nClimGrid-Daily and Daily Gridded Normals Now Available
NCEI’s new nClimGrid-Daily product contains 5-km gridded fields with area averages of daily temperature and precipitation amounts for the contiguous United States—with data from January 1, 1951, to the present. In addition to the daily gridded data, NCEI is now producing climate normals of key variables, based on the same underlying 5-km grid.
These all-new datasets will help place regional- to national-scale meteorological events into a long-term historical context in near-real-time. Additionally, these NOAA gridded datasets can be certified for official use.
Gridded datasets include several variables that can be used to understand the weather conditions on any given day.
nClimGrid-Daily includes the following variables:
- Daily Maximum Temperature
- Daily Minimum Temperature
- Daily Average Temperature
- Daily Precipitation Totals
Daily Gridded Normals feature 30-year and 15-year averages of these same four variables and two additional variables:
- Month-to-Date Precipitation Totals
- Year-to-Date Precipitation Totals
To provide an indication of observation density, NCEI is also rolling out a supplemental product called nClimGrid-Daily-Auxiliary. This product provides daily gridded fields of the numbers of maximum temperature, minimum temperature, and precipitation observations within 30 miles of each grid point.
New Daily Components
For nClimGrid-Daily, grid point values are derived by interpolating morning and midnight observations in NCEI’s Global Historical Climatology Network - Daily (GHCNd) dataset. The interpolation technique addresses the effects of station density, observation times, and other factors that could impact the quality of the gridded fields.
The grid point estimates provide consistency between daily maximum and minimum temperatures, as well as consistency with NCEI's monthly nClimGrid product (Vose et al. 2014).
For different applications, users may wish to use the area averages that are also part of nClimGrid-Daily. These averages are available for counties, states, census tracts used in the 2020 U.S. Census, large watersheds, the contiguous United States, and other defined regions. In most cases, the regional value is the area average of grid point values located within the region. For census tracts that are smaller than a gridbox, the value at the grid point closest to the center of the tract is used.
How Often is nClimGrid-Daily Updated?
Gridded fields and area averages for nClimGrid-Daily are updated each day. However, the data will only become available up to three days after the observation date because of the time it takes for observations to reach NCEI and become available in the GHCNd database.
Once a gridded field becomes available, its accuracy improves over subsequent days and months as additional data are received by NCEI. The amount of input data for a given day can potentially double after the first day on which data becomes available—most additional data is received in the first few days. For example, when a severe storm or other weather event is impacting a region, it will take a few days to process the precipitation data after the weather event has occurred.
Notable caveats:
- Occasionally, an interruption to the data streams can delay the production of data for nClimGrid-Daily.
- Estimates for days in the current month will not be fully consistent with either the corresponding monthly products or the daily estimates for previous months and years until approximately the fifth day of the following month.
- Users are cautioned to assess the impact of using the preliminary estimates on their particular application.
Daily Gridded Normals
The U.S. Climate Normals features a suite of station-based and gridded products designed to compare historical data with present day weather conditions.
The new daily gridded normals are calculated from the nClimGrid-Daily dataset, using the same techniques used to calculate the traditional station-based daily climate normals. The daily normals at each grid point are calculated using sophisticated algorithms, and are not simple 30-year or 15-year single-day averages.
Gridded normals are available for the conventional 30-year period of 1991–2020 period and the more recent 15-year period of 2006–2020.
