Posted: 9:00 am Friday, March 3rd, 2017
By Kirk Mellish
Finding clues from past weather history that match recent weather is the basis of making the long-range outlook for spring.
We have gone from a weak La Nina to neutral conditions in the Pacific Ocean over the winter and now the sea-surface temperatures in the Pacific are shifting toward El Nino while the Atlantic and Gulf are warmer than normal on average.
There are many past years which compare favorable to this winter, but 2002 and 2006 are good matches for global sea surface patterns and the 500mb configuration as well, making them top analogs for the spring prediction and early summer estimate.
Other analog candidates from the past arise from tracking the ENSO evolution and model projections going forward, combined with finding matches for the winter temperature pattern in the U.S. and key indices like the QBO. Following the sunspot cycle also yields candidates to include in the analog package. For example the current cycle is much like the late 1920s.
The analog derived outlook matches up well with global model output for temperatures and precipitation through spring. The strength and configuration of the sub-tropical jet stream keeps alive concern for a more active than normal severe weather season, although the worst may be in the Midwest and Southern Plains, perhaps staying just to our west and north, but its a close call depending on how quickly El Nino comes on.
The total analog list: 1929, 1951, 1957, 1960, 1961, 1963, 1965, 1967, 1968, 1979, 1981, 1983, 1986, 1990, 1993, 1994, 1998, 1999, 2002, 2006, 2009, 2011, 2012, and 2013.
The strongest matches are used for the forecast.
ANALOGS FOR SPRING TEMPERATURES:
ANALOGS FOR SPRING PRECIPITATION:
So a warmer than normal spring is anticipated with precipitation close to normal, but skewed above-normal the further north of I-285 you go and the drier the further south of I-285 you go. Remember this is the average for the entire spring, not every day or every week.
Below is the historical risk of tornadoes by month based on 30-year average climatology:
Still way too early for a summer outlook, but here is what history tells us about summers following warm winters:
FIRST GUESS for summer based on current best-fit analogs: