23/851 AM.
Very hot temperatures are expected this week with highs 6-12 degrees above normal. Patchy night through morning low clouds and fog will be confined to coastal areas, mainly north of Point Conception.
(tdy-Tue), 23/918 AM.
***UPDATE***
This will be the hottest week of the summer so far with highs 6-12 degrees above normal and likely some daily temperature records. In addition, overnight temperatures will be warming as well and many areas are set to break record high minimum temperatures this week. Heat advisories begin today for areas south of Pt Conception. Some, though likely not all areas will be upgraded to Excessive Heat Warnings Tuesday. Will have to see how the gradients respond the next couple days to determine the extent of the Warning coverage. The case for heat advisories north of Pt Conception is not as strong but will probably need some targeted advisories starting Tuesday across the inland coastal areas that are more heavily populated with less access to cooling sources.
***From Previous Discussion***
The theme of the short and long term will be heat.
A 597 dam upper high centered over NM will sit in place through Tuesday. Hgt will be near 592 dam today and Monday but will rise to 594 dam on Tuesday. At the sfc there will be near neutral flow in the W/E direction in the morning turning more onshore in the afternoon. There will be weak offshore flow from the north in the mornings turning weakly onshore in the afternoon. On Tuesday the offshore flow from the north will be stronger and the onshore push in the afternoon will be weaker.
Max temps today and Monday will be similar and 5 to 10 degrees above normal in most places. Max temps in the vlys, lower mtn elevations and far interior will range from 98 to 108 degrees with the warmest readings in the western San Fernando Vly. The increase in hgts and decrease in the afternoon's onshore flow will bring 2 to 4 degrees of warming to almost all areas on Tuesday. Triple digit heat will affect all areas away from the csts. The interior of the LA coast will see max temps in the mid and upper 90s.
Heat Advisories will go into effect this morning for LA and Ventura Counties except for the higher mountains of Ventura and the Antelope Valley. The Advisory also covers the Santa Barbara Mountains and Cuyama Valley, and the South Coast. These advisories last until 10 AM Tuesday. Following that, there is an Extreme Heat Watch in effect for the same areas, through Friday evening. At this time it is very likely (80 percent confidence) that the watches will be converted into Extreme Heat Warnings.
The fairly light gradients will not create too much in the way of gusty winds. The only exception will be the western SBA south coast where Sundowners will likely occur each evening. Gusts in these areas will generally peak at 25 to 35 mph, although with isolated stronger gusts near Gaviota and Refugio.
Skies through the period will be mostly clear. With limited onshore or even weak offshore flow and no eddy low clouds will be absent or very limited south of Pt Conception. Better onshore flow will likely bring some morning low clouds to western SBA county each overnight and morning.
(Wed-Sat), 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.
23/1615z.
At 1600Z at KLAX, the marine layer was 500 feet deep. The top of the inversion was at 2700 feet with a temperature of 28 degrees Celsius.
For 18Z TAF package, high confidence in KPRB, KSBA, KOXR, KCMA, KSMO, KWJF and KPMD.
For KSBP, there is a 50% chance that CIG/VSBY restrictions do not develop tonight. For KSMX, timing of flight category changes could be +/- 2 hours of current forecast.
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 10-20% chance of LIFR/IFR conditions 08Z-17Z. No significant easterly wind component is expected.
KBUR, High confidence in 18Z TAF.
23/738 AM.
For the Outer Waters, moderate to high confidence in current forecast. Today through Monday night, high confidence in Small Craft Advisory (SCA) winds. For Tuesday through Thursday, there is a 60-80% chance of SCA level winds continuing with seas approaching SCA levels.
For the Inner Waters north of Point Sal, moderate confidence in current forecast. Today through Monday, there is a 30-40% chance of SCA level winds in the afternoon and evening hours. For Tuesday through Thursday, there is a 40-60% chance of SCA level winds in the afternoon and evening hours.
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 Thursday. The only exception will be the western half of the Santa Barbara Channel where there is a 30% chance of SCA level winds today through Monday in the late afternoon and evening hours, then a 50-60% chance of SCA level winds Tuesday through Thursday 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 11 PM PDT this evening for zone 670. (See LAXMWWLOX). Small Craft Advisory in effect until 4 AM PDT Tuesday for zones 673-676. (See LAXMWWLOX).
