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), 21/922 AM.
***UPDATE***
The storm came in hot into Santa Barbara this morning with rain rates close to an inch per hour. Rates have since tapered down considerably but additional periods of heavy rain and thunderstorms are expected there through tonight. Elsewhere, the rain is coming, if not there already. Forecast amounts and rates are still on track. One interesting feature noted in the models this morning was a very unstable air mass Thursday. Forecast soundings are showing CAPE values upwards of 2000j/kg in the Los Angeles area and a favorable sounding for some weak rotation so there remains at least a 5% chance of a weak tornado.
***From Previous Discussion***
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.
21/1722z.
At 1715Z, at KLAX, there was no marine layer nor an inversion.
Low to moderate confidence in 18Z TAF package. Timing of rain could be off by +/- 2 hours of current forecasts. There is a 50% chance of MVFR CIGs with the rain.
There is a 10-20% chance of TSRA through the period with the chances spreading south and east this afternoon and evening.
KLAX, Low confidence in 18Z TAF. Timing of rain may be +/- 2 hours of current forecasts. There is a 50% chance that CIGs remain at VFR levels through the period. THere is a 20% chance of TSRA after 00Z. There is 30% chance of an easterly wind component of 7-10 knots after 22Z.
KBUR, Low confidence in 18Z TAF. Timing of rain may be +/- 2 hours of current forecasts. There is a 50% chance that CIGs remain at VFR levels through the period.
21/713 AM.
For the Outer Waters, high confidence in current forecast. Through this evening, there is a 70-80% chance of Small Craft Advisory (SCA) level winds around Point Conception with winds and seas remaining below SCA levels elsewhere. Late Thursday and continuing through Friday night, winds are expected to increase to SCA levels. For Saturday through Sunday, winds and seas will remain below SCA levels.
For the Inner Waters north of Point Sal, moderate to high confidence in current forecast. Today through Thursday, high confidence in winds and seas remaining below SCA levels. On Friday, there is a 50% chance of SCA level winds in the afternoon and evening hours. On Saturday and Sunday, high confidence in winds and seas remaining below SCA levels.
For the Inner Waters south of Point Conception, moderate to high confidence in current forecast. Through this evening, there is a 60-80% chance of SCA level southeasterly winds across all the southern Inner Waters. For Thursday through Sunday, high confidence in winds and seas remaining below SCA levels for most areas. The only exception will be the western half of the Santa Barbara Channel with a 50-70% chance of SCA level winds on Thursday and Friday.
Today through Thursday, showers and isolated thunderstorms will impact all of the coastal waters. Any thunderstorms that develop will be capable of producing gusty/erratic winds, locally rough seas and even waterspouts.
Ca, Flood Watch in effect 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 4 PM PDT this afternoon through Thursday afternoon for zones 362-369-370. (See LAXFFALOX). PZ, Small Craft Advisory in effect until 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).
