Much of interior northern California

Forecast cities/towns include, but not limited to: Sacramento, Fair Oaks, Orangevale, Gold River, Rancho Cordova, Folsom, El Dorado Hills, Roseville, Rocklin, Granite Bay, Loomis, Newcastle, Auburn, Grass Valley, Foresthill, Meadow Vista, Colfax, Cool, Coloma, Placerville, Cameron Park, Elk Grove, Plymouth, Jackson, Ione, Valley Springs, San Andreas, Sonora, Farmington, Yuba City, Oroville, Chico, Paradise, Woodland, Davis, Winters, Napa, Sonoma, Santa Rosa, Calistoga, Healdsburg, & St. Helena. Cities & towns nearby (within 10 miles) of each aforementioned location can be assumed/included in this forecast.

Mon, June 17

 High temperatures: 76 – 86 °F

Tue, June 18

 High temperatures: 83 – 93 °F

Wed, June 19

 High temperatures: 83 – 93 °F

Thu, June 20

 High temperatures: 85 – 95 °F

Fri, June 21

 High temperatures: 93 – 103 °F

Sat, June 22

 High temperatures: 96 – 106 °F

Sun, June 23

 High temperatures: 92 – 101 °F

Forecast details (6/16/24)

Tuesday, 6/18 update: lowered temperatures for Thursday slightly, slightly increased Fri/Sat temperatures, and lowered Sunday’s temperatures to reflect some minor changes in the overall pattern. Most notably is Sunday’s decrease in temperatures — as it now doesn’t look like Saturday’s repressive heat will repeat itself quite as much due to a stronger onshore breeze developing later on Saturday, which should continue through Sunday to help cool areas close to the delta. I may still make some minor changes to the second half of the forecast period, but at this point I think the updates would only update temperatures by a degree or two.

Additionally with these slight changes to temperatures, I reflected these updates in the afternoon condition quality (for snake activity): I increased Thursday afternoon’s quality up to “high”, and increased Sunday’s afternoon quality to “Medium/High”. This is due to the slightly cooler temperatures being safer for snake activity, though still primarily in shady areas.

Previous discussion, written Sunday evening @ 11:40 PM:

To start this week, increased/high fire danger as gusty north winds rapidly dry the lower atmosphere, with humidity values drop into the single digits for a pretty big chunk of interior northern California. Temperatures will drop slightly Monday compared to Sunday, but will still remain pretty comfortable for rattlesnake activity during much of the day. The cooler temps will likely support the highest level of snake activity on Monday to be during the afternoon hours, as highs in the 80s are ideal for rattlesnake activity.

Temperatures will, in general, increase through the rest of the workweek. As we approach the weekend, highs will surge back well inside of the widely accepted “hot” category, with highs in the upper-90s to low-100s across much of the foothills, coastal range, and valleys. Snake activity will slowly shift from primarily daytime activity early in the week, to mostly early morning (before 9 or 10 AM) and evening/overnight as highs reach dangerous temperatures for snakes in areas with lots of direct sunlight. Thus, most snakes will likely be in cover/shade between around 11 AM and roughly 6 PM Friday into the weekend.

Overnight lows will slowly warm through the week after around Tuesday/Wednesday, with overnight lows in foothill areas staying the warmest due to a thermal inversion around 3000 feet. Overnight lows inside of this thermal belt will struggle to fall out of the low-70s Friday into the weekend, which will support potential for rattlesnake activity quite late into the night, with potential for some snakes to be out all night through sunrise the following day. When nocturnal activity increases, rattlesnakes can sometimes find themselves in strange places by the following morning when temperatures rapidly climb and become dangerous, leading to snakes sheltering in less common areas — potentially putting them closer to people as they wait out the hot sun through the afternoon before they can carry on cruising around as the sun sets.

As of writing, there’s some slight differences in model output for high temperatures Friday – Sunday, and for now went with a blend of models. I may have to alter temperatures a bit as we get closer to this time period, as the uncertainty seems to be dependent on how strong the delta (onshore) breeze is able to get each evening. My current feeling is that I may need to increase temperatures slightly, but we shall see. These updates, if needed, will be in place by or before Thursday for the Fri – Sat period.

Date & time last updated: Tuesday, 6/18/2024, at 12:29 AM

Next update: 6/23/2024 (late) – 6/24/2024 (early)

Snake activity is heavily driven by weather conditions, not just large-scale seasonal changes such as the shift from Winter to Spring or Summer to Fall. While time of year has an impact on snake activity, it’s primarily driven by various meteorological factors including, but not limited to, surface/air temperature, cloud cover, humidity, and more.

Placer Snake Removal’s weekly snake activity conditions forecast combines large-scale seasonal trends, in addition to & perhaps more importantly, daily weather conditions. The forecast breaks the day up into 4 pieces: morning, afternoon, evening, and overnight. Each day chunk includes the expected quality level for rattlesnakes to be active. A conditions forecast of “Low” means that the conditions are not expected to be particularly ideal for rattlesnakes to be active for long periods of time at the surface. A conditions forecast of “High” means forecast conditions are likely to be very supportive of rattlesnake activity at the surface.

The forecast for each week is created the Sunday night leading up to the week, often released closer to midnight – 1 AM.

Forecast key & description

Low – conditions not ideal for surface activity.

Low medium – conditions may support small amounts of activity.

Medium – conditions supportive of some activity, perhaps short-range travel.

Mediumhigh – conditions supportive of activity, including travel.

High – conditions very supportive & comfortable for all forms of activity.


Do not solely rely on information from these forecasts for personal safety & always practice venomous snake awareness/safety no matter temperature or weather conditions.