2024 International Atmospheric Rivers Conference Held in San Diego, CA

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

2024 IARC attendees

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.

Science, Policies, Projects, and People: Seventh Annual Yampa Basin Rendezvous Highlights the Ingredients for Water Resiliency in the Yampa Basin

Science, Policies, Projects, and People: Seventh Annual Yampa Basin Rendezvous Highlights the Ingredients for Water Resiliency in the Yampa Basin

June 18, 2024

The 7th Annual Yampa Basin Rendezvous (YBR) was held 29th-30th May 2024, serving to highlight the multiple complementary ways that the region is working towards increasing climate and water resilience in the face of a changing future climate. The conference was held at the Allbright Auditorium at Colorado Mountain College’s Steamboat Springs campus and was organized by representatives from a plethora of organizations devoted to this goal, including the Center for Western Weather and Water Extremes (CW3E), Friends of the Yampa (FOTY), Yampa Valley Sustainability Council (YVSC), Colorado Mountain College (CMC), the Upper Yampa Water Conservancy District, River Network, Yampatika, The Nature Conservancy, and the Community Agriculture Alliance.

CW3E’s Dr. Deanna Nash presents to YBR attendees on the role of Atmospheric Rivers in Colorado’s precipitation and snowpack patterns. Photo Credit: Nathan Stewart.

This year’s conference theme, “Connecting the Drops: Linking Weather, Watersheds, and Communities for a Resilient Water Future”, highlights the interwoven and interdisciplinary nature of the path to water resiliency, with connection between diverse communities being the key to success. In that vein, YBR 2024 provided a forum for experts in the disparate fields of science and research, policy and advocacy, land management and project implementation, and science communication and outreach to share their work and ideas, with a focus on the Yampa River Basin. The two days of the conference featured three panel sessions each examining a different aspect of climate and water resilience. The panel sessions were complemented by ample opportunity for networking and casual conversations including two Field Excursions and an evening Community Showcase & Happy Hour event.

The first day of the conference opened with welcoming remarks from outgoing President of CMC and long-time YBR attendee, Dr. Carrie Besnette Hauser, who spoke of the close ties between CMC and the rivers that run through its district. She drew analogy between the founding stories of both CMC and YBR as small, dedicated groups of citizens banding together to advocate for something they believed was important to the rural Western Slope communities they cared deeply about. Dr. Hauser’s remarks were followed by speakers from the first panel, who together examined the State of the Science and Policy. This panel featured talks from Becky Bolinger, Colorado’s Assistant State Climatologist; Kelly Romero-Heaney, Assistant Director of Water Policy for the Department of Natural Resources; and Deanna Nash, CW3E Postdoctoral Researcher. Deanna shared her latest CW3E research into the role of atmospheric rivers on precipitation in Colorado and the Yampa Basin, including the potential role of atmospheric rivers as “drought busters”. Next, the second panel showcased examples of Connected Land-Water Planning and Management. The invited speakers were Andrea Harbin Monahan of the Colorado Water Conservation Board; Andy Rossi of the Upper Yampa Water Conservancy District, and 5th-generation Yampa Valley rancher Kyle Monger, who shared his perspectives from decades of family ranching operations on the Yampa River.

During the lunch break, YBR attendees were treated to a surprise visit by members of the Colorado State Legislature. Colorado Governor Jared Polis, Senator Dylan Roberts, House Speaker Julie McCluskie, and Representative Meghan Lukens visited the conference to sign two important pieces of water legislation into law. The bills, HB24-1362 and SB24-197, aim to help the State increase resilience to drought in the basin by incentivising greywater recycling, and by implementing recommendations from the Colorado River Drought Task Force. Their visit signifies a growing recognition of YBR as a venue for driving change on this issue and for channeling research and knowledge into action.

Gov. Polis signs SB24-197 at this year’s YBR. The bill implements some of the recommendations from the Colorado River Drought Task Force. Photo Credit: Madison Muxworthy.

