FLOOD00918

• County: Larimer
• Community: Fort Collins
• Title: Precipitaion Frequency Study
• Date: 7/16/1998
• Prepared For: Fort Collins
• Prepared By: WRC Engineering, Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

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correlations. Using all data points (a data point being one entry in one record pertaining to a single stonn
event), the average precipitation recorded by all of the weather watchers combined was 0.94 inches. The
average rainfall in the group of stations to the west (Region I) was 1.02 inches and the average for those
stations to the east (Region 2) was 0.86 inches for a difference of about 19% This infonnatlon has been
further summarized in Table 8.

Second, the average rainfall for each individual stonn event was calculated using only those weather
watcher reports for which data points existed for the stonn event in question. The data points were then
sorted and analyzed into same regions, i.e.: Region I for those stations west of the center ofthe City and
Region 2 for those stations to the east of the center of the City. The result was that there was a slight trend
as to a greater amount of precipitation falling on the western area (Region I) as opposed to the eastern
area (Region 2). The results are further summarized in Tables H-l thru H-8 in Appendix H.

Third, the data was filtered to include only those stations with known elevations that had recorded data
points for any ofthe stonn events in question. The average amount of precipitation was then calculated
for each of these weather watcher stations and then examined to see if there was a correlation between
the amount of rainfall and the elevation of the station (Since there is typically a rise in elevation from east
to west through the City). The result of this analysis (see Figure-lO) showed that there was not a
significant difference in the amount of rainfall that fell at the weather stations at lower elevations as
opposed to those that fell at higher elevations.

Fourth, the data was filtered to include only those data points from the weather watcher stations that had
recorded over seventy percent of the stonn events. The averages were then ranked and plotted so as to
highlight the locations ofthose stations with greater than the average rainfall as compared to those stations
with less than average rainfall. The result was examined and there appeared to be a weak correlation
between the location of the stations and the amount of precipitation recorded at the weather watcher
station. A map showing the results is presented on Figure I I and the corresponding data is presented in
Table 9. In order to eliminate the skewing ofthe averages by an extreme data point value, the maximum
and the minimum values were then removed and the infonnation was again ranked and plotted. Again,
only a weak correlation seemed to exist between the location of a station and the amount of precipitation
reported at that station. A map showing the results is presented on Figure 12 and the corresponding data
is presented in Table 10.

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