National Water and Climate CenterNational Water and Climate Center

PPRRIISSM M Probabilistic-Spatial QC (PSQC) System for SNOTEL DataProbabilistic-Spatial QC (PSQC) System for SNOTEL DataMTNCLIM 2006 CONFERENCE

September 19-22, 2006 at Timberline Lodge, Mt. Hood, Oregon

PRISM to help with Quality Control (QC)

When installation first began in the middle 1970s, the SNOTEL (SNOwTELemetry) network was never envisioned as a data source for climate change studies; however the network has become a de facto source for middle and higher elevation snowpack, precipitation and temperature data in the West. While sensor technology and communication capability continue to improve the quality of observations at these remote sites, PRISM methodology is now being employed to correct or back-fill all archived SNOTEL data that is suspect or missing. The results of this effort may indeed provide the basis for identifying a “benchmark” SNOTEL network for climate change studies.

COLORADO SNOTEL SITESCOLORADO SNOTEL SITES

46 Colorado SNOTEL sites with more than 5,000 daily (Tmax & Tmin) observations. Missing daysMissing days account for ~5.15% of POR. PRISM determined suspect observationssuspect observations account for ~1.75% of POR.

BBackgroundackground OOriginal riginal DData ata QQualityuality PPRRIISSMM MMethodologyethodology

http://mistral.oce.orst.edu/www/snotelqc/http://mistral.oce.orst.edu/www/snotelqc/“Advances in climate mapping technology now make it possible to estimate a reasonably accurate ‘expected value’ for an observation based on surrounding stations.

Assumption: Spatial consistency is related to observation validity.” – Dr. Chris Daly

Electronic Sensors and Modern Electronic Sensors and Modern Applications Create Challenges for Applications Create Challenges for

Traditional QC SystemsTraditional QC Systems

• Errors tend to be continuous Errors tend to be continuous drift, rather than categorical drift, rather than categorical mistakesmistakes

• Increasing usage of Increasing usage of computer applications that computer applications that rely on climate observationsrely on climate observations

• ContinuousContinuous estimates, rather estimates, rather than categorical tests, of than categorical tests, of observation validityobservation validity

• Quantitative estimates of Quantitative estimates of observational uncertainty, not observational uncertainty, not just flagsjust flags

Situation Need

PRISM Regression of “Weather vs. Climate”

PRISM Results

18

20

22

24

26

28

30

32

34

16.5

17.5

18.5

19.5

20.5

21.5

22.5

23.5

24.5

25.5

26.5

71-00 Mean July Maximum Temperature

Dai

ly M

axim

um

Tem

per

atu

re (

C)

21D12S

21D35S

21D13S

353402

21D08S

5211C70E

324045CC

3240335C

21D14S

Regression

Stn: 21D12SDate: 2000-07-20Climate: 21.53Obs:26.0Prediction: 25.75Slope: 1.4Y-Intercept: -4.37

20 July 2000 Tmax vs. 1971-2000 Mean July Tmax

This is a scatter-plot showing how this method can be used for daily interpolation. On the x-axis is the mean July temperature, and it is being regressed with the daily maximum temperature for July 20, 2000. This plot, for a location new Mount Hood in Oregon, shows that even though the temperature is nearly 5C above the mean, the spatial patterns are remarkably similar.

SNOTEL QCSNOTEL QC WWebsiteebsite

Issues to Consider*Issues to Consider*• How far can the assumption be taken that spatial consistency How far can the assumption be taken that spatial consistency

equates with validity?equates with validity?

• Are continuous and probabilistic QC systems useful for manual Are continuous and probabilistic QC systems useful for manual observing systems?observing systems?

• Can a high-quality QC system ever be completely automated?Can a high-quality QC system ever be completely automated?

• If a QC system works effectively, can it be used for SNOTEL site If a QC system works effectively, can it be used for SNOTEL site selection? If so, thenselection? If so, then

• What criteria should be employed for SNOTEL site selection?What criteria should be employed for SNOTEL site selection?

Jan CurtisNRCS - National Water & Climate Center

1201 NE Lloyd Blvd., Suite 802Portland, OR 97232

jan.curtis@por.usda.gov(503) 414-3017

• Range of applications is Range of applications is increasingly rapidly, and increasingly rapidly, and each has a difference each has a difference tolerance for outlierstolerance for outliers

• Data are often more Data are often more voluminous and voluminous and disseminated in a more disseminated in a more timely mannertimely manner

• Probabilistic information from Probabilistic information from which a decision to use an obs which a decision to use an obs can be made, not up-front can be made, not up-front decisiondecision

• Automated QC methodsAutomated QC methods