Looks like Southern California is in the heat of fall.
Although it's autumn, it's not going to feel like it for a couple of days. Santa Ana winds rolling through San Diego County starting Thursday are going to warm us up and dry us out.
The warming trend is going to leave the region vulnerable to wildfires, according to the National Weather Service. Forecasters did not issue red flag warnings but did predict elevated to briefly critical fire weather conditions.
The NWS and NBC 7 Meteorologist Dagmar Midcap forecast gusts as strong as 50 mph in some parts of the county. The wind should be at its strongest on Thursday and Friday mornings.
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Winds can contribute to the speed of spreading wildfires, and combined with heat can dry out fuels for flames to feast on.
Thursday will feature single-digit humidity in El Cajon (9%), and levels below 15% in places like San Diego, Chula Vista, Poway, Escondido, Fallbrook, Valley Center, Alpine and Borrego Springs, according to Midcap, and relative humidity below 20% is expected along the coast.
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San Diegans will only have to brave the heat for three days. Midcap expects high temperatures 10 to 20 degrees above seasonal averages through Saturday and then a cool down starting Sunday and lasting into the week.
Weekend Highs
Coastal: 84 Thursday, 87 Friday and 82 Saturday
Inland: 90 Thursday, 91 Friday and 89 Saturday
Mountains: 72 Thursday, 73 Friday and 75 Saturday
Deserts: 88 Thursday, 90 Friday and 89 Saturday
Thursday evening, the NWS said temperatures were 10-20 degrees hotter than they were at the same time Wednesday. Come Friday, record highs could be challenged in some areas of Southern California, including Escondido, the NWS said.
How Are Santa Ana Winds Different?
Santa Ana winds occur between September and May and are thus synonymous with fire season in San Diego. They flow in a southwestern curve over the mountains into San Diego, bringing along dry, warm air.
A process called adiabatic heating helps heat the air and suck out its moisture as it passes over the mountains to our east. Low humidity, winds and high temperatures together present the perfect environment for wildfires to spark and spread quickly.
As the wind rolls down off the mountain the air mass compresses, adding about 5.5 degrees of heat for every 1,000 feet of elevation drop, according to Meteorologist Ana Cristina Sanchez.
For example, the town of Julian sits just above 4,000 feet above sea level while Ramona rests at around 1,500 feet. Under a Santa Ana wind event, we could see around 15 degrees of temperature difference between the two towns. This helps explain why we see unseasonably high temperatures everywhere except the mountains in Midcap's high temperature forecast for this weekend.
