10/26/26 Monday 3:45 am
Overview
Expect nice fall weather through midweek. Flow will shift to the SW on Thursday, with slightly warmer temperatures and increasing humidity levels by Friday.
Upcoming Storm
Yesterday I was so close to talking about next weekend’s storm. I saw 4 very aggressive model runs showing eye-catching rain and snow totals, then I saw one with slightly lower totals than the other 4. So I decided to hold off until this morning.
Yes, snow levels will be lower with this next storm. For now, I am pretty comfortable with snow starting at 9,500-10,000 feet and then lowering through the weekend, perhaps much lower by Monday morning.
Given what the region has experienced, I felt a sense of urgency to share this information. But really, I’ve been hinting about this Halloween Storm for a while.
When I give you hints, it means I am seeing activity I have to keep an eye on, but I am not ready to commit because it is too far out. Fast forward to today, and we’re just a few days away. It’s time to start sharing.
With the last event, the model consensus was locked in on precipitation totals. By the way, the models have consistently underforecasted the highest totals over the last 2 months. That is something to keep in mind when interpreting “crazy” totals.
This system is slightly different than the last few. Here is what is the same: strong low pressure traveling down the coast, picking up tropical moisture to dump over the forecast area over a couple of days as the low pressure tracks across the region.
Here is what is different, and why the models may be struggling a little. There are two sources of tropical moisture. The first is remnants of Hurricane Vance.
The models are not sure how much of that moisture will get wrapped up with the low because, as we have seen, these lows take their time, and as I said the other day, the strengthening deep low-pressure systems don’t care what the models are forecasting; they are going to do what they want.
The other source is a plume of tropical moisture originating east of Hawaii. This plume has some Atmospheric River(esque) attributes. But unlike the mid-winter ARs that usually bury the Sierra and leave us with paltry leftovers, this one is different. This firehouse is pointed northeast right over San Diego. The models think it will take the familiar path directly into our forecast area.
I am going to stop there on the setup. Even I get weather fatigue after a while, so let’s move on to the early model forecasts.
I am going to hold off on projected snow totals for now, likely until Thursday or Friday. That said, many models forecast 1 to 2 feet of snow above 9,500 feet.
The initial storm window is: Onset, late Friday to early Saturday. Departure: Early Monday to early Tuesday. I’ll tighten this up as we get closer.
Here are the liquid equivalent forecasts for this next event; as always, these are subject to change (by a little or by a lot) before it starts. Also, don’t take these as exact forecasts. Look at the highs and the lows and use that as a range.
European
NOAA’s NBM
European AI
A huge smoothing factor with this version of the model. Keep in mind what I said about guidance versus forecast.
AI GFS “crazy” totals.
Canadian
What does this all mean for additional flooding? That is the question. On one hand, it could mean a lot of precipitation falling on already saturated soils. On the other hand, with lower snow levels, runoff from higher elevations may be limited this time.
I know there is a lot of “maybes ” and “potentiallys” in this post. That is normal a few days out. I am not trying to worry anyone yet. But I don’t want to spring this on everyone without a warning on Thursday or Friday, when the Winter Storm Watches come out for areas over 9,500 feet.
I would rather be wrong and have everyone be aware than wait until I am 100%. If anything changes, I will post again this afternoon.