Quick Take:

Downtown Santa Cruz will reach the upper 80s on Saturday but the higher points of the San Lorenzo Valley — such as Ben Lomond and Boulder Creek — will push as high as 104 and possibly not cool down below the low 80s at night.

The heat wave that is engulfing much of the Western United States — and creating major fire concerns — will largely leave Santa Cruz County feeling warm but pleasant Friday through the weekend.

But it will be hot at the highest points of the Santa Cruz Mountains — possibly hitting triple digits on Saturday in the upper reaches of Ben Lomond and Boulder Creek — and the National Weather Service on Thursday added that area to the Excessive Heat Warning that already included the North Bay mountains, East Bay hills, southern Salinas Valley, and interior Monterey/San Benito Counties.

Saturday will be the peak of the heat wave, with it tapering off by Tuesday.

“The main thing for the San Lorenzo Valley area is that it’s not going to cool down at night,” said David King of the NWS. “There’s such a compressed marine layer, and such a very dry air mass, that it will stay in the high 70s and maybe even low 80s at night.”

With the winds staying light and onshore, however, the heat won’t bring extra fire danger.

“We don’t anticipate a red flag warning,” King said. “But it’s dry out there and we don’t need any sparks.”

King said downtown Santa Cruz and most of the county’s flatland areas should top out in the upper 80s on Saturday. That’s when the upper San Lorenzo Valley can expect temperatures up to 104.

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