1. Limitations of Rain Gauges
Doug Lundquist with
Excerpt from:
Measurement of Precipitation Using Rain Gauges
Jennifer Adam
Department of Civil and Environmental Engineering
University of Washington

2. Undercatch of Precipitation Using Standard Gauges
Wind-Induced Undercatch
Snow: 10 to >50%
Rain: 2 to 10%
Wetting Losses
2 to 10%
Evaporation Losses
0 to 4%
Treatment of Trace Precipitation as Zero
Significant in Cold Arid Regions
Splash-out and splash-in
1 to 2%
Blowing and Drifting Snow ??
Sevruk, 1982

3. Wind-Induced Undercatch
Influencing Factors:
Wind speed
Temperature
Gauge type
Gauge height
Windshield
Exposure
Nespor and Sevruk, 1999

4. Wetting Losses Influencing Factors: Gauge type Climate
Measurement Methodology

5. Evaporation Losses Influencing Factors: Gauge type Climate
Measurement Methodology

6. Other Sources of Errors
Obstruction (ideally in a clearing surrounded by trees)
Occult Precipitation: fog drip and rime
Observer Errors: random, systematic, and gross
Errors due to differences in observation time (ideally midnight)
Instrument Malfunction
Specific to Recording Gauges – bad calibration…
Tampering / Vandalism
Observation Record Inhomogeneity – changes in instrumentation, site, and local environment

7. Example of Snow Melt Following data from Wednesday January 07 2009
CHAP SA 1000 AUTO9 M M M M/0/0/MMMM/M/0390 RMK PCPN 3.0MM PAST HR CLIMATE
39MM/6CM/88CM (ALLISON PASS/1340m) [22MM]= CHAP SA 1100 AUTO9 M M M M/0/0/MMMM/M/0420 RMK PCPN 3.0MM PAST HR CLIMATE
42MM/7CM/88CM (ALLISON PASS/1340m) [22MM]= CHAP SA 1200 AUTO9 M M M M/0/0/MMMM/M/0440 RMK PCPN 2.0MM PAST HR CLIMATE
44MM/8CM/89CM (ALLISON PASS/1340m) [22MM]= CHAP SA 1300 AUTO9 M M M M/0/0/MMMM/M/0490 RMK PCPN 5.0MM PAST HR CLIMATE
49MM/9CM/90CM (ALLISON PASS/1340m) [22MM]= CHAP SA 1400 AUTO9 M M M M/0/0/MMMM/M/0510 RMK PCPN 2.0MM PAST HR CLIMATE
51MM/10CM/91CM (ALLISON PASS/1340m) [22MM]= CHAP SA 1500 AUTO9 M M M M/0/0/MMMM/M/0020 RMK PCPN 2.0MM PAST HR CLIMATE
2MM/M/90CM (ALLISON PASS/1340m) [22MM]= CHAP SA 1600 AUTO9 M M M M/0/0/MMMM/M/0040 RMK PCPN 2.0MM PAST HR CLIMATE
4MM/2CM/92CM (ALLISON PASS/1340m) [22MM]= CHAP SA 1700 AUTO9 M M M M/0/0/MMMM/M/0070 RMK PCPN 3.0MM PAST HR CLIMATE
7MM/2CM/92CM (ALLISON PASS/1340m) [22MM]= CHAP SA 1800 AUTO9 M M M M/0/0/MMMM/M/0130 RMK PCPN 6.0MM PAST HR CLIMATE
13MM/2CM/92CM (ALLISON PASS/1340m) [22MM]= CHAP SA 1900 AUTO9 M M M M/0/0/MMMM/M/0150 RMK PCPN 2.0MM PAST HR CLIMATE
15MM/2CM/92CM (ALLISON PASS/1340m) [33MM]= CHAP SA 2000 AUTO9 M M M M/0/0/MMMM/M/0190 RMK PCPN 4.0MM PAST HR CLIMATE
19MM/4CM/93CM (ALLISON PASS/1340m) [44MM]= CHAP SA 2100 AUTO9 M M M M/1/1/MMMM/M/0300 RMK PCPN 11.0MM PAST HR CLIMATE
30MM/4CM/93CM (ALLISON PASS/1340m) [55MM]= CHAP SA 2200 AUTO9 M M M M/0/0/MMMM/M/0320 RMK PCPN 2.0MM PAST HR CLIMATE
32MM/5CM/94CM (ALLISON PASS/1340m) [33MM]= CHAP SA 2300 AUTO9 M M M M/0/0/MMMM/M/0340 RMK PCPN 2.0MM PAST HR CLIMATE
34MM/5CM/93CM (ALLISON PASS/1340m) [33MM]=
Following data from Thursday January
CHAP SA 0000 AUTO9 M M M M/0/0/MMMM/M/0360 RMK PCPN 2.0MM PAST HR CLIMATE
36MM/6CM/95CM (ALLISON PASS/1340m) [22MM]= CHAP SA 0100 AUTO9 M M M M/0/0/MMMM/M/0370 RMK PCPN 1.0MM PAST HR CLIMATE
37MM/7CM/94CM (ALLISON PASS/1340m) [22MM]= CHAP SA 0200 AUTO9 M M M M/0/0/MMMM/M/0390 RMK PCPN 2.0MM PAST HR CLIMATE

8. The Orographic Effect on Precipitation

9. References
Dennis Lettenmaier
University of Washington
Jennifer Adam