Synopsis

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.

Short Term

All signs still pointing towards a very hot week, especially south of Pt Conception. The combination of strong high pressure aloft, weakening onshore flow, and much warmer than normal ocean temperatures will create a long duration heat event, during which several daily records will likely be broken. The warmer than normal SST's will primarily impact the overnight temperatures, keeping those higher than normal and hindering any beneficial cooling. Heat advisories are in affect for most areas south of Pt Conception through Monday night with minimal changes in temperatures Monday over today. However, models have been consistent showing a 2-5 degree increase in highs Tuesday and Wednesday pushing some areas into the major heat risk category. The biggest factor determining which areas get upgraded to an Extreme Heat Warning will be the pressure gradients and will wait to see how those look with Monday's model runs. Currently there is a 30-40% chance of highs of 110 or higher in the San Fernando Valley and a 50% chance of highs of 100 or higher in Downtown LA.

For the Central Coast, the case for heat advisories is not as strong though by Tuesday or Wednesday low end advisories would likely be appropriate for inland coastal areas like Santa Maria and San Luis Obispo as well as the Salinas Valley.

Long Term

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 surface gradients. The EC is show a fairly strong offshore push which would bring near record very dangerous heat to the area. The the American global model 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 valleys, lower mtn elevations and far interior will have temperatures between 100 and 110 degrees during this period. If the EC verifies Vly temperatures could end up 2 to 3 degrees warmer than the current forecast. The interior cst sections (such as DTLA) have a 15 percent chance of high temperatures 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 temperatures in the upper 80s to mid 90s - there is a 10-20 percent chance 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 temperatures 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.