In the afternoon, participants ventured out on a field excursion to a climate and soil moisture monitoring station operated by the Y-BASIN project team. The Y-BASIN project is a partnership between CW3E, YVSC, and CMC and supported by the Upper Yampa Water Conservancy District, Colorado River District, and Colorado Water Conservation Board. Participants learned from CW3E Director Marty Ralph and YVSC Director Michelle Stewart about the goals of the Y-BASIN project and the importance of soil moisture measurements in accurately predicting seasonal water availability. They inspected the station and its sensors up close, and had the chance to collect their own soil moisture measurements using handheld probes, led by USFS Soil Scientist Ryan Adams. The field excursion was immediately followed by the Community Showcase event, which featured posters, booths, and other presentations from community organizations in an informal setting with conversation stimulated by light refreshments. The venue, right on the banks of the Yampa River, provided a charming opportunity to reflect on the day’s learning.

The next morning, returning attendees were welcomed by CW3E Director Dr. Marty Ralph, who reflected on the importance of YBR to CW3E’s mission and the history of the relationship between the center and the Yampa Basin. Dr. Ralph also showcased some of the critical research advancements in climate and water resiliency that the Center has been a part of and continues to work on. The third panel highlighted the work of communicators in the Yampa Basin. Filmmaker Cody Perry and journalist Luke Runyon shared their perspectives on storytelling around rivers and water in Colorado and Jessica Counts, of local non-profit YVPS3, shared her work on furthering education and career opportunities for young students in the Yampa Valley.

Field excursion attendees learn about soil moisture monitoring for water resource management at one of the Y-BASIN climate and soil moisture monitoring stations. Photo Credit: Nathan Stewart.

For the afternoon field excursion, participants were joined by invited speakers CJ Mucklow, Jeremiah Psiropoulos, Bill Badaracca, and Mark Monger, all local landowners and experts in ecology, ranching, and land management. The field party visited a series of ranches in the Elk River drainage to compare landscape characteristics in the presence and absence of beavers and BDA (beaver dam analogue) structures. The speakers not only discussed the challenges of managing the impacts of beaver activity on ranch operations, but also passionately emphasized the myriad benefits they can bring to both the rancher and the ecosystem thanks to their modulation of water movement through the landscape.

The end of the field excursion marked the end of the official YBR program, although participants were eager to continue their conversations into the evening at FOTY’s State of the Yampa Address and over the weekend at the Yampa River Festival. The sharing of knowledge and the connections made at this year’s conference will surely contribute to a better informed and more energized Yampa Basin community as we strive for a more sustainable and resilient future.

– Yampa Basin Rendezvous 2024 Steering Committee

CW3E Publication Notice: Rainfall intensification amplifies exposure of American Southwest to conditions that trigger postfire debris flows

CW3E Publication Notice

Rainfall intensification amplifies exposure of American Southwest to conditions that trigger postfire debris flows

June 12, 2024

A new paper entitled “Rainfall intensification amplifies exposure of American Southwest to conditions that trigger postfire debris flows” was recently published in Nature’s journal npj Natural Hazards. This work was authored by Matt Thomas (U.S. Geological Survey), Allison Michaelis (Northern Illinois University/CW3E affiliate), Nina Oakley (California Geological Survey/CW3E affiliate), Jason Kean (U.S. Geological Survey), Victor Gensini (Northern Illinois University) and Walker Ashley (Northern Illinois University).

Postfire debris flows pose a threat to life, property, and infrastructure in many mountainous areas of the Southwest. When areas of steep terrain with susceptible geologic and hydrologic characteristics are burned at moderate to high severity, short duration (<1 hour), high-intensity rainfall can trigger postfire debris flows. For some areas, debris-flow triggering rainfall intensities can be as low as 0.25 inches in 15 minutes. Minimum triggering thresholds in the Southwest are often less than the 2-year recurrence interval at the 15-minute duration. In a changing climate, with increasing wildfire activity and rainfall intensification, the question arises, how will postfire debris flow hazard change? Previous work demonstrated that debris flow probability is most sensitive to rainfall intensification. Thus, this study focuses on exceedance of estimated debris-flow rainfall thresholds across the Southwest using downscaled climate model projections to address this question.

In this work, authors use dynamically downscaled (3.75 km) convection-permitting simulations of short duration (15-min) rainfall for a historic period (1990-2005) and late century period (2085-2100) using both the RCP 4.5 and RCP 8.5 emission scenarios, developed by Gensini et al. (2022 ). Model output at high spatial and temporal resolutions relevant to postfire debris flows are very recent; we are just beginning to have sufficient information to address the questions of postfire debris-flow hazard changes in a warming climate. Statistical methods were applied to allow for comparison between the downscaled model output and rainfall thresholds for debris flows issued by the USGS for burn areas across the Southwest.

