CW3E AR Outlook: 14 December 2017 Ridge Update

CW3E AR Outlook: 14 December 2017 Ridge Update

December 14, 2017

Click here for a pdf of this information.

Dry Conditions Expected to Persist over CA for the Foreseeable Future

  • Persistent high pressure and ridging over the northeast Pacific and USWC is directing moisture transport towards AK and resulting in long periods of dry conditions over the USWC
  • The lack of precipitation over the southern USWC is increasing drought conditions and has resulted in the Northern Sierra 8-station index dropping below normal accumulations to date
  • While ridging is forecast to persist, AR conditions are currently forecast to impact the West Coast but the unfavorable north/northwesterly orientation of IVT will result in little or no precipitation over CA
  • Click IVT or IWV image to see loop of 0-180 hour GFS forecast

    Valid 1200 UTC 14 December – 0000 UTC 22 December 2017

    Click 500-hPa Geopotential Height & Vorticity image to see loop of 0-180 hour GFS forecast







    Summary provided by C. Hecht, J. Cordeira B. Kawzenuk, J. Kalansky, and F.M. Ralph; 1 PM PT Thursday 14 December 2017

    *Outlook products are considered experimental

CW3E Publication Notice: GPM Satellite Radar Measurements of Precipitation and Freezing Level in Atmospheric Rivers: Comparison with Ground-Based Radars and Reanalyses

CW3E Publication Notice

GPM Satellite Radar Measurements of Precipitation and Freezing Level in Atmospheric Rivers: Comparison with Ground-Based Radars and Reanalyses

December 6, 2017

Forest Cannon, postdoc at CW3E, along with CW3E director Marty Ralph, fellow postdoc Anna Wilson, and UCLA professor Dennis Lettenmaier, recently published a paper in the Journal of Geophysical Research – Atmospheres, titled: GPM Satellite Radar Measurements of Precipitation and Freezing Level in Atmospheric Rivers: Comparison with Ground-Based Radars and Reanalyses.

In their study, satellite radar reflectivity profiles from the Global Precipitation Measurement Dual-Frequency Precipitation Radar (GPM) were used to evaluate precipitation and temperature characteristics of Atmospheric Rivers (AR) over the western coast of North America and eastern North Pacific Ocean. Notably, their comparison of GPM bright band height with a network of ground-based vertically profiling radars along the West Coast demonstrated exceptional agreement, as did comparison with freezing level height from reanalyses over the eastern North Pacific Ocean (Figure 1; Figure 5 from the paper). These results indicate that GPM can be used to independently validate freezing level in models.

Figure Caption: (a) A GPM-DPR swath through AR conditions on February 4, 2015 at 0:00 UTC, and (b) the vertical profile of reflectivity from the Ka-band along the center of the GPM DPR swath subset within the red box in the top panel.

Additionally, the study identified significant differences in the frequency and intensity of precipitation between GPM and reanalyses over the eastern Pacific Ocean, indicating biases in both satellite-observed and modeled AR precipitation. Importantly, low-intensity precipitation rates accounted for a 20% increase in total precipitation in reanalyses compared to GPM-DPR, and AR conditions, specifically, contributed nearly 10% more to total GPM precipitation than reanalyses.

These results demonstrate that the advanced GPM satellite radar yields tremendous benefit for reducing the data gap over the global oceans and for supplementing the current understanding of precipitation processes in ARs.

Cannon, F. F.M. Ralph, A.M. Wilson, and D.P. Lettenmaier, 2017: GPM satellite radar measurements of precipitation and freezing level in atmospheric rivers: Comparison with ground-based radars and reanalyses. J. Geophys. Res. Atmos. DOI: 10.1002/2017JD027355


Click here for a personal pdf of the article

CW3E AR Update: 14 November 2017 Outlook

CW3E AR Update: 14 November 2017 Outlook

November 14, 2017

Click here for a pdf of this information.

Two ARs Forecast to Impact the USWC over the Next Week

  • An AR currently impacting the Pacific Northwest is expected to end in the next several hours
  • A potentially strong AR (IVT >750 kg m-1 s-1) is forecast to impact California between 15 and 17 November
  • A second AR is forecast to make landfall over the USWC between 19 and 21 November 2017
  • Precipitation forecasts range from 5–8 inches over higher elevations associated with the first AR
  • Forecast uncertainty is currently high for the 19–21 November AR

Click IVT or IWV image to see loop of 0-168 hour GFS forecast

Valid 1200 UTC 14 November – 2100 UTC 21 November 2017






Summary provided by C.Hecht, B. Kawzenuk, J. Kalansky, and F.M. Ralph; 1 PM PT Wednesday 14 November 2017

