A couple of weak cold fronts brought showers to northern tier basins early in the period and an area of low pressure brought light precipitation to southern tier basins during the middle of the month. Late in the month, a ridge of high pressure dominated and brought warmer and drier than normal conditions to most of the Pacific Northwest. In fact, September 2001 was the warmest on record in Helena.
The 31 station temperature index for the Pacific Northwest departed +3.3 degrees from normal relative to the 1961-1990 period. Mean temperature departures range from -1.5 to 6.3 degrees.
There were several record high temperatures reported in September and a vast majority of them occurred across Western Montana. They included: 90 at Pocatello on the 23rd, 85 (tie) at Kalispell, 85 at Butte, 87 at Helena, 90 at Missoula, 91 at Pocatello, and 91 at Great Falls on the 24th, 86 at Butte, 88 at Kalispell, 92 at Pocatello, 93 at Great Falls, 95 at Helena, and 96 at Havre on the 25th, and 89 at Pocatello on the 27th. September 2001 was the hottest September on record in Helena, where the average monthly temperature was 9.2 degrees above normal.
Only two record low temperatures were reported in September. They included: 38 (tie) at Eugene on the 6th and 29 at Pocatello on the 8th. There were not any daily precipitation records reported in September. However, several locations reported their driest water year on record. These included: Astoria, Portland, and Eugene, which reported 44.79, 23, and 20.36 inches of precipitation for the October 2000 to September 2001 water year. Salem reported the second driest water year on record with 21.97 inches of precipitation.
For SEPTEMBER, PRECIPITATION is:
48 percent of normal (1961-1990) at COLUMBIA ABOVE COULEE,
54 percent of normal at THE SNAKE RIVER ABOVE ICE HARBOR,
And 49 percent at COLUMBIA ABOVE THE DALLES.
For the WATER SUPPLY SEASON, PRECIPITATION is:
68 percent of normal (1961-1990) at COLUMBIA ABOVE COULEE,
70 percent of normal at THE SNAKE RIVER ABOVE ICE HARBOR,
