Swell Matrix

Area Forecast Discussion

National Weather Service Los Angeles/Oxnard Ca

917 am PST Fri Nov 16 2018

Synopsis

16/315 AM.

Weak offshore flow will keep dry and fairly warm weather across the region today. Onshore flow will return Saturday, bringing some cooling and a return of night through morning low clouds and fog to coastal and some valley areas. Temperatures will be near normal in most areas Sunday through Monday. Cooler weather is expected for Tuesday and Wednesday. A couple of upper level troughs moving into the West Coast could bring some rain to portions of the region late Wednesday into Thanksgiving Day.

Short Term

(tdy-Sun), 16/916 AM.

Lots of high clouds moving in today but not much stratus developed. Gradients are still trending onshore and the LAX profiler shows 3-5 degrees of cooling below 2000' so all signs pointing towards a cooler day despite the lack of stratus. Latest obs already trending cooler so forecast looks in good shape. Same for the weekend forecast so likely few changes if any with the afternoon update. Long range still a mess but more ensemble members now supporting some light rain for next Wed and Fri despite the operational GFS being dry.

***From previous discussion***

Heights and thicknesses will lower across the region tonight and Saturday as a weak trough drifts into the region. Pressure gradients will become increasingly onshore, from west to east and also from south to north. Models show somewhat of a southerly surge across the coastal waters tonight and Sat morning, and show low level moisture increasing in coastal and some valley areas. Expect low clouds and fog to push into coastal sections south of Pt. Conception tonight, and, at least initially, the fog may be dense in some areas. Southerly flow should help push clouds around Pt. Conception and into the Central Coast, and possibly into the San Gabriel Valley. After low clouds dissipate on Sat, there should be enough high clouds to make for a partly cloudy day. Max temps should be down a few degrees in most areas.

An upper ridge will push into the West Coast Sat night and Sunday, causing heights to rise again. Low level gradients will turn offshore again by Sun morning. Do not expect much in the way of wind, but it may reduce any low cloud coverage Sat night/Sun morning, and allow for a few degrees of warming in many areas Sun.

Long Term

(Mon-Thu), 16/403 AM.

The upper pattern is forecast to undergo fairly rapid changes next week, with timing differences between models. This is leading to below normal confidence in the forecast for much of next week.

It looks as though the upper ridge will hold across the region Sun night and early Mon and gradients will remain offshore. An upper low will race toward the region Mon afternoon passing to the south of the area Mon night, then moving into Arizona on Tue. Models show surprisingly little moisture from this system across the region, with mainly some mid and high level clouds Mon through Tue. The low cloud pattern will be tricky to forecast, and may be totally wiped out by this fast moving system. Still, lowering heights should bring a bit of cooling across northern areas for Mon, with little change elsewhere. Minor changes in max temps are expected for Tue, except there may be some warming in northern areas due to height rises.

A stronger upper trough will move across the eastern Pacific and into the West Coast Wed through Thu. The EC is sharper and faster with this system, bringing the trough axis through the region Wed night. The 06Z GFS shows a broader trough, with the trough axis remaining well off the coast through Thu. This is different from the 00Z run which was more similar to the EC. Have introduced slight chance to chance pops to much of SLO and SBA Counties for late Wed through Thu morning, with a slight chance extending into VTU County and much of L.A. County Wed night and early Thu. As mentioned, confidence is below normal, and the GFS maintains dry weather through Thu, but there is at least a slight chance of rain across the region during that time. Lowering heights and thicknesses and increased cloudiness should knock several degrees off max temps Wed, with temps down to normal or slightly below normal levels.

Aviation

16/1140z.

At 0831Z, there was a surface based inversion at KLAX. The top of the inversion was around 800 feet with a temperature of 20C.

N of Point Conception, Expect VFR conditions for most areas over the next 24-hours. Except for VLIFR/LIFR cigs at KSMX after 08z. There will be a 40% chance that similar cigs could develop at KSBP after 10z. Not expecting CIGs to develop at KPRB.

S of Point Conception, Moderate confidence with 12z TAFs with LIFR/IFR cigs possible for coastal TAFs for L.A. County. There will be a 40% chance for LIFR/IFR cigs to develop at KOXR after 10z. 10% chance for CIGS to develop across valley TAF sites tonight into Saturday morning.

KLAX, High confidence in the 12Z TAF with VFR conds thru 08z then moderate confidence for LIFR/IFR CIGs through 15z. There is a 30% chance that cigs could develop and scour out +/- 2 hours from current TAF. There is a 10% percent chance of VLIFR to LIFR conditions between 11Z and 15Z. Any east winds will likely remain less than 7 knots.

KBUR, High confidence in the 12Z TAF with VFR conds thru the pd.

Marine

16/901 AM.

High confidence in winds staying below Small Craft Advisory (SCA) through Tuesday. Patchy dense fog will be possible anywhere through Saturday.

Watches, Warnings, Advisories

Ca, NONE. PZ, NONE.

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