Swell Matrix

Area Forecast Discussion

National Weather Service San Diego CA

215 am PDT Sat Mar 28 2020

Synopsis

Fair and dry weather today will give way to increasing clouds and a chance for showers as a weak trough drops south over the West. Precipitation will be light, with the best chance over the mountains where snow is expected above 5500 feet. Some gusty westerly winds will develop over the mountains and deserts as well Sunday night. Fair, dry, and warmer weather develops on Monday and persists through much of the new week under northwest flow aloft.

Discussion

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

Other than some patchy low clouds along the coast, skies were clear over SoCal at 2 AM PDT. A veil of higher clouds in advance of a weak trough off the PacNW was visible approaching the Central Coast. Weak to moderate onshore sfc pressure gradients were in place over the region, keeping onshore flow and a moderately deep marine layer west of the mts.

Weak ridging aloft will quickly fade today, as yet another trough slides SE along the Coast, and across SoCal Sunday night. There appears to be sufficient moisture and lift for scattered showers to break out, with some enhancement over our mountains, where upslope flow will contribute. The westerly winds will become gusty over the ridges, desert slopes and deserts from Sunday evening through early Monday morning but likely remain just below Advisory criteria.

The trough will slide well east of the area on Monday, allowing a substantial increase in atmospheric heights/thickness and lighter winds. Some warming will be felt on Monday afternoon, but will it will be more noticeable on Tuesday, when afternoon temperatures will climb above average for the first time in a couple of weeks for many areas.

Weak ridging over the EastPac, and troughing over the lower 48, maintains a dry northwest flow aloft over CA most of next week. It should be a quiet period in an otherwise traditionally stormy part of the year. The marine layer will be challenged next week, until perhaps late in the week, when some weak troughing aloft redevelops over the West. This would support slightly better onshore flow. The model solutions seem more unstable beyond next week, with a number of cutoff systems and higher amplitude waves emerging over the EastPac.

Aviation

280900z, Coast/Valleys, FEW-SCT low clouds with bases 2500-3000 ft MSL will continue through 15Z. Some patches of BKN low clouds could impact the coast before daybreak, but low confidence in impacts to coastal TAF sites. Otherwise, high clouds at/above 20,000 ft MSL with unrestricted vis through today. Better chances for low clouds after 07Z Sunday, with bases around 2000-3000 ft MSL.

Mountains/Deserts, High clouds at/above 20,000 ft MSL with unrestricted vis through tonight.

Marine

No hazardous marine weather is expected through Sunday morning. Northwest winds will increase Sunday afternoon and evening, with gusts up to 25 kts possible, producing hazardous conditions for small craft. Winds will diminish by Monday morning.

Watches, Warnings, Advisories

Ca, NONE. PZ, NONE.

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