21/227 AM.
Widespread rain will develop later today and continue into Thursday with a chance of thunderstorms. A weak Santa Ana will develop in the storm's wake by the weekend for dry and warmer conditions.
(tdy-Fri), 21/227 AM.
Relative calm early this morning before the first significant storm of the season arrives later this morning.
A 555 dam upper low 250 miles west of the Central Coast will sink to a point 180 miles SW of PT Conception by late afternoon. Since the low is not north of the area it will not drag a cold front across the area as will happen when the low is further north. It will, instead, throw multiple vort lobes up from the SW and over the fcst area. This means that rain will start to fall across SLO/SBA/VTA counties at almost the same time later this morning. Rain will develop across LA county a few hours later since it is further to the east. The low will continue to pump rain bands into the over the area for the rest of the day. The combination of cold air aloft and strong PVA will bring a 20 to 30 percent chc of TSTMs to the SLO/SBA/VTA area in the afternoon.
The upper low will track to the ENE overnight and will bring the heaviest rain activity to LA county. The TSTM threat will also expand to the east and LA county will also have a 20-30 percent chc of a TSTM.
The rain will turn more convection Thursday morning as the core of the low moves over the area. The steadier rain will be replaced by showers and a chc of TSTMs. The shower activity will diminish from the west to east in the afternoon as the upper low accelerates and pulls out to the NE.
Rainfall totals for the this system will mostly be in the the 1.00 to 1.5 inch range with 2 to 3 inches possible across the coastal foothills and slopes. The highest rainfall totals and rates will likely be over the Santa Ynez range where .75 in/hr rates are likely as are 3.00 in rain totals. The Santa Monica mtns will have similar rain rates and totals. A Flood Watch will go into effect in affect for these areas later today.
The convective nature of this system driven by the instability created by the cold core of the upper low as well as the warm SSTs will bring a slim ~5% chc of a waterspout moving ashore as a tornado tonight into Thursday morning.
The snow level will remain above 8000 feet.
This is not an anomalous storm: statistically there is about an 80 percent chc of a storm system to move across the area in October.
On Friday, as is so often the case, offshore flow and ridging aloft will move in on the heels of the rain system. This will trigger a low end Santa Ana event with peak winds around 35 mph in the breeziest locations.
Max temps will mostly be in the mid 60s to lower 70s today and Thursday. Max temps will then warm under the sunnier and breezy conditions Friday - look for lower 70s across the csts and lower to mid 70s in the vlys.
(Sat-Tue), 21/227 AM.
Weak ridging and weak (1 to 3 mb) offshore flow from both the east and north will be in place for the entire xtnd period. The best upper level support will be on Saturday when there will be 30 to 40 mph gusts csts/vlys and as high as 50 mph in the mtns. The winds will be weaker starting Sunday.
High pressure and offshore flow should keep the skies clear.
There will be decent warming on Saturday (4 to 6 degrees) and then 1 or 2 degrees of extra warming Sun and Mon. Tuesday will cool some as the ridge and offshore flow weaken substantially. Cst/Vly temps will be a little above normal while the interior will be several degrees blo normal.
A quick look at the AI long range models shows dry conditions through the end of the month.
21/0858z.
At 0832Z at KLAX, there was no marine layer nor an inversion.
High confidence in VFR TAFs at KPMD and KWJF.
Moderate confidence in non desert TAFs through 17Z with a 30 percent chc of intermittent MVFR cigs.
Moderate confidence in all non desert TAFs after 17Z. Rain timing could be off by +/- 2 hours. There is a 40 percent chc that there will be MVFR cigs/vis with the rain.
There is a 10-20 percent chance of TSRA KSBA and north starting around 18Z. The chc of TSRA will then spread to KOXR and KCMA Wednesday afternoon, and into LA County after 03Z.
KLAX, Moderate confidence in TAF. There is a 30 percent chc of intermittent BKN020-030 conds thru 18Z. Cigs may be as low as BKN025 with rain. There is a 10 percent chc of TSRA after 03Z. An east wind component up to 7 kt is possible 12Z-18Z. An 8kt east wind component is possible after 03Z.
KBUR, Moderate confidence in TAF. There is a 30 percent chc of intermittent BKN020-030 conds thru 18Z. Cigs may be as low as BKN025 with rain. There is a 10 percent chc of TSRA after 03Z.
21/230 AM.
Expecting showers to continue moving into the coastal waters this morning as the low approaches from the west. Boaters can expect rain and a chance of thunderstorms and isolated waterspouts spreading from western waters to southeast. With any thunderstorm there is also the threat of lightning, gusty and erratic winds, small hail, and choppy seas. Winds still do not look too impactful, there is a good chance for periods of Small Craft Advisory (SCA) level (including the nearshore waters) southerly winds this morning through this evening. As the system leaves the area Thursday, fairly widespread west to northwest SCA winds will impact much of the coastal waters, creating steep, choppy wind waves.
Then a weak to locally moderate Santa Ana Wind event is likely this weekend, with some localized SCA level gusts possible nearshore in favored areas nearshore adjacent to Ventura and LA Counties.
Ca, Flood Watch in effect from 8 AM PDT this morning through Thursday afternoon for zones 348>353. (See LAXFFALOX). Beach Hazards Statement in effect through late Thursday night for zones 354-362-366. (See LAXCFWLOX). Flood Watch in effect from this afternoon through Thursday afternoon for zones 362-369-370. (See LAXFFALOX). PZ, Small Craft Advisory in effect from 11 AM this morning to 8 PM PDT this evening for zones 650-655. (See LAXMWWLOX). Small Craft Advisory in effect until 5 PM PDT this afternoon for zone 673. (See LAXMWWLOX).
