BREAKING NEWS Full U.S. Senate will vote on Judge Amy Coney's Supreme Court confirmation on Monday Full Story
BREAKING NEWS Extreme fire weather concerns for Northern California Sunday and Monday Full Story
BREAKING NEWS Point Fire is burning in Cottonwood on Gas Point Road Full Story
BREAKING NEWS Cal OES positions extra firefighting resources in Tehama and Colusa counties Full Story
BREAKING NEWS Latest from PG&E on potential PSPS power outages, possibly starting Sunday morning Full Story
SEVERE WX : Freeze Warning View Alerts

Why do we see some of the worst fires in Fall?

In the fall, the mountains get much cooler while the valley can still be pretty hot. The jet stream also drops south which means we see more weather systems passing near our region. A strong change in temperature and pressure can cause strong winds and the fact that these winds are offshore winds and downslope winds can emphasize the strength of them via the Venturi Effect and gravity.

Posted: Oct 13, 2020 4:29 PM
Updated: Oct 20, 2020 8:58 AM

CHICO, Calif. - In the fall, the mountains get much cooler while the valley can still be pretty hot. The jet stream also drops south which means we see more weather systems passing near our region. A strong change in temperature and pressure can cause strong winds and the fact that these winds are offshore winds and downslope winds can emphasize the strength of them via the Venturi Effect and gravity.

When you think of fall in California you probably imagine, rain, cooler weather, and the beautiful colors of mother nature.
But Fall often brings devastation to California. The Camp Fire, the Tubbs Fire, the Thomas Fire are just a few reminders.
Why is fall so dangerous?

In the fall, there are several factors that change compared to summer. The mountains get a lot colder at night while the valley can still see some pretty strong heat in October and sometimes even in November.
This cold air rushes down the mountains at night and the stronger the temperature difference between the valley and the mountaintops, the stronger the wind could be. This temperature difference is not as strong in the summer. In early spring, it's not a concern since vegetation is not dry.

Pressure difference also plays a factor in strong winds in the fall. In the summer, the jet stream is very far north. So all the strong low-pressure systems are usually too far north for us to worry about. But in the fall, the jet stream begins to drop south. This allows for much stronger low-pressure systems to get closer to California. When they enter our region, in opposition to a strong high-pressure system, the stronger the pressure gradient will be. A pressure gradient means how much pressure changes over a distance. The stronger a pressure gradient is, the stronger the wind will be. When low-pressure systems pass to our East they cause strong downslope and offshore winds across California. It is often referred to as offshore wind season. A low-pressure system nearing our area Wednesday through Friday is a big reason for stronger winds this week.

There are other factors that play into strong winds in our area not just in fall but at any time.

First, is the fact that downslope winds can be dry. When air travels downslope it can become dry. Rising air cools and condenses (meaning it becomes more moist) but falling air warms and drys (losing its moisture).

Also, air traveling downslope into the valley can often funnel into canyons and become a bottleneck. This causes much stronger winds locally and is known as the Venturi Effect. The Jabo Gap winds are a popular example of this locally and happen every night.

Climatologists believe the evidence shows wildfires will continue to get worse in the fall as significant rainfall has been arriving later, in recent years.

California Coronavirus Cases

Data is updated nightly.

Confirmed Cases: 903684

Reported Deaths: 17343
CountyConfirmedDeaths
Los Angeles2989376989
Riverside657571279
San Bernardino623531072
Orange583261444
San Diego54314868
Kern33775416
Fresno30590436
Sacramento25264484
Santa Clara24014388
Alameda23215460
San Joaquin21630489
Contra Costa18523241
Stanislaus17572396
Tulare17495286
Ventura14192164
Imperial12700336
San Francisco12069140
Monterey1132189
San Mateo11075159
Santa Barbara9760120
Merced9465155
Sonoma9163134
Kings821883
Solano728674
Marin7057128
Madera498174
San Luis Obispo414132
Placer408857
Yolo316658
Butte305952
Santa Cruz277125
Napa194215
Shasta184630
Sutter183712
San Benito143615
El Dorado13154
Yuba129310
Mendocino112421
Tehama8628
Lassen7661
Lake68915
Glenn6573
Nevada6088
Humboldt5629
Colusa5506
Calaveras34218
Amador32416
Tuolumne2684
Inyo22715
Siskiyou1930
Del Norte1781
Mono1782
Mariposa782
Plumas680
Modoc290
Trinity260
Sierra60
Alpine30
Unassigned00
Chico
Few Clouds
63° wxIcon
Hi: 71° Lo: 41°
Feels Like: 63°
Oroville
Clear
64° wxIcon
Hi: 73° Lo: 44°
Feels Like: 64°
Paradise
Few Clouds
63° wxIcon
Hi: 65° Lo: 41°
Feels Like: 63°
Chester
Clear
33° wxIcon
Hi: 47° Lo: 25°
Feels Like: 24°
Red Bluff
Clear
62° wxIcon
Hi: 68° Lo: 48°
Feels Like: 62°
Willows
Few Clouds
63° wxIcon
Hi: 67° Lo: 47°
Feels Like: 63°
Fire danger will be extreme Sunday-Monday as the biggest dry wind event of the season takes shape. A widespread freeze in the Sierra-Cascades as low as single-digit values possible Sunday night. Mild & sunny weather after Tuesday.
KHSL Severe
KHSL Radar
KHSL Temperatures

Community Events