17/858 AM.
Dry and warmer weather is expected into the weekend. Gusty northeast winds will be focused over Los Angeles and Ventura Counties today. It should turn cooler Monday, with an increasing chance of rain moving into the forecast area between late Monday and Wednesday.
(tdy-Sun), 17/919 AM.
***UPDATE***
Santa Ana winds started blowing overnight in the LA mountains but have been slow to migrate down to the lower elevations. Wind advisories remain in effect for portions of LA/Ventura Counties through this afternoon. Winds gusting to around 50 mph have been observed in the San Gabriel Mountains this morning as well in the Santa Susanna's, including the Porter Ranch area. Most of the winds will drop off later this afternoon.
Temperatures are trending significantly warmer in the areas where there are Santa Ana winds but little change elsewhere. Ultimately expecting highs to be around 2-4 degrees warmer in most areas except the far interior where some cold advection from the departed trough will keep temps either cooler or little change from yesterday.
***From Previous Discussion***
A broad NW flow aloft with H5 heights around 573 dam can be expected today, but then an upper level ridge over the E Pac will build into the area tonight and Sat, with H5 heights up to 574-575 dam by Sat afternoon. The upper ridge will move off to the E Sat night and Sun as a large upper level trof over the E Pac approaches the CA coast.
Mostly clear skies should prevail for the most part tonight thru Sat then some increase in clouds can be expected Sat night and Sun. It looks like some more gusty NE winds will affect the area tonight into Sat morning as decent offshore gradients continue, but upper level support for strong winds will be less so the winds should be generally below Advisory levels.
Temps will increase significantly S and W of the mtns today thanks to the offshore flow, where temps should be about 5-15 deg above normal, while from the mtns to deserts will cool to 4-8 deg below normal. Highs will then be 6-12 deg above normal for all areas on Sat, then cool about 3-6 deg for Sun, especially closer to the coast thanks to an earlier onset to the seabreeze. The warmest day overall will be on Sat when the inland coast and vlys are expected to reach into the 80s, with upper 80s in the western San Fernando Vly.
(Mon-Thu), 17/251 AM.
Still plenty of uncertainty next week with not too many changes in the forecast from yesterday. A cold upper level low, completely disconnected from the jet stream (also known as a cut- off low), will slowly wobble down the West coast into the middle of next week. Timing and exact totals still have yet to be nailed down, which tends to be common with cut-off lows. While most recent model runs do push the arrival of rain back about 6 hours, there is still that 24 hours of wiggle room with the onset of rain in any one area. As of now, the earliest time for rain is around Monday morning along the Central Coast and Tuesday morning in LA County. However, the recent model runs do show most of the rain across areas south of Point Conception falling in the Tuesday night to Wednesday morning period. There are also still about 20% of the ensemble solutions showing little or no rain south of Pt Conception.
Having said that, the most likely outcome is for periods of light rain to develop across most of the area (except possibly the far interior areas) by Tuesday afternoon with minimal impacts. The ensemble means have been pretty steady with the amounts around a half to one inch across SLO County (locally higher for the far NW tip of SLO County), then dropping to mainly less than half of an inch in LA County. However, if the upper low manages to slide all the way down to LA County, given the time of year and the cold air aloft, some isolated thunderstorms with heavy rain are possible and may bring totals a little bit higher where ever the thunderstorms form. Additionally, a few inches of snow are possible at higher elevations in the mountains, mainly above 6000 feet.
Lastly, there is a possibility of showers lingering as late as Thursday if the upper low takes a very slow track through the area. This solution would also likely mean that the initial onset of rain would be later as well. Due to the nature of cut-off lows, it may take until late weekend before models start to come into better agreement, and confidence increases in the forecast.
17/1243z.
At 06Z at KLAX, there was no marine layer nor an inversion.
Moderate confidence in TAFs, except high confidence in KPRB, KSMX, and KSBP.
Timing of wind changes may be off +/- 2 hours, with N-NE gusts off by +/- 5kt at any point through the morning. Lgt to moderate LLWS & turbulence is possible over and near mountainous terrain through 00Z Sat, especially across Los Angeles and Ventura counties.
There is a 40% chance of very brief MVFR cigs at KSMO, KLAX, KLGB, KBUR, and KVNY and at some point through 17Z Fri, however, conds may scatter and reform frequently due to the patchy nature of the marine layer clouds.
KLAX, Moderate confidence in TAF. There is a 40% chance of very brief BKN012-022 cigs through 17Z Fri, and conds may scatter and reform frequently. There is a 60% chance of east wind component reaching 7-8kts until 17Z, with a 30% chance of reaching 10 kts.
KBUR, Moderate confidence in TAF. Wind changes may be off by +/- 2 hours, with a 20% of no northerly winds through the period.
17/713 AM.
For the Outer Waters, moderate to high confidence in current forecast. A combination of Small Craft Advisory (SCA) level winds and seas are expected through this morning, with a 30% chance of lingering through tonight. Except for far northern outer waters (PZZ670) which the Small Craft Advisory has been extended through late tonight. Saturday through Monday afternoon, there is a 20-30% chance of SCA level winds. An approaching cold front may bring SCA level southerly winds, along with a chance for showers between Monday evening and Tuesday morning.
For the Inner Waters north of Point Sal, moderate to high confidence in current forecast. Seas may flirt with SCA levels through mid- morning across the western portion of the zone, but are forecast to drop below advisory levels through the morning. From late this morning through Monday, high confidence in winds and seas remaining below SCA levels. An approaching cold front may bring SCA level southerly winds, along with a chance for showers between Monday evening and Tuesday morning.
For the Inner Waters south of Point Conception, moderate to high confidence in current forecast. SCA level NE winds will develop early this morning from Ventura south to Santa Monica and spread out towards Anacapa Island. From Point Mugu to Malibu this morning, there is low chance for Gale Force wind gusts nearshore below any canyons/passes. Saturday through Monday, high confidence in winds and seas remaining below SCA criteria for all southern Inner Waters.
Ca, Wind Advisory remains in effect until 2 PM PDT this afternoon for zones 88-354-355-358-369-371-372-374>376-378>380. (See LAXNPWLOX). PZ, Small Craft Advisory in effect until noon PDT today for zones 650-655-673-676. (See LAXMWWLOX). Small Craft Advisory in effect until 2 PM PDT this afternoon for zone 670. (See LAXMWWLOX).
