14/736 PM.
A significant heat wave will kick off on Sunday, peak next Tuesday and Wednesday, and then continue through Friday. MODERATE to HIGH heat impacts will occur each day Monday through Friday.
(Sat-Tue), 14/823 PM.
***UPDATE***
Good cooling occurred across the area today, with most locations seeing high temperatures around 5 to 10 degrees cooler than Friday. Valley highs dropped from the lower to mid 90s on Friday to the 80s today, with similar trends in coastal areas of Ventura and LA Counties. Along the Central Coast, temperatures lowered around 2 to 6 degrees, with some locations in Central San Luis Obispo County showing little change. Gusty northerly winds are affecting isolated areas, mainly over SW Santa Barbara County and in the I-5 Corridor, with mainly sub-advisory gusts.
For the overnight period, broken low clouds with patchy dense fog will affect portions of the LA Coast, with a small chance that the clouds will spread north to the Ventura Coast. Northerly winds will continue over the interior of Ventura and LA Counties, with northeast flow developing for the interior of the counties north of Pt. Conception.
Sunday will be the first day of an extended heat wave, with highs increasing anywhere from 3 to 12 degrees warmer in most locations. Much more significant warming is expected to begin on Tuesday under strongly increasing high pressure aloft combined with offshore flow at the surface.
***From Previous Discussion***
Forecast-wise for the short term, main story remains a historic heat event for the area. With the ridge building overhead and the increase in offshore gradients, temperatures will be on a dramatic upswing through the period. On Sunday, temperatures will climb into the 80s to lower 90s for most areas with the beaches in the mid to upper 70s. On Monday, temperatures will climb into the mid 80s to upper 90s then into upper 80s to 104 on Tuesday. At the same time, overnight lows will also exhibit a warming trend, especially across the coastal foothills. Depending on the strength of the offshore flow, temperatures on Monday and Tuesday could even be little bit warmer than currently forecast for areas west of the mountains. Given the associated heat risk, have decided to issue a HEAT ADVISORY on Monday for all coastal and coastal valley zones as well as the mountains. For Tuesday, have left these same areas as an EXTREME HEAT WATCH, but this will likely be upgraded tomorrow to warnings.
Other than the temperatures, no significant issues are expected. There will be some gusty northerly winds through tonight across the usual areas (I-5 Corridor and Santa Ynez Range), but any advisory-level winds are expected to remain localized. For Monday and Tuesday, the offshore gradients in the morning will generate some gusty northeasterly winds, but again, any advisory-level gusts are expected to remain localized.
As for clouds, other than some stratus/fog across the Bight and the LA county coast tonight/Sunday morning, skies should remain mostly clear through Tuesday.
(Wed-Sat), 14/1251 PM.
Overall, 12Z models remain in good synoptic agreement through the period. At upper levels, the high will slowly meander to the southeast through the period. Near the surface, models continue the trend of previous runs, the GFS forecasts weak diurnal gradients while the ECMWF has weak offshore gradients through the entire period.
Forecast-wise, nothing in the latest model guidance deviates from the expectation of a historic, long-duration, heat event for the area. The only uncertainty remains around the surface pressure gradients. If the ECMWF is correct with the persistent weak offshore flow, then temperatures will even be warmer than the currently forecast temperatures (which have many areas breaking daily and even monthly records). Essentially, just how extreme will the extreme heat be is the major question. For the forecast, have continued toeing the line between the NBMEXP and the 75th percentile NBM numbers both for the maximum and minimum temperatures. So with the afternoon forecast, will keep EXTREME HEAT WATCHES in effect through Friday for all coastal and coastal valley zones as well as the mountains. Most likely, these will be upgraded tomorrow.
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, latest deterministic and ensembles have changed tunes slightly, indicating some low chances of light showers after the 25th. However, models do not indicate any significant storms.
15/0120z.
At 0020Z at KLAX, there was no marine layer. There was a sfc- based inversion with a top up to 2000 ft and a temp of 22 deg C.
Low to moderate confidence in TAFs south of Point Conception, high confidence in all other TAFs. LIFR-VLIFR conds possible at KCMA (30%), KOXR (40%), and KSBA (30%) between 07Z-17Z Sun. For KSMO, KLAX, and KLGB, VLIFR- LIFR conds may scatter and reform frequently until arriving for the night around 06Z, then lift to IFR around 12-18Z.
KLAX, Low confidence in TAF through 06Z, then moderate confidence in TAF. 1/4sm FG VV002 are currently hugging the coast and may scatter and reform at the site multiple times before arriving for the night around 06Z. Conds may lift to 3SM BR BKN005-10 through the night. Good confidence that any east wind component will be below 7 kts.
KBUR, High confidence TAF.
14/755 PM.
Small Craft Advisory (SCA) level NW-N winds of 20-30 kt will continue across the Outer Waters through Sunday night. Gusts will reach GALE FORCE (35 kt) through tonight especially beyond 30 NM from Shore. Short- period seas will also peak near 10 ft across these waters through tonight. 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 today, with localized SCA wind gusts lingering into Sunday. Otherwise, conds will likely remain below advisory levels through Thursday.
Inside the Southern California Bight, conditions are expected to remain below SCA levels for the foreseeable future, except for marginal SCA winds this afternoon and evening focused across the western portion of the Santa Barbara Channel.
Ca, Heat Advisory remains in effect from 10 AM to 8 PM PDT Monday for zones 87-88-340>342-345>358-362-366>376-378>380-548. (See LAXNPWLOX). Extreme Heat Watch in effect from Monday evening through Friday evening for zones 87-88-340>342-345>358-362-366>376-378>380-548>550. (See LAXNPWLOX). PZ, Small Craft Advisory in effect until 3 AM PDT Sunday for zone 645. (See LAXMWWLOX). Small Craft Advisory in effect until 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).
