Weather in Boise: Record warm temperatures, a ‘Pineapple Express’ — and then maybe snow?

If you were told at the start of January that the upcoming month would see both 22.1 inches of snow and record-warm temperatures in the upper 50s, you’d call it crazy talk.

But Boise’s latest version of Snowmageddon earlier this month has been followed by very warm temperatures to close out the month, so that’s exactly what we’re getting.

Record-breaking Boise warmth

Boiseans stepped outside Monday to a balmy afternoon with temperatures in the mid-50s, about 15 degrees warmer than usual for late January.

The National Weather Service in Boise recorded a temperature of 57 on Monday afternoon, meteorologist Les Colin told the Idaho Statesman, breaking the record of 56 set in 1967.

“We have high pressure aloft,” Colin told the Statesman on Monday afternoon. “And we lost our snow cover, so that allows the ground to also get warmer.”

If you thought Monday was something special, the Weather Service forecasts a high of 58 degrees on Tuesday and 61 on Wednesday. The current records for both dates are:

• Jan. 30, Tuesday - 59 degrees (2018)

• Jan. 31, Wednesday - 61 degrees (1992)

Rain, cold and ... and maybe light snow

The warmer temperatures will last through Thursday before a wetter storm system flushes out the warm air. The high temperature on Thursday is forecast to be 54, and the low temperature will drop to 30 by Saturday night into Sunday morning.

It will be so cold that, despite the warm week, the Weather Service forecasts a slight chance of snow over the weekend.

“Snow levels will drop to valley floors later on Saturday, so if we have a few showers over the weekend, it could turn into light snow,” Weather Service meteorologist Stefanie Henry told the Statesman. “Temperatures should stay relatively mild through then.”

The first hint of rain will arrive Wednesday night.

“Some very light precipitation may begin late Wednesday,” Henry said. “But the majority of the rain with this first low (pressure system) will arrive Thursday and Friday, tapering off Saturday and Sunday.”

The rain is a product of an atmospheric river, or what meteorologists have nicknamed the “Pineapple Express.”

A Pineapple Express is a long, narrow region in the atmosphere that transports large amounts of water vapor from the area around Hawaii to the West Coast, according to the National Oceanic and Atmospheric Administration. The average atmospheric river carries enough water vapor equal to the average flow at the mouth of the Mississippi River, with all of that moisture falling as rain or snow when it reaches land.

Most of that will fall along the West Coast, but some will make it inland. Henry said Boise can expect between 0.25 and 0.40 inches of precipitation by Friday night, with a 10% chance the city gets more than half an inch.