cw3e-web - Center for Western Weather and Water Extremes

CW3E Welcomes Andy Richards

October 15, 2024

Andy Richards joined CW3E as a Fiscal Analyst in October 2024. With nearly 20 years of experience in finance and operations, he brings a wealth of knowledge and a proven track record of driving efficiency and strategic growth across diverse industries, including technology, food and beverage, and manufacturing. A native San Diegan, Andy earned a professional certification in Brewing Science and Technology from UC San Diego, an MBA from the University of Phoenix, and a B.S. in Psychology from UC San Diego.

Before joining CW3E, Andy served as the Director of Finance & Operations at Second Chance Beer Co., where he optimized financial management and operational workflows across manufacturing, four sales channels, and two taprooms. He enjoys building dynamic financial models and dashboards, preparing financial reports, and implementing internal controls to enhance compliance and productivity.

Throughout his career, Andy has consistently focused on creative problem-solving and leveraging technology to deliver valuable insights and solutions. His expertise includes accounting, financial forecasting, and process improvement, complemented by proficiency in tools such as Excel, VBA, Power Query, and DAX.

At CW3E, Andy is excited to apply his analytical skills and operational experience to support financial decision-making and drive the organization’s growth initiatives.

CW3E Welcomes Subin Yoon

September 23, 2024

Subin Yoon joined CW3E’s as a Field Operations Manager in September 2024. She earned her B.A. in Geology with a concentration in Geochemistry from Bryn Mawr College in Bryn Mawr, PA (2011) and her Ph.D. in Environmental Sciences at Baylor University in Waco, TX (2020).

Before joining CW3E, Subin was a postdoctoral fellow (2020 – 2023) and a research scientist (2023 – 2024) at the University of Houston. Her research focused on using air quality measurements to understand major sources and drivers of urban and coastal air pollution. Her work on air quality spans studies across Texas, Northern California, China, and India. Her expertise involves utilizing advanced analytical instrumentation and technologies to measure the chemical composition and optical properties of environmental pollutants (aerosols, trace gasses, volatile organic compounds), as well as analyzing measurements with source apportionment models to address air quality and climate-related questions. Since her graduate studies, she has participated in numerous intensive field campaigns and long-term monitoring projects.

At CW3E, Subin is excited to use her research and field-based expertise to manage and assist in all facets of the land-based observations efforts serving as primary resource for these projects. She will also assist in the collaboration with the AR Recon and FIRO programs to ensure smooth coordination of research.

CW3E Welcomes Peyton Capute

August 26, 2024

Peyton Capute joined CW3E in August 2024 as a postdoctoral researcher. Prior to joining CW3E, she earned a B.S. in Geoscience with a concentration in Meteorology from Hobart and William Smith Colleges (2018) and a Ph.D. in Atmospheric Science from the University at Albany, SUNY (2024). As a Ph.D. student, Peyton worked under CW3E affiliate Dr. Ryan Torn analyzing the predictability of Arctic cyclones in comparison to Atlantic Basin cyclones under an Office of Naval Research (ONR) grant. A climatological comparison of the practical predictability of these storms is published in Monthly Weather Review (Capute and Torn 2021). Further, she used the Model for Prediction Across scales to evaluate the tropospheric features and surface thermodynamics that limit the position and intensity variability of Arctic and Atlantic Basin cyclones using ensemble-based sensitivity analysis. Her research was part of ONR’s Arctic cyclone Departmental Research Initiative, which allowed her to take part in forecast operations for the THINICE field campaign, collaborating with other US, British, and French scientists to better understand the predictability of Arctic cyclones.

At CW3E, Peyton’s postdoctoral research will focus on extreme precipitation events related to flood risk and New York City water supply reliability and contribute to ongoing AR Reconnaissance research. Peyton is eager to apply her skillset to ongoing efforts at CW3E, while continuing to learn new tools.

