Snotel QC Website Tutorial

Matt Doggett

SCAS

http://mistral.oce.orst.edu/www/snotelqc/

Updated: 21 Mar 2005

Overview

• Main window• Summary menu• Station Browser: How to find a station• Create a POR chart• Statistical analysis• Ways to select dates• Ways to select Stations• CI Analysis• Obs/Prediction blending replacement • Downloading data

Main Window• Action Bar

– Selects which functionality you want.

– User is presented with a form for inputs appropriate to the selected function.

• Popup help– Hover mouse over certain

input boxes will open a popup window with some helpful information.

• Action Button– Performs the selected action– Results will open in a new,

separate window

Summary Menu• Purpose: To provide a list of potential trouble stations

that are producing a high number of suspect observations. 1. Select the “Summary” tab

2. Check whether you want a “SNOTEL only” analysis. NOTE: station ID values in the text box are currently ignored.

3. Click the “QuickSum” button to bypass the following steps and generate a simple summary of the last 12 months analysis. (Limit: top 25 stations.)

OR4. Input a date range or leave blank for

the entire database record.Note: “temporal buffer” does not apply to this analysis.

5. Select the “Stnid” checkbox so that the results are segregated for each individual station.Note: Weekly separation does not apply.

6. Select what to sort the results by.7. Click the “Summary” button.

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Summary

• QuickSum– Displays a list of stations

with suspect obs counts for last 30, 60, 90, 180, and 365 days

• Summary– Displays list of stations

with suspect obs counts for the specified period.

Station Browser

• Click the ‘Find’ button on the main page.• Use the Mapserver browser to find a station.• Map tools: Zoom in/out, Pan, Identify• Enter text and click search to query Metadata for Station names

containing the text.• By default, the query only returns those results that are contained in

the given database. To see everything, select the checkbox located below the map.

Enter “Salt Creek” and click Search.

Station Browser

• If you click the station ID hyperlink, the window will close and you will be returned to the main QC window with the station ID value filled in the form input box.

Scroll Down and find the ID for SALT CREEK FALLS in the table. Enter this value “22F04S” in the Stnid text box and click “Nearest Stations”.

Station Browser

• When you click “Nearest Stations” the map will zoom into the area surrounding the indicated station.

Scroll down to see a table of all the nearest stations in the vicinity.

In the table, click on the hyperlink “22F04S” to select the station and return to the QC application.

POR Analysis

• POR Analysis is done when the Date field is left blank. Due to performance constraints, this is limited to single station analysis only.

Click Analysis menu

Fill out the form as you see here.

Click Chart button

POR Analysis

• A new analysis window opens containing a chart, map, and table.

• POR charts are nice to see long-term trends. But often, you’ll want to select a statistical measure to spot long-term trends.

• “zoom-in” on a particular time period. To do that, you need to select a date-range for analysis.

Chart

Table

Map

Statistics Charts

• Statistics. Calculate several statistics on the selected parameter grouped by the settings in the “Separate By” fields. If no statistic is selected, the separate by fields are not applicable.– None, Min, Max, Mean, Stddev, Threshold%

• Threshold%. When selected, evaluates the percent of records that exceed the indicated threshold value. This is performed using the indicated parameter type.

• Exclude missing obs. When analyzing CP statistics, missing data have a CP=0, which can influence the resulting statistic. Select this checkbox to ignore missing.

Select ‘mean’

Statistics Charts Grouping

• Ways to group statistics– By Stnid. Each station will be evaluated separately. If not

selected, all stations will be grouped into the same analysis.– By Year, Quarter, Month, Week.– By None. If no grouping is selected, then the analysis defaults to

a simple timeseries. Measures of statistics are not applicable.

•Select Stnid, Year, Month•Click ‘Chart’ button

Analysis

• A new chart of ‘Mean Observation’ grouped by Month and year.

• Note the period of unusual values in 1991.

• To get a better look, you’ll want to “Zoom in” on a particular date range. Do this by specifying values in the Date fields.

Ways to Select Dates

• Period of Record (POR). Leaving the Date box empty will return ALL dates available for the indicated station. This is ONLY available for single-station analysis.

