Why They Don’t Release Raw Model Guidance to the Public

This is called a meteogram:

It is a graphical representation of a model run for a single point on the Earth’s surface, in this case the weather station at Bellingham airport. Note that I should have said “suite of model runs” instead of “model run:” each so-called forecasting model is in fact multiple runs, each initialized with a slightly different set of parameters, all based on current observations. This is done to provide a measure of how reliable the model is: if each run in the suite is all over the map (like they are for the weekend after next), it means the model’s predictions cannot be trusted very much.

By contrast, every run in the suite above is in agreement that we are about to have a lowland snow event, totaling an inch or two. Very high confidence, but wait. This is for the GFS model, the one developed by the National Oceanic and Atmospheric Administration. This model has a tendency in our climate to underestimate the moderating effects of the Pacific Ocean and the Cascade Mountains, plus it is generally not as reliable as the ECMWF model developed by the EU nations. What does that model have to say?

Both significantly less snowy and significantly less confident in any sort of snow outcome. Let me let you in on another secret: any time those models forecast a snowfall range in the lighter gray colors, one almost never sees any accumulation unless the temperature is solidly below freezing at the onset of the event. The temperature is not forecast to be solidly below freezing. In other words, this model is saying there is an off chance of seeing some wet flakes in the air tonight, with no accumulation.

Now, if the ECMWF model had shown basically the same story as the GFS one, we would be in a situation much like we were going into the solstice, and I would be making a confident snow prediction regardless of what the official forecasts said. If both models consistently tell the same story, they are almost always correct.

But both models are not consistently telling the same story, so what to do about it? First, what we can do is limited: it’s going to be a lower-confidence forecast, no matter what. The signs are mixed as to what is going to happen. However, the more accurate of the two models is saying little if any snow tonight. Moreover, the less accurate model is known to have defects which can explain precisely this discrepancy.

Therefore, it is wise to go with the ECMWF guidance: an off chance of some wet flakes in the air.

But note what would have happened if a) I liked snow, b) I didn’t know about the defects in the GFS model, and c) I let my emotions cloud my judgement. I would have helped start a false rumor about there being a viable chance for an inch or two of snow overnight.

This is why the models are often called model guidance: they are not there to forecast the weather, they are merely there to help people forecast the weather.

Damp on Saturday, Wet on Sunday

That is both my forecast and the official forecast. On the subject of the official forecasts, they are usually pretty good, and usually the same forecast I would give, were I a professional weather forecaster. The times I make a big stink are the times the official forecasts don’t make much sense to me.

Anyhow, if you’re planning outdoor activities, Saturday definitely sounds like the better day. The source of the moisture that will make Sunday (and the beginning of the work week) so wet is coming out of the tropical Pacific, so it will drag some relatively warmer air up our way with it. Expect some high temperatures in the fifties, maybe well into the fifties (Bellingham is often one of the warmest spots in Western Washington when a strong south wind is blowing, more on why that is the case sometime later).

That means snow levels will be rising, though at this time it seems likely they will stay (just) below the elevation of the Heather Meadows area. Still, if I were skiing, I would opt for Saturday. Some light snow which is drier because temperatures are still reliably below freezing sounds a lot nicer than copious amounts of heavy, wet “Cascade concrete” snow.

This will likely prove to be just a temporary mild interlude to a generally cool pattern that we are for the next several weeks. The long-range models have all been consistent with things staying on the cool side at least through the first half or March.

This also means that we’re not out of the woods quite yet when it comes to lowland snow; yes we can get lowland snow in March, sometimes significant amounts of it. I must emphasize, however, that at this time there is no specific indication of any such thing. The dice are merely loaded so that outcome has a higher chance than normal, that is all.

More Weather Posts Coming Here

A bit of introduction for the unaware is in order here: one of my many interests in the sciences is meteorology. As such, I follow a number of weather forums. Those with more money to their name than I subscribe to professional services that give access to raw forecasting model data.

Maps and other graphics were getting reposted to the forums from those professional services which showed something interesting was probably going to happen, curiously enough, right on the first day of winter: a powerful cold front would suddenly cause the snow level to drop to sea level. Since precipitation rates were forecast to be quite intense at the time, a few inches of wet snow were likely to accumulate.

More interesting is that both of the two historically most accurate forecasting models, the ECMWF and the GFS, converged on that scenario a few days out, and then kept on saying the same thing. It has long been my experience that when this happens, the forecast event almost always verifies. Yet the official forecasts, be they from the National Weather Service or Weather.com, had no mention of lowland snow that day.

That made no sense at all to me. Again, when both those models consistently agree on something, it really tends to happen. So I made a post about the likelihood of a snowfall to the /r/Bellingham Reddit forum. Skepticism ensued, followed quickly enough by flabbergasted amazement as “this guy on Reddit” forecast a snowfall that was not mentioned in any official forecasts.

Last weekend it happened again. The model guidance had converged quite nicely on a significant lowland snow event, with the vast majority of runs clustered right around the 6 to 8 inch range. The official forecasters only reluctantly started forecasting snow, and then only a few inches of it. This time the skepticism was tempered, because I had been right before.

I knew going into last weekend that if I was right a second time with a radically different forecast, a lot of people would have difficulty seeing me as something other than possessing supernatural powers, even though my logic for my forecasts was rather simple.

Eight to ten inches fell. My forecast was off, but only by a bit (10 inches of snow is not significantly more disruptive than 8). It is, however, way more disruptive than 3 inches, which was the high end of the range the official forecast was going for. So my status was assured. For now, at least.

Given that the community is now funding my access to the official forecast models, I owe them some at least semi-regular weather analyses, which I plan to post here.