Jarbo Gap winds are very localized, potentially very strong North East winds that blow in the Feather River Canyon of Butte & Plumas counties. They're a version of the Santa Ana Winds of southern California, although more closely related to the Diablo Winds of the Bay Area.
These winds primarily happen in the Fall and Winter, usually on clear nights after a storm passes through and we're transitioning from stormy weather to dry weather for a while. After a storm passes through, surface high pressure will often build into northern Nevada/southern Idaho. Now we've got high pressure over the Great Basin, and lower pressure in the Pacific. Nature does not like this imbalance, and tries to even it out by sending air from higher pressure (the Great Basin) to lower pressure (the Pacific).
The problem is that the Sierra Nevada acts like a big wall to this airflow, and tries to block it. So, like a river, this air looks for a channel, pass, or gap through the Sierra to squeeze through, and get to the Coast.
The Feather River Canyon is one of the deepest and longest canyons in the Sierra Nevada, so it's a natural route for all that excess air pressure in the Great Basin to take to get to the Coast. Again like a river, the air is funneled between the Canyon walls, and accelerates through the skinny parts, which can create very strong wind gusts. These winds usually peak near sunrise (when the air is at its coolest), and can become enhanced when a strong cold front has brought cold air to Nevada, but not California. That's because cold air is heavy, and you'll get a little extra acceleration from the gravity of the cold, heavy air tumbling down the mountain.
These winds are very localized. It's not uncommon for there to be 50 mph gusts near the West Branch of the Feather River, which impacts areas near Pentz Road in Paradise... but light winds just a few blocks away from Pentz Rd.
I'm sure locals have known about these winds for years, but it was the installation of the Jarbo Gap weather station in 2003 that helped me really understand them. I returned from Alaska in 2007, and I remember noticing that one new station with the funny name in the Feather River Canyon reporting extreme winds occasionally on clear Fall nights. At first, I thought the Jarbo Gap anemometer needed repair. After all, it had reported numerous wind gusts to exactly 100 mph, and a few gusts up to 180 mph on clear nights (*those initial extreme gusts were NOT correct... see below), when every other station was reporting winds under 20 mph! Later that Fall/Winter, I would get an occasional call or email from folks living on Pentz Rd. or near Little Butte Creek Canyon, of these strong, nighttime winds. I soon made the connection between the two, figured out the meteorology that causes the winds, and realized that they happened often in the Fall and Winter. They seemed predictable and important enough for a name. But what to call them?
Initially, I thought they only happened in the North Fork of the Feather River Canyon (below Jarbo Gap) and in the West Branch of the Feather River Canyon, so I began to call them the Jarbo Gap winds, because of where they often peak in strength. Now, it's apparent they're happening in other Sierra/Cascade canyons as well. The 2020 Bear Fire absolutely roared down the Middle Fork of the Feather River Canyon, pushed by gusts up to 66 mph. New anemometers are showing gusty winds in the South Fork of Battle Creek Canyon in Tehama County when it's windy at Jarbo Gap. And while there aren't any anemometers (or many people) deep in Mill Creek Canyon in Tehama County to verify it just yet, high resolution models consistently show gusty winds there (and a bit in neighboring Deer Creek Canyon) that may rival the winds in the Feather River Canyon in strength.
* Those extreme (over 100 mph) readings happened between 2003 and 2013, and those were wrong... there was either a problem with the anemometer itself, or with the recording system. The problem was fixed in 2013, and the Jarbo Gap anemometer now reports wind gusts up to 70 mph, Sensors that have been installed after the Camp Fire agree with the newer readings.
The Jarbo Gap winds were gusting 40 to 50 mph the morning the Camp Fire started in November of 2018; over 60 mph the night the Bear Fire exploded down the Feather River Canyon in September 2020; there were 40-50 mph gusts during the Humboldt Fire in June 2008; gusts to around 45 mph on the first night of the Poe Fire in September 2001; 20-40 mph gusts on the first night of the Concow Fire in September of 2000, and to about 40 mph when the Milk Ranch Fire roared down the Feather River Canyon in September 1951.
What to look for: when looking at a model run of forecasted surface pressure, look for a large (~10mb) difference in pressure between western Nevada and the northern California coast. The higher pressure should be in Nevada, and lower pressure in California.
The opposite of that (higher pressure in CA, lower in NV) would bring a strong Delta Breeze.
North winds are another high fire danger type of wind that impacts us in the North State.
They can be similar in development to the Jarbo Gap winds, as they often happen after a storm passes through and we're transitioning from stormy to sunny weather. The day after the storm passage, surface high pressure often builds into the Pacific Northwest. If that high is strong enough, it will force air southward into California. As that air descends in elevation from the Siskiyous into the Sacramento Valley, it warms due to Compressional Heating. If you warm a parcel of air up without adding moisture, that will lower the Relative Humidity.
So, our North Winds are usually a warming and drying wind. Heat, low humidity, and gusty winds are all the signature of high fire danger days, so we can see that our North Wind often increases our fire danger significantly!
That surface high over the Pacific Northwest will often keep moving east, and end up over northern Nevada/southern Idaho by Day 2. That will let the North winds calm down in the Valley... but that also sets the stage for the Jarbo Gap winds to blow that night through the following morning.
North winds were gusting 30-40 mph and helped the Zogg Fire explode when it ignited in September of 2020; they also significantly pushed the Clover Fire in September 2013, and the Jones Valley Fire in October 1999.
They're most common in the Fall and Winter, and impact the West side of the Sacramento Valley (along Interstate 5) more than the East side (along Hwy 99). A moderate North wind (20-30 mph gusts in Red Bluff) may not bring much wind at all to Chico or Oroville, but a strong one (30-45 mph gusts) will bring windy weather throughout the entire Sacramento Valley.