Figure 1. (Fig. 4 from Thomas et al., 2024): a) Box and whisker plots that track changes in the exceedance ratio of 15-minute rainfall intensity thresholds for the HIST, FUT4.5, and FUT8.5 simulation scenarios for mountainous terrain throughout California and Colorado (Figs. 2, 3, Supplementary Fig. 1), as well as for 175 burned areas across the American Southwest (i.e., Arizona, California, Colorado, Nevada, New Mexico, and Utah) where the U.S. Geological Survey issued rainfall thresholds as part of emergency assessments of postfire debris-flow hazards between 2014 and 2022 (Fig. 1a, Supplementary Fig. 1). The boxes in (a) are bound by the first and third quartile, with the median indicated by a line, and the whiskers extend from the boxes to the farthest data point within 1.5 times the inter-quartile range. The bar plots illustrate differences in the seasonality of rainfall threshold exceedance for mountainous terrain throughout (b) California and (c) Colorado.

Results indicate that while seasonality of over threshold precipitation events remains similar in climate projections for the regions studied (b and c above), both the magnitude (a, above) and frequency (below) of threshold exceedances increases in both RCP 4.5 and 8.5 scenarios compared to historic. A greater magnitude of threshold exceedance indicates the potential for larger volume, more damaging debris flows. An increased frequency of over-threshold events indicates we may expect more opportunities for debris flows to occur before burn areas can sufficiently recover.

For California in particular, the largest increases in threshold exceedances per year are most prominent in the North Coast Range and Klamath Mountain geomorphic provinces in the RCP 4.5 scenario. Threshold exceedance frequency further increases in these areas and expands to include the Sierra Nevada province in the RCP 8.5 scenario (figure below). These areas historically have experienced less frequent postfire debris-flow activity than Southern California, where damaging events are commonplace. Communities, emergency managers, and weather forecasters in the Northern California areas projected to see an increase in over-threshold precipitation may be less accustomed to contending with postfire debris flow hazards as compared to their counterparts in Southern California. This study highlights the increased hazard potential and benefits of prefire planning, education, and outreach for postfire hazards.

Figure 1. (Fig. 2 from Thomas et al., 2024): State of California with an overlay of scatter plots that reflect 15-min rainfall intensity threshold (equivalent to a one-year recurrence interval under the present climate) exceedances in mountainous terrain for the WRF-BCC HIST, FUT4.5, and FUT8.5 simulation scenarios. Several areas are labeled for reference, including “KLM” (Klamath Mountains), “NCR” (Northern Coast Ranges), “Sierra Nevada” (SNV), “SCR” (Southern Coast Ranges), “TRV” (Transverse Ranges), and “PNR” (Peninsular Ranges). State boundaries provided by U.S. Census Bureau.

This work addresses the CW3E Strategic Plan priority area of “Monitoring and Projections of Climate Variability and Change”, and the area goal of advancing understanding and projections of extreme precipitation events. This work provides insight into how short-duration rainfall intensities conducive to postfire debris flows may change in the future in frequency, magnitude, space, and seasonality. The work also addresses the CW3E core value of Collaboration, as authors represent university as well as state and federal agencies.

Thomas, M.A., Michaelis, A.C., Oakley, N.S. et al. Rainfall intensification amplifies exposure of American Southwest to conditions that trigger postfire debris flows. npj Nat. Hazards 1, 14 (2024). https://doi.org/10.1038/s44304-024-00017-8

CW3E Welcomes Heather Dopke

CW3E Welcomes Heather Dopke

June 4, 2024

Heather is currently an undergraduate student at UCSD with a double major in Political Science – Public Law and Sociocultural Anthropology with minors in Law and Society and Psychology graduating in June 2025. She will be working with CW3E as a fiscal and administrative assistant under Lillian Gilmore and Laura Martin.

CW3E Welcomes Dr. Erfan Goharian

CW3E Welcomes Dr. Erfan Goharian

May 21, 2024

We are excited to announce that Dr. Erfan Goharian has joined the Center for Western Weather and Water Extremes (CW3E) as the Water Resources Engineering R&D Manager.

Dr. Goharian is an Associate Professor of Civil and Environmental Engineering at the University of South Carolina (USC). His research, education, and practice nexus is centered on developing multi-source heterogeneous data fusion, artificial intelligence (AI), and systems analysis techniques to advance the smart and informed operation and management of water resources systems. Dr. Goharian and his team develop and deploy cutting-edge systems and modeling techniques to enhance informed decision-making of integrated water and environmental resources systems in the face of climate change and extreme events.

