IEM Rainfall

IEM rainfall is a high resolution depiction of rainfall estimates over the state of Iowa. These estimates are provided freely via the Internet with no warranty or claim of accuracy. Currently, there are a number of ways you can view/download this dataset.

Request Data by Point

Instructions: With this form you can request daily estimates of rainfall for a particular year and for a particular point. This point can be specified in a number of ways. Caveat: Geocoding is not perfect. Your address may not be found in the database. If you first attempt fails, try using a popular building address for a location near you.

Start Year:   End Year (inclusive):
View Options:

Choose a method to select data point:
Specify Latitude & Longitude Geocode An Address Specify IEM Site ID
Latitude: Street Address: Enter ID:
Longitude: City in Iowa:

GIS Shapefiles

Instructions: Please select the date you would like to download a zip file containing a shapefile of rainfall estimates. The duration is the time period during which the estimates are valid for. For the current month or year, the estimates will be current for that period till yesterday.
Month:Day:Year:Coverage Type: DurationProjection:

The point coverage is simply the centroid of the polygon coverage.

OGC Web Services

If your GIS system supports accessing Web Map Service (WMS), you can directly pull in some of these rainfall estimates from the IEM server. Our WMS URI is:

Pulling data into GIS applications via these services has not been widely tested. If you run into any problems, please let us know!

About Precipitation Estimates

These rainfall estimates are directly based on the Stage 4 precipitation analysis produced by the National Center for Environmental Prediction. The IEM processes this data source in the following ways:
  • Extract data valid for Iowa from the national analyses.
  • Convert the data from Grib format to a relational database.
  • Produce summary totals for the local day instead of GMT day.
  • Provide instant access to this data from this page and others.

Rainfall estimates are produced each day at 3:30 AM for the previous day. These estimates are later revised as more information is made available to better refine the estimates. If you downloaded data for yesterday at the time, you may wish to redownload that dataset again later, since the estimates may be refined then. Sounds confusing. Please contact us if you have questions.

MRMS Q3 Estimates

NOAA has begun working on an advanced replacement of the system that produces rainfall estimates. This project is called Multi-RADAR Multi-Sensor System. The IEM processes some of the data found in this feed and produces products from it.

GIS RASTER PNG Images of Accumulation Estimates

The technique used provides 8-bit PNG images whereby a function can be used to convert the 8-bit value into a rainfall. This equation is different for the various products produced by the IEM in order to accomodate the data ranges necessary to capture. These images can be found in a current directory and date based archive. The units for the data is millimeters.

1,24,48,72 Hour Precipitation

8-bit value/indexPrecip [mm]Approx Precip [in]
1-100 (0.25mm)0.25 to 25~0.01 to 1 inch
101-180 (1.25mm)26.25 to 125~1.05 to 5 inch
181-254 (5mm)130 to 500~5 to 20 inch

GIS RASTER in ERDAS Imagine (.IMG) Format

This tool provides you an ERDAS Imagine file for the time and accumulation period of your choice. The IMG file is an unsigned 16 bit image, with a scale unit of 0.1mm. The 65535 value is set to missing and your GIS system hopefully will automatically understand that. The time you choose is the end time of the given accumulation period. This time is in UTC / GMT time! You could script against this service by using a URI like so:

Please be patient with this download! It may take 10-20 seconds to generate, the script converts the 8bit PNG mentioned above to uint16 IMG file on the fly!

Accumulation PeriodUTC Date UTC Hour

Please note that there is a current bug with how the one hour precipitation is generated by the MRMS project. The bug prevents the proper delination between zero and missing precipitation. The IEM has long whined to the MRMS project about fixing this bug.