Every fall the big question is what will this winter weather forecast bring?
Forecasting three days, or even seven days has become quite accurate in general. Going out three months however, the record leaves a lot to be desired for many of the recent forecasts.
Here in the Northwest skiers want to know how much snow is coming and should they buy a ski pass for the season. Highway departments want to know how much they should budget for snow removal. Ranchers who depend upon spring runoff for irrigation are hoping for much above normal snowpack. However if you live on the East Coast you might want to know the odds of getting several arctic outbreaks or what is now call the Polar Vortex. With the wrong forecast (cold) airplane tickets for warmer environs might be part of the plan.
Numerical Weather Prediction (NWP) uses the power of computers to make a forecast. The mathematics and sheer computer power that is required to synthesize all of the data is stunning. The MET office in England is unveiling a $100 million dollar supercomputer capable of performing 1.2 Trillion,(!), calculations per second. The office takes in ten million weather observations per day and issues 3,000 forecasts daily. The sheer universe of data is unbelievable.
Here in the United State, NOAA and the NWS are using much less robust computers. Dr. Cliff Mass of the University of Washington discusses some of the short comings of the US models compared to the European Models in this article.
We did say our article is for the layman so if want to look at more details on forecast models you can check this article
For making winter forecasts for the West Coast of the US forecast models looked to see if there a forecast for El Nino or La Nina. In “general” a strong El Nino will bring warmer temperatures to the Northwest with lower precipitation amounts, (thus low snowfall for the mountains). Stronger La Nina does the opposite. This year, we are looking at a La Nina thus “generally” the Northwest gets above normal snowpack. Thus the skiers, ranchers and water resource managers would be happy if this forecast verifies.
How have the winter forecasts have done over the last few years? The Climate Prediction Center (CPC), a part of NOAA, did rather poorly for much of the west coast over the last 2 winters. To their credit however, the CPC does keep records of their accuracy. Other organizations don’t make them available to the public.
For the CPC they have a scale of 0 to 100 with 0 meaning did no better than what would be expected by chance. If the score is 100 that is a perfect score.
The forecast (for the entire US) issued in November of 2014 for the ’14-’15 winter was a score of 30 for temperature and 3.8 for precipitation.
The forecast (for the entire US) issued in November of 2012 for the 12-13 winter was a score of 0.65 for temperature and 5.9 for precipitation.
This is not to pick on the CPC but I think the main point is that there is not a lot of skill in consistently making an accurate forecast 3 months out. Skill scores.
We are asked where I find seasonal forecasts. Here are some handy links and frankly we have not taken the time to judge the accuracy of these but you can track it and see.
Links for Seasonal Forecast
Article written by Robert Morthorst and edited by Michael Fagin