Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000 FXUS66 KLOX 201756 AFDLOX Area Forecast Discussion National Weather Service Los Angeles/Oxnard CA 956 AM PST Mon Nov 20 2017 .SYNOPSIS...
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A ridge of high pressure building into the region and weak offshore flow will likely bring record heat to portions of southwest California sometime Tuesday Through Thanksgiving day. The ridge will gradually break down as a trough of low pressure approaches the West Coast, supporting a cooling trend heading into this weekend.
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&& .SHORT TERM...(TDY-WED) Plenty of high level clouds were moving into the forecast area this morning, with some mid level clouds also noted N of Point Conception. Filtered sunshine thru the high clouds will prevail today over much of the area, altho for SLO/SBA Counties, mostly cloudy skies at times cannot be ruled out. Fairly decent offshore gradients this morning (e.g., at 16Z -2.0 mb LAX-DAG, -2.8 mb LAX- BFL, and -3.6 mb SBA-BFL) was supporting locally gusty N winds over the Santa Ynez Mtns and L.A. County mtns. The winds are expected to continue into the afternoon, and may expand some over these areas, with gusty NW winds possible along the I-5 corridor by late today. Temps are forecast to be a bit warmer today and several degrees above normal, with highs in the warmest vlys and inland coastal areas expected to top out in the mid 70s to low 80s. Generally flat and dirty upper level ridging over the forecast area today, with 500 mb heights around 582-584 dm, will gradually build tonight thru Wed. By Wed afternoon, 500 mb heights will increase to 590-592 dm across the region. The mid and hi level moisture over the region will linger into tonight then clear out by early Tue for mostly clear skies Tue thru Wed. Northerly gradients will increase some thru tonight which will support gusty N canyon winds for the SBA County S coast and mtns, with some gusts to advisory levels possible. Gusty NW winds can also be expected in the L.A./VTU mtns along the I-5 corridor this evening, then transition to N to NE and expand S into the favored foothills and vlys of VTU/L.A. Counties later tonight into Tue morning. Locally gusty NE winds will be possible over these areas of VTU/L.A. Counties again Tue night into Wed morning. Otherwise, there will generally be weak offshore low level flow over swrn CA tonight thru Wed, especially during the night and morning hours. The rising 500 mb heights, warming boundary layer and 950 mb temps, and offshore flow, will all help to bring much warmer than normal temps to the forecast area Tue and Wed. Near record to record high temps will be possible for several climate stations, with temps on Wed increasing to 15 to 20 deg above normal for many areas. Temps in the warmest vlys and inland coastal areas should reach the mid 80s to low 90s on Tue, and low to mid 90s on Wed. Even overnight temps should be very mild in the breezy foothill and lower mtns Tue night and Wed night where lows in the low to mid 70s will be possible. ***FROM PREVIOUS DISCUSSION*** .LONG TERM...(THU-SUN) The upper high will begin to be forced eastward on Thanksgiving Day as a large trough moves into the eastern Pacific. However, latest computer models show the upper high remaining firmly entrenched across the region through Thu morning, and low level gradients remaining offshore. While there may be a few degrees of cooling, especially near the coast, it will likely be another very warm to hot day in most coastal and valley areas Thu, after a warm Wed night. Max temps could still reach or exceed 90 degrees on Thu, possibly even across interior sections of the coastal plain. The highest temperature ever recorded at downtown Los Angeles on Thanksgiving Day since 1877 (on which the date varies from year to year of course) was 90 degrees on November 26th, 1903. This record has the potential to be tied or broken this upcoming Thanksgiving day. The upper high will continue to be suppressed southward and will weaken on Fri as a large trough slowly approaches the West Coast. There will be several degrees of cooling across the entire region on Fri, but still, temps will be at least 10 degrees above normal in many areas. The cooling trend is expected to continue through the weekend as heights gradually fall and onshore flow increases, but temps will likely remain a bit above normal even through Sunday. Any rain with the approaching trough is likely to stay to the north of the region. && .AVIATION...
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20/1800Z. At 1722Z, there was a suggestion of a marine layer 400 feet deep with an inversion top of 1700 feet with a temperature of 19 degrees c. However, marine clouds are not expected through the period. High confidence in 18Z TAF package as weak offshore flow will keep all sites VFR through the period. KLAX...high confidence in 18Z TAF. KBUR...high confidence in 18Z TAF.
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&& .MARINE...20/900 AM... For the Outer Waters, moderate confidence in current forecast. A SCA has been issued for zones 673 and 676, although the winds are only expected to gust to about 25 knots through 05z this evening. Winds will stay below SCA speeds Tuesday and Wednesday. For Thursday and Friday, SCA level winds are likely. For the Inner Waters, good confidence in current forecast. For the waters north of Point Sal, winds and seas are expected to remain below SCA levels through Friday. For the waters south of Point Conception, winds and seas are expected to remain below SCA levels through Friday. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...NONE. PZ...Small Craft Advisory in effect until 9 PM PST this evening for zones 673-676. (See LAXMWWLOX). && .HAZARD POTENTIAL OUTLOOK...(WED-SUN) Hot and very dry conditions are expected Wednesday and Thursday, with warm and dry conditions Wednesday night. There will be gusty winds at times across portions of Los Angeles and Ventura Counties. There will likely be elevated fire danger across portions of Los Angeles and Ventura Counties during this time. && $$ PUBLIC...Sirard/DB AVIATION...Sweet MARINE...Sweet SYNOPSIS...Munroe weather.gov/losangeles

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