CW3E Publication Notice: Reinterpreting ENSO’s Role in Modulating Impactful Precipitation Events in California

CW3E Publication Notice

Reinterpreting ENSO’s Role in Modulating Impactful Precipitation Events in California

August 9, 2024

A recent study has shed new light on the seasonal behavior of winter weather patterns that impact California, revealing the intricate ways El Niño and La Niña influence the State’s hydroclimate. This research is described in a new paper entitled “Reinterpreting ENSO’s Role in Modulating Impactful Precipitation Events in California”, which was recently published in Geophysical Research Letters by authors Kristen Guirguis (CW3E), Benjamin Hatchett (NOAA), Alexander Gershunov (CW3E), Mike DeFlorio (CW3E), Rachel Clemesha (UCSD), Tyler Brandt (CW3E), Kayden Haleakala (CW3E), Christopher Castellano (CW3E), Rosa Luna Niño (CW3E), Alexander Tardy (NWS), Michael Anderson (DWR), and Marty Ralph (CW3E). This research was sponsored by the California Department of Water Resources Atmospheric River Program, and supports CW3E’S 2019-2024 Strategic Plan by seeking to improve subseasonal-to-seasonal (S2S) predictability of extreme hydroclimate variables over the western U.S. region.

This research was motivated by recent seasonal forecast challenges in which winter precipitation in California deviated substantially from the seasonal forecasts issued 1-3 months in advance. Despite predictions of dry winters due to La Niña, California experienced unexpectedly wet conditions in both 2017 and 2023. Conversely, the strong El Niño of 2016 was expected to bring wet weather, but the season turned out to be normal-to-dry across the state.

Figure 1. (a) The wet weather regimes (WR8-14) responsible for most of California’s precipitation, which are a subset of sixteen weather regimes studied, shown as 500 mb geopotential height anomalies. (b) Percent of historical (1979-2023) precipitation that fell during WR8-14 with outlines of the Northern, Central, and Southern Sierra Nevada and locations of Tahoe City and Hetch Hetchy Coop stations. (c) AR landfall probability at different coastal latitudes for WR8-14. (d-e) Average daily precipitation and snow fraction from WR8-14.

In this new article, we delved into historical data to first examine how recurring atmospheric weather patterns influence California precipitation and Sierra Nevada snowpack (Figure 1). We then investigated if/how El Niño Southern Oscillation (ENSO) interacts with these recurring weather patterns to produce the known ENSO-precipitation teleconnection pattern (Figure 2). Our findings indicate that while ENSO significantly affects the characteristics of storms once they reach California—making El Niño storms generally wetter in coastal southern California and the Desert Southwest—it does not strongly influence how often these weather patterns occur in a season. This complexity makes seasonal precipitation forecasts particularly challenging.

The study highlights that the frequency of certain weather patterns not tied to ENSO played a crucial role in the unexpected rainfall of 2017, the heavy snowfall of 2023, and the drier-than-expected winter of 2016. This new understanding of how ENSO influences these hydrologically critical weather patterns provides valuable insight that could help to inform future seasonal forecasts. It emphasizes that while ENSO has a minimal impact on the frequency of impactful storm types, it does alter the precipitation characteristics of these storms, offering operational and scientific context for meteorologists and water managers.

This research links daily weather with seasonal climate and underscores the need for more nuanced and comprehensive approaches to seasonal weather forecasting in California, aiming to better prepare for the diverse and often unpredictable impacts of El Niño and La Niña in future California winters.

Figure 2. (a) Seasonal weather regime frequency (y-axis) conditional on ENSO phase (color scale), shown as a hybrid of a boxplot and histogram where the bar width represents the proportion of data in a bin and the “o” denotes the mean. (b-d) 500 mb geopotential height anomaly patterns for WR9, WR10, and WR12 during El Niño (left) and La Niña (right). (e-g) Difference in Z500 fields shown as El Niño minus La Niña. (h-j) Difference in IVT shown as El Niño minus La Niña for WR9, WR10, and WR12. (k-m) Precipitation anomalies for WR9, WR10, WR12 during El Niño (left) and La Niña (right). Stippling in e-g and h-j indicates statistically significant differences (5% level, student’s t-test).

