Sunshine and mild temperatures should prevail through the weekend, the National Weather Service says, ahead of a gradual warm-up that could push inland highs to 90 by Wednesday.

And forecasters give the usual explanation: low pressure over the western United States, combined with air-flow from the northwest, to keep things cool, then high pressure over the Great Basin to warm things up.

Article Tab: The lake at Rancho Santa Margarita last week.
The lake at Rancho Santa Margarita last week.

Friday and Saturday both look mostly sunny, with highs of 73 to 78 inland, 69 on the coast.

More low pressure will knock a few degrees off the highs for Sunday – 70 to 75 inland, 67 on the coast – with mostly sunny skies after a mostly cloudy morning with patchy fog.

On Monday, Columbus Day, it will be sunny after partly cloudy skies and patchy fog in the morning, with highs of 77 to 82 inland and 71 on the coast.

Air flow is expected to turn toward the ocean as the Great Basin high pressure builds.

Then Tuesday looks sunny, Wednesday and Thursday mostly sunny as the warming trend takes off.

Inland highs should be 85 Tuesday, 85 to 90 Wednesday and 83 to 88 Thursday.

On the coast it will be 78 to 83 Tuesday, 77 to 82 Wednesday and 73 to 78 Thursday.