19/452 PM.
Mostly clear skies are expected through Saturday except for overnight to morning low clouds and fog near the coast. It will be cooler each day, but high temperatures will remain above normal. There will be increasing clouds, cooler temperatures and a slight chance of rain over San Luis Obispo county Sunday and Monday. A strong storm will bring many inches of rain to the entire area Tuesday through Wednesday.
(Fri-Mon), 19/812 PM.
***UPDATE***
Really not much to talk about for the update this evening. High temperatures today were in the 60s and 70s, with the warmest valleys in the high 70s to low 80s. Low clouds and fog have made a return to southeast LA county, and are expected to expand northward across the coasts, though a little less confident in the clouds making it into the Central Coast tonight since there are no low clouds over the nearby coastal waters.
A few degrees of cooling is expected for areas south of Point Conception tomorrow, as onshore flow slightly increases as well as a slight decrease in 500 mb heights. North of Point Conception, a few degrees of warming is expected. Overall, no change in the messaging with temperatures continuing above normal for this time of year.
Only slight adjustment of high temps for the Central Coast tomorrow, otherwise forecast is in shape and no other updates were needed this evening.
***From Previous Discussion***
Overall, 12Z models in good synoptic agreement through the short term period. At upper levels, zonal flow will prevail through Saturday then will tilt to the southwest Sunday/Monday as the AR begins to sag southward. Near the surface, weak onshore flow will prevail through Monday.
Forecast-wise for the short term, no significant issues are expected. With falling H5 heights and return of onshore flow, the marine layer stratus will increase in depth and coverage through the weekend, pushing into most coastal valley areas by Sunday and Monday. Outside of the marine layer stratus, there will be increasing mid/high level clouds through the weekend.
As the AR begins to sag southward, there will likely be some light precipitation developing across the Central Coast, beginning tonight and continuing through Monday. At this time, most, if any, of the precipitation looks to be over San Luis Obispo county. Rainfall totals will generally be around 0.10 inches or less. However, the northwest corner of the county (think Rocky Butte) could receive between 0.25 and 0.75 inches.
As for temperatures, the combination of increasing clouds, onshore flow, and lowering thicknesses will bring a cooling trend for all areas through the weekend.
Finally with respect to winds, no significant winds are anticipated. Northerly offshore gradients will continue across the area tonight, but will weaken. So, there will be some gusty north winds across the Santa Ynez Range through tonight, but expect any advisory-level winds to remain localized.
(Tue-Fri), 19/210 PM.
For the extended, 12Z models differ somewhat with details, but all generally have the same idea. A SIGNIFICANT winter storm will impact the area during the Christmas holiday as a Pineapple Express takes aim on the area.
As mentioned, models are still a bit out of phase with timing, so confidence in details is moderate at best (especially with respect to timing). However for current forecast, the peak of the AR associated rainfall looks to occur in the Tuesday evening through Christmas Eve night period. In this period, rain totals will generally range between 1 and 3 inches with up to around 5 inches across the mountains. Snow levels look to remain rather high, above 7500 feet, through Christmas Eve.
From Christmas Day through Friday evening, a secondary shot within the AR, as well as copious shower activity, will bring even more rainfall to the area. In this time period, additional rainfall totals will generally range between 1.00 and 2.50 inches with up to around 4.00 inches in the mountains. Snow levels will drop during this time period as colder air moves, dropping into the 6000 to 7000 foot range.
As for winds, strong and gusty southeasterly winds are likely, beginning Tuesday and continuing through Christmas Day. The peak winds look to occur on Christmas Eve. There is a good chance that many areas will have at least advisory-level winds with some mountain areas possibly getting warning-level gusts (especially the Santa Lucia Range).
Overall, next week looks to be a very soggy and impactful holiday week. Given the significant amount of rainfall, there will likely be widespread hydrologic issues, including potential for mud and debris flows and widespread urban flooding. Also, there could be some significant winter weather issues up in the mountains. So, if traveling on Christmas Eve or Christmas Day, be prepared for impactful weather. Stay tuned for the latest forecast information as the details of this pattern could change over the coming days.
20/0048z.
At 2322Z, the marine layer was about 600 feet deep. The inversion top was near 4800 feet with a temperature of 19 degrees C.
High confidence in VFR TAFs for KPMD and KWJF. Winds may gusts up to 10 kt higher than forecast.
Low to moderate confidence in the remaining TAFs due to reduced certainty in flight categories and timing. Lowest confidence in KSBA with a 40% chance of LIFR/VLIFR conds after 12Z. Also lower confidence KBUR and KVNY with a 30% chance that VFR conds prevail through the period. Otherwise, LIFR/VLIFR conds expected during the overnight period, and timing of flight category changes could be off by +/- 3 hours. N
KLAX, Moderate confidence in the 00Z TAF. IFR conds expected to reduce to LIFR/VLIFR but the flight cat changes may be off +/- 3 hours. 20% chance for vsbys under 1/2SM from 06Z-16Z. Moderate confidence that any east wind component will remain below 8 knots.
KBUR, High confidence in the 00Z TAF through 06Z, then low confidence through 18Z. If cigs arrive, 50% chance for vsbys less than 1/2SM. However, 30% chance VFR conds prevail.
19/719 PM.
Moderate to high confidence in winds and seas peaking this evening, then decreasing to relatively calm levels by Saturday evening through Monday across the entirety of the coastal waters.
On Tuesday, winds and seas will rapidly increase to dangerous levels, with widespread Gale Force Winds likely, including very strong Gales along the Central Coast. Winds will be from the SE-SW through Thursday, then there's a moderate chance for winds weakening and transitioning to NW-W 15-25 kts Friday.
A short to moderate period SE-SW swell will produce steep-choppy seas Tuesday through Thursday, transitioning to a longer period NW-W swell by Friday. Along the Central Coast and across the Outer Waters waves the most likely outcome are seas in the 10-16 foot range. South of Point Conception in the 6-12 foot range.
In addition to hazardous seas, rain will be continuous from Tuesday through Thursday, with chances continuing into next weekend.
Boaters should remain in safe harbor during this significant storm. Unprotected south facing harbors may be especially vulnerable to the south swell and winds.
19/200 PM.
A short to moderate period southerly wind swell will produce dangerous surf and strong rip currents from Tuesday through Thursday. A longer period NW swell will take over Friday, and surf will continue to be significant.
There is a range of outcomes, but the most likely scenario will yield max surf heights of 12-16 feet along the Central Coast, and 7-12 feet south of Point Conception. However, wave heights could be a couple feet larger Tuesday through Thursday as strong southerly winds will be occuring concurrently with the south swell.
While peak tides are not very high, minor to potentially moderate coastal flooding may occur, especially for south facing shores Tuesday through Thursday.
It is best to remain out of the water during this time.
Ca, NONE. PZ, Small Craft Advisory in effect until 9 AM PST Saturday for zones 673-676. (See LAXMWWLOX).
