Swell Matrix

Area Forecast Discussion

National Weather Service Los Angeles/Oxnard Ca

914 am PST Tue Feb 19 2019

Synopsis

19/808 AM.

It will be cold through the week with early morning temperatures near freezing in many locations. There is a chance of light rain and mountain snow Wednesday through Thursday, but otherwise conditions will be dry.

Short Term

(tdy-Thu), 19/913 AM.

***UPDATE***

Downtown LA was about ten degrees cooler than the seasonal average this morning under clear skies and light winds. Clouds will start to return late tonight but LA lows will be in the 40s for the rest of the week. No impactful changes to the short term forecast expected

***From Previous Discussion***

Dry north flow will bring sunny skies to the area today. The clear skies, light winds and a cool (554 DM) airmass is making for a very cold start to the morning with most areas away from LA urban heat island will wake up to temps in the 30s or colder. Max temps today, while warmer than ydy, will still struggle to reach 60 degrees.

It will be a touch warmer tonight but the coastal vlys will likely need another round of frost advisories.

Wednesday will start off partly cloudy but clouds will soon increase as the next system arrives. A weak impulse will drop down and move through the state. It will bring a chc of showers to areas north of Pt Conception in the morning and to SLO/SBA/VTA county during the afternoon. Snow levels will range from 3000 to 3500 feet. There will be little in the way rainfall or snow fall since the very cold air cannot hold that much moisture and it will entrain no extra moisture. Max temps will continue to be 12 to 15 degrees blo normal.

The shower activity will continue Wednesday night as weak PVA moves through the cold and unstable air. Snow levels will fall to 3000 feet and perhaps down to 2500 feet. There will be some snow on all mtn roads. The only saving grace will be that there will not be that much snowfall.

Thursday looks to be the interesting day. A very cold upper low that was spawned from the Canadian interior will move into the state from NV (its overland route means that the airmass will not be modified by the relatively warm ocean waters) By afternoon the upper low will be over Bishop and 534 DM hgts will be over LAX with 500 mb temps of -35 degrees Celsius. These cold temps aloft along with the weak PVA associated with the upper low will keep the shower threat going through the day. By afternoon the very cold air aloft will destabilize the atmosphere enough to allow for a slight chc of TSTM development. Snow levels could fall as low as 1500 feet and will generally be near 2500 feet. Snow could fall almost anywhere except for the coast. Again this will be a dry system so it will not produce much in the way of snowfall or rainfall totals. It will be yet another day where the coasts and vlys will only see max temps in the mid 50s.

Long Term

(Fri-Mon), 19/332 AM.

A little ridge will pop up on Friday. It will be a sunny day but still cool with max temps still in the 50s.

On Sunday and continuing through Tuesday a cold stationary upper low spinning Alberta Canada will extend its flow over the western US. It will push the ridge away and bring cool dry NW flow to Californian. Skies will be either mostly clear or partly cloudy. Max temps will warm some but will still be 5 to 10 degrees blo normal through the period.

Aviation

19/1712z.

At 18Z at KLAX, there was no marine layer nor was there a sfc based inversion.

High confidence in CAVU TAFs. North winds will create turbulence over and near the mtns.

KLAX, High confidence in the 18Z CAVU TAF. There is a 20 percent chance of local north cross winds of 10 to 15 kt through 20z.

KBUR, High confidence in the 18Z CAVU TAF. There is a 20 percent chance of north winds through 20z.

Marine

19/908 AM.

For the outer waters, moderate to high confidence in the forecast. SCA level seas will continue today. Winds may drop below SCA levels this morning, but should increase to SCA level again in the afternoon. Then, SCA level winds and seas are likely through Thu night, with seas possibly staying above SCA levels into Fri. SCA level winds are expected across the southern outer waters Fri afternoon and evening. There is a 30-40% chance of gale force winds Wed afternoon thru Thu evening.

Across the northern inner waters, moderate confidence in the forecast. There is a 20-30% chance of SCA level winds this afternoon and evening. SCA conds are expected Wed afternoon through Thu evening. Winds may drop below SCA levels late Wed night/Thu morning but seas will likely remain at or above SCA levels. There is a 20-30% chance of SCA level winds Fri.

For the SBA Channel and southern inner waters zone (PZZ650, PZZ655), moderate to high confidence in the forecast. SCA level conds are not expected through Wed morning. SCA level winds are likely Wed afternoon through Thu evening. There is a 20-30% chance of gale force winds gusts Wed evening, and during the afternoon and evening hours Thu, mainly across western sections.

Watches, Warnings, Advisories

Ca, NONE. PZ, Small Craft Advisory in effect until 3 AM PST Friday for zones 670-673-676. (See LAXMWWLOX).

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