Appendix D — GIS Shapefile Download Reference
All 13 IEM GIS download endpoints under /request/gis/, plus related spatial download resources. These portals produce shapefiles, CSVs, and GeoJSON files suitable for use in QGIS, ArcGIS, Python (geopandas), R (sf), or any GIS-capable application.
All endpoints are at https://mesonet.agron.iastate.edu + the path shown.
/request/gis/ Endpoints
| Endpoint | Data Type | Output Format | Date Range | Notes |
|---|---|---|---|---|
| /request/gis/watchwarn.phtml | NWS Watch / Warning / Advisory polygons | Shapefile | 2005–present (VTEC era) | Includes full VTEC metadata: phenomena, significance, ETN, WFO, issuance and expiration times. Pre-2007 events use county boundaries rather than storm-based polygons. |
| /request/gis/lsrs.phtml | Local Storm Reports | Shapefile / CSV | 2003–present | Point data. Filterable by event type (tornado, hail, wind, flood, snow, etc.), magnitude threshold, WFO, and date range. |
| /request/gis/spc_outlooks.phtml | SPC Convective Outlooks | Shapefile | ~2002–present | Includes Day 1, Day 2, Day 3 categorical and probabilistic outlooks. Also covers Fire Weather outlooks. One shapefile per outlook day/category. |
| /request/gis/spc_watch.phtml | SPC Tornado and Severe Thunderstorm Watches | Shapefile | 1986–present | Includes ETN, issuance and expiration times, watch type, and PDS flag. Watch polygons are the county-list-based areas, not the parallelogram watch boxes. |
| /request/gis/spc_mcd.phtml | SPC Mesoscale Convective Discussions | Shapefile | ~2003–present | Polygon boundaries of each MCD with issuance time and MCD number. Text of the discussion is not included in the shapefile but retrievable from the IEM text archive by PIL. |
| /request/gis/sps.phtml | Special Weather Statements | Shapefile | ~2007–present | Polygon-bearing SPS products only. Not all SPS products contain polygons; this endpoint captures those that do. |
| /request/gis/wpc_mpd.phtml | WPC Mesoscale Precipitation Discussions | Shapefile | ~2003–present | Polygon boundaries with issuance time and MPD number. Pairs well with the WPC QPF data for precipitation event analysis. |
| /request/gis/cwas.phtml | Center Weather Advisories | Shapefile | ~2008–present | Aviation product. Polygons issued by ARTCCs for significant in-flight weather. Useful for correlating flight delays with atmospheric hazards. |
| /request/gis/awc_sigmets.phtml | SIGMETs | Shapefile | ~2008–present | Aviation product. Covers both domestic and international SIGMETs, including Convective SIGMETs. Polygon or line geometry depending on product type. |
| /request/gis/awc_gairmets.phtml | G-AIRMETs | Shapefile | ~2008–present | Aviation product. Graphical AIRMETs for turbulence, icing, and IFR conditions below 18,000 feet MSL. Replaced text AIRMETs operationally in 2017. |
| /request/gis/nexrad_storm_attrs.php | NEXRAD Storm Attributes | Shapefile / CSV | ~2010–present | Point data. One point per tracked storm cell per volume scan, with attributes including estimated hail size, probability of severe hail (POSH), storm top height, and rotation (azimuthal shear). Updated approximately every 5–6 minutes during active periods. Also available as a live shapefile at /data/gis/shape/4326/us/current_nexattr.zip. |
| /request/gis/pireps.php | Pilot Reports | Shapefile / CSV | ~2005–present | Point data at the reported aircraft position. Attributes include altitude, turbulence intensity, icing intensity, sky condition, and visibility. |
| /request/gis/misc.phtml | Miscellaneous GIS Products | Various | Varies | A catch-all for spatial products that do not fit the other categories. Contents vary; check the page directly for current offerings. |
Coordinate System
All IEM shapefiles use EPSG:4326 (WGS84 geographic coordinates, decimal degrees). No reprojection is needed for web mapping or for loading into GIS software that handles projection on-the-fly. If your workflow requires a projected coordinate system (e.g., for area calculations or distance measurements), reproject after download.
Attribute Fields
Shapefile attribute field names are truncated to 10 characters per the DBF format specification. The IEM’s own dataset documentation at /info/datasets/ and variables reference at /info/variables.phtml are the authoritative references for field name definitions when the truncated names are not self-explanatory.
For the warning polygon shapefile specifically, the key fields are: PHENOMENA (2-letter code), SIGNIFICANCE (1-letter code), ETN (event tracking number), WFO (4-character office ID), ISSUED and EXPIRED (UTC timestamps), and WINDTAG, HAILTAG, TORNTAG for impact-based warning tags where applicable.