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Boulder monthly mean temperature and precipitation
Relationship to El Niño/La Niña
What is the weather in Boulder in relationship to El Niño? In order to examine this question, I looked at Boulder monthly mean temperature and precipitation for a set of 11 El Niño years and a set of 11 La Niña years (as defined by COAPS) from 1949-1996. This excludes the current El Niño. For each of the 11 years, I computed the mean value of that variable and the number of years that that variable was above and below the mean. The former gives an idea of the strength of the "signal". The latter indicates the possibility that only a few years are dominating the average response. Note that any set of 11 years will differ from the mean; whether the difference is statistically significant or not is another question. Also, a different or smaller set of El Niño years will most likely not give the exact same result. For example, see a precipitation comparison for Denver during El Nino winters (choose Denver) from the Desert Research Institute.
To interpret tables
For each of the months listed, the variable of interest is averaged for the 11 El Niño years (column 2) and 11 La Niña years (column 5), respectively. If a month is missing data for a year, less years are used than the 11 possible. The total mean (1949-1996) is calculated from all non-missing years and is in the last column. Then for the El Niño average, the number of the 11 years that are below (column 2) and above (column 3) this mean is calculated. This gives an idea of the odds that an El Niño year will be below/above the mean. The same is done for La Niña years. For example, for January precipitation, the average during El Niño is .45 inches; during La Niña years it is .72 inches and the total mean is .68 inches. Of the 11 El Niño years, 8 had below normal precipitation and 3 had above normal. For La Niña, 5 were below normal and 6 were above.Warm YearsYears listed are for the spring at the end of an El Niño/La Niña. That is, 1983 for a warm year is the El Niño starting in autumn 1982 and ending in spring 1983.
1952,1958,1964,1966,1970,1973,1977,1983,1987,1992,1988Cold years
1950,1955,1956,1957,1965,1968,1971,1972,1974,1976,1989
Precipitation
Month | El Niño average | below | above | tot | La Niña average | below | above | tot | mean |
---|---|---|---|---|---|---|---|---|---|
Jan | 0.45 | 8 | 3 | 11 | 0.72 | 5 | 6 | 11 | 0.68 |
Feb | 0.68 | 8 | 3 | 11 | 1.01 | 3 | 8 | 11 | 0.77 |
Mar | 2.52 | 3 | 8 | 11 | 1.15 | 9 | 2 | 11 | 1.73 |
Apr | 2.21 | 5 | 6 | 11 | 2.74 | 6 | 5 | 11 | 2.30 |
May | 2.88 | 6 | 5 | 11 | 2.79 | 8 | 3 | 11 | 3.26 |
Jun | 1.78 | 8 | 3 | 11 | 1.89 | 7 | 4 | 11 | 2.19 |
Jul | 1.73 | 7 | 4 | 11 | 1.72 | 8 | 3 | 11 | 1.82 |
Aug | 1.21 | 7 | 4 | 11 | 1.36 | 5 | 6 | 11 | 1.47 |
Precipitation: Different set of El Nino years
To see how using a different set of years might affect the results, I used the same years as the Desert Research Institute for their analysis of El Nino and precipitation the west. Partly the different results are caused by using the earlier El Ninos but partly they are caused by using different events (which depend on exactly how an El Nino is defined). These differences give an indication of the sensitivity of the results to the technique.
