Swell Matrix

Area Forecast Discussion

National Weather Service Los Angeles/Oxnard Ca

511 am PDT Sat Oct 21 2017

Synopsis

Gusty northwest to north winds will affect much of the forecast area through this morning. The winds will shift to the northeast this afternoon with gusty Santa Ana winds persisting through Tuesday. Temperatures will be on the increase through early next week with record heat possible Monday and Tuesday. For Wednesday through Friday, a cooling trend is expected.

Short Term

(tdy-Mon)

Overall, 00Z models in very good synoptic agreement through the period. At upper levels, ridge will build over California through Monday. Near the surface, offshore gradients will strengthen through the period.

Forecast-wise, two main issues through the short term period will be temperatures and offshore winds. With respect to temperatures, all ingredients are in place for a significant round of heat for Southwestern California. H5 heights increase from 587 DM today to 594-595 DM by Monday with an associated increase in thicknesses. Near the surface, offshore gradients will be on the increase through Monday with the NAM forecasting a -5.9 mb LAX-DAG gradient Monday morning (while the GFS forecasts -4.0 mb). The combination of these parameters indicate an impressive warming trend from a few degrees above normal today to potentially widespread record high temperatures on Monday. Given the potential for record heat on Monday, Excessive Heat Watches will remain in effect for the south coast of Santa Barbara county as well as the coasts/valleys of Ventura and Los Angeles counties.

As for winds, currently there are some very gusty northerly winds across the Santa Ynez Range (in southern Santa Barbara county) as well as across the mountains of Ventura and Los Angeles counties and Wind Advisories will remain in effect for these areas through 10 AM this morning for southern SBA county and 200 PM for the Ventura/LA mountains. By this afternoon, the flow will turn northeasterly, setting the stage for an extended period of Santa Ana winds. At this time, all models indicate increasing offshore gradients and upper level wind support tonight through Monday. So, northeast winds will be on the increase across Ventura and Los Angeles counties. At this time, expect advisory-level winds to be localized tonight/Sunday, so will not issue or extend any advisories at this time. However for Sunday night/Monday, the likelihood of widespread advisory-level winds across Ventura and Los Angeles counties looks pretty good. For San Luis Obispo and Santa Barbara counties, the northeast winds tonight through Monday will be noticeably weaker.

As for clouds, there are some clouds this morning across interior sections of San Luis Obispo and Santa Barbara counties as well as the northern mountain slopes of Ventura and Los Angeles counties. These clouds will dissipate later this morning, then clear skies will prevail across the entire area this afternoon through Monday.

Long Term

(Tue-Fri)

For the extended, 00Z models remain in good synoptic agreement through Thurday then start to diverge on Friday. At upper levels, ridge peaks in strength on Tuesday then a deep trough will drop across the interior West Wednesday and Thursday. On Friday, the GFS starts to build a ridge in from the west while the ECMWF develops an upper low over the 4-Corners area. Near the surface, offshore gradients will peak on Tuesday then weaken Wednesday and Thursday, turning weakly onshore by Thursday. On Friday, the GFS continues with weak onshore gradients while the ECMWF indicates offshore gradients.

Forecast-wise, Tuesday will be a very hot and dry day with another round of record high temperatures likely for many areas with gusty Santa Ana winds across the area. So, the Excessive Heat Watch still looks good for Tuesday along with the high likelihood of wind advisories for Ventura and Los Angeles counties.

On Wednesday, a noticeable cooling trend will begin as the upper ridge weakens and weak onshore flow returns to the area. This cooling trend will continue on Thursday for all areas. For Friday, will go with near-persistence forecast for temperatures, given the model discrepancies at this time. Additionally, there could be some stratus redeveloping across the coastal plain by Friday morning (and maybe as early as Thursday morning).

Aviation

21/12z,

At 08z at KLAX, there was no notable marine inversion per AMDAR soundings. At 12z however there was a cloud deck near 1900 feet.

Overall, High confidence in the current TAFs. KLGB will have an MVFR CIG periodically through 20z and there is a thirty percent chance of the CIG impacting KLAX as well. Otherwise and elsewhere VFR conditions will prevail. Locally strong and gusty west to northwest winds continue to diminish across the region then gusty northwest winds strengthen after 15z at KSBP and KSMX.

KLAX, High confidence in the current TAF. There is a thirty percent chance of an MVFR CIG periodically impacting the terminal through 18z. Otherwise VFR conditions will prevail. There is a twenty percent chance of east winds to 10 knots 13z-16z and again 22/10z-17z.

KBUR, High confidence in the current TAF. VFR conditions will prevail throughout the forecast period.

Marine

21/200 AM,

For the Outer Waters, Winds will diminish today but remain at Small Craft Advisory (SCA) level through Monday.

For the Inner Waters north of Point Sal, Winds will diminish today but remain at SCA level through Sunday.

For the Inner Waters south of Point Conception, Winds will diminish to below SCA level by mid morning. The strongest winds will be across western sections and the western Santa Barbara Channel. From Sunday night through Tuesday, there is a sixty percent chance of SCA level northeasterly winds nearshore from Ventura southward.

A large long-period northwest swell will move through the coastal waters through the weekend. Seas up to 15 feet are likely across the outer and northern waters. There will be dangerous breaking waves on the Central Coast through the weekend with dangerous conditions in and near harbors. South of Point Conception, the westerly swell will contribute to continued hazardous conditions along the coastline through the weekend.

Beaches

21/200 AM,

A large long-period northwest swell will move through the coastal waters through the weekend.

North of Point Conception, A High Surf Advisory continues through Sunday morning. Surf will increase to between 14 and 20 feet through midday then will begin to diminish this afternoon but remain above 10 feet through Tuesday. Some impacts from these large and powerful waves and strong currents are the risk of ocean drowning and sneaker waves that can suddenly overrun previously dry beaches and jetties. With surf approaching 20 feet along some northwest facing beaches, low lying beach parking lots, harbor walkways and campgrounds could see local coastal flooding during the peak of the highest surf.

South of Point Conception, A Beach Hazards Statement continues through Sunday afternoon for surf of 4 to 7 feet with local sets to 8 feet. Dangerous rip currents are a primary impact of this elevated surf.

Watches, Warnings, Advisories

Ca, High Surf Advisory in effect until noon PDT Sunday for zones 34-35. (See LAXCFWLOX). Wind Advisory in effect until 10 AM PDT this morning for zones 39-52. (See LAXNPWLOX). Excessive Heat Watch in effect from Monday morning through Tuesday evening for zones 39>41-44>46-88-547. (See LAXNPWLOX). Beach Hazards Statement in effect through Sunday afternoon for zones 40-41. (See LAXCFWLOX). Wind Advisory in effect until 2 PM PDT this afternoon for zones 53-54. (See LAXNPWLOX). Fire Weather Watch in effect from Sunday morning through Tuesday afternoon for zones 240-241-244>246-547-548. (See LAXRFWLOX). Red Flag Warning in effect until 10 AM PDT Sunday for zone 252. (See LAXRFWLOX). Red Flag Warning in effect until 6 PM PDT Tuesday for zones 253-254-288. (See LAXRFWLOX). PZ, Small Craft Advisory for hazardous seas in effect until 3 PM PDT this afternoon for zone 645. (See LAXMWWLOX). Small Craft Advisory in effect until 3 PM PDT Monday for zones 670-673. (See LAXMWWLOX). Small Craft Advisory in effect until 9 AM PDT Monday for zone 676. (See LAXMWWLOX).

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