*Outlook products are considered experimental

CW3E Welcomes Dr. Leah Campbell

CW3E Welcomes Dr. Leah Campbell

November 1, 2017

Dr. Leah Campbell joined CW3E as a Postdoctoral Scholar in October 2017 after earning her PhD in Atmospheric Science from the University of Utah. Her research focuses on hydrometeorological processes, particularly the mechanisms that modulate precipitation distribution in complex terrain. Leah’s PhD research focused on lake- and sea-effect precipitation systems in the Great Lakes regions and the Sea of Japan. Her work highlights the role of relatively model mesoscale processes, shaped by coastal terrain features and shoreline configuration, in determining the distribution of precipitation produced by these frequently intense and localized snowstorms. The publications that made up her dissertation were some of the first to examine these mechanisms in the context of precipitation forecasting. In addition to her PhD research, Leah spent much of 2016 in Chile as a Fulbright fellow, studying the interactions of mid-latitude cyclones with the Andes Mountains. At CW3E, she plans to use radar and other observational platforms to examine the atmospheric processes that shape precipitation distribution over the Sierra Nevada, coastal mountains of California, and the Andes. This research will improve weather and streamflow forecast skill for severe precipitation events and advance our understanding of the processes that build the seasonal mountain snowpack.

CW3E Graduate Student Participates in 18th Biennial Cyclone Workshop

CW3E Graduate Student Participates in 18th Biennial Cyclone Workshop

October 23, 2017

On 1-6 October 2017, CW3E graduate student Reuben Demirdjian had the opportunity to attend the 18th Biennial Cyclone Workshop at the hotel Mont Gabriel in Mont in Sainte-Adèle Quebec, Canada hosted by the State University of New York at Albany. Discussion topics included research on any cyclone related meteorological phenomena ranging from extra to tropical cyclones on synoptic and mesoscales. Reuben gave a talk on his recent research focused on observing low-level jets within atmospheric rivers using hundreds of dropsonde observations from recent CalWater I, I and El Niño Rapid Response winter field campaigns. Following his talk, he discussed his work with several senior researchers and professors who provided feedback and suggestions on possible methodologies to implement in order to test his hypotheses. The results of the meeting will improve Reuben and CW3E’s current research and motivate new topics.

Group photo of the workshop participants. Reuben is pictured first from the left in the fourth row.

CW3E Graduate Student Accepted into Science Policy Fellows Program

CW3E Graduate Student Accepted into Science Policy Fellows Program

October 3, 2017

Third-year graduate student, Meredith Fish, has been accepted into the Science Policy Fellows Program at the School of Global Policy and Strategy (GPS). The fellowship, which is open to Ph.D. candidates at Scripps Institution of Oceanography, Jacobs School of Engineering and School of Medicine, works with GPS faculty to discover the policy relevance and potential implications of their dissertation. Created with the goal of bridging physical and social sciences across the UC San Diego campus, the students gain an understanding of the benefits of using a multidisciplinary approach to help solve some of our global issues.

Meredith will be working with GPS faculty members, Kate Ricke and Jennifer Burney, on the policy implications of successive atmospheric rivers (ARs). ARs are a large contributor to California’s water supply, providing approximately 50% of it’s water year precipitation, but can also have negative impacts, such as widespread flooding and debris flows. Families of events, which are defined as ARs that successively occur within 120 hours of each other, can have enhanced impacts as pre-conditioning from the first AR can elevate the chances of high streamflow and saturated soils, which leads to shorter time frames to safely release stored water downstream. She will work with her GPS mentors on the issues of aging infrastructure, snowpack becoming a less reliable water storage system, and the potentials of implementing a flexible rule curve for dam operators.

The fellowship will conclude with a presentation of the fellow’s research findings in the spring quarter. The fellow will also have the opportunity to attend policy-related seminars, workshops and courses.

CW3E graduate student, Meredith Fish (center), with her GPS Faculty Mentors Kate Ricke (left), and Jennifer Burney (right).

CW3E Accepted as a National Oceanic and Atmospheric Administration Weather Ready Nation Ambassador

CW3E Accepted as a National Oceanic and Atmospheric Administration Weather-Ready Nation Ambassador

September 7, 2017

CW3E recently became a NOAA Weather-Ready Nation (WRN) Ambassador. The Weather-Ready Nation Ambassador Initiative is a collaborative entity that brings numerous organizations, businesses, and people together in order to strengthen national resilience against extreme weather and water events.

