This fall has seen the earliest snowfall on record at Rattlesnake Mountain, according to the Hanford Meteorological Service.
The unusually cold and damp weather is expected to continue for the Tri-Cities this month, according to the National Weather Service’s monthly outlook.
Temperatures could warm to near normal by Monday, after an unusually cold start to the month, according to the weather service forecast.
On Saturday, an unusually cold air mass moved over the Mid-Columbia, coating 3,531-foot-high Rattlesnake Mountain near Richland with snow.
The previous record for earliest snow on the mountain was Oct. 5 in 1957, according to the Hanford service. Records are kept back to World War II.
The cold weather also brought some sleet mixed with rain to the Hanford Meteorology Station on Sept. 29, the first time a wintery mix was recorded there in September.
A low of just 30 degrees early Wednesday morning in the Tri-Cities just missed tying the record for the date, by 1 degree. That helped bring the average temperature for the month down for the Tri-Cities.
The weather service expects Eastern Washington and Oregon temperatures to average below normal this month, while much of the East Coast continues to bake with temperatures that are above normal.
Cold records set in September
Normal highs in the Tri-Cities in October average about 73 at the first of the month, dropping to about 57 at the end of the month. Normal lows drop from about 45 to about 37.
Thursday, highs should be up to about 65 degrees, gradually increasing to about 75 degrees in the Tri-Cities by Monday. However, the early forecast calls for highs to drop to as much as 10 degrees below normal for the rest of the week.
The weather service is predicting a wetter month than usual in the Pacific Northwest, including the Tri-Cities.
Normal precipitation in the Tri-Cities for October is about 0.6 inch.
September averaged about 2 degrees warmer than usual in the Tri-Cities, despite a cooldown in the last few days of the month.
At the Pasco airport, the high was 94 degrees on Sept. 1, dropping to a high of 50 degrees on Sept. 29.
At the Hanford Meteorological Station, two daily temperature records were set and one tied in September, all for cool weather at the end of the month:
▪ On Sept. 28 the station recorded a high of 54, colder than the previous coldest high for the date of 58 in 1977.
▪ On Sept. 29 the station recorded a high of 46, smashing the previous coldest high for the date, 57 degrees in 1977.
▪ On Sept. 30, the station recorded a high of 54 degrees, tying the record for coldest high, set in 2007.
The peak wind gust recorded in the Tri-Cities in September was 31 mph on Sept. 7 and 44 mph at the Hanford met station the same day.