PRISM
PRISM provides daily, modeled climate data at 4 km resolution grid cells from 1981 to present, capturing fine-scale spatial variation in weather across the U.S.
Precipitation (ppt)
Daily total precipitation (rain+melted snow in mm) calculated on a cell by cell basis on three temporal scales (daily, monthly, and annually).
- Daily data represent the raw value from PRISM(Averaged for spatial layer units and raw values for a specific cell)
\[\text{Daily ppt area} = \frac{\sum_{j=0}^{n} ({ppt}_j)}{n}\]
\[\text{Daily ppt cell} = \text{ppt}_{j}\]
\(j\): current cell | \(n\): # of cells in the spatial layer unit
- Monthly data are the summation of each day’s value within the month
\[\text{Monthly ppt} = \sum_{i=1}^{d} \text{daily ppt}_i \] \(d\): # of days in the month | \(i\): Current day (iterator)
- Annual data are the summation of each day’s value within the water year (Oct 1 - Sep 30 of the given year, e.g. 10/01/1981 - 09/30/1982 would be labeled as 01/01/1982).
\[\text{Annual ppt} = \sum_{i=1}^{d} \text{daily ppt}_i \]
\(d\): # of days in the water year | \(i\): Current day (iterator)
Minimum Temperature (tmin)
Daily minimum temperature (Celsius) calculated on a cell by cell basis on three temporal scales (daily, monthly, and annually).
- Daily data represent the raw value from PRISM
\[\text{Daily tmin area} = \frac{\sum_{j=0}^{n} ({tmin}_j)}{n}\]
\[\text{Daily ppt cell} = \text{tmin}_{j}\]
\(j\): current cell | \(n\): # of cells in the spatial layer unit
- Monthly data are the average of each day’s tmin value over the month
\[\text{Monthly tmin} = \frac{\sum_{i=1}^{d} \text{daily tmin}_i}{d} \] \(d\): # of days in the month | \(i\): Current day (iterator)
- Annual data are the average of each day’s value within the water year (Oct 1 - Sep 30 of the given year, e.g. 10/01/1981 - 09/30/1982 would be labeled as 01/01/1982).
\[\text{Annual tmin} = \frac{\sum_{i=1}^{d} \text{daily tmin}_i}{d} \]
\(d\): # of days in the water year | \(i\): Current day (iterator)
Maximum Temperature (tmax)
Daily maximum temperature (Celsius) calculated on a cell by cell basis on three temporal scales (daily, monthly, and annually).
- Daily data represent the raw value from PRISM
\[\text{Daily tmax area} = \frac{\sum_{j=0}^{n} ({tmax}_j)}{n}\]
\[\text{Daily tmax cell} = \text{tmax}_{j}\]
\(j\): current cell | \(n\): # of cells in the spatial layer unit
- Monthly data are the average of each day’s value within the month
\[\text{Monthly tmax} = \frac{\sum_{i=1}^{d} \text{daily tmax}_i}{d} \] \(d\): # of days in the month | \(i\): Current day (iterator)
- Annual data are the average of each day’s value within the water year (Oct 1 - Sep 30 of the given year, e.g. 10/01/1981 - 09/30/1982 would be labeled as 01/01/1982).
\[\text{Annual tmax} = \frac{\sum_{i=1}^{d} \text{daily tmax}_i}{d} \]
\(d\): # of days in the water year | \(i\): Current day (iterator)
Mean Temperature (tmean)
Daily mean temperature (Celsius) calculated on a cell by cell basis on three temporal scales (daily, monthly, and annually).
- Daily data represent the raw value from PRISM
\[\text{Daily tmean area} = \frac{\sum_{j=0}^{n} ({tmean}_j)}{n}\]
\[\text{Daily tmean cell} = \text{tmean}_{j}\]
\(j\): current cell | \(n\): # of cells in the spatial layer unit
- Monthly data are the average of each day’s value within the month
\[\text{Monthly tmean} = \frac{\sum_{i=1}^{d} \text{daily tmean}_i}{d} \]
\(d\): # of days in the month | \(i\): Current day (iterator)
- Annual data are the average of each day’s value within the water year (Oct 1 - Sep 30 of the given year, e.g. 10/01/1981 - 09/30/1982 would be labeled as 01/01/1982).
\[\text{Annual tmean} = \frac{\sum_{i=1}^{d} \text{daily tmean}_i}{d} \]
\(d\): # of days in the water year | \(i\): Current day (iterator)
# of Days Temperature < 0 F° (tmean-tempdays)
This is a derived variable from PRISM mean temperature (tmean) and represents a portion of Winter Severity. It is the count of the number of days the mean daily temperature was below -17.78 C° (0 F°), calculated on a cell by cell basis on three temporal scales (daily, monthly, and annually).
- Daily data represent a binary response of 1 (true) or 0 (false)
\(\text{tmean daily} <\) 0 \(^{\circ}\) F : 1 tmean-tempday
\(\text{tmean daily} >\) 0 \(^{\circ}\) F : 0 tmean-tempday
- Monthly data are the summation of each day’s value within the month
\[\text{Monthly tmean-tempdays} = \sum_{i=1}^{d} \text{daily tmean-tempdays}_i \] \(d\): # of days in the month | \(i\): Current day (iterator)
- Annual data are the summation of each day’s value within the water year (Oct 1 - Sep 30 of the given year, e.g. 10/01/1981 - 09/30/1982 would be labeled as 01/01/1982).
\[\text{Annual tmean-tempdays} = \sum_{i=1}^{d} \text{daily tmean-tempdays}_i \]
\(d\): # of days in the water year | \(i\): Current day (iterator)
Source
Methods used to develop PRISM variables can be found in Daly et al. 2008