Pasadena, Altadena Face Dangerous Midweek Heat, National Weather Service Warns

Pasadena and Altadena residents should prepare for several days of dangerous temperatures next week, with the National Weather Service issuing an Extreme Heat Watch from Tuesday morning through Thursday evening for the San Gabriel Valley and the western San Gabriel Mountains.

The federal weather agency said in its statement that temperatures could reach up to 100 degrees, with the hottest conditions expected next Wednesday and Thursday.

Forecasters warned that the heat poses a high risk of illness, especially for young children, older adults, people without air conditioning, and anyone active outdoors.

According to the National Weather Service, the heat will build as a ridge from an upper high near the Arizona–New Mexico–Mexico border pushes into Southern California beginning Monday.

Atmospheric heights are expected to rise to about 594 decameters, roughly 8 decameters above normal, compressing the marine layer to 1,000 feet or less. This will greatly reduce low clouds in the valleys, including inland areas such as Pasadena and Altadena.

Inland valleys will warm by 3 to 6 degrees of warming per day, locally up to 8 degrees, due to the absence of a marine layer and the rising heights.

By Tuesday, valley temperatures are expected to reach the upper 80s and lower 90s. Wednesday is forecast to be the warmest day as temperatures peak, with valley temperatures likely in the upper 80s to mid-90s.

The National Weather Service noted a 25 percent chance of even hotter temperatures if the upper high shifts westward and onshore flow weakens further. Because of this possibility, the agency issued the heat watch and said the situation will be monitored over the next three days.

Thursday looks a little cooler as the upper high weakens. Temperatures are expected to cool slightly after Thursday, but will remain well above normal through next weekend, according to the National Weather Service.