By Bryan Allegretto, Forecaster Posted 3 years ago March 30, 2020
One of the questions we get asked the most is, "how much snow will we see during my trip on "x" date?". As much as we would love to be able to accurately predict storms 2 weeks to 2 months in advance, it is just not the reality with the tools we have and the way the atmosphere works.
How Far In Advance Can We Predict A Storm?
For weather forecasts, one of our main tools are the weather forecast models. These models take current weather data from around the globe and extrapolate it out into the future based on algorithms scientists have created over the years.
The issue is that these models have an inability to measure every variable around the world due to a lack of data. The computer takes the variables that we have measured and extrapolates numbers for the areas that are missing. Using this data it creates a model that is mostly correct. This provides a short-range forecast that can be fairly accurate, about 5-6 days out.
The computer has extrapolated some of the data on the short term forecast which fills in missing gaps, and it will be correct for many of these gaps, but not all of them. When you increase the time frame for the forecast you are building a new model based on the first model, which has extrapolated data and gaps in it. Each successive model that you build off of that one will have more and more errors because you are building off of the initial errors.
Because of this, the accuracy starts dropping off each day into the future, with a fast drop beyond a week, and almost no accuracy at all beyond 2 weeks.
There are long-range models that show specific storms up to 2 weeks out but we tend to not trust any models showing specific storm details more than a week out at most. We can look at weather patterns beyond a week to know if the pattern will be favorable for storm development in certain areas, but we can't forecast specific storm tracks and details.
Most forecasters will keep their weather forecasts within a week to avoid being wrong or changing their forecasts constantly. When it comes to specific details like potential snowfall amounts, many of us won't even discuss those details until we are within 5 days or less of a storm.
We can use an average of long-range model data to try and come up with the best snowfall forecasts we can up to 10 days out as we do for the ski area pages in OpenSnow, but many times those numbers can change quite a bit by the time the storms arrive.
Some scientists believe, with more data points added and with new technology, we will be able to forecast storms more accurately 2 weeks out in the future. But some scientists believe we may never be able to forecast accurately beyond 10 days due to the extreme variability of the weather.
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