CW3E is being recognized as a WRN Ambassador because it promotes the Weather-Ready Nation messages and themes to their stakeholders and engages with NOAA personnel on potential collaboration opportunities. CW3E is doing this through scientific research to improve forecasts of extreme precipitation and flooding on the west coast, as well as communicating about extreme events through the hydrometeorological outlooks and post-event summaries on the CW3E website and Twitter. CW3E in collaboration with NOAA, will assist in improving the nation’s readiness, responsiveness, and overall resilience against extreme weather.

Becoming a WRN Ambassador advances CW3E one step further in executing our mission to provide 21st Century water cycle science, technology and outreach to support effective policies and practices that address the impacts of extreme weather and water events on the environment, people and the economy of Western North America.

Visit NOAA’s WRN website to learn more about the initiative, its goals, and its participants.

CW3E Field Trip to Experience the North American Monsoon in Southern Arizona

CW3E Field Trip to Experience the North American Monsoon in Southern Arizona

August 14, 2017

Several members of CW3E spent a recent weekend observing the North American monsoon in the Tucson, Arizona area, including Nogales and Sonoita. It provided an opportunity to experience an iconic type of “extreme event” that occurs in the Western U.S.

Activities included early-morning hiking in Ventana Canyon (Fig. 1), touring southern Arizona from Tucson to Nogales, Patagonia and Sonoita, learning about Sonoran Desert and nearby grassland landscapes and climate (Fig. 2), observing long-lived monsoon convection and its impacts, and discussing active topics of research related to the North American monsoon, including a recent paper on the role of the Chiricahua Gap (Ralph and Galerneau 2017 –

Fig.1. The CW3E group with a saguaro during the Ventana Canyon hike. From left Marty Ralph, Brian Henn, Anna Wilson, and Maryam Asgari-Lamjiri.

Fig.2. Example of landscape 30 miles southeast of Tucson, near Sonoita, AZ on 29July 2017 at about 5000 ft MSL.

A highlight was observing flood water in normally dry washes, such as Tanque Verde Wash in northeast Tucson (Fig. 3).

Fig.3. The Tanque Verde River looking east from the bridge on Kolb Road after monsoon storms in the Tucson area. The Rincon Mountains, including their high point at 8664 ft MSL, are in the background. Photograph taken at 6:45 pm local time on 29 July 2017.

Precipitation totals in Tucson were significantly above normal. Fig. 4 shows the July 2017 climate summary from NWS. In fact, the CW3E team experienced the heavy downpour near the Tucson airport on Saturday, 29 July 2017 that broke the all-time record for July monthly precipitation (now 6.8 inches; previously 6.24 inches in July 1921).

Fig.4. National Weather Service July 2017 climate summary with dates of the CW3E field trip highlighted.

CW3E’s goal is to revolutionize the physical understanding, observations, weather predictions and climate projections of extreme events in Western North America (, including the North American summer monsoon.

Points of contact: Anna Wilson, Marty Ralph.

CW3E Announces 4 New Post-Doctoral Positions

Post-Doctoral Positions Available at the Center for Western Weather and Water Extremes

August 3, 2017

Location: La Jolla, California
Deadline: Positions are available immediately. Applications will be considered until positions are filled. Preference will be given to applications received by 1 September 2017.
Number of new positions available: 4

The Center for Western Weather and Water Extremes (CW3E), is a research and applications center established in 2013 at Scripps Institution of Oceanography by its Director, Dr. F. Martin Ralph. CW3E focuses on the physical understanding, observations, weather predictions, seasonal outlooks and climate projections of extreme weather and water events to support effective policies and practices to improve resilience in the Western U.S. Funding for this set of Postdoctoral positions is in place from several federal, state and local agencies, with a major emphasis on the unique science and applications needs associated with water supply and flood risk in the Western United States. CW3E carries out its goals with a diverse network of research and operational partners at more than ten other institutions across the U.S. Individuals will be joining a group of several existing Postdoctoral scholars and graduate students, and a number of experienced faculty, researchers and staff at Scripps who are involved with CW3E.

Per normal Postdoctoral appointment policies, all positions are envisioned as being initially for 1-year, with extension possible contingent upon performance and availability of funding. The University of California, San Diego is an AA/EOE.

Interested individuals are encouraged to submit their resumes and a 1-page statement of relevant personal interests, goals, range of potential start dates and at minimum two references. These should be sent to the person listed below as the “position coordinator” for the position you are interested in.

Applicants should have 0-2 years of Postdoctoral experience, or be nearing completion of their Ph.D. (estimated within 3 months), and be self-motivated and hard-working. Good written and verbal communication skills, including the ability to produce scientific publications and presentations and meet project milestones are required. Strong analytical backgrounds with a Ph.D. in atmospheric science, meteorology, atmospheric chemistry, climate science, hydrology or environmental engineering is preferred. Programming experience working in a Unix environment with experience in scripting languages such as Python, Perl, R and Matlab along with true programming language experience in C and Fortran is highly desired. Experience with using high performance computing is also desired. Successful applicants should be comfortable independently working with large code libraries and producing novel visualizations.


