COLUMBIA--GRAND COULEE DAM (GCDW1)
| Observed | Forecast/Trend |
| Date/Time (PDT) | Pool Height | Date/Time (PDT) | Pool Height |
| 2021-06-15 23:59 | 1287.66 | 2021-06-16 23:00 | 1288.44 |
| 2021-06-14 23:59 | 1287.56 | 2021-06-17 05:00 | 1288.44 |
| 2021-06-13 23:59 | 1287.42 | 2021-06-17 11:00 | 1288.44 |
| 2021-06-12 23:59 | 1287.01 | 2021-06-17 17:00 | 1288.46 |
| 2021-06-11 23:59 | 1286.65 | 2021-06-17 23:00 | 1288.48 |
| 2021-06-10 23:59 | 1286.58 | 2021-06-18 05:00 | 1288.51 |
| 2021-06-09 23:59 | 1286.29 | 2021-06-18 11:00 | 1288.53 |
| 2021-06-08 23:59 | 1285.66 | 2021-06-18 17:00 | 1288.55 |
| 2021-06-07 23:59 | 1285.17 | 2021-06-18 23:00 | 1288.56 |
| 2021-06-06 23:59 | 1284.67 | 2021-06-19 05:00 | 1288.56 |
| 2021-06-05 23:59 | 1283.94 | 2021-06-19 11:00 | 1288.57 |
| | | 2021-06-19 17:00 | 1288.63 |
| | | 2021-06-19 23:00 | 1288.74 |
| | | 2021-06-20 05:00 | 1288.88 |
| | | 2021-06-20 11:00 | 1289.04 |
| | | 2021-06-20 17:00 | 1289.16 |
| | | 2021-06-20 23:00 | 1289.26 |
| | | 2021-06-21 05:00 | 1289.37 |
| | | 2021-06-21 11:00 | 1289.48 |
| | | 2021-06-21 17:00 | 1289.59 |
| | | 2021-06-21 23:00 | 1289.69 |
| | | 2021-06-22 05:00 | 1289.78 |
| | | 2021-06-22 11:00 | 1289.85 |
| | | 2021-06-22 17:00 | 1289.9 |
| | | 2021-06-22 23:00 | 1289.93 |
| | | 2021-06-23 05:00 | 1289.94 |
| | | 2021-06-23 11:00 | 1289.94 |
| | | 2021-06-23 17:00 | 1289.93 |
| | | 2021-06-23 23:00 | 1289.93 |
| | | 2021-06-24 05:00 | 1289.92 |
| | | 2021-06-24 11:00 | 1289.91 |
| | | 2021-06-24 17:00 | 1289.89 |
| | | 2021-06-24 23:00 | 1289.85 |
| | | 2021-06-25 05:00 | 1289.81 |
| | | 2021-06-25 11:00 | 1289.65 |
| | | 2021-06-25 17:00 | 1289.5 |
| | | 2021-06-25 23:00 | 1289.34 |
| | | 2021-06-26 05:00 | 1289.18 |