The atmospheric river that’s been hammering the Pacific Northwest and Northern California this week may be turning its attention in our direction, although it could look more like an atmospheric stream by the time it starts up in the Fresno area Friday afternoon.

National Weather Service meteorologist Dan Harty said Wednesday that meteorologists are struggling with their forecasts because their models are producing wildly divergent results.

But what is pretty definite at this point is that the storm will arrive Friday afternoon and could drop a half inch of rain on Fresno through Saturday afternoon, he said.

(Reminder: If you still have your sprinklers scheduled for their once-a-week on Saturday or Sunday, now would be a good time to turn them off and let Mother Nature take care of your watering needs.)

Rain is forecast to fall in the Valley and lower elevations of the Central Sierra, with snow levels starting at 8,000 feet and then possibly dropping to 7,000 feet, Harty said. While some locations such as Huntington Lake could see snow, Shaver Lake will get rain, he said.

Up to a foot of snow is forecast for locations such as Tuolumne Meadows and Tioga Pass in Yosemite National Park by 4 p.m. Saturday, Harty said.

Uncertainty in Forecast

After Saturday afternoon the forecast is much less certain but could include more rain in the Valley and snow in the Sierra, he said.

Right now it’s unclear what will happen to the low-pressure system that’s parked off-shore and its impacts on Central California’s weather, Harty said.

“It’s likely to get some (rain), but the exact timing and location and amounts is very uncertain,” he said. “There’s been a lot of variability from model to model and different runs of the model. So, it’s gonna definitely remain unsettled, that system’s not exiting the area by any means. It’s just that the placement of the precipitation bands is very uncertain.”

Forecast models depend on a number of variables, and a small shift in one variable can lead to a big swing in the weather down the road, Harty said.

“That whole butterfly effect you may have heard of, where a butterfly flaps his wings and then three days later somewhere else across the world, it may have become a very strong wind,” he said. “That small change can become a big change over time.”

According to Harty’s two favorite forecasting models, Thanksgiving Day in Fresno will be either wet or dry.

Get Out Your Shorts Again

Those near-freezing overnight temperatures we had early Tuesday? Get ready for a warm-up. The daytime highs Wednesday and Thursday will be as much as 10 degrees above normal before the arrival of Friday’s rain, Harty said.

The forecast highs and lows for Fresno for the next seven days: Wednesday, high of 68, overnight low of 46; Thursday, high of 71, overnight low of 48; Friday, high of 70, overnight low of 55; Saturday, high of 61, overnight low of 52; Sunday, high of 60, overnight low of 50; Monday, high of 62, overnight low of 49; Tuesday, high of 59, overnight low of 58; and Nov. 27, high of 61.

Yesterday’s bomb cyclone off the US West Coast near peak intensity, accompanied by an atmospheric river.

One of the most amazing satellite photos I’ve ever seen. pic.twitter.com/Bc8FnZ06JG

— Colin McCarthy (@US_Stormwatch) November 20, 2024