| SPI value | Interpretation |
| ≥2.0 | Extremely wet |
| 1.5 to 1.99 | Severely wet |
| 1.0 to 1.49 | Moderately wet |
| 0.99 to −0.99 | Near normal |
| −1.0 to −1.49 | Moderately dry |
| −1.5 to −1.99 | Severely dry |
| ≤−2.0 | Extremely dry |