Moving to CW3E, Dr. Goharian will establish and lead the Water Resources Engineering Research and Development (WRE R&D) program. The CW3E WRE R&D Group is dedicated to advancing knowledge, fostering collaboration, and driving innovation at the intersection of academia, community, and partnerships. This initiative will promote multidisciplinary collaborations, with a focus on advancing intelligent and integrated modeling techniques, particularly to support the implementation of Forecast-Informed Reservoir Operations (FIRO). Our mission is to pioneer cutting-edge solutions in FIRO, comprehensive monitoring and forecasting of floods and droughts, integrated water resources modeling and management, and the application of machine learning and AI through fostering strong partnerships with local communities and stakeholders, and a focus on global leadership.

Previously, Dr. Goharian has led various projects funded by national agencies such as NOAA, NSF, USGS, and DoD, state agencies like the SC Sea Grants Consortium and SCDOT, and companies including Microsoft and Amazon. His publication record includes over 60 top-notch peer-reviewed journal papers and over 100 invited talks and conference presentations. Dr. Goharian has been honored with numerous prestigious awards, including the NSF CAREER Award, ASCE Young Civil Engineer of the Year, UCOWR Early Career Award, ASCE’s Best Research-Oriented Paper of the Year, ASCE Outstanding Reviewer awards, and served as a member of the South Carolina Floodwater Commission, appointed by Governor McMaster. He also serves as an associate editor of Nature’s Scientific Reports and the Journal of Water Resources Planning and Management.

CW3E is thrilled to welcome Dr. Erfan Goharian and looks forward to the significant contributions he will bring to our team and the broader water resources community.

Reservoirs-plus-Snowpack Water Storage in the Sierra Nevada

Reservoirs-plus-Snowpack Water Storage in the Sierra Nevada

April 19, 2024

Current measures of water stored in Sierra Nevada reservoirs and snowpacks are now continually updated and available from CW3E. Mountain snowpacks provide an “extra” way that water gets stored in California and across the Western US, acting as natural reservoirs that hold winter precipitation (as snow) from the cold wet season until spring and summer when the water is released as snowmelt when water demands for human and environmental uses, including irrigation, are high. Thus the combination of water stored as snow and water stored in human-built reservoirs is a useful indicator of development, persistence, and termination of droughts in many western water-supply systems. As the climate warms in coming decades, the “typical” mix of water in snowpack versus reservoir is projected to change, with far less snow holding far less water in future winters. Whether the water no long stored in snow ends up residing instead in reservoirs for more of the year in the future will depend on a variety of tradeoffs associated with winter-weather and hydrological changes, infrastructure constraints, and flood- and resource-management responses that tracking of the combined storage amounts may help to highlight.

This approach to tracking water-supply status was initially developed for drought early-warning and tracking purposes, but has also demonstrated value in wet years. Notably, last year, these figures attracted widespread attention when they showed that the 2023 snowpack in drainages above the ancient Tulare Lake bed contained as much as three times the total amount of space in the reservoirs in that drainage even if all the water currently in the reservoirs was released to make space. This highlighted that nearly all of the water that entered the reservoirs that year was going to have to be routed out of the Tulare Basin or else flooding would certainly occur. However, that much water could not be routed out of the Basin with existing infrastructures and so flooding did occur, and Tulare Lake refilled, covering large expanses of agricultural land and impacting communities. In the three preceding drought years (2020-2022), by contrast, snowpacks never grew to sizes that would refill Sierra Nevada reservoirs, and so water in storage declined each year.

Since 2015, scientists at Scripps have been developing and circulating simple graphics that showed how the combination of these two forms of storage evolved, in order to better communicate water resource status as the water years progressed. CW3E researcher Mike Dettinger demonstrated the value of tracking of water supply status by tracking these combined storages during the 2012-2015 California drought (Dettinger and Anderson, 2015), and has been producing and circulating them on a roughly monthly (or more frequent, depending on circumstances) basis since. The development and original updates were supported by NOAA’s National Integrated Drought Information System (NIDIS) via the California Nevada Adaptation Program (CNAP).

