with high temperatures only topping out in the 60s to lower 70s. At this time, no significant wind issues are expected.
17/0053z.
At 00Z over KLAX, there was no marine layer or inversion.
High confidence in VFR conditions, unless a fire breaks out upwind of an airport. NE-E winds will be ongoing for many sites with UDDF near any mountains and LLWS 10-20 knots near most airports, especially those with winds above 20 knots. Moderate confidence on wind forecasts (speed +/- 5 mph and direction +/- 30 degrees).
KLAX, High confidence in VFR conditions through at least Saturday. High confidence in east winds dominating this evening and Saturday morning with little to no west influence during those times. Moderate confidence in speed and timing. LLWS 5-15 knots also possible through 03Z. East winds should fall below 08 knots by 07Z. East winds around 8 knots with gusts to 15 kt are likely Saturday 14-20Z.
KBUR, High confidence in VFR conditions through at least Saturday. High confidence in east winds dominating today with little to no south influence. LLWS 15-25 knots also possible at times through 06Z.
16/733 PM.
NE to E winds will bring short period and hazardous seas to most of the nearshore waters into Saturday. Winds will be strongest from Ventura to Santa Monica where winds where pockets of 20 to 30 knot winds will form at times. This is a a few knots lower than earlier today, so the previous Gale Warning has been replaced with a Small Craft Advisory. Gusts of 10 to 20 knots will likely also affect the nearshore Central Coast waters as well as the waters from Orange County to Catalina Island. These winds will likely have rapid fluctuations. Benign conditions are expected on Sunday. If you have the option, go out on Sunday and try to stay off the waters Friday and Saturday. Small Craft Advisory NW winds will increase Sunday Night and Monday, especially off the Central Coast. A moderate- strength storm system is becoming more likely in the Tuesday through Thursday timeframe.
Ca, Wind Advisory in effect until 2 PM PDT Saturday for zones 88-354-355-358-362-369>380. (See LAXNPWLOX). Heat Advisory in effect until 8 PM PDT Saturday for zones 340-341-346-347-349-350-354-355-362-366>368. (See LAXNPWLOX). Red Flag Warning in effect until 8 PM PDT Saturday for zones 288-354>358-362-369>382-548. (See LAXRFWLOX). PZ, Small Craft Advisory in effect until 2 PM PDT Saturday for zones 650-655-676. (See LAXMWWLOX).