- Unlike the Jarbo Gap winds, they often weaken at night as the atmosphere cools, and the surface winds and upper level winds "decouple" from each other. The lack of support from the upper level winds will mean lighter surface winds at night in this case.
- These winds will heat Valley high temperatures up a few degrees, and can keep overnight lows MUCH warmer than they would be under calm winds. I've seen lows in Redding and Red Bluff 15 degrees warmer than Chico when the North winds are blowing, because Chico usually sees less of those winds at night.
- At night, if there are 15 mph north wind gusts on the West side of the Valley, it's not unusual for the winds to be calm in Chico or other towns on the East side of the Valley. This lets Chico get much colder at night when the North winds blow than Orland does, which is only 20 miles away.
Pretty much the opposite of a North wind, the Delta Breeze can bring cooler Summer temperatures to the Valley and increase our humidity a little.
The Sacramento Valley gets HOT in the Summer. That hot air wants to rise, like the air in a hot air balloon does. So, by the afternoon, warm air is rising from the Valley floor, creating a mini vacuum in the Valley at the surface. That mini vacuum is now going to try to pull cool air from the Pacific... but how can that ocean air get inland? The Coast Range acts like a barrier to all that cool, marine air. Cooler air is heavier than warmer air, so the cool, coastal air (and Delta Breeze) does not climb mountains.The one place a significant amount of coastal air can flow into the Valley is through the Bay Area... the only sea-level pass through the Coast Range in California.
This is how Sacramento and South Lake Tahoe or Chico and Chester can have similar high temperatures occasionally in the Summer... when there's a strong Delta Breeze. That cools the Valley down nicely, but that cool air doesn't climb into the Sierra Nevada, so they stay toasty.This is also why the winds often pick up in San Francisco in the Summer... it's the very beginning of the Delta Breeze!
It rushes inland on a hot Summer afternoon, cooling down the places it reaches first. This is why Sacramento is usually cooler than Redding or Chico in the Summer. By the time the Delta Breeze makes it all the way north through the Valley to Redding, there's just no cool air left. Redding is left without much (if any) cooling from the Delta Breeze, and cooks in the Summer sun.You can see this summertime daily pressure change in the Sacramento Valley by looking at a graph of the barometric pressure for a Valley city. The barometer will drop through the day, reaching its lowest pressure at the hottest part of the day. When temperatures cool back down at night, the barometric pressure will rise back up. This happens just about every Summer afternoon in the Sacramento Valley.
Why is it called the Delta Breeze? Sacramento residents of the 1800s noticed this cooling, summertime breeze coming from the Sacramento-San Joaquin River Delta in the afternoons, and so named it for what they thought was it's source region. As we talked about above, we now know it's source region is the Pacific Ocean/Bay Area.
The Delta Breeze brings cool, ocean air into the hot Sacramento Valley in the Summer.
Graphic by KXTV
Low temperatures in northern California can be influenced by many things that can change them, especially in the mountains. Even at places of similar elevation, morning lows can be much different from one place to another. Why is that?
Burney, Quincy, and Shingletown are all around 3500', but Burney just about always starts their day 5 to 15 degrees cooler Shingletown. The reason for that is the local topography. Shingletown sits basically on the side of the Cascades, similar to Paradise in the Sierra Nevada. Quincy is in a mountain valley, with mountains on most sides, while Burney is in a bowl, with mountains practically surrounding it.
We talked about how cool air is heavier than warm air in the Delta Breeze discussion above, and that's what's also going on here. The cold air from high country of the Sierra or Cascades drains down the mountains at night. In places basically on the side of the mountains (like Paradise or Shingletown), the cold air just keeps moving on through, and doesn't accumulate. Lows will stay mild.
In a mountain valley like Quincy, some cold air will settle into the valley, and cool Quincy down. The rest of the cold, heavy air will simply drain out to a lower elevation. Chester and Weaverville are other examples of local towns in mountain valleys.
Finally, cold air that settles into a bowl at night has difficulty draining out, so the cold air can often accumulate in the bowl... and the bowl will get very cold! This is why Burney is one of the coldest towns at night in the North State. Truckee (near Lake Tahoe) is close to 6000' in elevation, and also in bowl, like Burney. This is why Truckee can often have the coldest overnight low temperature in the U.S.! (besides Alaska).
This mainly happens on clear nights. Temperatures are usually more uniform under cloudy, stormy nights.
Chico and Redding are big enough that low temperatures across town can be quite variable on clear nights as well, because of this cold air drainage.
In Chico, low temperatures on the East side of town (up against the foothills. Places like Cal Park, Canyon Oaks, or Stilson Canyon) can be 5-10 degrees warmer at night compared to locations on the West side of town (like Nord Ave/Walnut St, Big Chico Ck. Estates, or Oak Way Park).
In Redding, it's the same idea. Places adjacent to the foothills, like the North side of town (Lake Blvd, for example) or West side of town (West of Benton Airpark or Shasta High School) can be 5-10 degrees warmer at night than the East side of town (like Palo Cedro, or the Redding Airport).
Afternoon high temperatures are much more uniform. There's little difference across town in the highs of Chico or Redding.
But those nighttime low temperatures can be very... variable!
Even though their temperatures can soar over 110° in the Summer, it's not unusual for Redding to see snowfall in the Winter. A day-before-Valentine's Day storm in 2019 dropped around 1 foot of snow in town! But the rest of the Sacramento Valley rarely (if ever) sees snow. What's going on in Redding?
Short answer: the mountains surrounding Redding trap cold air in the far north end of the Valley. If it's dry enough, a cold rain will turn to snow by Evaporational Cooling.
Longer explanation: it takes pretty specific conditions, but Redding does see snow in the Winter.
You'll find a more detailed explanation of this near the bottom of my Climate section.