Author: cw3e-web

CW3E Leadership Meets with Dr. Rick Spinrad, Under Secretary of Commerce for Oceans and Atmospheres & NOAA Administrator

CW3E Leadership Meets with Dr. Rick Spinrad, Under Secretary of Commerce for Oceans and Atmospheres & NOAA Administrator

February 16, 2023

CW3E Director, Marty Ralph, and Field Research Manager, Anna Wilson, met with Dr. Rick Spinrad, the Under Secretary of Commerce for Oceans and Atmospheres & NOAA Administrator, on 15 February 2023 at Scripps Institution of Oceanography. Discussion focused on the unique challenges around water in the western US, including conditions that vary more dramatically between wet and dry than elsewhere in the nation. The importance of water to the western environment and economy was highlighted along with the vital role of the west coast states in the US economy. These states represent roughly 20% of the entire US economy, including California, at 15% of US GDP, which is by far the largest contributor of any of the 50 states.

The role of atmospheric rivers as the drivers of both flood and drought was described and efforts to better understand, observe and predict them were summarized. Advances in modeling, with West-WRF and its super-ensemble, machine learning research and other topics were described. The AR Scale was discussed deeply, including its primary role as a situational awareness aid, with the associated need for experienced forecasters to translate that into point forecasts that factor in antecedent conditions on the ground. AR Recon was described as a breakthrough in improving west coast precipitation forecasts through our CW3E Research And Operations Partnership with NWS, OMAO, the Air Force/Weather Reconnaissance Squadron and other agencies and universities. The use of dropsondes, drifting buoys and airborne radio occultation were highlighted. The need for extending the AR Recon operating season to start in November and to expand coverage to the western Pacific were noted. Finally, the Forecast-Informed Reservoir Operations program was summarized, as well as its use of, and need for, accurate AR forecasts.

CW3E is very appreciative of the chance to meet with Dr. Spinrad and his colleagues from the NOAA Corps who accompanied him, to share our work, receive feedback, discuss key topics and consider the future.

CW3E and Yuba Water Agency Bring Science to Life for Students at Browns Valley Elementary School in Yuba County

CW3E and Yuba Water Agency Bring Science to Life for Students at Browns Valley Elementary School in Yuba County

February 14, 2023

Browns Valley Elementary School students in Yuba County recently had the opportunity to learn about weather forecasting and natural resource management first-hand from the Center for Western Weather and Water Extremes and Yuba Water Agency.

In mid-January, researchers Chad Hecht and Anna Wilson spoke with kindergarten and third-grade students about a weather station that CW3E operates at the school with support from Yuba Water, and how that data informs weather forecasting and water management in the region. This was the first time CW3E had a chance to talk with students about the weather station since it was installed in April 2021.

During CW3E’s visit, students explored the variety of instrumentation at the station, including the inside of a tipping bucket rain gauge. Third-grade students learned about how the weather station’s instrumentation works, what they measure, how the observations can be useful to understanding the atmosphere and how this knowledge and research can be used to improve forecasting and water resource management.

Students were also able look at the data coming in from the station in real time using graphs, which aligns with third-grade learning objectives. This was also an opportunity for Chad and Anna to highlight the importance of observations at this specific weather station as a key part of a larger, watershed-wide network.

The students were actively engaged throughout Anna and Chad’s visit, asked numerous questions, and explained with great enthusiasm the rain gauges they had recently designed and collocated with the weather station.

One week after CW3E’s visit, Yuba Water visited the third-grade class to connect how data from the weather station directly supports decisions by Yuba Water and other natural resource management agencies in the region. Yuba Water’s director of resource planning, John James, explained how weather data fits into the agency’s management of the Yuba River watershed and New Bullards Bar Reservoir, which is near the school and is critical to flood risk reduction and water supply reliability in the region. The discussion gave students the opportunity to ask more questions about the watershed and how it is studied and managed, especially during times of flood and drought.

CW3E and Yuba Water Agency are grateful for the opportunity to work with Browns Valley Elementary School students and teachers, and we look forward to our next visit!

