- El Niflo and La Nifia are oceanographic and atmospheric phenomena that have been
catalogued for well over a centuly. In El Nifio years, Peru's otherwise thy west coast is
subjected to torrential rainfall. Higher ocean temperatures off the coast are deemed the
culprit. Attempts to quantify this began in the early part of the 20th Century in the
western Pacific/eastern Indian Ocean region. By approximately the 1980's, what is
known as the Southern Oscillation Index (501) became established as a benchmark for
understanding circulation in the Pacific Ocean.
This present study compared summer SOl averages with average fall and winter
precipitation at 260 locations in Montana, Washington, Oregon, and Idaho. The time
periods analyzed included 1948-97, 1951-80, 1961-90, 1951-65, 1966-80, 1961-75,
1976-90, and 1983-97. Linear regression and means-difference analysis (t-tests) were the
statistical methods employed. The former test was used to test hypothesized positive
correlations (r>0) for each station. A p-value less than or equal to 0.01 was established as
verifying the correlations. This same level of significance was used to verify a second
hypothesis using t-tests. This hypothesis states that mean seasonal precipitation values
following La Nifla episodes exceed that which follows El Niflo episodes. It was
theorized that there would be geographical correspondence between results of the two
models. In addition, these relationships were theorized to remain regardless of the period
that was analyzed. Results were also hypothesized to yield notable spatial variation.
The hypothesis pertaining to the two statistical models were largely rejected. For
approximately half of the time periods analyzed, however, high levels of statistical
significance were noted in western portions of Montana, Washington, and Oregon, as well as northern parts of Idaho. Most sites appear to be near the western slopes of major
mountain ranges, or are located near mountainous provinces. The hypothesis regarding
uniformity of results for all time periods was also rejected. However, three out of eight
time periods analyzed utilizing the means-difference model showed roughly the same
geographic distribution of high significance as noted with the linear regression model.
The lack of correspondence between the two models is thought to be the result of marked
diversity in precipitation averages that correspond to El Niflo and La Nifia events. The
high West Coast precipitation totals that followed the El Niflo of 1982-83 demonstrated
how an event can violate the assumption that accompanies use of the statistical models.
This fundamental assumption is that low precipitation totals follow El Niflo events, while
higher totals characteristically follow La Nifia events. Marked spatial variation of the
statistical results confirmed the final hypothesis.