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Precipitation and Temperature
Tendencies During El Nino & La Nina Years
at Salt Lake City, Cedar City,
and Blanding, Utah
David Hogan, NWSFO Salt Lake City, October 2000
This study compiled monthly precipitation and temperature records during El
Nino and La Nina years for three cities in Utah: Salt Lake City (representing
northern Utah), Cedar City (representing southwest Utah), and Blanding (representing
southeast Utah). El Nino and La Nina seasonal precipitation and temperature
averages were compared to historical (long-term) averages for each site.
The precipitation data showed some distinct tendencies so bar charts were created to illustrate these tendencies. On the other hand, temperature tendencies were not very significant and were only
mentioned where significant. The remainder of this study will focus on the El Nino/La Nina precipitation tendencies.
As stated above, the first step in analysis of the data was to calculate El Nino and La Nina seasonal precipitation averages for each site. These averages were then compared to historical averages, first
by purely statistical means, and secondly by qualitative analysis.
Statistical analysis was performed using the "T-test". The T-test was calculated for each site by season for both El Nino and La Nina years. The T-test scores were not statistically significant. This
result came as no surprise owing to the small sample sizes (analysis of small sample sizes rarely yields statistically significant results).
In light of the lack of rigorous statistical results, a qualitative approach
was taken. Seasonal El Nino or La Nina precipitation was labeled as "normal"
if the value was within 10% of the historical average. A particular El Nino/La
Nina season was considered "dry" or "wet"
if both of the following 2 criteria were met, and "somewhat
dry" or "somewhat wet" if only 1 criteria
was met:
1. 2-to-1 Imbalance of Wet and Dry Years (summarized at bottom of
each individual bar chart)
2. Seasonal Precipitation Average of El Nino/La Nina Years more than
10% off Historical Averages (indicated by horizontal lines on each individual
bar chart)
CONCLUSIONS/RESULTS:
This subjective analysis approach resulted in pronounced precipitation
tendencies for the lesser-known La Ninas and little if any tendencies over
Utah for the much-hyped El Ninos. There was a nearly
across-the-board dry tendency statewide for La Ninas, whereas there were
only a few minor tendencies for El Nino years.
DETAILED RESULTS : (remember to reference
definitions of "dry"/"wet" and "somewhat dry"/"somewhat
wet" above)
During El Nino Years:
***
Little or No Temperature or Precipitation Tendencies Overall
***
Minor Temperature and Precipitation Tendencies as follows:
- "Dry" (and Warm) Winters in Cedar City
- "Wet" (and Cool) Springs in Cedar City
- "Dry" Summers in Salt Lake City
- "somewhat dry" winters
in Blanding
- "somewhat wet" falls
in Blanding and Cedar City
During La Nina Years:
*** "DRY" AT ALL 3 SITES SPRING,
SUMMER, AND FALL
(3/4 OF THE YEAR)!!***
Minor Temperature and Precipitation Tendencies as follows:
- "Wet" in Western Utah (SLC and CDC) during
the Winter
- "Dry" in Blanding during the Winter
Links
to the BAR CHARTS: (organized BY SEASON)
1. WINTER (all 3 locations): El
Nino, La Nina
2. SPRING (all 3 locations): El
Nino, La Nina
3. SUMMER (all 3 locations): El
Nino, La Nina
4. FALL (all 3 locations): El
Nino, La Nina
Links
to the TABLES: (organized BY LOCATION)
1. SALT LAKE CITY Precipitation and Temperatures: El
Nino, La
Nina
2. CEDAR CITY Precipitation and Temperatures: El
Nino, La
Nina
3. BLANDING Precipitation and Temperatures: El
Nino, La
Nina
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