CW3E’s Anna Wilson discusses the Browns Valley Elementary School weather station with the 3rd grade class.

Yuba Water Agency’s John James leads a discussion on the Yuba watershed in the Browns Valley Elementary School 3rd grade classroom.

CW3E Publication Notice: Evaluation of Subseasonal Drought Forecast Skill over the Coastal Western U.S.

CW3E Publication Notice

Evaluation of Subseasonal Drought Forecast Skill over the Coastal Western U.S.

February 10, 2023

Lu Su, a Ph.D. student from UCLA, with her advisor and CW3E collaborator, Professor Dennis Lettenmaier, alongside co-authors Qian Cao (CW3E), Shraddhanand Shukla (UCSB), Ming Pan (CW3E) have recently published a paper titled “Evaluation of Subseasonal Drought Forecast Skill over the Coastal Western U.S.” in the Journal of Hydrometeorology (Su et al., 2023; https://journals.ametsoc.org/view/journals/hydr/aop/JHM-D-22-0103.1/JHM-D-22-0103.1.xml). The research aligns with the Subseasonal to Seasonal Prediction of Extreme Weather Area and the Modeling Capabilities for the Western United States Area within CW3E’s 2019-2024 Strategic Plan because it evaluates the subseasonal drought forecast skill using the Noah Multi-parameterization (Noah-MP) model.

Predictions of drought onset and termination at subseasonal (from two weeks to one month) lead times could provide a foundation for more effective and proactive drought management. This study used reforecasts archived in NOAA’s Subseasonal Experiment (SubX) to force the Noah Multi-parameterization (Noah-MP), which produced forecasts of soil moisture from which we identified drought levels D0-D4. It evaluated forecast skill of major and more modest droughts, with leads from one to four weeks, and with particular attention to drought termination and onset. Usable drought termination and onset forecast skill was found at leads one and two weeks for major D0 -D2 droughts; and limited skill at week three for major D0-D1 droughts, with essentially no skill at week four regardless of drought severity (see Figure 1 and Figure 2). Furthermore, for both major and more modest droughts, limited skill or no skill was found for D3 -D4 droughts. Skill is generally higher for drought termination than for onset for all drought events. In addition, drought prediction skill generally decreases from north to south for all drought events. Evaluation of the subseasonal drought forecast skill can better support water resource and emergency management decisions.

This work used the COMET supercomputer, which was made available by the Atmospheric River Program Phase 2 and 3 supported by the California Department of Water Resources (awards 4600013361 and 4600014294 respectively) and the Forecast Informed Reservoir Operations Program supported by the U.S. Army Corps of Engineers Engineer Research and Development Center (award USACE W912HZ-15-2-0019). The research was funded in part by NOAA Regional Integrated Sciences and Assessments (RISA) support through the California–Nevada Applications Program (Grant NA17OAR4310284).

Figure 1: SubX-based debiased Brier skill score (BSS) for lead weeks 1-4 for drought termination. The columns show results for drought levels D0-D4; the rows show leads from week1 to week4. Blank areas denote no drought at this level in this location.

Figure 2: SubX-based debiased Brier skill score (BSS) for lead weeks 1-4 for drought onset. Columns show drought levels D0-D4; rows show leads from week1 to week4.

Su, L., Q. Cao, S. Shukla, M. Pan, and D. P. Lettenmaier, 2023: Evaluation of Subseasonal Drought Forecast Skill over the Coastal Western U.S. J. Hydrometeor., doi: https://doi.org/10.1175/JHM-D-22-0103.1

CW3E Publication Notice: Impacts of Northeastern Pacific Buoy Surface Pressure Observations

