As a youngster in the foothills of southern New Mexico , I became very involved in taking daily weather records. One of the main features that intrigued me was the apparent significant discrepancy year after year of precipitation totals over relatively short spans of distance and elevation in foothill environs.
The goal of this study was to focus on the differences in precipitation totals between the National Weather Service Office (NWSO) in Pueblo, Colorado and the observing site at Rye, Colorado, that is approximately 30 miles southwest and 2200 feet higher than the NWSO Pueblo.
Pueblo is approximately 40 miles east-southeast of the Royal Gorge, at the junction of the Arkansas and Fountain Rivers. The foothills and mountains west of the city extend from within 25 miles to the southwest (including the Wet Mountains in which the community of Rye, Colorado is located) to about 35 miles to the northwest. The Wet Mountains rise abruptly to an average elevation of 7,500 - 8,500 feet mean sea-level with peaks above 12,000 feet.
The physical location of the official observing station in Pueblo is at the NWS office approximately 7 miles east of downtown Pueblo at an elevation of 4640 feet. The physical location of the Rye foothill station is at the base of the Wet Mountains approximately 30 miles southwest and 2,200 feet higher than the official site. The period of concentration in this study was January 1973 to December 1982.
Figure 1 depicts the yearly precipitation totals of the Pueblo NWS office verses the Rye foothill station. Figure 2 shows the percent difference between the two sites. As can be inferred, the Rye foothill station has a 109 percent higher precipitation average than the Pueblo NWS office. Note that there are wide fluctuations from year-to-year; for example, in 1981 the Rye foothill station received 231 percent more precipitation than the Pueblo NWS station, while in 1979 the difference was only 21 percent more precipitation (Figure 2).
Figure 1. Pueblo and Rye, Colorado yearly precipitation totals (1973-1982).
Figure 2. Pueblo and Rye, Colorado yearly precipitation percent difference (1973-1982).
Figure 3 depicts the monthly precipitation totals of the Pueblo NWS office verses the Rye foothill station for 1973 through 1982. As can be seen from the graph, the Rye foothill station has most of the higher precipitation months. However, anomalies do exist, e.g., July of 1973 and April of 1980 (Figure 3).
Figure 3. Pueblo and Rye, Colorado monthly precipitation totals (1973-1982).
Figure 4 displays the average monthly precipitation totals of the two observing sites while Figure 5 exhibits the average monthly percent difference. These figures show that the greatest differences in average monthly precipitation occur in November, December, January and February while the smallest differences in average monthly precipitation occur during June, July, August and September. Physical reasons for this are not addressed in this paper. However, convective precipitation, upslope or downslope conditions as well as mesoscale and microscale features are likely factors.
Figure 4. Pueblo and Rye, Colorado average monthly precipitation totals (1973-1982).
Figure 5. Pueblo and Rye, Colorado average monthly percent difference (1973-1982).
Results of this study document that relatively minor differences in distance and elevation can significantly affect precipitation totals in the Southern Colorado Foothill/Plains corridor. Each precipitation event must be addressed separately. However, awareness of the possibility of large differences in precipitation amounts will aid the operational forecaster.
The author would like to thank Nolan J. Doesken and Thomas B. McKee at the Colorado Climate Center and William F. Fortune for their helpful contributions to this paper.
DOC/NOAA, 1990: Local Climatological Data, Annual Summary with Comparative Data. Pueblo, Colorado, 8pp.
Doesken N.J., and T.B. McKee, 1991: Monthly Climatic Data. Rye, Colorado 4pp.