May 23 - July 29
Synoptic Analysis of Two 14-Day Extreme Precipitation Events in the Northwestern United States
Erika Pruitt (University of Illinois at Urbana-Champaign), Ty Dickinson (OU/SoM), Melanie Schroers (OU/SoM), Dr. Jason Furtado (OU/SoM), Dr. Elinor Martin (OU/SoM), and Dr. Michael Richman (OU/SoM)
What is already known:
- Extreme precipitation events are uncommon, but can be very dangerous when they occur.
- Extreme precipitation events have been regionally developed but not sufficiently researched as case studies.
- Stakeholders would benefit from information at a subseasonal to seasonal timescale, two weeks to two months, but the skill is very low compared to weather timescale, 0 days to 7 days.
What this study adds:
- Case studies are beneficial for future studies.
- The extreme events may be a combination of multiple precipitation systems impacting the region.
- The location of the jetstream and constant moisture advection are the two biggest influences of extreme events in the northwestern CONUS.
- Although ENSO conditions may exist, they are not the only drivers.
Abstract:
Stakeholders would benefit from knowing more in advance when extreme weather events will happen. Therefore, information on a sub-seasonal to seasonal timescale will be needed, but the skill is very low, and research is needed to improve it. Research has already been done for broad regional information of 14-day extreme precipitation events. This study looked at two case studies of extreme precipitation events out of the northwestern region, one in 2015 and the other in 2018. ERA5 data, PRISM, and Wyoming soundings, was used to find synoptic drivers that caused the two events to occur. It was found that the 2015 event in the West Coast region happened due to the position of the trough over the Pacific Ocean, creating an atmospheric river. For the 2018 event in the Mountain West region, the ridge was the main cause of the event, as it assisted in bringing a supply of moisture in from the Pacific Ocean. In both cases, the jetstream played a role in determining if an area will get a lot of moisture to create the extreme events. Both of these events also had the same supplier for moisture, the Pacific Ocean. It was also found that these events were not just one system precipitating for over 14 days, but rather from three different systems. This study will be useful for stakeholders, who can use the information from these case studies to better mitigate risk from future events.