CW3E Publication Notice

Impacts of Northeastern Pacific Buoy Surface Pressure Observations

February 8, 2023

A new study using data from the Atmospheric River Reconnaissance program finds potential for improving weather forecasts, particularly errors in short range prediction of atmospheric rivers (ARs), by increasing the number of drifting buoy surface pressure observations over the world oceans. The paper “Impacts of Northeastern Pacific Buoy Surface Pressure Observations” was recently published in Monthly Weather Review by authors Carolyn Reynolds (U.S. Naval Research Laboratory), Rebecca Stone (Science Applications International Corporation), James Doyle (U.S. Naval Research Laboratory), Nancy Baker (U.S. Naval Research Laboratory), Anna Wilson (CW3E), Marty Ralph (CW3E), David Lavers (European Centre for Medium-Range Weather Forecasts), Aneesh Subramanian (University of Colorado Boulder), and Luca Centurioni (University of California San Diego). This work contributes to the goals of CW3E’s 2019-2024 Strategic Plan to lead AR Research and Applications because the paper illustrates how novel observations of ARs improve forecasts.

Atmospheric River Reconnaissance (AR Recon) is a program led by CW3E and guided by an international, interagency Atmospheric River Modeling and Data Assimilation Steering Committee (Ralph et al. 2020; OFCM 2022). Dropsondes released from Air Force Reserve Command and the NOAA Aircraft Operations Center aircraft are the cornerstone of this effort. The effort also includes a partnership with the NOAA-funded Global Drifter Program led by Dr. Centurioni at the Scripps Lagrangian Drifter Laboratory to add barometers to the regular drifters (Centurioni et al. 2017). Those observations are critical in filling observation gaps in and near ARs over the North Pacific Ocean (Zheng et al. 2021). In this study, the authors investigated the impact of drifter-observed sea level pressure in the northeastern Pacific during the AR Recon 2020 season for their impact on the U.S. Navy’s global atmospheric forecasting system. The authors used Forecast Sensitivity Observation Impact (FSOI) to measure the contribution of individual observations and sets of observations on short-term forecast error reduction, and data-denial experiments to quantify forecast error associated with removing observations.

The results of this study find that observational impacts vary with placement, observation value, and timing. Drifters placed in time-averaged low-pressure regions, such as the Gulf of Alaska, and in isolation from other drifters, have the largest average impacts. Observations in the lowest quartile of sea surface pressures are significantly more beneficial to the model than higher pressure quartiles at the 95% level, with 54.5% beneficial impacts from the lowest quartile, and between 47.6% and 51.3% for the higher quartiles. The greatest impacts for individual drifters occur during periods of tight pressure gradients and strong integrated vapor transport (IVT), which are associated with fronts and ARs, respectively. The time when the observations are taken within the data assimilation (DA) window is also important. The lowest quartile of sea surface pressure observations have smaller beneficial impacts during the first half of the DA window and increasingly larger beneficial impacts during the second half of the DA window, whereas the small beneficial impacts of the upper quartile observations early in the DA window become nonbeneficial as the window progresses. Lastly, data-denial experiments show that AR Recon drifters better constrain the analysis of nearby non AR-Recon drifters, help correct for biases in the model, and contribute statistically significant improvements to tropospheric winds and geopotential height forecasts over the Northern Hemisphere at 72- and 96-hour lead times (Fig. 1).

The results of this study have applications for future AR Recon seasons and the Global Drifter Program to expand the density and targeted spatial coverage in the northeastern Pacific. Motivated in part by this investigation, the 2022 AR Recon deployment included drifters in the Gulf of Alaska and additional buoys off southern Greenland.

This research was funded by the Chief of Naval Research through the Naval Research Laboratory Base Program, by the California Department of Water Resources AR program, the U.S. Army Engineer Research and Development Center, and the National Ocean and Atmospheric Association.

Figure 1: (Fig. 10 from Reynolds et al. 2023): Standard scorecard metrics for North America and Northern Hemisphere NAVGEM forecasts as a function of forecast hour as verified against ECMWF operational analyses for forecast start times of 0000 UTC 22 Jan 2020–0000 UTC 13 Mar 2020. Green colors indicate improvements in the metric with the assimilation of the AR-Recon drifter surface pressure observations that are statistically significant at the 95% level. Pink colors indicate degradations at the 95% level.