Position 1: Hydrometeorological Advancements for Management Decision Support

CW3E position coordinator – Dr. Brian Henn;

CW3E seeks a Postdoctoral researcher to design and contribute to efforts that lead toward improved operational application of distributed hydrologic and hydrometeorological sciences. The position would work on research that improves hydrologic model performance associated with extreme events. Anticipated methodologies include data assimilation (DA) techniques that leverage in-situ soil moisture observations and remotely sensed observations, improving hydrologic model parameterization and determining the most appropriate unbiased atmospheric forcing’s for hydrologic model applications from NWP output. Additionally the candidate would develop guidelines for parsimonious application of hydrologic models in time and space and evaluation processes and metrics for hydrologic model simulations and forecasts that isolate areas of potential improvement. The research would support the development, by the candidate, of a prototype decision support system that combines a variety of observed and forecast information to aid in operational decision making. Through the research the candidate would continually develop and support a connection between CW3E and California-Nevada River Forecast Center operational forecasts systems. The candidate should have experience with hydrological model development, calibration, application, and verification. Additional experience in developing observed datasets for forcing hydrologic models and operating hydrologic and hydraulic models in a forecasting mode using NWPs or other sources is also desired.


Position 2: Aerosols Influence on Winter Precipitation

CW3E position coordinator – Dr. Amato Evan;

CW3E seeks a Postdoctoral researcher to investigate the manner by which aerosols influence wintertime precipitation in the western US, with a focus on ice nuclei from marine and terrestrial sources, using high-resolution numerical modeling. The goal of this work is to improve basic understanding of aerosol-cloud interactions and their affect upon precipitation from atmospheric rivers to improve forecasts of precipitation from such events. In order to address the scientific needs of the project the postdoctoral scholar will be expected to design, implement and validate aerosol emission, transport, removal, cloud condensation and ice nuclei activation models within West-WRF, which is a version of the Weather Research and Forecast Model (WRF) that has been developed at CW3E to improve the accuracy of forecasting extreme precipitation events and as a testbed for understanding the physical processes that drive extremes in weather. These activities will be conducted in collaboration with a team of students, faculty and scientists at CW3E. The successful candidate will have the opportunity to present at conferences and will be expected to publish major results in peer-reviewed journals as first author.


Position 3: Terrestrial Water Storage

CW3E position coordinator – Dr. Julie Kalansky;

We seek a postdoctoral researcher to investigate variability in regional terrestrial water storage, including groundwater and snowpack, as revealed by a growing archive of GPS crustal displacements collected throughout California and across the United States. The GPS-inferred water storage contains variability over a range of time scales, much of which is driven by extreme events from synoptic scale storm activity to interannual wet and dry spells. Regionally, the high density of the GPS network may afford resolution at 10’s of km scales and thus provide new insight into catchment water balances. This investigation will require synthesis and comparison with other observational data, along with model-simulated hydrological variability. The postdoc will use the GPS data for information about snowpack and groundwater and relate these to weather and climate events. As part of the project, the postdoc may develop online tools for tracking this information for decision support. Support for this position will come from CW3E, in partnering with CNAP ( and the Institute of Geophysics and Planetary Physics ( The post-doc should be familiar with climate and hydrological phenomena in western North America.


Position 4: Mesoscale Dynamics and Predictability of Atmospheric Rivers

CW3E position coordinator – Dr. Jason Cordeira;

The position will explore the mesoscale dynamics and predictability of ARs affecting the western U.S. coast. The research will use a variety of observational and modeling-based tools and analysis techniques to diagnose the multiscale processes associated with persistent AR conditions culminating in extreme precipitation. The candidate should have experience forecasting extreme events from an operational or modeling perspective, and the ability to conduct in depth case studies and verification analyses. The position will involve participation in an atmospheric river airborne reconnaissance project “AR Recon” effort that is aimed at improving the 1-to-3-day skill of AR landfall forecasts. For example, the incumbent will develop methods to utilize targeting observations in order to improve prediction of mesoscale frontal waves that are key to determining position and duration errors associated with landfalling ARs. The project involves active collaboration with NCEP (GFS) and the Navy (COAMPS) to identify, analyze, and diagnose dynamical processes associated with skillful AR landfall and precipitation characteristics. The candidate should have strong knowledge of mesoscale and synoptic-scale atmospheric dynamics and forecasting techniques, including but not limited to frontal circulations, jet streaks, cyclone kinematics, multiscale precipitation processes, data assimilation, and mesoscale modeling.