13/925 AM.
A large storm system will move into the Central Coast this afternoon and will continue further south tonight into Friday. The storm will generate periods of moderate to heavy rain this evening through Saturday, and possibly into early next week. Flooding of roadways and burn scars is possible, especially Friday and Saturday.
(tdy-Sat), 13/954 AM.
***UPDATE***
No significant changes to the forecast. A large and slow moving storm is approaching the area. There have been a few stray sprinkles but the first bands of heavier rain are still at least several hours away, and in the case of LA County not until Friday morning at the earliest and more likely Saturday with the second burst of rain as the upper low is expected to move through. A Flood Watch has been issued for southern Santa Barbara County, including the Santa Ynez Range, and the southern Ventura County mountains later tonight through noon Friday with the initial impulse coming through creating rain rates up to an inch per hour in the upslope areas. As this impulse moves east into LA County and farther away from the upper low Friday morning it will weaken but could still produce some isolated rain rates up to a quarter inch per hour. Light to occasionally moderate showers will continue across Ventura and LA Counties Friday afternoon into early Saturday morning before the second impulse arrives around daybreak Saturday, though there are still uncertainties with this second one. Will be considering a Flood watch issuance for Saturday for all areas south of Pt Conception this afternoon.
***From Previous Discussion***
POTENTIAL FOR SEVERAL INCHES OF RAIN ACROSS THE AREA WITH MAJOR IMPACTS MAINLY FRIDAY AND SATURDAY.
A large long wave pattern covers the CONUS with a huge ridge covering a width from NV to MO. A compact low is moving up the backside of the ridge, but will not be able to make much eastward progress and this will allow it to affect CA for the next 3 days with an emphasis on Srn CA on Friday and Saturday.
Today will not be that action packed as the system is still a ways off of the coast. Rain will likely develop across NW SLO county later this morning. Rain will overspread the entire Central Coast late this morning and during the afternoon as the front moves into the area. Rainfall amounts will mostly be under a quarter inch with the usual exception of the far NW tip of SLO county where .75" of rain could fall. The sfc gradient will increase over SLO and SBA counties as the front approaches. The winds will increase in kind and advisory level wind gusts will develop across much of the two county area. A Wind Advisory from 8 AM to 6 PM is in effect for south wind gusts up to 45 mph. The rest of the area will see partly cloudy skies turning mostly cloudy during the afternoon. Max temps will mostly be in the 60s up and down the csts and vlys.
Tonight through the predawn hours Saturday the low will move due south and will end up 250 miles to the SW of Pt Conception. At the same time a front that originates well to the north of the area and is separate from the upper low will push through the area. The entire area will get rain during this period. The strongest rain will occur over the Central Coast at this time. From late this evening through dawn the front and the heaviest rain will move across southern SBA county and
However, there are some solutions that place the upper low in a much less favorable location that results in quite a bit less rain. This is a less likely scenario than the one above but still possible. By Thursday there should be more clarity on the track of the low and at that point consideration will be given to any possible Flood watches. VTA county. It is during this period when the south flow ahead of the front will interact with the transverse ranges and produce the heaviest rain. Rain will move in to LA county around dawn and the entire morning commute will be wet. Mdls have consistently shown the front weakening as it moves over LA county and rainfall rates and amounts will likely end up not as strong as they were over srn SBA county and VTA county. Still the Malibu area could see a period of heavier rain right around sunrise. There will be a lull in the rainfall in the afternoon with even some dry periods (esp for the Central Coast) and much less in the way of rainfall rates. Peak Rainfall rates will be mostly around a half inch per hour except across the south facing slopes from Pt Conception to Ventura county where 1 inch per hour rates will be possible. There is also a slight chc of a TSTM with the threat mostly confined to the Central Coast. Rainfall totals for most of the csts and vlys will be around an inch (.5 to .75 inches for LA County) with the exceptions of NW SLO and the transverse range coast
However, there are some solutions that place the upper low in a much less favorable location that results in quite a bit less rain. This is a less likely scenario than the one above but still possible. By Thursday there should be more clarity on the track of the low and at that point consideration will be given to any possible Flood watches.
There is still some uncertainly in the Friday night Saturday forecast as it involves the trajectory of a cut off low. Ensemble forecasts and the short range hi rez mdls are currently favoring a trajectory (sweeping up to the NE and over LA/Orange counties) that will be favorable for another burst of moderate to heavy rain. This system will bring the heaviest rain to areas south of Point Conception. The key factor with this system will be its PWAT values which are a little over 1.5 inches as it picks up some sub tropical moisture. As mentioned there is less certainty with this system but it looks like it will deliver an additional 2 to 4 inches of rain with the peak occuring Saturday morning. Again rainfall rates would be in the half inch per hour with local one inch per hour amounts possible. Much less rain will fall across the Central Coast - a half inch to an inch.