Guirguis, K., Hatchett, B., Gershunov, A., DeFlorio, M., Clemesha, R., Brandt, W. T., Haleakala, K., Castellano, C. Niño, R. L., Tardy, A., Anderson, M., & Ralph, F. M. (2024). Reinterpreting ENSO’s role in modulating impactful precipitation events in California. Geophysical Research Letters 51, e2024GL110326. https://doi.org/10.1029/2024GL110326

California Extreme Precipitation Symposium Honors CW3E with Special Recognition Award

August 7, 2024

At the University of California, Davis on July 11, 2024, CW3E was presented with the Special Recognition Award during the 30th Annual California Extreme Precipitation Symposium (CEPSYM). CEPSYM is a day-long symposium consisting of scientific and technical presentations to broaden our understanding of extreme precipitation events to benefit flood management planning and increase warning time for large floods. The theme for this year’s conference was “Anticipating and Planning for California Floods – Past and Future.” This theme focused on looking back over the last 30 years and what we have learned about local extreme events while looking forward at what questions remain. CW3E’s research and mission are highly aligned with this theme. ARs have been identified as the source of all major flood events in California from 1861 through the present, beginning with the Great Flood of 1861-1862. Looking forward, climate change and its impacts are anticipated to amplify flood risk from ARs in California, and investigating this in more detail in order to provide more information for decision makers and resource managers is a major element of CW3E’s research. The symposium consisted of members from Federal, State, and local agency perspectives adding to the conversation about how society plans for anticipated future flood risk. Click here for the slides from all presentations given at this year’s event.

CW3E director Marty Ralph accepting the award on behalf of CW3E with (left) George Booth, Executive Director of Floodplain Management Association and (right) Gary Estes, Founder and Coordinator of California Extreme Precipitation Symposium.

CEPSYM awards the Special Recognition Award each year to “highlight and honor the outstanding contributions of individuals and institutions that have supported and advanced the professions of meteorology, flood hydrology, and flood risk management. These professions share the public safety goal of protecting life and property from the ravages of flooding. Together these professionals provide the tools, information, and knowledge essential for forecasting flood events before they occur, estimating potential flood magnitudes and impacts used in designing flood risk reduction projects, and responding to floods when they occur. Each honoree contributed to making the people of California safer from flood events over their many years of service.” This year, CEPSYM honored CW3E with this award. Click here to read more about this year’s special recognition award.

CW3E Welcomes Kyla Semmendinger-Raney

August 7, 2024

Kyla Semmendinger-Raney joined CW3E in July 2024 as a Research & Development Engineer on the Water Resources Engineering Team.

Kyla earned her MS and PhD in Environmental Engineering from Cornell University in Ithaca, New York (2023) and her BSE in Environmental Engineering from Mercer University in Macon, Georgia (2018). Prior to joining CW3E, Kyla completed a postdoctoral research fellowship at the Cooperative Institute for Great Lakes Research, housed at the NOAA Great Lakes Research Environmental Laboratory in Ann Arbor, Michigan. Kyla’s doctoral and postdoctoral research focused on improving outflow regulation within the Great Lakes region. Kyla’s work leveraged subseasonal-to-annual forecasts, many-objective optimization, and impact analysis modelling to explore improvements to the existing operations under current climate conditions as well as under plausible future climate. During this work, Kyla worked extensively with a bi-national science advisory board, stakeholders, and water managers to identify improvements to the current outflow regulation policy.

At CW3E, Kyla will work on the Water Resources Engineering Team and support FIRO efforts by developing and evaluating forecast-informed operating policies throughout the Western United States. She hopes to translate her experience working in highly regulated and constrained water systems in the Great Lakes to the West and make meaningful contributions to FIRO-related projects.

2024 International Atmospheric Rivers Conference Held in San Diego, CA

June 24, 2024

IARC-2024 was a jam-packed, 4-day, fast-paced, and lively hybrid (virtual and in-person) conference, held June 24 – 27.

The conference, hosted by CW3E, returned to Scripps Institution of Oceanography in 2024 and included over 60 oral presentations, 20 three-minute “lightning” presentations, and 38 posters! The audience exceeded 150 participants from North and South America, Europe, Asia and Oceania. This year, the conference expanded to include the following themes, representing the continued growth in enthusiasm and interest among the global AR community in AR science and research:

IARC-2024 Themes

Physical, dynamic, & microphysical aspects of ARs
Aerosol & biochemical aspects of ARs
ARs as a component of compound events
Environmental and socioeconomic impacts of ARs
Observing, identification, and monitoring of ARs
Forecasting of ARs in the short-range, medium-range, S2S, and seasonal time horizons
ARs in past, present, and future climates
Role of ARs in the changing Cryosphere

The idea of IARC was born from an AR Workshop hosted by CW3E in 2015. Dr. F. Martin Ralph organized a steering committee of international experts, which then convened the first IARC.

