Detailed Update On Next Week’s Storm Potential

If you are hoping for a significant storm to arrive mid-week, I can tell you that the models are digging in their heels and while they are handling the storm differently, they are reaching pretty similar conclusions. I have a lot of content today and if you want to scroll down to the summary portion of the post I will share my thoughts.

A couple of weeks ago, I talked about mid to long-range forecasting (10-16) days and the good reasons to use an ensemble version of a model, I also talked about my own take on ensembles and my experience with the best time to switch over to individual model runs from the ensembles. Basically, in the early stages, I use the ensembles while also tracking the trend of the underlying deterministic models. The closer we get to the storm arrival the more heavily I rely on the run to run consistency of the deterministic model runs.

The Euro has 50 family model member under its umbrella, the GFS has 25. According to the Euro’s site here is the proper definition of the ensemble:

“An ensemble weather forecast is a set of forecasts that present the range of future weather possibilities. Multiple simulations are run, each with a slight variation of its initial conditions and with slightly perturbed weather models. These variations represent the inevitable uncertainty in the initial conditions and approximations in the models. They produce a range of possible weather conditions.”

The downside and this is according to me, is that in my opinion, the extremely low resolution that is used in all ensemble models plays a big role in missed forecasts in our area because of our topography. At this stage, I am watching both the deterministic models and the ensemble models and as I mentioned, and as you will soon see all of the models are doubling down on this storm.

We will start with the Euro ensemble mean run. This displays the average of the 50 models. The onset of precipitation starts sometime between overnight Tuesday into Wednesday but may be delayed.

We’ll start with total liquid precipitation regionally. This is the average of the 50 euro models


Here is how that translates to snow



Next to the GFS ensemble for QPF (total liquid precipitation)


GFS ensemble snow


Here are the zoomed-in versions, as you will see using the ensembles I can’t show you the level of detail that I do with the deterministic models, which is fine because we are watching the trend with the ensembles. Later in the post, I will show you both of the latest operational model runs.

Euro ensemble precip


GFS ensemble (GEFS) precip


Euro ensemble snow



GFS ensemble snow


This would be a really good time to remind you not to take this 100 % at face value, rather it just instills some confidence about our first major snow event for the mountains next week. It will probably be Tuesday or Wednesday before I attempt a snowfall forecast. The NWS is keeping an eye on this system, depending on who you talk to, and we may hear some early talk about the need to issue a Winter Storm Watch by Monday or Tuesday.


What do I think? Well, while it is great to see the models pick up on the moist sub-tropical air getting involved, the dry conditions that we have experienced for months are difficult to overcome with the first major storm. There seems to be a feedback mechanism we get where if our soil moisture is abnormally dry, as it has been, it takes a considerable amount of moisture to overcome the tendency to evaporate the moisture before and as it falls. If you have followed me for a while you know the opposite is true as well, when the soil is excessively wet it takes very little energy to revive or enhance a storm as it moves across the area. Some of the model runs I have seen generate a HUGE amount of precipitation in Arizona, as much as 3-5 inches from some of the models, this is the type of set up that would be enough to overcome the dry conditions, similar to last New Years. So I am cautiously optimistic, and I will be watching every model run between now and then to observe any trend that arises.

I promised you a look at the deterministic model runs, here were last night’s Euro and GFS for precip and snow.

Euro precip


Euro snow1116eurocol

GFS precip


GFS snow


What is amazing to me is how similar the model runs are this far out.

Beginning Monday I will update every day. For those traveling, it appears once you get out of our area you should be fine, assuming the models continue to trend in this direction.

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