With this in mind, residents, especially those in vulnerable areas, should start taking precautions immediately to prepare for the storm and protect their interests. This scenario would potentially create many significant impacts area-wide, including possible debris flows in the burn areas, significant ponding of roads and highways, mudslides through the canyons, fallen trees, etc.
Later today both systems will be well in the range of the hi rez short range weather mdls and ensembles. These will be analyzed and decisions will be made on the issuance of any needed Flood Watches.
(Sun-Wed), 12/1154 PM.
Both the EC and GFS while not in the greatest synoptic agreement show enough moisture and energy to keep a 30 to 40 percent chc of rain in the forecast through the period. Much of these pops are likely the result of ensemble smearing and there will be some dry periods as well as wet ones. PWs are much lower than during the Fri/Sat stormy period and additional rainfall amounts across the entire 4 day period will probably end up in the half inch to 1 inch range. That said this weather pattern has be so changeable would not be surprised if this period's actual weather turns out to be something else.
Good confidence that there will be little day to day changes in the temperatures. Max temps will mostly be in the lower to mid 60s across the csts/vlys which is 6 to 12 degrees blo normals.
13/1710z.
At 1645Z at KLAX, the marine layer depth was around 500 feet. The top of the inversion was near 2300 feet with a temperature around 17 degrees Celsius.
Overall, moderate confidence in 18Z TAF package. High confidence in rain impacting all sites through the period. However, low confidence in timing of rain, and associated CIG and VSBY restrictions, could be +/- 4 hours of current forecasts.
There is a 10-20% chance of thunderstorms from KSBA northward in the 21Z-12Z time frame. Any thunderstorms that develop will be capable of producing frequent lightning, brief heavy rain and gusty/erratic winds.
KLAX, Overall, moderate confidence in 18Z TAF. High confidence in rain developing through the period, but low confidence in timing of rain, and associated CIG and VSBY restrictions, could be +/- 4 hours of current forecasts. Winds will shift to an easterly direction after 03Z with high confidence in easterly winds above 8 knots in the 10Z-20Z time frame.
KBUR, Overall, moderate confidence in 18Z TAF. High confidence in rain developing through the period, but low confidence in timing of rain, and associated CIG and VSBY restrictions, could be +/- 4 hours of current forecasts.
13/910 AM.
High confidence in the forecast for impacts and moderate confidence for timing. A storm system will bring gusty winds, steep short period seas, and a slight chance of thunderstorms across the entire waters through at least Saturday morning. Any thunderstorms that develop will be capable of producing frequent lightning, gusty and erratic winds, locally rough seas and even waterspouts. These will be dangerous conditions for boaters, especially for the coastal waters along the Central Coast to the western Channel Islands with gale force winds, steep choppy waves, and seas in excess of 10 feet. Boaters are advised to remain in safe harbor.
Expecting Small Craft Advisory (SCA) conditions to become more widespread for the waters southwest to northwest of the Channel Islands including the nearshore Central Coast waters into this morning from northwest to southeast. Gale Force winds are expected for the waters adjacent to the Central Coast, including nearshore, from this morning through this afternoon. 20-30 knot winds will follow. Seas will build to hazardous levels (up to 15 feet) throughout today, then likely decrease to below 10 feet after Saturday morning.
Inside the California bight, winds and seas will remain below SCA levels through this morning, then winds will begin to increase this afternoon. SCA level south-southeast winds (20-30 knots) will be common through at least early Friday morning, but there is a moderate chance that SCA conditions (winds and seas) may linger into Friday evening. Ocean conditions are then expected to be relatively calm for the rest of the weekend.
13/109 AM.
A moderately long period west-northwest swell will bring hazardous surf conditions to portions of Southwest California late Thursday through at least Saturday morning. In addition to the west- northwest swell, a storm system will bring produce southerly winds which will add a southerly wind swell component to the surf. High Surf Advisories have been issued for the Central Coast and Ventura County beaches. Please refer to the CFWLOX and SRFLOX for details.
There is a chance for High Surf Advisories to be issued for Los Angeles County (50%) and Santa Barbara County (20%) for the late Thursday night to early Saturday morning period.
Ca, Wind Advisory in effect until 6 PM PST this evening for zones 340>348. (See LAXNPWLOX). High Surf Advisory in effect from midnight tonight to 9 AM PST Saturday for zones 340-346. (See LAXCFWLOX). Flood Watch in effect from late tonight through Friday morning for zones 349>352-376. (See LAXFFALOX). High Surf Advisory in effect from 3 AM Friday to 9 AM PST Saturday for zone 354. (See LAXCFWLOX). PZ, Gale Warning in effect until 4 PM PST this afternoon for zones 645-670-673. (See LAXMWWLOX). Small Craft Advisory in effect from 4 PM this afternoon to 3 PM PST Friday for zone 650. (See LAXMWWLOX). Small Craft Advisory in effect until 3 AM PST Saturday for zone 676. (See LAXMWWLOX).