Centurioni, L., Horaìnyi, A., Cardinali, C., Charpentier, E., & Lumpkin, R. (2017). A global ocean observing system for measuring sea level atmospheric pressure: Effects and impacts on numerical weather prediction. Bulletin of the American Meteorological Society, 98, 231-238. https://doi.org/10.1175/BAMS-D-15-00080.1

ICAMS, 2022: National Winter Season Operations Plan (NWSOP). Interagency Meteorology Coordination Office, 124 pp., https://www.icams-portal.gov/resources/ofcm/nwsop/2022_nwsop.pdf.

Reynolds, C. A., Stone, R. E., Doyle, J. D., Baker, N. L., Wilson, A. M., Ralph, F. M., Lavers, D. A., Subramanian, A. C., & Centurioni, L. (2023). Impacts of Northeastern Pacific Buoy Surface Pressure Observations. Monthly Weather Review, 151, 211-216. https://doi.org/10.1175/MWR-D-22-0124.1

Ralph, F. M., Cannon, F., Tallapragada, V., Davis, C. A., Doyle, J. D., Pappenberger, F., Subramanian, A., Wilson, A. M., Lavers, D. A., Reynolds, C. A., Haase, J., Rutz, J. J., Cordeira, J. M., Zheng, M., Hecht, C. W., Kawzenuk, B., & Delle Monache, L. (2020). West Coast Forecast Challenges and Development of Atmospheric River Reconnaissance. Bulletin of the American Meteorological Society, 101, E1357-E1377. https://doi.org/10.1175/BAMS-D-19-0183.1

Zheng, M., Delle Monache, L., Wu, X., Ralph, F. M., Cornuelle, B., Tallapragada, V., Haase, J. S., Wilson, A. M., Mazloff, M., Subramanian, A., & Cannon, F. (2021). Data Gaps within Atmospheric Rivers over the Northeastern Pacific. Bulletin of the American Meteorological Society, 102, E492-E524. https://doi.org/10.1175/BAMS-D-19-0287.1

Extreme Atmospheric River Incidents are the Subject of Committee Hearing in California State Assembly

Extreme Atmospheric River Incidents are the Subject of Committee Hearing in California State Assembly

February 6, 2023

At a February 1 Joint Hearing of the State Assembly’s Committees on Emergency Management; Water, Parks, and Wildlife; and Utilities and Energy, CW3E Director F. Martin “Marty” Ralph was one of three speakers who briefed committee members on the latest research on predicting and forecasting the impact of atmospheric rivers. Dr. Ralph referenced CW3E’s AR Scale to demonstrate how the catastrophic impact of an atmospheric river incident increases exponentially for the highest ranked (4 and 5) incidents. Knowing when and where torrents of rain will strike can therefore save property and lives. Weather modeling innovations and ongoing research at CW3E, he noted, continue to improve the skill with which atmospheric rivers can be predicted. CW3E’s “West-WRF” forecast model, for example, is tailored to be the best forecast model for atmospheric rivers.

California’s State Climatologist, Dr. Michael Anderson, and Dr. Daniel Swain, a climate scientist at UCLA’s Institute of Climate and Sustainability also addressed the prediction and forecasting of extreme atmospheric river incidents.

AR Recon Makes Headlines in New York Times and LA Times

AR Recon Makes Headlines in New York Times and Los Angeles Times

February 2, 2023

AR Recon, a CW3E led program in partnership with NCEP and the U.S. Air Force, has made headlines in both the New York Times and the Los Angeles Times in recent weeks. CW3E’s leadership of AR Recon is enabled by strong support from California DWR’s AR Program and the USACE through the Forecast Informed Reservoir Operations (FIRO) program. Reporters from both papers had a chance to fly on NOAA’s G-IV and talk to CW3E Director, Marty Ralph (PI of AR Recon) and Anna Wilson (AR Recon Coordinator). For the full articles, please use the links below.