The main goal of the conference was to bring together a diverse and global community of experts across the fields of atmospheric, hydrologic, oceanic, and polar sciences, as well as water management, civil engineering, and ecology, to advance the state of atmospheric river science and to explore new directions, improved means of disseminating AR forecast information, and upgrades to existing monitoring techniques.

The conference is designed to maximize interaction time and encourage collaboration, and included breakout sessions and panel discussions along with traditional oral and poster sessions. The conference also strongly encouraged student participation.

Conducted every two years, IARCs have been held in La Jolla, California, (2016, 2018 and 2024), fully virtually (2020), and in Santiago, Chile (2022). For a detailed description of the history of IARC, meeting summary articles, and more, please see the website: https://cw3e.ucsd.edu/iarc/.

The entire IARC Steering Committee would like to thank everyone who has contributed and participated in the conference, and for helping make it such a resounding success! We hope to see, in person, all the familiar faces, as well as many new ones, for the next IARC.

Please see the IARC website for program information and abstracts, and be on the lookout for details on the next International Atmospheric Rivers Conference, which will be held in 2026 in Portugal.

GNSS Geodesy Quantifies Water‐Storage Gains and Drought Improvements in California Spurred by Atmospheric Rivers

CW3E Publication Notice

GNSS Geodesy Quantifies Water‐Storage Gains and Drought Improvements in California Spurred by Atmospheric Rivers

July 12, 2024

In the recent publication, “GNSS Geodesy Quantifies Water‐Storage Gains and Drought Improvements in California Spurred by Atmospheric Rivers” published in the AGU journal by CW3E collaborator and University of Montana professor Hilary R. Martens, among co-authors across institutions including CW3E’s Qian Cao, Ming Pan, Anna Wilson, Ellen Knappe, and Marty Ralph, researchers utilize observations from Global Navigation Satellite Systems (GNSS), including surface-loading deformation, to quantify the impacts of Atmospheric Rivers in California on Terrestrial Water Storage (TWS) and drought indices. This work contributes to CW3E’s 2019-2024 Strategic Plan, in particular the Priority Area dedicated to Atmospheric River Research and Applications by integrating observations, theory, and modeling into decision support.

Figure 1. (a) Vertical displacement of Earth’s surface (red = uplift, blue = subsidence) from GNSS, (b) terrestrial water storage from the GNSS displacements, (c) snow water equivalent, (d) cumulative precipitation, (e) CW3E-modeled runoff, (f) CW3E-modeled evapotranspiration, (g) CW3E-modeled TWS changes for the western US from 1 October 2022 – 1 April 2023

Drought conditions and decreased water availability over the past few decades have become more common, raising concerns of a “mega drought” and the economic, political, health and safety, and ecological risks of continuing in a drought-like state. This urgently drives the need for studies such as this to utilize observational data to improve long-term and comprehensive water-management. As Atmospheric Rivers (ARs) typically account for about 30-50% of precipitation on the west coast with mountains serving as critical water reservoirs, this study focused on quantifying the increase in TWS following ARs hitting California using Earth-surface displacement from GNSS networks to track the changes in Earth’s shape to detect water losses and gains while focusing on Water year 2023 (WY23). WY23 (October 1, 2022 – April 1, 2023) was one of the strongest storm seasons in the western US on record and punctuated a severe drought period, and provided an opportunity to examine water storage changes in an extreme precipitation cycle. This study particularly looked at the Sierra Nevada mountains and the Sacramento-San Joaquin-Tulare (SST) river basin to observe the TWS gains over 17 years in comparison to drought conditions, evaluate the impact of ARs on the TWS, and identify the impact of individual storms in GNSS series to help improve water management.

