From the National Weather Service:
A ridge of high pressure building over the region will dominate the weather pattern through midweek. Expect temperatures 10 to 15 degrees above normal and sunny skies. By late Thursday, a low pressure system will bring cloudy and cold weather with a chance of precipitation and gusty west winds to Southern California. Temperatures will fall to 10 to 20 degrees below normal for inland areas, and 5 to 10 degrees below normal for the coast.
The National Weather Service forecast for Poway:
Monday afternoon: Sunny, with a high near 92. West wind around 10 mph.
Monday night: Clear, with a low around 56. Calm wind becoming east around 5 mph in the evening.
Tuesday: Sunny, with a high near 85. Light and variable wind becoming west 5 to 10 mph in the afternoon.
Tuesday night: Patchy fog after 10pm. Otherwise, partly cloudy, with a low around 54. Northwest wind around 5 mph becoming east after midnight.
Wednesday: Patchy fog before 10am. Otherwise, mostly sunny, with a high near 80. Northeast wind 5 to 10 mph becoming west in the morning.
Wednesday night: Patchy fog after 10pm. Otherwise, increasing clouds, with a low around 54.
Thursday: Patchy fog before 10am. Otherwise, cloudy, then gradually becoming mostly sunny, with a high near 70.
Thursday night: A slight chance of showers. Cloudy, with a low around 53.
Friday: A chance of showers. Cloudy, with a high near 61.
Friday night: Showers likely. Cloudy, with a low around 46.