09/235 AM.
Much cooler conditions are expected today as a coastal eddy brings southeast flow to the area. The cooling trend will continue into Tuesday, with another warm up expected to start on Wednesday, lasting through at least Friday and possibly into next week.
(tdy-Wed), 09/921 AM.
***UPDATE***
No significant changes in forecast thoughts.
Temperature trends were 10 to 20 degrees cooler than this time yesterday for many coasts and coastal valleys this morning, on track with the advertised major cool down today. The strong southerly surge associated with this will probably lead to a slow to no clearing of low clouds and fog across the Central Coast with pockets of low clouds potentially developing across south facing foothills further south at times through the day.
The cool down will be brief as heat is still expected to build Wednesday and peak for coastal and coastal valley areas Thursday and Friday when we may need a Heat Advisory. We may be talking about heat for some time well into next week as a stubborn ridge will likely become anchored over the region.
***From Previous Discussion***
Today will be much less windy and much cooler than Sunday. A large 554 dam upper low is spinning well south of San Diego and is bringing some showers and isolated TSTMs to southern San Diego County. Further north it is bringing some easterly winds to southern LA county. There is a large mass of low clouds to the west of the Central Coast and some beaches there may have low clouds this morning. An eddy may bring some clouds to the LA south coast as well. The gradients will actually be onshore this morning and will turn moderately onshore in the afternoon. This will bring an earlier and stronger sea breeze to the area. Hgts will only be around 570 dam and this along with sea breeze will contribute to a 10 to 15 degree cooling trend across the csts and vlys. The lack of cool air advection from the San Joaquin Vly will allow for a couple degrees of warming across the far interior.
The onshore flow peaks on Tuesday along with a decent eddy. This should create a deep marine layer cloud deck that will cover the coasts and many of the vlys. Its likely that low clouds will also move over the interior of SLO county. Tuesday will be the coolest day of the next 7. Look for 3 to 5 degrees of additional cooling. This will bring max temps down to 60s and lower 70s across the csts and vlys. These max temps are a few degrees blo normal. The interior, however, will end up mostly in the lower 70s, which is 4 to 8 degrees over normal.
Just as fast as it cooled down it will warm up again on Wednesday. A large E pac high will set up and a ridge will extend into Srn CA. More importantly sfc high pressure will move back into the Great Basin and will set up another round of offshore flow (this time it will be more northerly). The offshore push should limit the marine layer clouds to only the LA south coast. It will also bring some northerly winds to the I-5 corridor and Santa Ynez range. Hgts will increase to about 582 dam and this increase along with the switch to offshore flow will bring 8 to 12 degrees of warming to the area (4 to 8 degrees for the far interior). Look for max temps in the 70s across the csts and lower to mid 80s in the vlys.
(Thu-Sun), 09/235 AM.
The warm up really kicks into gear on Thursday. Offshore flow peaks (about 2 mb from the east and 6 mb from the north). Hgts jump to 588 dam as the ridge strengthens. These two items under sunny skies will create 4 to 12 degrees of warming. Max temps will be in the mid and upper 70s at the beaches, the 80s across the rest of the csts, and upper 80s to lower 90s for the vlys. These max temps are 15 to 25 degrees over normal. There is a slight risk that the temps will be a tad warmer and will reach heat advisory levels. The strong north flow will bring gusty near advisory level winds to the I-5 corridor as well as the Santa Ynez Range and SBA south coast.
The offshore flow weakens some on Friday - enough to lower the morning offshore winds some, but not enough to affect temps, which will end up very close to Thrusday's very warm values.
Over the weekend the ridge will break down while the offshore flow from the north will weaken and the onshore push to the east will increase. Look for a couple of degrees of cooling each day with max temps remaining well above normal with moderate heat impacts potentially continuing through the weekend and even into next week away from the coast.
Both AI-EC and AI-GFS are dry through the 22nd of the month. The AI-GFS is dry on the 23rd but the AI-EC does bring rain to the area on the 23rd.
09/1747z.
At 1710Z, the marine layer depth was around 2800 feet deep at KLAX. The top of the marine inversion was near 4900 feet with a temperature around 10 degrees Celsius.
High to moderate confidence in VFR TAFs through this afternoon. Low confidence in min flight cats and timing of marine layer return. There is a 30% chance for VLIFR to LIFR conds at KPRB, KSBP, and KSMX once cigs arrive tonight. Otherwise, min flight cats may be off at one at any site. Arrival of cigs may be off +/- 4 hours.
Moderate confidence in winds, although there is a chance winds are 5-10 kt stronger at times as winds will rapidly shift to onshore later today.
KLAX, High confidence in VFR TAF through at least 00Z. Then high confidence in cigs returning tonight, but low confidence when (+/- 4 hours from TAF). There is a 50% chance for IFR conds when cigs are present. Any east wind component is expected to remain below 6-8 kt.
KBUR, High confidence in VFR TAF through at least 06Z. 30% chance for no cigs tonight. Timing of arrival may be off +/- 4 hours, and 40% chance for LIFR conds, 10% chance for VLIFR.
09/822 AM.
Inside the southern California bight, marginal SCA southeast to east winds will occur, especially from the San Pedro Channel into the Anacapa Passage and the Santa Barbara Channel through this afternoon. Then, winds and seas should remain below SCA level through the period, except for a moderate (30-40 percent) chance of SCA level west to northwest winds developing across the Santa Monica Bay and into the San Pedro Channel on Wednesday afternoon and evening.
For the waters southwest through northwest of the Channel Islands and the nearshore waters along the Central Coast, marginal SCA level winds will occur beyond 30 NM offshore of the Central Coast to around Point Conception and south to San Nicolas Island through early Thursday morning. More widespread SCA conditions will develop from each afternoon and evening with a moderate to high (30-50 percent) chance of affecting the nearshore waters along the Central Coast, highest Tuesday afternoon and evening.
Ca, NONE. PZ, Small Craft Advisory in effect until 3 PM PDT this afternoon for zones 650-655. (See LAXMWWLOX). Small Craft Advisory in effect until 3 AM PDT Thursday for zones 670-673. (See LAXMWWLOX). Small Craft Advisory in effect until 3 AM PDT Tuesday for zone 676. (See LAXMWWLOX).
