Figure 1: 1.6 m ISM values and standard deviations temporally averaged over the study period. (a) represents the HRRR model, (b) represents the CPC model, and (c) represents their difference. (d-f) are the same as (a-c), except for the ISM standard deviations. Filled circles represent locations of the 172 in situ observations from the USCRN and SCAN networks that pass quality control checks, as described in the text. In (c) and (f), the filled circles represent the HRRR minus in situ differences, while the filled circles represent the in situ station ISM mean and standard deviations, respectively, for the other panels.

3.3 Quintile Analysis

To determine whether differences in soil moisture estimates vary in different soil moisture regimes (i.e., wetter versus drier conditions), we composite the comparisons over locations with similar soil moisture amounts. The ISM or VSM values for each dataset are averaged temporally for each location and are then averaged among the available datasets (i.e., all three datasets for ISM and the in situ and HRRR datasets for VSM). Using this mean, the locations are separated into five quintiles. For example, locations with a mean ISM estimate that is greater than or equal to the 0^th percentile ISM and less than the 20^th percentile ISM are placed in the lowest quintile of soil moisture amounts (i.e., driest locations). These locations are termed L_00-20. Similarly, locations that fall within the 20^th-40^th, 40^th-60^th, 60^th-80^th and 80^th-100^th percentiles are termed L_20-40, L_40-60, L_60-80and L_80-100, respectively and represent dry to wet soil moisture regimes. There are either 34 or 35 locations that are included in each of these quintiles.

4 Soil Moisture Amounts

4.1 ISM Mean Comparisons

Stark, regionally-dependent differences are apparent in the ISM estimates (Figure 1c,f). The HRRR ISM values (Figure 1a) have a more muted range than the CPC ISM values (Figure 1b). The HRRR ISMs are larger (i.e., wetter) than the CPC ISMs across the drier regions of CONUS (most of the western CONUS; Figure 1c) and are smaller (i.e., drier) than the CPC ISMs in the wetter regions of CONUS (eastern half of CONUS and the coastal regions of the Pacific Northwest). This regional dependence is also clearly associated with varying soil moisture amounts.