Two-Day Heat Wave to Scorch Pasadena Before Dramatic Cooling Next Week

A brief but intense heat wave will push temperatures to potentially dangerous levels across Southern California valleys and foothills through Saturday before a dramatic cooling trend arrives next week, National Weather Service forecasters said Friday.

High pressure aloft is driving temperatures into the mid-90s in Pasadena and surrounding valley areas Friday, with Saturday expected to be the hottest day as readings approach 96 degrees.

“Summerlike temperatures will develop across the valleys, foothills, and mountains today and Saturday as a brief period of hot temperatures develops,” National Weather Service meteorologists said in their morning forecast discussion.

Heat advisories have been posted through Saturday evening for many valley and foothill locations, including the San Gabriel Valley where Pasadena is located.

Forecasters warned that overnight low temperatures in foothill areas and lower mountain slopes may not offer much relief, with readings expected to remain in the 70s to lower 80s through Saturday morning.

The National Weather Service recommends residents plan outdoor activities for the cooler parts of the day, avoid midday sun and seek shade or air-conditioned buildings.

“If planning on hiking in the mountains and foothills the next several days, it may be best to delay your plans,” forecasters advised.

A cooling trend will begin along the Central Coast on Saturday and reach the Los Angeles area valleys by Sunday, though temperatures will remain above seasonal norms throughout the weekend.

Broad troughing developing across the West Coast early next week will bring a much more significant cooldown. By Tuesday, high temperatures in Pasadena are expected to drop to the mid-60s — nearly 30 degrees cooler than Saturday’s peak.

The dramatic shift will come as onshore flow strengthens and the marine layer deepens across the region. Forecasters said the cooling pattern will likely be accompanied by low clouds and fog stretching well into coastal slopes each night and morning.

A slight chance of showers or morning drizzle is possible Monday night and Tuesday as a weak frontal boundary moves through the region.

Winds will likely reach advisory levels at beaches and immediate coastal locations during this transition, as well as in the Antelope Valley and adjacent foothills.

Cooler temperatures are expected to persist into late next week under continued onshore flow and a deep marine layer.

Here is the latest forecast for Pasadena from the National Weather Service as of 3:58 a.m. on Friday, May 9:

Today: Sunny, with a high near 94. Light and variable wind becoming west southwest 5 to 10 mph in the afternoon.

Tonight: Mostly clear, with a low around 65. West southwest wind around 5 mph becoming east in the evening.

Saturday: Sunny and hot, with a high near 96. Light and variable wind becoming southwest 5 to 10 mph in the afternoon.

Saturday Night: Partly cloudy, with a low around 67. South southwest wind 5 to 10 mph becoming light and variable in the evening.

Sunday: Mostly sunny, with a high near 85. Light and variable wind becoming south southwest 5 to 10 mph in the afternoon.

Sunday Night: Patchy fog after 11:00 p.m. Otherwise, mostly cloudy, with a low around 57.

Monday: Patchy fog before 11:00 a.m. Otherwise, partly sunny, with a high near 72.

Monday Night: A slight chance of showers after 11:00 p.m. Mostly cloudy, with a low around 53.

Tuesday: A slight chance of showers before 11:00 a.m. Partly sunny, with a high near 66.

Tuesday Night: Partly cloudy, with a low around 50.

Wednesday: Sunny, with a high near 70.

Wednesday Night: Patchy fog. Otherwise, mostly cloudy, with a low around 51.

Thursday: Patchy fog. Otherwise, partly sunny, with a high near 72.