13/1138 PM.
It will be cooler today with onshore flow and some high clouds. A significant heat wave will kick off Sunday, peak next Tuesday and Wednesday and then continue through Friday. MODERATE to HIGH heat impacts will occur each day Monday through Friday.
(tdy-Mon), 14/848 AM.
***UPDATE***
Latest satellite and surface observations indicate mostly clear skies this morning some cirrus clouds drift overhead. Some stratus and fog is observed across the Bight, between Catalina Island and the OC coast. Current sounding data indicates a strong, surface- based inversion. Some northerly winds, gusting 20-30 MPH, are observed across the mountains.
Forecast-wise for the immediate short term, no significant issues are expected. Mostly sunny skies will remain through the day. As for temperatures, morning TEMP STUDY database indicates a cooler boundary layer and weak onshore gradients. So, today temperatures will drop generally 4-8 degrees from Friday's levels. Still above normal, but more comfortable than the last few days. As for winds, no advisory-level gusts are anticipated.
Overall, current forecast has great handle on the immediate short term. So, no significant updates are expected. For the afternoon forecast suite, attention remains on a extreme period of hot temperatures for the area next week.
***From Previous Discussion***
There will be one brief respite from the heat today. The upper level high will be flattened and hgts will drop down to 582 dam (down from 588 dam). More importantly There will be onshore flow to the east through the day with a peak value of 5 mb in the afternoon. This afternoon onshore push is about 4 mb strong than on Thursday. Offshore flow from the north will continue but it will only be half as strong as it way ydy. There will also be periods of high cloudiness which will also serve to mitigate temps some. All and all these items will combine to bring 4 to 8 locally 10 degrees of cooling to the area today. Max temps will end up in the mid 70s to lower 80s across the csts and in the lower to mid 80s in the vlys. Despite all of this cooling max temps will end up 8 to 12 degrees over normal.
Sunday will see the kick off of a rather remarkable heat wave. The upper high to the west of the state will begin to reassert itself. The onshore push to the east will reverse and become weakly offshore while the offshore push from the north will increase. The northerly offshore push may create some canyon winds but nothing worthy of an advisory. Most of the high clouds will be gone and skies will be mostly sunny. Max temps will rise 3 to 6 locally 8 degrees and the warmest vly locations will once again see max temps in the lower 90s. These temps will be close to advisory levels but will not quite reach them.
The heat wave kicks into gear on Monday. The upper high will approach the cst and hgts over Srn CA will rise to 588 dam (the average hgt for this time of year is 571 dam). Offshore flow will increase further and it looks like there will be 3 to 4 mb of offshore flow from both the N and E. This will generate NE winds but with only a little upper support it does not look like an advisory level event. The offshore flow and rising hgts will team up to bring 4 to 8 degrees of warming to the area. This will bring cstl temps into the mid 80s to lower 90s. The vlys will see max temps in the 90s. These very warm temps (20 to 25 degrees above normal) along with warming overnight lows will bring at a minimum HEAT ADVISORIES to most of the area. There is also a potential for more dangerous conditions to develop and for that reason an EXTREME HEAT WATCH has been issued for all of the csts/vlys.
(Tue-Fri), 14/242 AM.
The entire area remains on track for a historic March heat event. There is a near 100% chance of HEAT ADVISORIES for most areas in Tuesday through Friday. Additionally, the chances for extreme heat are growing, so EXTREME HEAT WATCHES have been issued from Tuesday through Friday for all coastal and coastal valley zones. The watches may need to be expanded into interior sections as well.
The upper high will reside over Srn CA Tuesday through Friday. Hgts will range from 592 to 594 dam. When the center of the upper high is overhead subsidence will bring synoptic scale compressional warming.
The biggest question mark for this event is the sfc gradients. There has been no change in the competing mdls with the GFS forecast period of onshore flow along with weaker offshore flow in the diurnal cycle. The EC is more offshore and in fact keeps the flow offshore in the afternoon when the onshore tendencies are the strongest. If the EC verifies the best both the highs and many of the lows will need an upward adjustment. Once again, here are the details that make this such an extreme event:
1. 500 MB heights are forecast to range between 590 and 594 DM which would be the highest March H5 heights since records began in 1948. The record is 591 dam which occurred on March 7 1997.
2. 1000-500 MB thickness are forecast to peak in the 580 to 583 DM range. Based on the 25+ year history of TEMP STUDY, the highest thicknesses recorded in March are 576 dam.
3. The Extreme Forecast Index (EFI) indicates values between 0.8 and 1.0 for both Maximum and Minimum temperatures, signifying a very usual or extreme event.
4. If the weak offshore flow, forecasted by the ECMWF, pans out then temperatures west of the mountains could be higher than currently forecast.
5. Based on current forecasts, both daily and monthly March temperatures records could fall for most climate sites.
6. Max temps during this period will be 20 to 30 degrees above normal.
7. For all 4 days (Tue-Fri) most cstl locations will see highs in the upper 80s and lower 90s. The vlys will see highs from 95 to 102. There will be plenty of 90s across the interior excluding the higher elevations.
With little change in the overall forecast,
Given the unprecedented length and magnitude of this extreme heat wave, heat stress will be a real threat each day, especially in areas that aren't used to the heat, like the coastal areas, where people may not have methods to cool off their homes. Try to complete outdoor activities early in the day or in the evening, and don't leave people or pets in cars.
As for any rain chances, deterministic and ensembles do not indicate any chances for significant rain through the 28th.
14/0947z.
At 0439Z at KLAX, there was no marine layer. There was a sfc based inversion with a top at 1200 ft and a temperature of 26 C.
High confidence in TAFs except for KLAX & KLGB where there is a 20% chance of LIFR ocig/vis 14Z-16Z.
KLAX, Good confidence in TAF with only a 20% chance of 1/2SM FG VV002 conds 14Z-16Z. Any east wind component will be below 7 kts.
KBUR, High confidence TAF.
13/1026 PM.
Small Craft Advisory (SCA) level NW-N winds of 20-30 kt are likely across the Outer Waters through Sunday night.Gusts will reach GALE FORCE (35 kt) at times especially beyond 30 NM from Shore. Short-period seas will also peak near 10 ft across these waters. Conditions are likely to improve early next week, with relatively small seas expected.
SCA level NW winds will affect the Inner Waters along the Central Coast especially during the afternoon and evening hours through Saturday, with localized SCA wind gusts lingering into Sunday.
Inside the Southern California Bight, conditions are expected to remain below SCA levels for the foreseeable future, except for marginial SCA winds Saturday afternoon and evening focused across the western portion of the Santa Barbara Channel.
Ca, Extreme Heat Watch in effect from Monday morning through Friday evening for zones 87-88-340>342-346>352-354>358-362-366>375-548>550. (See LAXNPWLOX). PZ, Small Craft Advisory in effect until 3 AM PDT Sunday for zone 645. (See LAXMWWLOX). Small Craft Advisory in effect from 3 PM this afternoon to 10 PM PDT this evening for zone 650. (See LAXMWWLOX). Gale Warning in effect until 3 AM PDT Sunday for zones 670-673-676. (See LAXMWWLOX).