NY Times: Getting Inside California’s Wild Weather, 8 Miles Over the Pacific

(NY Times Print Article) (NY Times Article PDF)

LA Times: How do you track an atmospheric river? Climb aboard this highflying reconnaissance jet

(LA Times Print Article) (LA Times Article PDF)

Marty Ralph, center, watches as meteorologists Rich Henning, left, and Sofia de Solo track data while flying above an atmospheric river over the Pacific Ocean. (Ian James / Los Angeles Times)

CW3E Publication Notice: A 440-Year Blue-Oak Reconstruction of Heavy Precipitation in California

CW3E Publication Notice

A 440-Year Blue-Oak Reconstruction of Heavy Precipitation in California

February 2, 2023

Ian Howard, a post-doc from the University of Arkansas and CW3E collaborator, alongside co-authors David W. Stahle (University of Arkansas), Michael D. Dettinger (CW3E), Cody Poulsen (CW3E), F. Martin Ralph (CW3E), Max C.A. Torbenson (Johannes Gutenberg University), and Alexander Gershunov (CW3E), have published a paper titled “A 440-Year Reconstruction of Heavy Precipitation in California From Blue Oak Tree Rings” in the American Meteorological Society’s Journal of Hydrometeorology. This research advances the goals of CW3E’s 2019-20024 Strategic Plan by its contribution to Atmospheric Rivers Research and Applications, quantifying longer-than-instrument-period variations of extreme precipitation in Northern California through a novel analysis of blue-oak ring-width chronologies. The strong relationship between certain blue oak chronologies and total water year precipitation (correlation, r ≥ 0.90) has been known for years (Stahle et al. 2013). However, this study (Howard et al. 2023) advances our understanding of this relationship by discovering that some blue oak chronologies are equally well correlated (r = 0.82) with annual totals of just the heavy-precipitation fraction of precipitation (daily totals ≥ 1 in, ≈95th percentile of historical daily totals). In contrast, the correlation with non-heavy precipitation totals using the same chronologies is much weaker (daily totals < 1 inch; r = 0.55). On average, heavy precipitation accounts for only 39% of water year totals in the study region but largely determines year-to-year precipitation variations. Thus, as noted in previous studies of California heavy-precipitation variability (e.g., Dettinger and Cayan 2014), these days of heavy precipitation dictate most of the occurrence of our droughts and flood years.

The study developed a reconstruction of heavy-precipitation totals in northern California from 1582-2021 (Fig. 1), 440 years in all. The reconstruction identifies decadal to multi-decadal surges in extreme precipitation totals and volatility. Return-period estimates based on the 440-year heavy-precipitation reconstruction are quite close to recurrence estimates based on just the instrumental record. This suggests that the 73 yearlong instrumental record over the study area provides a good representative of the variance in heavy precipitation during the last 440 years (Fig. 2). Finally, a comparison of annual landfalling atmospheric river counts to the reconstructed and instrumental heavy precipitation records shows large contributions of atmospheric rivers to the variations of heavy precipitation and blue oak growth (Fig. 3).

Figure 1: (a) The tree-ring reconstruction of heavy precipitation totals in the northern California study area are plotted (gray) along with the sub-decadal smooth values (black) and the heavy instrumental totals (red). The reconstruction extends from 1582-2004 and the CPC instrumental observations are appended from 2005-2021. The mean and upper and lower 20th percentiles computed for the full period 1582-2021 are also plotted. The reconstruction and instrumental values are correlated from 1949-2004 at r = 0.82.

Figure 2: Return periods and probabilities are plotted for the instrumental and reconstruction heavy precipitation totals (daily amounts ≥25.4mm). The black line connects the discrete return periods computed for the full 440-year reconstruction (1582-2021) and the blue dots are return periods for non-overlapping 50-year intervals in the reconstruction. Instrumental return periods are plotted for 1949-1998 (orange circles) and 1949-2021 (squares). Reconstructed return periods restricted to 1949-1998 are also plotted for comparison (red circles).

