Each August, as we start hearing outlooks for the upcoming winter season, I always find it amusing to go back and look at the forecasts for the upcoming winter season from this time last year.
Most of you likely find it humorous that forecasters even attempt a forecast 4-6 months out when they struggle to get the forecast right 4-6 days out. But many of you, like me, can't help yourself and read all of them anyway.
One thing is certain, snow enthusiasts wish they could know the forecast for next season 6 months in advance, especially as they are buying expensive gear, shelling out hundreds for their season's pass, or planning their annual ski vacation.
"What's going to happen this winter?" is the #1 question we as forecasters get this time of year.
Can Forecasters Actually Make an Accurate Forecast 3-6 Months before Winter?
The track record for U.S. forecasters making accurate winter predictions is usually so bad, that here at OpenSnow we don't even attempt to publish an official forecast for the upcoming season. Our forecasters will analyze other forecasts and make their own guesses for their region as we get closer to winter, but we focus on shorter-range snow forecasts aimed at accuracy.
When I first started forecasting I remember being taught, "the forecast models lose 10% of their accuracy for each day they forecast out into the future". That would mean 0% accuracy beyond 10 days! The actual stats are a bit different than this general rule of thumb, but 10 days is still about the limit of a skillful forecast for individual storm systems.
While we cannot predict specific storms more than 10 days out, forecasters do try to predict general weather patterns months in advance, such as the chance that an area will be colder or warmer than average, or wetter or drier than average.
What Did the Forecast Models Show Us Last Year?
The long-range forecast models are heavily used by forecasters when they are putting together their winter forecasts. One of the first things they look at well in advance of the upcoming season is the forecast for the sea surface temperatures, especially in the ENSO regions along the equator which will signal a possible El Niño or La Niña.
This time last year (August 2019), the forecast models were pointing towards ENSO neutral conditions for the 2019-20 winter season. Meaning neither warmer nor colder than average temperatures overall along the equator in the ENSO regions. This is shown by a mix of red & blue colors west of South America.
Most of the winter forecasters and forecast models will look at the forecast for ENSO regions and compare it to historical weather patterns during similar ENSO patterns. Here is a typical ENSO Neutral weather pattern for the U.S. based on historical records.
We saw the forecast models like the CFSv2 predicting a similar pattern with above-average precipitation for the Pacific NW & Eastern U.S. for last winter.
Typically we would see warmer than average temperatures across the southern U.S., and cooler than average into the north-central/northeastern U.S. The CFSv2 was predicting warm temperatures for almost the entire U.S. except for the far northwest and northeast.
What Were Forecasters Predicting for Temperatures?
Forecasters and forecast outlets were releasing varying forecasts last summer and fall for the upcoming winter season temperature departures from average. But most of them where showing cooler than average temperatures nosing down from Canada into the northern/northeastern U.S. Here were the temperature forecasts from several outlets.
The Weather Channel
What actually happened with temperatures last winter?
The temperature pattern ended up being above average for almost the entire country except for an area over the central Rockies! The northeast was forecast to be one of the coldest regions and ended up being one of the warmest!
What Were Forecasters Predicting for Precipitation?
For precipitation, the forecasters again had varying forecasts. Some with wetter than above-average precipitation forecast across the northern U.S., and others across the southern U.S.
Some of the forecast outlets produce a 'type-of-precipitation' forecast, not just a "precipitation compared to average" forecast so that they can show areas with above or below-average snowfall as well.
Old Farmer's Almanac
First Hand Weather
What actually happened with precipitation last winter?
Just looking at the precipitation part of the forecasts, it doesn't look like anyone got the forecast perfect. We saw above-average precipitation in the Pacific NW, across the north-central U.S., and in the southeastern U.S. The bottom 3 outlets above look to have been the closest with precip departures from average.
Most Importantly, What Were Forecasters Predicting for Snowfall?!
Not all forecasters or forecast outlets breakout the snowfall forecast on its own. Below are a few that do, and some have it mixed into the precipitation forecast (above).
Most predictions were for the cold air and above-average precipitation to bring above-average snowfall to the northeastern U.S. A couple of forecasts had above average snowfall for the northwest, a couple for the southwest, and a couple the north-central U.S. as well.
What actually happened with snowfall last winter?
With the coldest air and storm track expected across the north-central into the northeast U.S., that is where most outlets were showing above-average snowfall. We saw that on the ground by the end of February from the eastern Dakotas across to the far northern parts of the northeast. But none were right about the cold and the warmer temperatures likely kept the snowfall farther north than expected.
For the western U.S., the Pacific NW and the northern Rockies were expected to be near to above average for snowfall. That seemed to pan out mostly. By April the snowpack was near to above average in those regions, and near to below average farther south, with much below average for the far southwest.
The Sierra and the southern Rockies were dry into early March. But had a nice comeback with another season of late snowfalls from the 2nd half of March into early April. Too little too late, especially thanks to the pandemic closing ski areas in mid-March just as the snow finally arrived...
All of the forecast outlets blew the temperature forecast for below average in the north/northeast as we saw a mild winter everywhere.
Most forecast outlets did a good job in predicting above-average precipitation across the northern and southeastern U.S. The few that added the southwest were wrong.
Most of the forecast outlets were right about average to above-average snowfall across the northern U.S. but were a little too far south with the snowfall forecast. A few had average to above average for the southwestern U.S. and those were wrong.
I'm struggling with which forecast was the most accurate. I'll let you decide. Comment below or add another forecast we may have missed. Overall, the fact that long-range forecasts are nearly impossible and typically inaccurate continues to stand.
So How Do I Plan My Powder Skiing 3-6 Months In Advance?!
The simple answer is, you can't!
It would be pure luck to nail a powder trip this far out for the winter season. The winter forecasts coming out this time of year are based on scientific weather models and long-term patterns that could affect our weather this winter based on history. But the skill is not there yet to make a reliable winter forecast 3-6 months out.
Some forecasters will use years of experience to adjust what the models are predicting, and a few forecasters could get it right some years. But as you can see above, most of the predictions for temperature, precipitation, and snowfall were off in at least one region or variable last season. There are too many short-term patterns throughout the winter season that control whether a certain region is cold and snowy or warm and dry.
Technology will continue to advance and someday we may be able to accurately and consistently forecast the weather patterns 3-6 months in advance, maybe with super AI?!
Until then, stay tuned to OpenSnow throughout the winter season. We will be working hard to get you accurate snow forecasts within a reasonable 5-10 day range!
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