The Tri-Cities was under its first freeze warning of the fall for Tuesday morning.
The temperature was expected to drop to as low as freezing between 2 and 10 a.m. under clear skies, according to the National Weather Service forecast.
Tuesday night should be a little warmer, with temperatures a few degrees above freezing.
Normal lows for the start of October in the Tri-Cities are about 45 degrees.
The frost and freezing conditions had the potential to kill crops, other sensitive vegetation and possibly damage unprotected outdoor plumbing, according to the warning.
Some plants, including some vegetables and tropical plants, should be moved indoors during a freeze and in the winter. Others, including certain herbs, just need to be covered up, say experts.
It’s time to have in-ground sprinkler systems drained. To prevent freezing and possible bursting of outdoor water pipes that have not yet been drained, they can be allowed to drip slowly.
Parts of the Mid-Columbia, including just east of Walla Walla and north of Connell, already were under a freeze warning over the weekend.
Temperatures dropped low enough that snow covered Rattlesnake Mountain near Richland on Sunday, with the mountain remaining white Monday.
Cloudy skies Wednesday night are expected to end the threat of freezing or near-freezing weather in the Tri-Cities, at least for the next six days.
The lows Wednesday night through Saturday night should be back to normal in the mid 40s.
Highs will be near 60 on Tuesday, warming to the mid 60s through Saturday, according to the weather service.
The weekend just past was unusually cold for the end of September in the Tri-Cities, particularly the high temperatures under cloudy skies.
Sunday the high, as recorded at the Pasco airport, was 50 degrees and the low was 41. Saturday the high was 58 and the low as 41.