23/758 PM.
Very hot conditions will dominate the week, with a high risk for heat illness. Patchy night through morning low clouds and locally dense fog will be confined to coastal areas, mainly north of Point Conception.
(Sun-Wed), 23/818 PM.
A large dome of high pressure aloft, affecting the southern half of the United States, will dominate the week ahead. The core of the high is currently centered over New Mexico and Texas, and will change little through Monday, but then start to shift to the west on Tuesday. By Thursday, the core of the high will be centered over Arizona, right on our doorstep. Meanwhile, Onshore flow will weaken a little and the low-level prevailing flow will become more northerly. These two ingredients will bring even hotter conditions that what we saw over the weekend, with the noticeable jump happening on Tuesday or Wednesday. All areas 5-10 miles inland of the beaches will likely see high temperatures in the 100-110 range by Tuesday or Wednesday, with little change through Friday or Saturday. The northerly shift in the flow means that the hottest conditions will not be in the desert, but in the coastal valleys. Expecting several calendar day records to fall. Overnight conditions will be warm as well. The magnitude of the daytime temperatures, the limited relief overnight, and the prolonged nature of this heat event raises the bar to the high level in terms of the risk for heat-related illness. The current suite of Heat Advisories and Extreme Heat Watches looks good. Expecting most of the areas, especially inland of the beaches, to be upgraded to Extreme Heat Warnings by tomorrow or Tuesday, with most of the rest of the area not covered (SLO and northern Santa Barbara Counties) being added to the part with either Advisories or Warnings.
Sundowner winds will affect southern Santa Barbara County through the week, and should increase some each night. Wind Advisories might be needed by Tuesday.
The shallow marine layer will likely keep low clouds and dense fog on the Central Coast through Tuesday, but developing offshore flow may either keep it off the coast after that or complete scour it out. If that happens, expect temperatures to increase above current projections (although they have been upped to better account for this possibility). How the marine layer will behave over Los Angeles and Ventura Counties is anyones guess at this point. There are indications of a coastal eddy forming by Tuesday, which increases the odds of some shallow low clouds at the coast, but it is a really tough call.
(Thu-Sun), 23/300 AM.
The only real question for the Wed through Fri forecast is: will it be very hot or extremely hot. This forceast problem is driven by a wide range of possibilities with the sfc gradients. The EC is show a fairly strong offshore push which would bring near record very dangerous heat to the area. The GFS keeps the E/W gradient onshore but even it has some offshore flow forecast from the north (just much less than the EC does). The upper high moves a little to the west but hgts really do not change much and should remain around 594 dam through the period.
Almost all of the vlys, lower mtn elevations and far interior will have temps between 100 and 110 degrees during this period. If the EC verifies Vly temps could end up 2 to 3 degrees warmer than the current forecast. The interior cst sections (such as DTLA) have a 15 percent chc of high temps of 100 to 103 degrees. The Central Coast will not be immune from the heat this time around. Offshore trends will lead to an 8 to 12 degree warm up on Wednesday leading to max temps in the upper 80s to mid 90s - there is a 10-20 percent chc that SLO could see 100 degrees.
In addition to the daytime highs overnight lows will be 8 to 12 degrees above normal and this will greatly exacerbate the heat risk as there will be no time for people's body to release the heat stress.
It is very likely that almost the entire forecast area will be blanketed by some combination of heat advisories and Extreme Heat Warnings starting Wednesday.
One additional local concern will be very hot sundowners across southern SBA county. A decent N to S gradient will set up over the county each evening and gusty north canyon winds will develop. These hot winds could drive max temps into the 100-105 degree range and could also keep temperatures in the 80s until almost dawn.
Some cooling is forecast on Saturday, but in the past these heat waves have held on a little longer than forecast.
24/0025z.
At 2327Z at KLAX, the marine layer was 500 feet deep. The top of the inversion was at 2500 feet with a temperature of 30 degrees Celsius.
For the 00Z TAF package, high confidence in KPRB, KSBA, KOXR, KCMA, KSMO, KWJF and KPMD.
For KSBP, there is a 40-50% chance that CIG/VSBY restrictions do not develop tonight. For KSMX, timing of flight category changes could be +/- 2 hours of current forecast, with a 20% chance of brief or no CIGs forming.
For KLAX and KLGB, there is a 10-20% chance of LIFR/IFR conditions 08Z-17Z.
KLAX, Overall, good confidence in 18Z TAF. There is a 20% chance of LIFR/IFR conditions 08Z-17Z. No significant easterly wind component is expected.
KBUR, High confidence in the 00Z TAF.
23/806 PM.
For the Outer Waters, high confidence in current forecast. Tonight through Friday, Small Craft Advisory (SCA) winds are expected to continue although the winds will drop briefly across PZZ670 tonight and Monday. Short period SCA level seas (5 to 7 feet at 6-8 seconds) will continue along with the gusty winds. Wednesday into Thursday, larger seas approaching 7-9 feet are likely.
For the Inner Waters north of Point Sal, moderate to high confidence in current forecast. Tonight through Monday night, high confidence in winds and seas remaining below SCA levels. For Tuesday through Friday, there is a 50-70% chance of SCA level winds each afternoon and evening.
For the Inner Waters south of Point Conception, moderate to high confidence in current forecast. For a majority of the southern Inner Waters, high confidence in winds and seas remaining below SCA levels through Friday. The only exception will be the western half of the Santa Barbara Channel where there is a 60-80% chance of SCA level winds Monday through Friday, mainly in the late afternoon and evening hours.
Ca, Heat Advisory in effect until 10 AM PDT Tuesday for zones 38-87-88-349>358-362-366>376-378>380-548. (See LAXNPWLOX). Extreme Heat Watch in effect from Tuesday morning through Friday evening for zones 38-87-88-349>358-362-366>376-378>383-548. (See LAXNPWLOX). PZ, Small Craft Advisory in effect until 4 AM PDT Tuesday for zones 673-676. (See LAXMWWLOX).
