Every year since the early 1990s I have made a forecast for the upcoming winter. This year I issued my forecast in September, and now, in mid-October, I am finally getting around to posting it. Sorry for the delay!!
As always, I create a composite forecast using data from past years which are similar to this year. Mostly I look at changes in the tropical Pacific. I look for years which have spring-summer Pacific conditions similar to the current year. Then I create a composite picture of the fall-winter-spring months for those similar “analog” years.
The main Pacific indicators I use are the Multivariate ENSO Index (http://www.esrl.noaa.gov/psd/enso/mei/) and the Pacific Decadal Oscillation (PDO). Using data through July, 2013, I identified 5 past years with similar distribution of these variables:
1970-71 1973-74 1975-76 1988-89 2007-08
Here is what I found:
Most indicators suggest a wetter-than-average winter. The map below shows precipitation anomalies by climate division for the lower 48, based on a composite of the analog years. Indicated are significant positive anomalies for the Northwest — that is, wetter than average conditions — for November through January.
Looking at cumulative precipitation for Salem (below), most of the analog years were near or above average, with 1973-74 particularly wet.
The nationwide temperature anomalies (below) suggest near-average temperatures for the Northwest. Salem temperatures in the analog years showed near-average winter temperatures but generally cool springs.
Average temperatures and wetter than average precipitation would suggest abundant mountain snowfall, and that is exactly what the analog years showed. Below is a chart with cumulative snowfall at Government Camp, on the slopes of Mt. Hood at about 4,000 feet. Four of the five analog years saw significantly above-average snowfall.
Based on the indicators described above, I predict:
– A wetter than average winter
– Average temperatures
– Above average snowfall; a good year for skiers!!