SEATTLE — Friday, Dec. 20 was the darkest day ever observed at the University of Washington during the 20 years that the college has been recording solar radiation.

Over the entire day, UW measured .37 million Joules of solar radiation over a square meter surface. The old record low was .39 on Dec. 14, 2006. The runner up was .44 on Dec. 7, 2015.   

For some perspective, there were several days in July this year that measured 27 million Jules of solar radiation over a square meter surface. 

UW said there were a few factors that contributed to the gloomy record. With the winter solstice happening on Saturday, the solar radiation reaching our atmosphere is about as low as it can be.

The heavy rain and thick clouds were also factors. Clouds and precipitation scatter solar radiation back to space.

RELATED: Seattle experiences the 5th rainiest day on record

Sea-Tac Airport recorded 3.25 inches of rain, making Friday the 5th rainiest day on record, according to the National Weather Service.

The top three rainiest days in the area of the past decade are:

  • December 20, 2019 - 3.25"
  • March 15, 2015 - 2.20" 
  • December 12, 2010 - 2.19"

Friday's record-breaking rainfall occurred amid a number of weather advisory and warnings. Several counties, including portions of King, Pierce, Thurston, and Kitsap were under Flood Advisories or a Flood Watch.

Several other areas also broke daily precipitation records on Friday:

  • Olympia: 2.87" – previous record of 1.87" was set in 1955
  • WFO Seattle: 2.64" – previous record of 1.02" was set in 1994
  • Hoquiam: 2.35" – previous record of 1.88" was set in 2014
  • Bellingham: 1.02" – previous record of 0.88" was set in 1974

RELATED: Rain continues into the weekend amid flooding throughout western Washington