This spring the process of updating and generating these diagrams was automated so that now they will be updated on a daily basis, with support from the California Department of Water Resources via the AR Program. Updated storage diagrams will be available at:

https://cw3e.ucsd.edu/water_storage_tracking/

along with background information, explanations, and archives of the diagrams from previous years (to put the current year’s progress into historical contexts).

Dettinger, M.D., and Anderson, M.L., 2015, Storage in California’s reservoirs and snowpack in this time of drought: San Francisco Estuary and Watershed Science, 13(2), 5 p., http://dx.doi.org/10.15447/sfews.2015v13iss2art1.

CW3E Publication Notice: Impact of atmospheric rivers on Arctic sea ice variations

CW3E Publication Notice

Impact of atmospheric rivers on Arctic sea ice variations

February 5, 2024

A new paper titled “Impact of atmospheric rivers on Arctic sea ice variations” led by Linghan Li with co-authors Forest Cannon (Tomorrow.io), Matthew Mazloff (UCSD), Aneesh Subramanian (University of Colorado Boulder), Anna Wilson (CW3E), and Fred Martin Ralph (CW3E Director), was recently published in the European Geosciences Union’s journal The Cryosphere. This paper examines how atmospheric rivers (ARs) contribute to variations in Arctic sea ice, which has been rapidly decreasing especially in the summer in recent decades. The research first focuses on physical processes in two case studies of ARs in 2012 and 2020, then expands to a larger statistical analysis for 1981-2020 over the entire Arctic Ocean. This research contributes to the Atmospheric River Research and Applications, and the Monitoring and Projections of Climate Variability and Change Priority Areas in CW3E’s 2019-2024 Strategic Plan by adding to the understanding of the global impacts of atmospheric rivers and the relationship with climate change in polar regions.

Li uses hourly data at 0.25° × 0.25° resolution from ERA5, the most recent atmospheric reanalysis from ECMWF, to study causal relationships between ARs and decreases in sea ice concentration. In August 2012 and July 2020, ARs associated with large cyclones triggered rapid sea ice melt through modulating turbulent heat fluxes and winds. In a statistical analysis on weather timescales, Li finds a significant negative correlation between atmospheric moisture content and the rate of changes in sea ice concentration over almost the entirety of the Arctic Ocean (Figure 1, Figure 10 from Li et al. 2024). Ice concentration changes are also shown to be negatively correlated with northward winds and with latent and sensible heat fluxes. The work demonstrates how conditions associated with ARs play an important role in the changing Arctic sea ice cover.

Figure 1: (Figure 10 from Li et al. 2024) (a) Rank correlation between anomalies of IWV and sea ice concentration tendency. Only significant correlations are plotted. (b) Rank correlation between anomalies of northward wind and sea ice concentration tendency. (c) Rank correlation between anomalies of latent heat flux and sea ice concentration tendency. (d) Rank correlation between anomalies of sensible heat flux and sea ice concentration tendency.

Li, L., Cannon, F., Mazloff, M. R., Subramanian, A. C., Wilson, A. M., & Ralph, F. M. (2024). Impact of atmospheric rivers on Arctic sea ice variations. The Cryosphere, 18(1), 121-137. https://doi.org/10.5194/tc-18-121-2024

CW3E AR Update: 2 February 2024 Outlook

CW3E AR Update: 2 February 2024 Outlook

February 2, 2024

Click here for a pdf of this information.

Strong Atmospheric River to Drive High-Impact Precipitation Event Over California

  • A strong AR and low pressure system are forecast to make landfall over Central CA Sun 4 Feb and progress down the CA coast through Mon 5 Feb.
  • There is uncertainty between the GFS and ECMWF deterministic models on the strength of the low pressure system and AR as well as the landfall location.
  • The GFS is forecasting the low pressure and AR to be stronger than the ECMWF and make landfall further north in CA.
  • The GEFS and West-WRF ensemble are forecasting AR3 conditions (based on Ralph et al. 2019 AR scale) over the central CA coast, with AR1/2 conditions in northern and southern CA.
  • This AR is forecast to bring significant precipitation to much of CA, including heavy rainfall along the central and southern CA coasts and heavy snowfall in the Sierra Nevada.
  • The WPC is forecasting greater than 6 inches of precipitation over the Sierra Nevada and Transverse Ranges over the next 7 days.
  • The WPC Excessive Rainfall Outlook indicates a Moderate Risk (level 3 of 4, or at least 40% chance) for flash flooding in Central CA coast for the 24 hour period ending 4 AM PT Mon 5 Feb and Los Angeles Metro Area for the 24 hour period ending 4 AM PT Tue 6 Feb.
  • NWS San Francisco has issued a high wind warning from the South Bay area to San Luis Obispo County for southerly wind gusts possibly exceeding 60 mph from 4am to 10pm Sunday 4 Feb

