More Rain Tuesday Evening

10/4 Monday 1:30 pm

The next weather maker is set to come onshore in Southern California on Tuesday. There is still some model disagreement on the track of this closed low. Storm track determines the precipitation amounts, so there is obvious uncertainty with the totals as well. There is good agreement at the moment that the snow levels will be above 11,000 feet.

It will take a while to moisten up the atmosphere tomorrow, the models have slowed down the onset of precipitation and it may be Tuesday evening before things get going. The models are trending a bit further west with the heaviest precipitation, we’ll see.

Here is the approximate location of the closed low as of noon Monday.

I drew the L in there. The circle indicates that it is a closed circulation low-pressure system. Closed lows eventually become open waves. When this happens they speed up. Models struggle with the timing of this evolution. That is why we see disagreement among the models.

When the system opens up, it moves faster. If this happens too early the system moves northeast more quickly. This sometimes results in the system heading north when it reaches northern Arizona. The precipitation path then focuses on the far western portions of the forecast area and into southeast Utah then towards Grand Junction.

The longer the low remains closed, the further east it will head before opening-up and heading northeast. This results in a more favorable track for heavier precipitation for the southern portions of the forecast area.

At this point, I do not favor one solution over the other. The models are flipping back and forth between the two. Hopefully, in another 24 hours, I will have a better idea.

Here are the latest model runs showing the precipitation totals from Tuesday night to Wednesday night.


GFS-the accumulation pattern in this model run makes little sense.

Canadian-showing a near miss.

German-it looks a lot like the Euro.

Speaking of struggling, the models are still struggling with next weekend’s system. They have backed off the intensity. Fortunately, there is still pretty good agreement with the third system (Tuesday 10/12-Wednesday 10/13), the models are still showing accumulating snow for the mid-elevations and higher, with some wet snow possible down to 6,500 feet. It is too early to start talking about snow totals. I probably won’t address that before Friday or Saturday.

Two updates on Tuesday, the first will be before 9 am, the second will be around 1:30 pm. Thanks for following and supporting the site!

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