The warmth this month has been more impressive than some might think around these parts, especially with respect to daytime highs. Should finish the month with a monthly mean max of 55° which would be good for 6th warmest on record, and is closer to an average April than March.
Lows haven't been as warm though. It seems like in recent years a lot of the warm Marches have featured quite large diurnal ranges with daytime highs carrying most of the warmth, which may seem contrary to expectations.
It really was a sort of perfect storm scenario. Everything came together just right and the Seattle area really made something out of nothing, somewhat like January 2017 in Portland metro or April 2022 in Clark County.
January 2017 wasn't only a perfect storm with snow, it was a perfect storm with cold too. It's hard to overstate how insane Hillsboro's 3F reading was - that is their coldest reading since December 1972. Dead gradients, clear skies, and a foot of snowcover really squeezed every last drop of cold out of a pretty pedestrian upper level airmass.