Click images to see loops of GFS IVT and IWV forecasts

Valid 1200 UTC 2 February 2024 – 1800 UTC 6 February 2024


 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Summary provided by M. Steen, S. Bartlett and S. Roj; 2 February 2024

To sign up for email alerts when CW3E post new AR updates click here.

*Outlook products are considered experimental

CW3E Publication Notice: Keeping Water in Climate-Changed Headwaters Longer

CW3E Publication Notice

Keeping Water in Climate-Changed Headwaters Longer

February 2, 2024

Figure 1. A parched landscape at Tuolumne Meadows, Yosemite National Park, captured in October 2011 highlights a growing concern for the Park Service: the recent dryness, a troubling trend over the past two decades, affecting mountain meadows across the West. Credit: Mike Dettinger.

In the recent essay “Keeping Water in Climate-Changed Headwaters Longer” published in the San Francisco Estuary and Watershed Science journal, CW3E authors Michael Dettinger, Anna Wilson, and Garrett McGurk delve into strategies for improving water retention in California’s headwaters affected by climate change. The article recommends more proactive measures in headwater regions to address the adverse impacts of climate change on water resources, to augment current downstream-focused adaptation strategies. This research contributes to the Monitoring and Projections of Climate Variability and Change Priority Area in CW3E’S 2019-2024 Strategic Plan, by discussing water management decision-making in scenarios including current and future extremes.

The article emphasizes that current water management practices are not sufficient to tackle the root problems caused by climate change, such as warmer temperatures, increased evapotranspiration, more intense winter storms, flashier flows, and drier summer conditions. It proposes upstream interventions like beaver repopulation, forest health treatments, and Forecast Informed Reservoir Operations (FIRO) as means to delay water movement to downstream systems, better mimicking historical hydrographs, which could help mitigate winter flood risks, reduce summer dryness and wildfire dangers, and improve groundwater recharge.

The authors highlight that even minor efforts to prolong water retention in headwaters could significantly benefit downstream water supplies, potentially reducing the need for extensive, and more invasive, water management adaptations across California to cope with the impacts of climate change on water availability. For a detailed exploration of the challenges and ideas to spark work towards real and sustainable solutions, the full paper is available here.

Figure 2. View east from the Tahoe Rim Trail, captured in July 2019, showcases a dense yet vibrant forest of the sort being addressed by state-led treatments for wildfire prevention and forest health, with the rain-shadowed Pinon Range and expansive Great Basin stretching into the distance. Credit: Mike Dettinger.

Dettinger, M., Wilson, A., & McGurk, G. (2023). Keeping Water in Climate-Changed Headwaters Longer. San Francisco Estuary and Watershed Science, 21(4) https://doi.org/10.15447/sfews.2023v21iss4art1. Retrieved from https://escholarship.org/uc/item/7mq8174f

CW3E Publication Notice: An Assessment of Dropsonde Sampling Strategies for Atmospheric River Reconnaissance

CW3E Publication Notice

An Assessment of Dropsonde Sampling Strategies for Atmospheric River Reconnaissance

January 31, 2024

A new article titled “An Assessment of Dropsonde Sampling Strategies for Atmospheric River Reconnaissance” By Minghua Zheng (CW3E), Ryan Torn (University at Albany), Luca Delle Monache (CW3E), James Doyle (Naval Research Laboratory), F. Martin Ralph (CW3E), Vijay Tallapragada (NOAA/NCEP/EMC), Christopher Davis (NCAR), Daniel Steinhoff (CW3E), Xingren Wu (NOAA/NCEP/EMC), Anna Wilson (CW3E), Caroline Papadopoulos (CW3E), and Patrick Mulrooney (CW3E) was recently published in the American Meteorological Society’s Monthly Weather Review. As part of CW3E’s 2019-2024 Strategic Plan to support Atmospheric River Research and Applications, CW3E seeks to enhance global AR monitoring through a transformative modernization of atmospheric measurements over the Pacific and in the western United States. In alignment with this goal, the study explores the impact of varying mission frequency, dropsonde spacing, and aircraft utilized during AR Reconnaissance (AR Recon) on the forecast skill of an AR-related heavy precipitation event that was sampled over a 6-day sequence of Intensive Observing Periods (IOPs) in 2021.

