Mid January 1888 was perhaps the most intense arctic airmass in recorded history in the PNW.
After an impressive early month airmass (21/10 at Portland), a front came barreling in on the 13th and the temps grew progressively colder for the next few days before bottoming out on the 15th-16th.
Temp spreads include 23/-3 at Ashland, an incredible 20/1 at Newport on the coast, 13/-5, at Eola, all time records of 9 and -2 in Downtown Portland (with bare ground!) on the 15th, a 16/10 day at Astoria on the 16th, and all time records of 18/-2 at Downtown Olympia.
East of the Cascades the airmass was phenomenal, Spokane set all time records on the 15th with a high of -10 and low of -30. Miles City, MT plunged to -65 on the 14th, still a record for that part of the state, and the historic blizzard that hit the plains with this arctic front was the deadliest in American history.
The cold wave lasted for several days before a fairly significant overrunning snowstorm moved in on the 16th-17th. The late part of the month featured a pretty impressive blowtorch.