mean 1940-1996
years used: 1941,1942,1966,1973,1978,1983,1988,1995
Month | El Niño average | below | above | tot | mean |
---|---|---|---|---|---|
Jan | 0.72 | 4 | 4 | 8 | 0.75 |
Feb | 0.86 | 4 | 4 | 8 | 0.76 |
Mar | 1.91 | 5 | 3 | 8 | 1.77 |
Apr | 3.78 | 2 | 6 | 8 | 2.46 |
May | 4.55 | 3 | 5 | 8 | 3.21 |
Jun | 1.96 | 5 | 3 | 8 | 2.15 |
Jul | 1.37 | 6 | 2 | 8 | 1.79 |
Aug | 1.30 | 5 | 3 | 8 | 1.54 |
Month | El Niño average | below | above | tot | La Niña average | below | above | tot | mean |
---|---|---|---|---|---|---|---|---|---|
Jan | 8.25 | 7 | 4 | 11 | 9.40 | 6 | 5 | 11 | 10.78 |
Feb | 9.22 | 7 | 4 | 11 | 14.00 | 5 | 6 | 11 | 10.50 |
Mar | 22.63 | 3 | 8 | 11 | 15.04 | 7 | 4 | 11 | 17.11 |
Apr | 12.62 | 5 | 6 | 11 | 11.28 | 7 | 4 | 11 | 10.94 |
May | 0.93 | 9 | 2 | 11 | 1.61 | 9 | 2 | 11 | 1.57 |
Maximum Temperature
Month | El Niño average | below | above | tot | La Niña average | below | above | tot | mean |
---|---|---|---|---|---|---|---|---|---|
Jan | 45.28 | 4 | 6 | 10 | 45.64 | 3 | 8 | 11 | 45.02 |
Feb | 49.30 | 4 | 6 | 10 | 47.74 | 6 | 5 | 11 | 48.45 |
Mar | 51.36 | 7 | 4 | 11 | 54.79 | 4 | 7 | 11 | 53.64 |
Apr | 61.96 | 6 | 5 | 11 | 62.25 | 6 | 5 | 11 | 62.65 |
May | 72.98 | 3 | 8 | 11 | 71.21 | 6 | 5 | 11 | 71.66 |
Jun | 82.35 | 5 | 6 | 11 | 82.55 | 4 | 7 | 11 | 82.01 |
Jul | 87.57 | 5 | 6 | 11 | 87.45 | 5 | 6 | 11 | 87.40 |
Aug | 85.69 | 5 | 6 | 11 | 85.03 | 7 | 3 | 10 | 85.64 |
Minimum Temperature
Month | El Niño average | below | above | tot | La Niña average | below | above | tot | mean |
---|---|---|---|---|---|---|---|---|---|
Jan | 20.64 | 4 | 6 | 10 | 20.87 | 6 | 5 | 11 | 20.01 |
Feb | 24.01 | 4 | 5 | 9 | 23.16 | 5 | 6 | 11 | 23.51 |
Mar | 26.78 | 9 | 2 | 11 | 27.61 | 5 | 6 | 11 | 27.86 |
Apr | 35.13 | 6 | 5 | 11 | 35.67 | 5 | 6 | 11 | 35.75 |
May | 45.94 | 3 | 8 | 11 | 44.31 | 7 | 4 | 11 | 44.67 |
Jun | 53.78 | 4 | 7 | 11 | 53.60 | 4 | 7 | 11 | 53.23 |
Jul | 58.84 | 6 | 5 | 11 | 58.82 | 6 | 5 | 11 | 58.71 |
Aug | 57.37 | 5 | 6 | 11 | 57.50 | 4 | 6 | 10 | 57.42 |
Discussion of the 1997-1998 El Niño in Boulder
For precipitation and snowfall, values from the current El Niño "match" the Boulder El Niño signal for 8 out of the 10 categories. Red indicates the 1998 values that match the sign of the average El Niño signal in Boulder.For temperature, the signal for January and February is warmer than normal for both max and min temperatures. For both March and April it was colder than normal. For May, it was again warmer than normal. This was matched in 8 of the 10 categories, Feb maximum and May minimum temperatures being the exception. For every month, the sign of the composite was matched in at least 3 out the 4 possible categories.
Month | 98 precip | mean | 98 snow | mean |
---|---|---|---|---|
Jan | 1.07 | .68 | 10.4 | 10.78 |
Feb | 0.23 | .77 | 1.7 | 10.5 |
Mar | 3.41 | 1.73 | 42.6 | 17.11 |
Apr | 4.56 | 2.30 | 19.4 | 10.94 |
May | 1.84 | 3.26 | 0.0 | 1.57 |
Month | 98 Max T | mean | 98 Min T | mean |
---|---|---|---|---|
Jan | 48.6 | 45.02 | 24.4 | 20.01 |
Feb | 48.0 | 48.45 | 24.8 | 23.51 |
Mar | 52.1 | 53.64 | 25.2 | 27.86 |
Apr | 59.1 | 62.65 | 33.9 | 35.75 |
May | 74.2 | 71.66 | 43.3 | 44.6 |