A Halloween Storm? And An Open Storm Door Into November?

Overview

My friends...

Dry and windy weather prevails until the end of the week. Then, a possible storm approaches California, with uncertain outcomes for us in the Sierra Nevada.

We've been tracking this one for quite some time, and it still admittedly looks like somewhat of a coin toss. This looks like at most a weak to moderate storm, but with colder air on tap than our last storm.

Beyond that, the first week of November and possibly beyond may keep the storm door open...

The storm

This storm is a tenuous forecast because there are two moving parts. An upper level low will swing down from the north and merge with an active subtropical jetstream. As the two combine, the low taps into a plume of subtropical moisture and pulls it towards California.

Southern California currently looks favored to take the brunt, but this is ultimately a delicate setup with the two moving parts, making it difficult to forecast...

Fortunately, we look to have colder air either way, which could be a good window for snowmaking. Our last storm also came from a low to the north, however it pulled moisture up on a more southerly track. This meant we were warmer and that Mammoth was in a rain shadow. Last time, snow levels started around 9,500 to 10,000 feet. This time, we appear to have much colder air on tap, so snow levels start out around 6,500 to 7,000 feet Friday and could dip to around 5,500 feet late Saturday into Sunday. This could be an entirely snow event on the mountain and in the town of Mammoth Lakes.

For liquid, the 25th to 75th percentile range for the storm at Main Lodge is roughly 0.2-1.4" in the Euro AI (AIFS ENS) and 0.2-0.9" in WeatherNext 3, with Saturday possibly being the wettest day.

Still a coin toss...

So the ensemble guidance still shows a very wide range of outcomes. The low end is a few showers, and the high end is a solid storm. Some members keep us almost entirely dry, while others bring us a moderate storm.

With the current uncertainty, it's still too soon to talk about snowfall amounts. We need another day or two for the models to settle on how the northern low and the southern stream line up, and then we can actually forecast this storm.

An open storm door in November?

Longer range, the ensembles agree on a deep trough setting up in the Gulf of Alaska by the end of the first week of November. The Euro (IFS ENS), Euro AI (AIFS ENS), and WeatherNext 3 all show it. This has been advertised for a long time by ensembles, as well as extended modeling, and is well supported by the current trajectory of the MJO (which looks likely to remain in phase 3 for a long time) and our monster El Niño driving an active jetstream. I'm quite optimistic about the first week of November until mid November for something to align...

WeatherNext 3: © 2024-6 Google LLC, whose machine learning models were used to create the experimental data made available under the following licence terms https://storage.googleapis.com/weathernext-public/terms-of-use.pdf. This data is intended for experimental modelling only and is not intended, validated, or approved for real world use.

A Gulf of Alaska trough is an open storm door. It doesn't guarantee a storm will reach California, but it means the large scale pattern is amenable to one. With the main wave energy just to our west, we'd be right downstream of the storm track.

This is still far out, but it looks promising. Time will tell!