Figure 3: (a) Instrumental heavy precipitation (a) was correlated with gridded AR counts (Gershunov et al. 2017) on the specific days each year when heavy precipitation (≥25.4mm) was measured for the study area in northern California. These days of heavy precipitation vary from 2 to 28 days (1949 and 2017, respectively). (b) Non-heavy precipitation was also correlated with gridded AR counts on the corresponding non-heavy days also defined for northern California. The regional blue oak chronology was correlated with gridded AR count on the days with (c) heavy and (d) non-heavy precipitation in the study area [p <0.05 for all correlations mapped, 1949-2004, contour intervals plotted above 0.80 in (a), above 0.60 in (c)]. Note the area of highest correlations (>0.95) near Monterey Bay in (a). (e) A photomicrograph of ring porous annual rings in blue oak from Mt. Diablo is reproduced for 1980-1995, along with the count of landfalling ARs near the Golden Gate to illustrate the proportionality between oak growth and AR-delivered heavy precipitation. The annual rings are oriented vertically, and two medullary rays run horizontally through the ring sequence.

Dettinger, M., & Cayan, D. R. (2014). Drought and the California delta – A matter of extremes. San Francisco Estuary and Watershed Science, 12,, 1-6. https://doi.org/10.15447/sfews.2014v12iss2art4

Howard, I. M., Stahle, D. W., Dettinger, M. D., Poulsen, C., Ralph, F. M., Torbenson, M. C. A., & Gershunov, A. (2023). A 440-Year Reconstruction of Heavy Precipitation in California from Blue Oak Tree Rings*. Journal of Hydrometeorology (published online ahead of print). https://doi.org/10.1175/JHM-D-22-0062.1

Stahle, D. W., Griffin, R. D., Meko, D. M., Therrell, M. D., Edmondson, J. R., Cleaveland, M. K., Stahle, L. N., Burnette, D. J., Abatzoglou, J. T., Redmond, K. T., Dettinger, M. D., & Cayan, D. R. (2013). The Ancient Blue Oak Woodlands of California: Longevity and Hydroclimatic History. Earth Interactions, 17, 1-23. https://doi.org/10.1175/2013EI000518.1

CW3E Talks Atmospheric Rivers with UC San Diego Students

CW3E Talks Atmospheric Rivers with UC San Diego Students

February 2, 2023

CW3E Lead Engineer Douglas Alden provided an engaging presentation on water supply, meteorological instrumentation, storm sampling and atmospheric rivers for UC San Diego undergraduate students. The students are enrolled in SIO 172: Physics of the Atmosphere, taught by CW3E research collaborator Dr. Joel Norris. They learned some of the many ways which CW3E is working with partners to improve reservoir water storage through research into atmospheric rivers and associated extreme precipitation. Observations are a critical part of this work, and the students participated in a radiosonde launch from the Scripps Pier. Radiosondes are used by CW3E to study atmospheric river development and strength. During storm events, CW3E launches radiosondes from multiple locations in California. Radiosondes are carried aloft by helium-filled balloons and collect data from the surface up to approximately 25,000 meters (82,000 feet) on air temperature, humidity, atmospheric pressure, and winds. The students also were able to handle a dropsonde. Dropsonde data are used for similar analyses as the radiosonde data. Dropsondes are released from aircraft flying over the Pacific Ocean during Atmospheric River Reconnaissance (AR Recon) missions. All CW3E radiosonde and dropsonde data are sent into the Global Telecommunications System and included in weather modeling efforts around the globe such as the National Centers for Environmental Prediction’s (NCEP) Global Forecast System (GFS), North American Mesoscale Forecast System (NAM), and Global Ensemble Forecast System (GEFS), and the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecast System (IFS). The use of dropsondes over the Pacific Ocean has been shown to significantly improve weather forecast models for atmospheric rivers expected to hit the west coast of the United States. After the weather sounding from the pier had completed the data were provided to the students for class analysis and discussion. CW3E appreciated the opportunity to get to know the students and introduce them to our work!

Figure 1: CW3E Lead Engineer Douglas Alden talks to UC San Diego undergraduate students assisting with radiosonde launch.

Figure 2: Skew-T plot of sounding data.