Central Region Snowfall Analysis Brian P. Walawender NWS Central Region Headquarters Matt W. Davis NWS WFO La Crosse, WI 5/26/2011

History In the early 2000’s, NWS offices began creating precipitation analysis graphics for display on their web pages. Two primary software packages were utilized for the creation of the graphics –ArcMap –GFE Both software packages interpolated the random points into a graphical analysis 2

Weaknesses of Previous Methods Manually created, via a multistep process, on a non routine basis Typically restricted to the local forecast area, requiring the user to view several graphics to see the big picture Color and contour intervals typically varied from office to office, leading to confusion when viewing graphics from multiple offices. No ability to zoom the graphics or add/remove layers 3

Central Region Prototype Collaborative effort between NWS Central Region Headquarters and WFO La Crosse, WI. Key Requirements –Use commonly available to Open Source GIS tools –Automated –Output can be zoomed and panned –Consistent colors and contour intervals 4

Open Source Tools Utilized Postgresql/PostGIS database – allows for the storing of a geometry object (latitude and longitude in our case) with any database entry GDAL - Geospatial Data Abstraction Library –Used perform the interpolation of the raw data into the output analysis graphic –Used perform the contour analysis from the output image –Used to create the multiday analysis products 5

Open Source Tools Utilized Mapserver – web mapping server used to serve out the raster and shapefile output products OpenLayers – web mapping API –Similar to Google Maps –Allows for adding interactive maps to web pages 6

Dataflow Input data of consists of: –NWS Cooperative Observer Reports –Community Collaborative Rain, Hail and Snow Network (CoCoRaHS) reports Typical Analysis will consist of about 7500 observations NWS Local Storm Reports (LSR) were purposely left out because of time range concerns –LSR reports currently contain no start, stop or duration information (yet) 7

Dataflow Reports are received via LDM from MADIS and NOAAport Reports are decoded and databased in realtime –Database can hold several months of data 8

Data Analysis The scattered point to grid analysis is done via an inverse distance weighted interpolation scheme. –Grid box is a moving1.8 degs, requiring three observations. Inverse power is 6, and output is smooth very slightly at 0.2. Output is a georeferenced tagged image file format (GeoTIFF) –2000 x 2000 GeoTIFF covering CONUS. 9

Data Analysis To increase the display performance, the large GeoTIFF is converted into polygon shapefile via GDAL The conversion into the polygon shapefile bins the analysis into the standard contour intervals The analysis is run every 30 minutes from 12 UTC until 20 UTC to continuously update the analysis 10

Multiday Products Multiday products pose a challenge since there is dilemma on whether or not to include stations that do not report each day of the reporting period –Example – a station reports three days over a four day period – do you use it in a four day analysis To avoid this concern, the multiday products are created by summing the output analysis for each day in the period, instead of the raw data. 11

Quality Control An internal web interface allows offices to quality control the analysis The interface allows the forecaster to flag stations with questionable data, causing them to be removed from the analysis The analysis is automatically run twice per hour, including new observations, and removing those which were quality controlled. 12

Web Display The final analysis products are displayed on the web page via an interactive map The interactive map can be panned and zoomed The interactive map has multiple layers that can be toggled on and off The map includes output for the last 24, 48 and 72 hours 13

Web Display The snowfall analysis can be viewed at: – Note this URL may change for the 2011/2012 snow season Future enhancements will included increased resolution, and more observations (Snotel, etc.) 14

Customer Response Customer Survey ran from Jan 10 th until April 30 th, 2011 –300 responses –180 users rated the technical quality of the product as a nine or higher (out of ten) –207 users rated the ease of use as a nine or higher 15

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Authors Matt W. Davis –La Crosse, WI Weather Forecast Office –N2788 County Road FA –LaCrosse, WI Brian P. Walawender –Central Region Headquarters Regional Office –7220 NW 101st Terrace –Kansas City, MO

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