Swell Matrix

Area Forecast Discussion

National Weather Service San Diego CA

347 am PDT Tue jul 17 2018


Monsoonal moisture will increase into Wednesday as an easterly wave moves westward across Southern California tonight and Wednesday. This will bring chances for showers and thunderstorms, greatest for the mountains, deserts, and inland valleys for Wednesday and Thursday afternoon and early evening with lesser chances at other times and west of the mountains. Drying and a little warming is expected for Friday through the weekend with greater warming possible for early next week as high pressure aloft centered over New Mexico on Saturday, moves westward to a position centered over Arizona on Tuesday. This will bring steadily increasing heat risk for inland areas for the early to middle part of next week.


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

Short Term

(today through Thursday), Early this morning, satellite imagery shows widespread stratus over the coastal waters extending inland across the Orange County coastal plane and inland across coastal sections of San Diego County into the portions of the far western valleys.

An easterly wave centered over southeastern Arizona continues to move towards the west, preceded by a swath of moisture and clouds that extends into the eastern deserts of Southern California early this morning. Overall into Wednesday, instability across southwestern California is weak and easterly steering level flow of around 15 knots is stronger than optimal for convective development.

There is a slight chance of thunderstorms, mostly near the mountains, for this afternoon and early evening. There are small chances for convection for late tonight into Wednesday morning that could move west of the mountains with the easterly steering level flow. Instability may be a little more favorable for convective development on Wednesday afternoon for the mountains, deserts, and inland valleys as higher level moisture decreases allowing for greater surface heating.

That trend will continue into Thursday with the higher level moisture continuing to decrease and the flow aloft becoming southeasterly and weakening. This will continue the chance for afternoon and early evening thunderstorms on Thursday, mainly for the mountains, deserts, and inland valleys. It should be noted that the 36 hour run of the the new 06Z HRRR has little to no precipitation across southwest California into late morning on Wednesday.

Long Term

(Friday through Monday), For Friday through the weekend, strong high pressure aloft will be centered over New Mexico. This will turn the flow aloft more southerly being some drying. With the drying, there will also be some slight warming for inland areas as well. High pressure aloft centered over New Mexico on Saturday, will move towards the west and be centered over Arizona on Tuesday. This will bring a greater warming trend for inland areas for early next week with the heat risk for inland areas steadily increasing from Monday through mid week.


No hazardous marine weather is expected through Saturday.

Watches, Warnings, Advisories


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