interpolation error of station into gridded data

I'm trying to interpolate random data into gridded data.
But it's so big differences between input and output value.

--> before interpolation
(0) min_val of in_rain= 0
(0) max_val of in_rain= 80.33
--> after interpolation
(0) min_val of out_rain= -931.531
(0) max_val of out_rain= 1026.31

Here is ncl scripts and output log

Does anybody know the reason?

Best regards,
Jin-Young Kim

-- 
Ph. D. Student
Jin-Young Kim (jin_at_climate.pknu.ac.kr)
Integrated Climate System Modeling Lab.
Department of Environmental Atmospheric Sciences
Pukyong National University, Busan 608-737, South Korea
Web : http:climate.pknu.ac.kr/~jin
Visiting Scholar
Jin-Young Kim (Jin-Young.Kim_at_noaa.gov)
Global Systems Division
Earth System Research Laboratory
R/GSD7
325 Broadway
Boulder, CO80305-3328
+1-303- 497-4422 (Office)
+1-303- 497-7262 (FAX)

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