09/836 AM.
A cooling trend will begin today and continue through the weekend. A couple storms will move through the area late Friday through Monday with showers and thunderstorms possible, especially Sunday.
(tdy-Sat), 09/853 AM.
***UPDATE***
An upper low is approaching northern California this morning which will be followed by an even colder upper low late Saturday into Sunday. For the short term the main impacts locally will be cooler temperatures as onshore flow returns as well as increasing morning low clouds and fog. As mentioned below, the first system for late Friday into Saturday will have minimal impact as the upper low remains mostly over northern California. A few showers but amounts from a trace of rain to around a quarter inch, highest north of Pt Conception.
The second system for late Saturday into Sunday will be the stronger of the two and with the potential for heavy showers and severe storms, especially north of Pt Conception.
***From Previous Discussion***
A series of late season storms is still on track to affect the state Friday into the weekend. There is now a broad consensus that the 1st storm will pull up to the north and will not bring as much moisture and dynamics to the area as once thought. A weak front will likely bring rain to SLO and most of SBA county on Friday with just a chc of afternoon rain over VTA county. LA county will likely be dry during the morning and afternoon hours. SLO county will see the bulk of the weather action, since they will be closest to the upper low. There is just enough dynamics and instability there to warrant a slight chc of TSTMs. Rainfall north of Pt Conception looks like it will be around a tenth of an inch with up to a half inch over the far NW corner of SLO county and anywhere a TSTM forms. A trace to a tenth of an inch is possible across the SBA south coast and VTA county. Clouds, rain and falling hgts will all contribute to a 3 to 6 locally 8 degree cooling trend.
The weak front will move through the entire area Friday night into Saturday morning. Most areas will see a 40 to 50 percent chc of rain during this time. Rainfall amounts will not be too much at all mostly around a tenth of an inch.
Right now it looks like Saturday will mostly be between storms. A cold 535 dam system will work its way down the coast during the day. During the morning there is about a 40 percent chc that rain from this system will reach the Central Coast. A slight chc of rain from the outgoing system will linger over SE LA county. Rain will likely (70 percent chc) develop over SLO county in the afternoon with a 50 to 60 percent chc for western SBA county. There is a chc (30 to 40 percent) that rain will reach the rest of SBA county and VTA county. Rainfall amounts during this time are not looking impressive. Except for nrn SLO county most areas will not see more than a tenth of an inch of rain during the day. Nrn SLO county could see a quarter to a third of an inch. Another 3 to 6 degrees of cooling will bring all cst/vly temps into the 60s or 4 to 8 degrees blo normal.
(Sun-Wed), 09/220 AM.
On Saturday night a colder and more vigorous upper low will move into nrn CA. It will bring a wetter and much more dynamic front into the area. There is a greater than 80 percent chc that all areas will see rain overnight. The front will likely produce a number of TSTMs. It will have at least advisory level southerly winds in the mtns and interior vlys and perhaps over the Central Coast as well. The south winds will bring enhanced precip totals and rates to the transverse ranges. Any TSTM that forms will also bring enhanced precip totals and rates to areas they pass over.
At this point it looks like the flatter portions of the csts and vlys will see a half to three quarters of an inch of rain overnight with inch plus amounts on the across the foothills and coastal slopes and any area affected by TSTMs. Most rainfall rates will be between 0.25 to 0.75 in/hr but higher rates will be possible under any TSTM that develops.
Snow levels will fall to about 5500 ft and accumulating snow will fall above 6000 ft.
These rainfall and snowfall numbers are still preliminary and are still subject to change. The most likely factor that would change the numbers are the speed of the front (slower = more rain / faster = less rain) and the trajectory of the parent upper low. Still confidence in this forecast is higher than it has been.
The main front will exit LA county sometime between dawn and mid morning on Sunday. There will be some shower activity behind the front but additional rainfall amounts will not amount to much. It will feel more like a rainy January day with max temps only in the lower to mid 60s.
There is a 20 to 30 percent chc of lingering showers Sunday night and a low by non zero chc Monday morning. These showers should just be stray nuisance showers. By mid morning Monday dry NW flow will set up over the area. Sunnier skies and rising hgts will bring 2 to 4 locally 6 degrees of warming to the area. Max temps, however, will be 8 to 12 degrees blo normal.
Tue and Wed will see a nice warming trend as the cold air moves out of the area and high April Sun angle combine to bring 4 to 8 degrees of warming Tuesday and 2 to 4 additional degrees on Wednesday. Wednesday's highs across the csts and vlys will almost all be in the 70s.
09/1800z.
At 1654Z at KLAX, the marine layer was 1600 ft deep. The top of the inversion was at 2000 ft with a temperature of 17 C.
Overall, moderate confidence in 18Z TAF Package. Timing of flight cat changes may be off +/- 2 hours and cig hgts by +/- 300 ft. PROB30 -SHRA chances after 10/14Z for KPRB, KSBP, and KSMX.
KLAX, Moderate confidence in TAF. Low clouds could arrive as early as 09Z or as late at 13Z. Cigs could range between 008 and 015. No significant east wind component expected.
KBUR, Moderate confidence in TAF. There is a 40% chc MVFR CIGs (015) do NOT develop (remaining FEW-SCT) after 10/09Z.
09/808 AM.
Current Small Craft Advisories are on track. Refer to MWWLOX and CWFLOX for more details.
A weak Cold Front will move across the coastal waters Friday into Saturday morning bringing showers and a slight chance for a thunderstorm north of Point Conception.
A second system will arrive later on Saturday into Sunday with a more traditional cold front. This stronger front will bring numerous showers and a slight chance for thunderstorms across all waters. Potential hazards include: heavy downpours, dangerous cloud to ocean lightning, small hail, and erratic gusty winds. Boaters, especially those with small vessels should avoid these conditions.
Ca, NONE. PZ, Small Craft Advisory in effect until 11 PM PDT this evening for zone 650. (See LAXMWWLOX).
