Mattawa Weather in September
Average highs run from 86°F on September 1 to 74°F on September 30, and lows from 62°F to 53°F. Normal precipitation for the month is 0.15 in over about 2 wet days.
September day by day
The normal high and low for each date, and the record, in °F.
- Normal low
- Normal high
- Record high
- Record low
September at a glance
- Average high
- 80°F
- Average low
- 58°F
- Precipitation
- 0.15 in
- Record high
- 101°FSep 3, 1998
- Record low
- 25°FSep 23, 2000
- Chance of a freeze
- 0%
- Days of 90°F or more
- 4.7
- Daylight
- 13 h 19 min to 11 h 44 min
- Cloud cover
- 40%
- Humidity
- 48%
- Dew point
- 42°F
- Wind
- 6.9 mph
Every day of the month
A wet day has at least 0.01 inch of precipitation; snow means at least 0.1 inch of snowfall.
| Date | Normal high | Normal low | Record high | Record low | Chance wet | Chance of snow |
|---|---|---|---|---|---|---|
| Sep 1 | 86°F | 62°F | 99°F 1998 | 36°F 2000 | 5% | 0% |
| Sep 2 | 85°F | 62°F | 98°F 1998 | 39°F 1999 | 6% | 0% |
| Sep 3 | 85°F | 62°F | 101°F 1998 | 36°F 2000 | 6% | 0% |
| Sep 4 | 85°F | 61°F | 100°F 2025 | 37°F 2002 | 6% | 0% |
| Sep 5 | 84°F | 61°F | 98°F 2003 | 39°F 2002 | 6% | 0% |
| Sep 6 | 84°F | 61°F | 96°F 1998 | 35°F 2002 | 6% | 0% |
| Sep 7 | 84°F | 60°F | 98°F 1998 | 36°F 2002 | 6% | 0% |
| Sep 8 | 83°F | 60°F | 93°F 1998 | 34°F 2002 | 7% | 0% |
| Sep 9 | 83°F | 60°F | 94°F 2011 | 37°F 2000 | 7% | 0% |
| Sep 10 | 83°F | 60°F | 96°F 2011 | 40°F 1998 | 7% | 0% |
| Sep 11 | 82°F | 59°F | 97°F 2011 | 39°F 2007 | 7% | 0% |
| Sep 12 | 82°F | 59°F | 95°F 2013 | 35°F 2012 | 7% | 0% |
| Sep 13 | 82°F | 59°F | 96°F 2011 | 34°F 2014 | 7% | 0% |
| Sep 14 | 81°F | 58°F | 96°F 2013 | 34°F 2014 | 8% | 0% |
| Sep 15 | 81°F | 58°F | 95°F 2001 | 38°F 2008 | 8% | 0% |
| Sep 16 | 81°F | 58°F | 95°F 2001 | 33°F 2006 | 8% | 0% |
| Sep 17 | 80°F | 57°F | 94°F 1998 | 35°F 2006 | 8% | 0% |
| Sep 18 | 80°F | 57°F | 90°F 2000 | 34°F 2002 | 9% | 0% |
| Sep 19 | 79°F | 57°F | 89°F 1999 | 33°F 2004 | 9% | 0% |
| Sep 20 | 79°F | 56°F | 90°F 1999 | 35°F 2004 | 9% | 0% |
| Sep 21 | 79°F | 56°F | 89°F 2025 | 33°F 2002 | 9% | 0% |
| Sep 22 | 78°F | 56°F | 88°F 2014 | 31°F 2002 | 9% | 0% |
| Sep 23 | 78°F | 55°F | 91°F 1999 | 25°F 2000 | 10% | 0% |
| Sep 24 | 77°F | 55°F | 90°F 2001 | 27°F 2000 | 10% | 0% |
| Sep 25 | 77°F | 55°F | 89°F 2001 | 28°F 2000 | 10% | 0% |
| Sep 26 | 76°F | 54°F | 89°F 2003 | 30°F 2000 | 11% | 0% |
| Sep 27 | 76°F | 54°F | 90°F 2003 | 30°F 1999 | 11% | 0% |
| Sep 28 | 75°F | 54°F | 91°F 2003 | 28°F 1999 | 11% | 0% |
| Sep 29 | 75°F | 53°F | 90°F 2003 | 28°F 2001 | 12% | 0% |
| Sep 30 | 74°F | 53°F | 86°F 1998 | 28°F 2002 | 12% | 0% |
Chance of rain
- Chance of a wet day
- Chance of snowfall
Sunrise and sunset
Times for 2026, local time (PDT).
- September 1
- sunrise 6:20 AM, sunset 7:39 PM
- September 30
- sunrise 6:57 AM, sunset 6:41 PM
Other months
Sources
Normals: NOAA NCEI U.S. Climate Normals, 1991-2020, station USC00456747 (Priest Rapids Dam), public domain. Records: NOAA GHCN-Daily, station USC00457522, every year on file, quality-flagged values removed. Cloud, humidity, wind and sunshine: NASA POWER (MERRA-2, CERES and GEWEX SRB), 1991-2020. The data was obtained from the National Aeronautics and Space Administration (NASA) Langley Research Center's Prediction Of Worldwide Energy Resources (POWER) project funded through the NASA Earth Science Division: POWER Daily API v2, accessed 2026-09-24. Sun and moon: computed with the NOAA solar equations and Meeus.