As a part of the 2022 National Weather Center Research Experience for Undergraduates the PRES2iP team hosted Erika Pruitt, a senior Atmospheric Science student at the University of Illinois. During her time she analyzed two 14-day extreme periods from our database, seen below.

Extreme Period 1

West Coast Extreme Precipitation Period from 12/6/2015 – 12/19/2015

This extreme rain period occurred during the wet season within parts of Oregon, Washington, northern California, and western Idaho. There was a total of $36.5 million in property damages due to heavy precipitation and high winds. Impacts seen during the period ranged from wide-spread flooding, mudslides, power outages, water contamination from sewer overflow and loss of life (NOAA-NCEI 2020). The extreme precipitation period polygon, red, and total precipitation over the 14-day period can be seen to the right. If you would like to learn more about how this extreme period was defined, please read our fact sheet here.
The maximum in 14-day precipitation within the region was 47in. The yearly average for rainfall in this region is 84in, therefore this extreme period alone made up more than 50% of typical yearly rainfall (Western Regional Climate Center).

Precipitation occurred over all 14-days, with three storm systems creating a majority of the rainfall seen. The systems occurred on December 9th, 13th and 18th. Synoptic analysis of this extreme precipitation period shows a consistent 500hPa geopotential height dipole over the Pacific Ocean throughout a majority of the 14-days. This helps to drive large amounts of moisture into the region via an atmospheric river during the first half of the extreme period. The region experienced three systems that aided to create the extreme precipitation. The first from the 8th to the 9th, event days 3 and 4. The second on the 13th, event day 8, and lastly from the 17th to the 19th, event days 12 and 13.

This extreme precipitation period occurred during the winter of an El Niño. Yet the jet stream, seen below, was anomalously poleward compared to a typical El Niño pattern. Helping to bring unprecedented rainfall into the region.

Extreme Period 2

Northern Mountain West Extreme Precipitation Period from 2/3/2018 – 2/16/2018

This extreme period occurred during the dry season of Montana and northern Wyoming, seen to the right as a red polygon. It resulted in a total of $10 million in property damages with many reports of high wind and winter storm (NOAA-NCEI 2020). Besides high property damages, this extreme precipitation period also resulted in up to 58 inches of snow, icy roads, power outages and brutally cold wind chills as low as -58ºF. Temperatures during this time were also as low as -40ºF in some areas as well. After a further look into this extreme precipitation period, it was found to be a record-breaking snow period.

Similar to the previous extreme period, there was three systems that contributed to the precipitation. The systems passed through on February 5th, 9th and 15th.

Synoptic analysis show a consistent anomalous 500 hPa ridge over the western United States and Pacific Ocean throughout the entire 14-day period. Helping to bring moisture from the Pacific into the region. The surface temperature in the region stays below freezing for the entire event, with the coldest temperatures experienced at the end of the 14-day period.