San Diego

Why Have the Mornings Been So Cold in San Diego? And When Will it Warm Up?

Overnight temperatures are expected to drop into the low 40s on Tuesday

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Let's face it -- San Diegans are pretty spoiled when it comes to weather most days of the year. There's a reason our unofficial motto is 75 degrees and sunny. So it's pretty noticeable when temperatures plunge into overnight lows in the 30s, leaving residents to ask "why?" And, "When will it warm up again?"

NBC 7 Meteorologist Sheena Parveen has the answers. Here's what to know:

Why has it been so cold lately?

San Diego's weather patterns are controlled by high and low systems that shift wind direction. A high-pressure system pulls winds from the south to the north, moving warmer airmass over the county. But a low-pressure system can shift the wind pattern allowing cold air to move in.

In the last several weeks, the region has been met by several storm systems, which have been accompanied by cold fronts, allowing for cooler air to move into the county.

"A cold front has colder air on the back side," Parveen said. "So as it moves through, winds generally switch to a north or northwest wind, pulling in cooler air."

That cold airmass has been combined with other recent weather factors -- including dry air, clear skies and calm winds -- which have allowed temperatures to drop even further overnight and have even allowed frost to develop.

Parveen explains when the air is dry, the county's dewpoint is lower and temperatures are able to drop even further, Parveen said. Clear skies allow for the heat of the day to escape at night. And, calm winds allow for colder air to settle instead of mixing.

How cold has it been?

San Diego saw overnight low temperatures over the weekend drop to the low to mid-40s along the coast and in the deserts, in the mid-30s for parts of the inland valleys and even lower for the mountains.

"For [Tuesday] morning, it's going to be cold again," Parveen said. "Around the mid-40s for the coast, inland valleys, mostly the upper-30s, mountains will be around freezing.

"Make sure you bring the pets inside and cover any sensitive plants that you don't want damaged."

A few more cold nights are ahead. Some areas in the valleys could even experience overnight frost in the coming days. A frost advisory is in effect from 10 p.m. Monday to 8 p.m. Tuesday.

Daytime temperatures were also expected to be mild for most of the week with highs at the coast, valleys and deserts in the upper 60s. By the end of the week, temperatures could rise slightly to the low 70s.

When will San Diego warm up?

Good news, you can expect warmer temperatures this week.

Santa Ana winds, which push from the east to the west, are picking up in San Diego, which means things will finally warm up by the end of the week, Parveen said. Santa Anas will increase on Thursday.

Santa Ana winds flow downward from the mountains and when this happens, the airmass warms, pushing warmer temperatures to the coast and inland valleys.

"It is going to get pretty windy in the mountains as we head towards the middle to the end of the week and it'll also be warming us up," Parveen said.

By Thursday, temperatures will be around 70 at the coast and inland, the upper 50s in the mountains and low-70s in the deserts.

Don't expect the warmer weather to last for too long. Next week could see another weather pattern shift for the region.

Stay tuned to NBC 7's First Alert Forecast for daily weather updates.

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