IEM Reanalysis (IEMRE)

IEMRE Animation

IEM Reanalysis (IEMRE) is an effort to provide near real-time gridded analyses of a number of variables useful to drive downstream modeling projects, like the Daily Erosion Project. The IEM presently does not have the compute, nor storage capacity to run this effort globally at high resolution, so a number of regional domains are curated.

Use better products!
IEMRE is nothing special. It was cool maybe 15 years ago, but now days there are superior products available. Use those instead!
Why do this?

Previously, the IEM has only provided raw observations with limited quality control checks in place. Quality control is hard! Many times, users are simply looking for something "close" and perhaps not as perfect as high quality sensor observations can be. Producing a gridded analysis is one way to produce a dataset from point observations which can be sampled as a means of spatial interpolation.

Isn't this a duplication of effort?

While there are other "reanalysis" type projects out there with data freely available, many times their data does not update in near real-time and does not include many of the datasets the IEM uniquely collects.

Alternatives:

Product Changes

  • 26 Jul 2025: Non-CONUS domains are now available for South America, Europe, and Southeast Asia/China.
  • 4 Jan 2023: Near realtime solar radiation is sourced from the HRRR model. For dates prior to 8 days ago, it is sourced from ERA5Land. This is a change as it used to be sourced from MERRAv2.
  • 1 May 2018: Grid domain expanded to cover CONUS. It will take a while to fully populate the grids. At the moment, just the previous midwestern US data is available. Grid resolution increased to 0.125x0.125 degree.

Data Flow

1. Input Datasets

  • NCEP Stage IV Precipitation
    This is an hourly gridded product with precipitation estimates derived by RADAR and then bias corrected by gauge data. The IEM caches the grib data and makes hourly plots available here.
  • MRMS Precipitation
    Currently, this is only used to populate a daily total in a dedicated netcdf file.
  • ASOS/AWOS Daily Summaries
  • NWS Daily Climate Summaries
  • HRRR/MERRA/NARR Daily Solar Radiation
  • NWS COOPerative Observations
  • Manually QC'd Iowa COOP data from Iowa's State Climatologist
  • NCDC QC'd COOP Data

2. IEM ReAnalysis Gridded Datasets

3. Climodat Station Data

The location of the IEM Longterm tracked climate stations are used to sample from the IEMRE grid to produce daily values of high / low temperature, precipitation, snowfall, snow depth, and radiation. For some stations, a direct copy of the corresponding ASOS station data is used.

  • Climodat Reports
    These are pre-generated reports answering many of the commonly asked climatology questions.

Hourly Data Sources

Yearly netcdf files since 1950, with updates at about 10 after the hour. Since we want real-time data, some of these model sources are not available immediately, so the denoted intermediate source fills the gap until the final source is available.

Variable Intermediate Source Final Source
Precipitation Stage IV (CONUS)
DWD ICON Short Term Forecast (non-CONUS)		 1997+ Stage IV adjusted by PRISM (CONUS)
1950-1997 ERA5-Land (CONUS)
ERA5-Land (non-CONUS)
2m Air Temperature
2 m Dew Point Temperature
10m Wind Speed 		Crude ASOS grid analysis 2010+: RTMA, once available (CONUS)
1950-2010 ERA5-Land
4 inch (cough 0-10 or 0-7cm) Soil Temperature HRRR 1950+: ERA5-Land
Sky Coverage Crude ASOS grid analysis Crude ASOS grid analysis

Daily Data Sources

Since IEMRE intends to support real-time modeling needs, the goal is to have at least a first guess analysis of all fields by approximately midnight. These fields are refined as better and more detailed data is processed.

Variable Intermediate Source Final Source
High/Low 4 inch (cough 0-10 or 0-7cm) Soil Temperature HRRR 1950+: ERA5-Land
Average 2m Dew Point Temperature Simple average of hourly RTMA 2010+: RTMA, once available
1950-2010 ERA5-Land
24 Hour Snowfall at 12 UTC NOHRSC Snowfall 2008+: NOHRSC
Prior: COOP snowfall analysis.

Data Access

Here are some JSON web services you may try.

MultiDay Request

Form:

https://mesonet.agron.iastate.edu/iemre/multiday/{YYYY-MM-DD::date1}/{YYYY-MM-DD::date2}/{LAT}/{LON}/json

Example:

https://mesonet.agron.iastate.edu/iemre/multiday/2010-05-01/2010-09-30/42.54/-96.40/json
Single Day Request

Form:

https://mesonet.agron.iastate.edu/iemre/daily/{YYYY-MM-DD}/{LAT}/{LON}/json

Example:

https://mesonet.agron.iastate.edu/iemre/daily/2010-05-01/42.54/-96.40/json
Hourly Request

Form:

https://mesonet.agron.iastate.edu/iemre/hourly/{YYYY-MM-DD}/{LAT}/{LON}/json

Example:

https://mesonet.agron.iastate.edu/iemre/hourly/2010-05-01/42.54/-96.40/json Single Day's Hourly (CDT/CST) Request

Raw Data Access

The IEM makes extensive use of the NetCDF file format to store these gridded datasets. You can find individual web directories for various IEMRE related datasets:

IEMRE CONUS Files IEMRE CONUS Files IEMRE China Files IEMRE China Files IEMRE Europe Files IEMRE Europe Files IEMRE South America Files IEMRE South America Files ERA5Land Hourly Netcdf Files MRMS CST Daily Netcdf Files
NCEP Stage IV Hourly Data Oregon State PRISM Daily Data

Publications Citing IEM Data (View All)

These are the most recent 10 publications that have cited the usage of data from this page. This list is not exhaustive, so please let us know if you have a publication that should be added.