This study found, through GNSS observations, that net gains in TWS in the first half of WY23 was the highest on record for the two watersheds studied, which demonstrated the seasonal storms’ abilities to bolster water resources in the area. This study also found that nearly all the water that was delivered into these watersheds from ARs remained in the watersheds as snowpack or liquid water, with subsurface reservoirs accounting for about 40% in the Sierra Nevada and 60% in SST watersheds of the total TWS gains. It was also shown that there was a recovery from meteorological and hydrological drought during the first half of WY23 based on two drought metrics.

This study was able to effectively broaden our understanding of how GNSS observations may be used to understand the signature of heavy AR storm seasons, and improve our water management practices. To read more about this application of GNSS, access the entire publication here.

Martens, H. R., Lau, N., Swarr, M. J.,Argus, D. F., Cao, Q., Young, Z. M., et al.(2024). GNSS geodesy quantifies water‐storage gains and drought improvements in California spurred by atmospheric rivers. Geophysical Research Letters, 51,e2023GL107721. https://doi.org/10.1029/2023GL107721.

CW3E Publication Notice: Association of Western US compound hydrometeorological extremes with Madden-Julian oscillation and ENSO interaction

CW3E Publication Notice

Association of western US compound hydrometeorological extremes with Madden-Julian oscillation and ENSO interaction

June 18, 2024

A new paper entitled “Association of western US compound hydrometeorological extremes with Madden-Julian oscillation and ENSO interaction” was recently published in Nature Communications Earth & Environment and authored by CW3E researcher Jiabao Wang, Mike DeFlorio (CW3E), Alexander Gershunov (CW3E), Kristen Guirguis (CW3E), Luca Delle Monache (CW3E Director of Research), and Marty Ralph (CW3E Director). As part of CW3E’s 2019-2024 Strategic Plan, CW3E seeks to improve understanding of the subseasonal (2-6 week lead) and seasonal (6-week to 6-month lead) predictability of extreme weather over the western US and develop a comprehensive understanding of the physics and the probabilistic and statistical characteristics of extreme events in the West to inform current and future resource and risk management. This study discovered a strong linkage between variability in the occurrence frequency of boreal winter hydrometeorological (precipitation and temperature) compound extremes over the western US and the dominant subseasonal predictability source in the tropics, Madden-Julian oscillation (MJO), and showed that the linkage is largely dependent on ENSO phases. This research was sponsored by the California Department of Water Resources Atmospheric River Program.

Four different types of compound extremes are examined in this study: compound dry conditions and warm spells (dry-hot), compound extreme precipitation and cold spells (wet-cold), compound dry conditions and cold spells (dry-cold), and compound extreme precipitation and warm spells (wet-hot). We find that the occurrence frequency of compound extremes over the western US changes significantly with the eastward movement of MJO convection. When the MJO is located over the Maritime Continent (Phases 4-5), the frequency of dry-hot extremes tends to increase and wet-cold extremes tend to decrease over most of the western US (Fig. 1). When the MJO is located over the western Pacific (Phases 6-7), more wet-cold extremes and less dry-cold extremes are likely to occur over the southwestern US. The MJO-compound extreme relationship, however, changes significantly in response to different ENSO phases. The ENSO impacts are manifested as either opposite-sign signals of extreme event frequency in response to MJO or different magnitudes of MJO influence between the two ENSO phases (Fig. 1).

Variations in the MJO-compound extreme relationship associated with ENSO originate from the different MJO teleconnection patterns (Fig. 2). When the MJO is over the Indian Ocean or western Pacific (Phases 2-3 and 6-7), its teleconnections tend to extend more eastward in El Niño years and MJO impacts tend to persist longer during El Niño; while in La Niña, although the amplitude of MJO teleconnections is stronger, the responses are more offshore and thus MJO impacts are generally weaker. As a result, the response in compound extremes is more significant during these MJO phases in El Niño years than in La Niña years. For the other MJO phases (Phases 8-1 and 4-5), an opposite response in MJO teleconnections along the US West Coast is seen between two ENSO phases, leading to the opposite response in the compound extremes.

Figure 1. Averages of absolute changes in compound extreme frequency (unit: %) over a California and b the Pacific Northwest (Washington/Oregon). Four different categories of compound extremes are shown: wet-cold, dry-hot, wet-hot, and dry-cold extremes. Brown bars indicate the changes after active MJO phases in all years; Blue and green stripped bars represent the seasonal changes in active El Niño and La Niña years, respectively; Blue and green solid bars show the averages for each MJO phase in active El Niño and La Niña years, respectively. The numbers in each figure represent the climatological frequency of that compound extreme type over that region. The asterisks indicate the significance of the changes based on the bootstrap test.