Throughout the 6-day IOP in late January of 2021, AR Recon aircraft sampled a series of ARs over the northeastern Pacific, resulting in heavy precipitation over coastal regions of California and the Sierra Nevada Mountains. Using these observations, data denial experiments were conducted with a regional modeling and data assimilation system to explore the impacts of different flight scenarios and dropsonde sampling strategies.

Results indicate that dropsondes significantly improve the representation of ARs in the model analyses and positively impact the forecast skill of ARs and quantitative precipitation forecasts (QPF), particularly for lead times > 1 day. Reduced mission frequency and reduced dropsonde horizontal spatial resolution both degrade forecast skill. On the other hand, experiments that assimilated only G-IV data and experiments that assimilated both G-IV and C-130 data show better forecast skill than experiments that only assimilated C-130 data, suggesting that the inclusion of two types of aircraft (G-IV and C-130s) is an effective strategy to enable the benefits of missions on a consecutive way.

This study suggests some promising guidance for flight planning in future operational AR Recon missions. The findings recommend that future operational AR Recon missions incorporate daily mission or consecutive back-to-back flights, maintain current dropsonde spacing, support high-resolution data transfer capacity on the C-130s, and utilize G-IV alongside C-130s.

Figure 1: Box plot of (a) the interest value, (b) the intersection area, and (c) the object size error for the coastal object validation in Figure 10 of Zheng et al. (2024). The box plots are calculated by combining all 19 lead times together, with the non-matched forecast object excluded in the corresponding lead time. The bottom and the top of each box represents the 25th percentile and the 75th percentile, respectively. The magenta line in the middle of the box is the median. The cyan asterisk is the mean value of each experiment. The magenta horizontal line is the median of each data. Panel (d) shows the p-value representing the degree of significance for the mean value differences between two experiments. The green shades in (d) correspond to that the 1st experiment in the parentheses has less errors for the three metrics while the red shades show the 2nd experiment has less errors. Bold values in the chart of (d) show two experiments are significantly different at the 80% confidence levels. TS stands for “temporal sampling”. This figure is modified from Figure 11 of Zheng et al. (2024).

Figure 2: Same as Figure 1 but for the SS (spatial sampling) experiments. This figure is modified from Figure 15 of Zheng et al. (2024).

Zheng, M., Torn, R., Delle Monache, L., Doyle, J., Ralph, F. M., Tallapragada, V., Davis, C., Steinhoff, D., Wu, X., Wilson, A. M., Papadopoulos, C., & Mulrooney, P. (2024). An Assessment of Dropsonde Sampling Strategies for Atmospheric River Reconnaissance. Monthly Weather Review (published online ahead of print 2024). https://doi.org/10.1175/MWR-D-23-0111.1

CW3E Subseasonal Outlook: 31 January 2024

CW3E Subseasonal Outlook: 31 January 2024

January 31, 2024

Click here for a pdf of this information.


 

 

 

 

 

 

 

 

 

 

 

 

Summary provided by J. Wang, C. Castellano, Z. Yang, M. DeFlorio, and J. Kalansky; 31 January 2024

To sign up for email alerts when CW3E post new AR updates click here.

*Outlook products are considered experimental

CW3E Event Summary: 22 January 2024

CW3E Event Summary: 22 January 2024

31 January 2024

Click here for a pdf of this information.

Weak Atmospheric River Brought Heavy Rain to Southern California and Southern Arizona

  • On January 22, 2024, a weak (AR0 on the Ralph et al. 2019 scale) atmospheric river (AR) moved across southern California and into Arizona
  • Broad light to moderate rain accompanied the AR, bringing notable rainfall amounts to the Southwest
  • An area of heavy rain developed offshore from San Diego and persisted for a few hours across the region
  • While IVT was not particularly high, heavy rainfall was supported by strong low-level moisture flux and mesoscale forcing for ascent beneath the left exit region of an upper-level jet
  • San Diego/Lindbergh Field (KSAN) recorded 2.73” of rain, which set a new daily record (previous record was 1.57” in 1963
  • This ranks as the 4th highest daily rainfall amount on record (since 1850)
  • The rolling 3-hr precipitation (computed from 1-min data) peaked at 2.13”. Based on NOAA Atlas 14 data, this represents a return interval of 178 years (0.6% chance of occurring in a year)

