Swell Matrix

Area Forecast Discussion

National Weather Service San Diego CA

205 pm PDT Sun Sep 22 2019

Synopsis

A trough of low pressure will bring slightly cooler weather Monday, but it will still be quite warm. The trough will stall over northwest Mexico Tuesday and Wednesday, resulting in gusty offshore winds in the mountains and inland valleys. Wrap around moisture may bring a few showers to the mountains and deserts, mainly on Wednesday. It will turn cooler toward the end of the week as a large trough settles over the West.

Discussion

For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,

Today was a very warm day with highs west of the mountains in the 80s and 90s except within a mile of the coast. It would have been even warmer if not for a layer of high cirrus clouds that muted the suns heating. Tomorrow will be another warm day, just not quite as warm as today, with lower heights and somewhat stronger onshore flow in the afternoon ahead of a trough moving down the California interior. The exception will be the lower deserts where the highs tomorrow will be nearly the same as they were today.

The marine layer will remain shallow through Wednesday morning, and there may be areas of dense fog in the coastal zones or far western San Diego valleys the next three mornings.

The trough evolves into a closed low over the Lower Colorado River Valley Monday night before drifting into NW Mexico Tuesday. Remnant tropical moisture from Lorena surges into AZ tonight and will bring heavy rain to eastern neighbors Monday and Monday night. The western edge of deep moisture will clip eastern Imperial County and eastern Riverside County, and SPC has a risk of thunderstorms in these areas. At this time the chances for showers are small in the San Diego County deserts and the Coachella Valley as the rapidly digging shortwave forces most of the deep moisture east of the area.

The greatest impacts from this system will likely be the gusty offshore winds in the mountains and inland valleys on the backside of the low on Tuesday. Downslope flow on gusty northeast winds will send a dry, warm airmass into the Inland Empire for what will be a warm afternoon. Confidence is lower for potential wrap around moisture reach the mountains and deserts on Wednesday for possible showers.

On Thursday the upper low slowly fills and drifts east as a longwave trough begins settling over the western states. Most of its shortwave energy will stay to the north, but lower heights and stronger onshore pressure gradients will bring cooler weather and a deeper marine layer Friday and Saturday, perhaps deep enough for scattered light showers along and west of the mountains.

Aviation

222000z, Coast, SCT-BKN high clouds AOA 20000 ft MSL and unrestricted vis through this evening. Low clouds to redevelop after 06Z Monday with bases 900-1400 ft MSL, spreading up to 15 miles inland overnight. Scatter out expected around 16-17Z Monday.

Valleys/Mountains/Deserts, SCT-BKN high clouds AOA 20000 ft MSL and unrestricted vis through Monday.

.MARINE, No hazardous marine weather is expected through Thursday.

Marine

No hazardous marine weather is expected through Thursday.

Watches, Warnings, Advisories

Ca, NONE. PZ, NONE.

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