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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Fifth, the infonnation was filtered to include only those stations which had reported on the same stonn
event. This infonnation was again ranked and plotted so as to highlight the locations of stations with
above average rainfall versus stations with below average rainfalL The results, which are presented both
on Figure 13 and in Table I I, again showed only a very weak correlation between the location of the
station as referenced from the center ofthe City to the average rainfall event. The infonnation was then
filtered to eliminated extreme values as before with the same result. These results are presented in Figure
14 and in Table 12.

Finally, a data set was prepared which only included stonn events which were driven by moderate to
strong upslope weather conditions. The stonns in this data set are presented in Table-13. This data set
was filtered into four sub-data sets similar to the filtering ofthe full data set. The description and resulting
Tables and Figures are as follows:

FlL TER

RESULTS PRESENTED ON

Table-I4 and Figure-IS

Table-IS and Figure-I6

Table- I 6 and Figure- I 7

Table-17 and Figure- I 8

A. Reporting of at least 70% of the stonn events

B. nAil above but with minimum and maximum values removed

C. Stations with stonn events in common
D. "C" above but with minimum and maximum values removed

The results of these analyses showed trends and scatter similar to the full data set analyses.

The 1997 stonn event was included in this analysis only as measured by weather watchers stations. Non-
weather watcher data (i.e. rainfall amounts measured or estimated by the general public) was not included
to maintain consistency in the data analysis. If included, then the same type of data would need to be
included for the other stonn events.

c.

CONCLUSIONS:
The conclusion that was drawn from the examination and analysis of the weather watcher data is that
there is a trend in a larger amount of precipitation occurring in the region west of the center of the City
of Fort Collins as compared to the amount that occurs to the east of the center of the City. The trend
mainly occurs along the Cache La Poudre River. However, there was not a significant difference in the
amount of rainfall due to the elevation ofthe weather watcher station. Given this infonnation, we would
not recommend the use of different design precipitation data for the eastern versus western areas of the

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