• Single Year. Enter a 4-digit year in the Date block to return a single year.• Single Month. Enter YYYY-MM to return a single month.• Single Day. Enter YYYY-MM-DD to return a single date (not very useful

unless specifying a date range).• All months. Enter MM to return the specified month for all years.• Date Range. If the “End” block is selected, the analysis will span from the

Date to End date supplied. Both dates must follow the same format (eg. both blocks contain YYYY-MM or YYYY-MM-DD, etc).

• Temporal buffer. Returns a range of dates centered on the date given in the Date block and surrounded by X number of days.

• NOTE. Pay attention to which radio button is selected before you click the Chart button!!

• Enter 1991-05 in the Date block and 1991-10 in the End block. • Make sure “End” is selected.• Select “None” for statistic.

Analysis

• When dates are provided, the analysis window is limited to the selected time period.

• Now you probably want to compare this station with it’s neighbors to see if the cool-down in July-Aug is legitimate.

• To do that, you need to specify more than one station ID.

• Note the period of cooler summertime temperatures.

Ways to Select Station ID

• List. In the Stnid field, you can enter a single ID or a comma-separated list of IDs.

• Search radius. If search radius is selected, all stations within the specified distance (in degrees) will be analyzed.

• State. Supply the two-character state abbreviation to analyze all stations in a given state.

• SNOTEL only. If this box is selected, only SNOTEL sites will be included for analysis.

• NOTE. Pay attention to which radio button is selected before you click the Chart button!!

•Select “Search Radius” and enter a value of .25 degrees.

Analysis

• A new window opens that shows:– A separate line for each

station. This is because Separate By: Stnid checkbox is selected.

– The cooldown during July-Aug 1991 at Salt Creek Falls is clearly anomalous compared to it’s nearest neighbors.

Confidence Interval Analysis

• If you select “CI Analysis”, the chart will show a special analysis of the observations compared to the PRISM predictions

• When the red line (observation) lies between the blue lines, then it fits within a 67% confidence that the observation “agrees” with the PRISM prediction.

• When the red line falls outside the area, then the observation is highly suspect.

• The more outside the lines, the less likely the observation is valid.

• In this example, the observations are clearly erroneous.

• Now you might like to “Clean up” the data to produce a timeseries of valid data. To do this you need to select “Obs/Prediction Blending”

Obs/Prediction Blending

• When selected, obs blending will attempt to blend the observation record with the PRISM predictions to produce a consistent timeseries of data.

• Weighting is applied linearly from the max to the min threshold. At the max threshold, weighting is applied entirely to the observation. At the min threshold, the PRISM prediction has all the weight.

• The resultant value is– CP > Max: Observation– CP <= Max and CP > Min: Blend between Obs and Prediction– CP <= Min: Prediction

• NOTE. Blending is only valid for “observation” related variables:– Observation, Residual, and CI Analysis.

• Complete the table as you see here.• Click the “Chart” button

Obs/Prediction Blending

• Note that with replacement, the CI Analysis window ‘fixes’ the observations to fit between our confidence levels.

• Also, the observation analysis shows that the blended observation is entirely consistent with the neighbors.

• Now that we have a ‘clean’ timeseries, you might be interested in downloading data for your own application or analysis.

Download

• When downloading, all the options selected for station ID and dates are applicable.

– single or group of stations.– POR or a specific date range.– SI or English units.

• The query process may take 15-30 seconds or more depending on how many stations and date range.

• When complete you will be presented with a link to download the data.

• Click “Retrieve File” to save the file to your computer.

• Complete the table as you see here.• Click the “Download” button

• Click “Retrieve File” to copy file to your computer.

Download

Fill in the form with values as you see here.

Click Download button

So how do you know what CP threshold to use? That’s what the rest of the SnotelQC application is for.

Click Download menu

Summary

• Database: snotel – Currently only OR, AZ, and CO

• Variable: tmax, tmin• Dates: 1978-2003• Processing/Procedure inquiries

– Chris Daly, 541-737-2531– daly@coas.oregonstate.edu

• Website issues– Matt Doggett, 541-737-9153– mdoggett@coas.oregonstate.edu