Click images to see loops of GFS IVT/IWV analyses

Valid: 0000 UTC 21 January – 1800 UTC 23 January 2024

Click image below to see loop of infrared satellite imagery

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Click image below to see the regional Southern California radar loop

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Click image below to see the San Diego radar loop

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Click image below to see the Integrated Water Vapor Transport loop

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Summary provided by P. Iniguez, M. Steen, S. Bartlett, S. Roj, and J. Kalansky; 31 Jan 2024

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CW3E Event Summary: 13-23 January 2024

CW3E Event Summary: 13-23 January 2024

29 January 2024

Click here for a pdf of this information.

Four Atmospheric Rivers Highlight Active Weather Period Across US West Coast

  • A series of four distinct atmospheric rivers made landfall along the US West Coast between Jan 13 and Jan 23 2024
  • This prolonged period of active weather for the region resulted in a variety of liquid and frozen precipitation impacts
  • The first AR made landfall along the OR/CA border early on Sat 13 Jan alongside a low pressure system, bringing heavy precipitation to the OR/CA border and the Southern Cascades.
  • A cut-off low pressure system brought the second AR to the USWC. The burst of IVT with the AR alongside the persistence of the low pressure system resulted in heavy precipitation in the PNW, including significant freezing rain in the Portland Metro, and heavy snowfall in the Cascades.
  • The third AR in the sequence developed as the persistent low pressure system shifted into the Gulf of Alaska, resulting in counterclockwise moisture transport around the cyclone, leading to southerly IVT transport along the US West Coast
  • A fourth AR developed over the eastern North Pacific, with a robust corridor of elevated moisture transport extending greater than 2,500 miles from north of Hawaii to the US West Coast
  • The highest 10-day precipitation totals (> 10 in.)were observed along CA/OR border and over Northern Sierra Nevada
  • Snowfall accumulations during this period ranged from 2-6 feet in the Cascades, Sierra Nevada, and the higher terrain in the Upper Colorado River Basin
  • Addition impacts during this active period included river level rises due to heavy precipitation and a multi-day freezing rain event in the Pacific Northwest

Click images to see loops of GFS IVT/IWV analyses

Valid: 0000 UTC 13 January – 0000 UTC 23 January 2024


 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Summary provided by M. Steen, S. Bartlett, J. Kalansky, and P. Iniguez; 29 Jan 2024

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CW3E AR Update: 29 January 2024 Outlook

CW3E AR Update: 29 January 2024 Outlook

January 29, 2024

Click here for a pdf of this information.

Pair of Strong ARs Forecast to Bring Heavy Precipitation to USWC

  • An active weather pattern for the US West Coast is forecast to continue through Fri 2 Feb as two more strong ARs make landfall along the USWC.
  • The first AR made landfall late 28 Sun Jan into British Columbia and the PNW. A second pulse of IVT associated with this system continues AR conditions in the PNW through Tue 30 Jan.
  • The second AR is forecast to make landfall across the USWC later on Tue 30 Jan and progress down the USWC through Fri 2 Feb.
  • There is likely development of a ridge over the Northeast Pacific following the second AR, leading to a break in AR conditions for the USWC.
  • Both ARs are forecast to bring precipitation to the USWC, with the heaviest rainfall expected from the second AR over Northern CA and heavy snowfall over the Sierra Nevada.
  • The WPC Excessive Rainfall Outlook indicates a Slight Risk (level 2 of 4, or at least 15% chance) for flash flooding in Northern CA for the 24-hour period ending 4 AM PT Thu 1 Feb and in Southern CA for the 24-hour period ending 4 AM PT Fri 2 Feb with the second AR.
  • Although there is potential for flooding in areas discussed in this outlook, the forecasts are not predicting anything in the magnitude of the ARkStorm scenarios developed by Porter et al., 2011 or Huang et. al., 2022

Click images to see loops of GFS IVT and IWV forecasts

Valid 1200 UTC 29 January 2024 – 1200 UTC 2 February 2024


 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Summary provided by M. Steen, S. Bartlett and J. Kalansky; 29 January 2024

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*Outlook products are considered experimental