IEM Reanalysis (IEMRE)

IEM Reanalysis is an effort to provide a regular dataset of Iowa Environmental Data without many of the problems associated with single site observations. The IEM will continue to provide single site observational data, but for some purposes, this dataset will be easier to work with. No dataset is perfect and this dataset is provided without warranty.

Use better products!
The IEM Reanalysis 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.
    Having said that, here are some alternatives:
    ERA5Land
    DayMet
    GridMet
    PRISM

Product Changes

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.

VariableIntermediate SourceFinal Source
Precipitation Stage IV 1997+ Stage IV adjusted by PRISM
1950-1997 ERA5-Land
2m Air Temperature
2 m Dew Point Temperature
10m Wind Speed 		Crude ASOS grid analysis 2010+: RTMA, once available
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

Yearly netcdf files since 1893. Some of these variables are directly sourced from the hourly grids above. The concept of a daily variable is a bit nebulous, but is intended to be a 6 to 6 UTC period.

VariableIntermediate SourceFinal 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

Single Day's Hourly (CDT/CST) 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

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:

Publications Citing IEM Data

These are 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. Hopefully by early 2025, this listing can be more complete.