The findings in this study uncover a strong intraseasonal variation in the MJO-related compound extremes and demonstrate a need to consider the impacts of both the intraseasonal modulation and the seasonal background state when predicting temperature and precipitation at subseasonal and seasonal lead times relevant to water managers and other end users across the western US.

Figure 2. 5–9-day averaged lagged response of 25-90-day filtered 500hPa geopotential height anomalies (Z500a; shading: m) and 850–700-hPa integrated vapor transport anomalies (IVTa; vectors: kg m⁻¹ s⁻¹) to MJO activity at day 0 [OLR contour: green (brown) represents enhanced (suppressed) convection, interval: 5 W m⁻²] in all years, El Niño years, and La Niña years. The dotted areas represent the significant Z500a exceeding the 90% confidence level. Vectors that are shown are significant IVTa.

Wang, J., DeFlorio, M. J., Gershunov, A., Guirguis, K., Delle Monache, L., & Ralph, F. M. (2024). Association of western US compound hydrometeorological extremes with Madden-Julian oscillation and ENSO interaction. Communications Earth & Environment, 5, 314. https://doi.org/10.1038/s43247-024-01449-w

CW3E Publication Notice: Response of Sea Surface Temperature to Atmospheric Rivers

CW3E Publication Notice

Response of Sea Surface Temperature to Atmospheric Rivers

June 18, 2024

A new article titled “Response of sea surface temperature to atmospheric rivers” by Tien-Yiao Hsu (SIO /CW3E), Matthew R. Mazloff (SIO), Sarah T. Gille (SIO), Mara A. Freilich (Brown University), Rui Sun (SIO/CW3E) and Bruce D. Cornuelle (SIO) was published in Nature Communications on June 12, 2024. This work investigates the impact of atmospheric rivers (ARs) on sea surface temperature (SST) over the North Pacific by analyzing 25 years of ocean reanalysis data using an SST budget equation. Authors show that in the region of strong ocean modification, ocean dynamics can offset over 100% of the anomalous SST warming that would otherwise arise from atmospheric forcing (Figure 1). Among all ocean processes, ageostrophic advection and vertical mixing (diffusion and entrainment) are the most important factors in modifying the SST tendency response. The SST tendency response to ARs varies spatially. For example, in coastal California, the driver of enhanced SST warming is the reduction in ageostrophic advection due to anomalous southerly winds. Moreover, there is a large region where the SST shows a warming response to ARs due to the overall reduction in the total clouds and subsequent increase in total incoming shortwave radiation. This work adds tangible understanding to the Subseasonal to Seasonal Prediction of Extreme Weather priority area in CW3E’s Strategic Plan, where SST prediction is a crucial boundary condition.

Figure 1. (Figure 5 from Hsu et al. 2024). The response of sea surface temperature (SST) tendency to atmospheric rivers (ARs), decomposed into distinct contributing processes. Variables shown are: (a) Θ̅̇_loc, (b) Θ̅̇_ocn, (c) Θ̅̇_adv, (d) Θ̅̇_mix, (e) Θ̅̇_det, (f) Θ̅̇_sfc, (g) Θ̅̇_sw, (h) Θ̅̇_lw, (i) Θ̅̇_sen, and (j) Θ̅̇_lat. Each panel shows the mean of the composite anomalous SST tendency associated with a particular process (shading) and its standard deviation (contours). Dotted areas show response regions that pass the significance test (p = 0.05). For each grid point, we compute the mean and standard deviation by grouping all of the AR day data. The significance test is tested against the climatology group, i.e., every single day. The anomalous SST tendencies Θ̅̇_dilu and Θ̅̇_hdiff are very small such that they are not shown.

Hsu, T.-Y., Mazloff, M. R., Gille, S. T., Freilich, M. A., Sun, R., & Cornuelle, B. D. (2024). Response of sea surface temperature to atmospheric rivers. Nature Communications, 15, 508. https://doi.org/10.1038/s41467-024-48486-9