09/1136 PM.
A cooling trend is expected this week, with cooler than normal temperatures expected across much of the area by Tuesday. More robust marine layer cloud coverage is expected, expanding into most coastal valleys by midweek. There remains a low chance of mountain thunderstorms each afternoon through the week.
(tdy-Wed), 10/859 AM.
***UPDATE***
Forecast is on track with a gradual cooling trend continuing today. Many areas will remain within a few degrees of mid-August normals today, becoming widespread below normal by tomorrow. There remains a 10-15% for thunderstorms/showers to develop this afternoon over eastern LA County mountains and deserts as well as the northern Ventura County mountains, with some high resolution models showing development right along the LA County/San Bernardino County border in the Antelope Valley. Convection chances look a bit more promising tomorrow, so we will update those chances later today.
Lower confidence in terms of marine layer coverage due to mid and high clouds potentially disrupting the formation of the marine layer. However, a still very solid marine layer is still present everywhere except LA County, so we will continue to forecast marine layer clouds returning tonight to coastal areas and even some lower valleys.
***From Previous Discussion***
The ridge which has brought the state such warm temperatures will weaken during the short terms with hgts falling to near 590 dam on Wednesday. At the same time strong onshore flow will develop to both the north and east.
There should be a steady increase in the amount of morning low clouds. Today's low cloud pattern may, however, be disrupted by the mid level moisture/clouds moving overhead. Low clouds should make their way into some of the vlys Tuesday morning and many of the vlys on Wednesday. Clearing will be slower and slower and some beaches may not see any clearing on Tue and Wed afternoons.
Max temps will be the big talking point as the lowering hgts and strong onshore flow team up to lower max temps 2 to 5 degrees each day. Most max temps will dip to blo normal on Tuesday (With the exception of July 30 and 31 DTLA has been above average every day since July 13th). Wednesday's max temps in the vlys will mostly be in the 80s or about 6 degrees less than normal.
The strong onshore push to the east will bring near above advisory level wind gusts to the western Antelope Valley and foothills today with a 40 percent chc of advisory level gusts Tue and Wed.
SE flow over the area from the upper high to the east will still bring some monsoon moisture to the area each afternoon. PW's around 1.50" will continue through the 3 day period. High rez convection allowing mdls keep the convection to the east and south of the area, but still with the strong afternoon Sun and differential heating there is a 10-15 percent chc of afternoon convection over the SBA/VTA/LA mtns with the best chc over the eastern San Gabriels.
(Thu-Sun), 10/225 AM.
Weak troffing will set up over the state for late this week and over the weekend. Gradients will remain strong through Friday and the weaken over the weekend.
The night through morning low cloud regime should continue through Friday but will lessen over the weekend as the gradients relax. The lower hgts and strong onshore flow will allow for plenty of low clouds in the vlys as well as slow to no clearing at the beaches through Friday.
The onshore flow peaks on Thursday and this will likely generate low end wind advisories for the western Antelope Vly and its foothills.
Temperatures bottom out on Thursday and there will not be a single 90 degree reading in the vlys and the Antelope Vly will only see highs from 88 to 92. Max temps on Thursday will end up 5 to 10 degrees blo normal. Not much change slated for Friday. There will be slight warming over the weekend as the gradients relax.
PW's remain high enough Thursday to continue the small (5 to 15 percent) of mtn convection in the afternoon. The atmosphere really drys out overnight and this should end the convective chc for Friday through the weekend.
10/1801z.
At 17Z at KLAX, the marine layer was 800 feet deep. The top of the inversion was at 4800 feet with a temperature of 25 Celsius.
There is a chance of IFR/LIFR conditions tonight into Tuesday morning at KSBP (50%) KSMX (70%) KSBA (50%) KOXR (40%) KCMA (20%), and MVFR/IFR conditions at KLGB (20%), KLAX (40%), KSMO (30%).
There is a chance of -TSRA at KWJF KPMD this afternoon (10%) and on Tuesday (30%). All other sites have a 5% chance of of -TSRA on Tuesday
KLAX, High confidence in VFR through 23Z. Low confidence after that, with windows for BKN008-012 during 00-05Z and 10-16Z Tuesday. There is also a 5% chance of -TSRA on Tuesday. High confidence in minimal easterly winds.
KBUR, High confidence in VFR TAF with typical winds through Tuesday, with a 5% chance of -TSRA Tuesday.
10/845 AM.
High confidence that conditions will remain below Small Craft Advisory (SCA) across all of the southwestern California coastal waters through at least Friday night. Patches of dense fog are possible on the Central Coast each morning. There is also a 5-10% chance of a thunderstorm over the coastal waters Tuesday through Wednesday.
Ca, Coastal Flood Advisory in effect from 6 PM this evening to midnight PDT Wednesday night for zones 349-350-354-362-366. (See LAXCFWLOX). PZ, NONE.
