1991-2020 Division Averages (Inches)
Snake River
DIVISION NAME	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Henrys Fork River Basin	3.35	2.63	2.80	2.73	2.98	2.36	1.07	1.14	1.59	2.26	2.79	3.56
Upper Snake Tributaries	2.96	2.49	2.51	2.53	2.78	1.90	1.02	1.19	1.70	2.04	2.45	2.91
Upper Snake River Basin abv American Falls Dam	2.37	1.87	1.98	2.04	2.34	1.62	0.80	0.92	1.31	1.65	1.89	2.40
Middle Snake Tributaries	2.47	1.93	2.16	1.93	2.13	1.42	0.52	0.52	0.85	1.45	1.92	2.84
Malheur-Owyhee-Boise River Basins	2.05	1.50	1.71	1.58	1.78	1.06	0.39	0.33	0.57	1.13	1.58	2.29
Payette River Basin	4.18	3.23	3.52	2.69	2.48	1.81	0.53	0.53	0.98	2.05	3.40	4.93
Snake River Basin abv Hells Canyon Dam	2.27	1.71	1.89	1.78	2.01	1.31	0.54	0.55	0.85	1.36	1.79	2.48
Clearwater River Basin	4.95	4.02	4.33	3.77	3.52	3.17	1.18	1.07	1.61	3.28	4.98	5.16
Salmon River Basin	3.35	2.78	3.12	2.81	2.74	2.54	0.99	0.88	1.34	2.18	3.07	3.85
Grande Ronde River Basin	3.60	3.00	3.22	2.98	3.08	2.17	0.71	0.76	0.99	2.25	3.53	4.00
Palouse River Basin	2.60	1.95	2.22	1.76	1.79	1.35	0.51	0.48	0.66	1.69	2.63	2.88
Snake River Basin abv Ice Harbor Dam	2.71	2.12	2.35	2.15	2.28	1.70	0.67	0.65	0.98	1.69	2.37	2.97
Upper Columbia Basin
DIVISION NAME	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Clark Fork River Basin	2.78	2.51	2.48	2.50	2.75	3.02	1.23	1.18	1.56	2.23	2.92	3.01
Flathead River Basin	4.01	3.13	3.43	3.15	3.20	3.95	1.39	1.28	2.09	3.02	3.95	3.83
Pend Oreille River Basin abv Waneta Dam	3.61	2.91	3.15	2.81	2.93	3.33	1.27	1.16	1.74	2.72	3.69	3.71
Kootenai River Basin	4.20	2.88	3.54	2.70	2.84	3.43	1.84	1.54	2.23	3.41	4.70	4.31
Spokane River Basin	5.40	4.00	4.58	3.30	3.09	2.84	1.02	1.00	1.49	3.54	5.29	5.57
Columbia River Basin abv Arrow Dam	6.15	4.00	4.47	2.98	3.02	3.61	2.93	2.54	3.22	5.51	6.86	5.72
Middle Columbia Basin
DIVISION NAME	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Middle Columbia Upper Tributaries	4.07	2.78	2.83	1.92	2.05	2.07	1.20	1.02	1.39	2.88	4.26	4.24
Yakima River Basin abv Kiona	4.73	3.44	3.12	2.09	1.64	1.19	0.46	0.46	0.97	2.76	4.44	5.20
Middle Columbia Lower Tributaries	3.12	2.38	2.41	2.00	1.96	1.33	0.45	0.47	0.71	1.83	2.91	3.57
Columbia River Main Stem
DIVISION NAME	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Columbia River Basin abv Grand Coulee	4.29	3.08	3.51	2.72	2.86	3.27	1.73	1.47	2.05	3.45	4.60	4.33
Columbia River Basin abv The Dalles	3.33	2.47	2.71	2.23	2.32	2.13	1.00	0.89	1.29	2.34	3.26	3.53
Western Washington
DIVISION NAME	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Northwest Washington River Basins	12.81	8.29	9.98	6.35	4.61	3.66	2.02	2.38	4.77	9.87	14.34	12.41
Skagit River Basin	13.28	8.88	9.75	6.01	4.09	3.29	1.74	2.04	4.24	9.85	15.07	13.10
Snohomish River Basin	13.80	9.67	10.73	7.97	5.71	4.60	1.81	2.04	4.72	10.08	14.85	12.85
Middle Sound River Basins	10.67	7.56	8.26	6.53	4.76	3.99	1.47	1.71	3.50	7.54	11.24	10.28
South Sound River Basins	9.81	6.92	7.45	5.80	4.23	3.42	1.25	1.34	2.83	6.60	10.16	9.67
Olympics River Basins	16.73	10.85	12.82	6.94	3.77	2.71	1.23	1.84	3.61	9.94	19.08	16.59
Satsop River Basin	19.72	11.93	14.01	9.23	4.72	3.29	1.49	2.26	4.67	12.21	19.70	19.19
Chehalis River Basin	9.34	6.40	7.02	5.14	3.16	2.33	0.78	1.14	2.48	6.16	10.08	9.72
Cowlitz River Basin	11.04	8.05	8.33	6.04	4.09	2.98	0.93	1.22	2.86	7.06	11.31	11.52
Lewis River Basin	16.37	11.87	12.40	8.69	5.18	3.68	0.97	1.45	3.78	9.61	16.27	17.28
Western Oregon
DIVISION NAME	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Coastal River Basins	14.02	10.48	10.54	7.30	4.10	2.75	0.68	0.99	2.93	7.66	14.01	16.00
Clackamas River Basin	10.35	7.65	8.26	6.49	4.61	3.18	0.67	0.86	2.36	6.34	10.65	11.65
Willamette Headwater River Basins	9.32	6.96	7.02	5.13	3.16	1.99	0.46	0.60	1.94	5.13	9.21	11.01
Willamette River Basin abv Harrisburg	9.91	7.28	7.96	6.61	4.49	2.72	0.66	0.77	2.18	5.62	9.88	11.60
Santiam River Basin	11.09	8.37	9.19	7.39	4.98	3.29	0.67	0.85	2.62	6.68	11.35	12.94
Willamette River Basin above Portland	9.54	7.09	7.55	5.92	3.94	2.49	0.56	0.70	2.11	5.47	9.57	11.16
Coquille River Basin	11.28	8.56	9.39	7.17	3.78	1.86	0.45	0.49	1.64	4.76	10.22	13.00
Umpqua River Basin	7.56	5.50	6.00	4.92	3.32	1.81	0.54	0.53	1.42	3.83	7.50	9.32
Rogue-Illinois River Basins	7.97	5.96	6.10	4.49	2.75	1.39	0.46	0.44	1.01	3.41	6.86	9.77