CW3E AR Update: 31 October 2017 Outlook

CW3E AR Update: 31 October 2017 Outlook

October 31, 2017

Click here for a pdf of this information.

Atmospheric River to potentially make landfall over California

  • A weak to moderate AR is predicted to make landfall over California during 3-8 November 2017
  • Current forecasts indicate the geometry of the AR conditions may not meet standard criteria to be considered and AR by AR conditions (IVT >250 kg m-1 s-1 and IWV >20 mm) are expected to impact the majority of CA
  • Precipitation amounts up to 5 inches are expected over the Sierra Nevada with the majority of CA receiving at least 0.25 inches of precipitation
  • Forecast certainty is currently low on timing and strength of AR conditions but confidence of at least weak AR conditions over central and southern CA is high

Click IVT or IWV image to see loop of 72-180 hour GFS forecast

Valid 1200 UTC 3 November – 0000 UTC 8 November 2017






Summary provided by B. Kawzenuk, J. Kalansky, C. Hecht, and F.M. Ralph; 3 PM PT Tuesday 31 October 2017

*Outlook products are considered experimental

CW3E AR Update: 18-23 October 2017 Summary

CW3E AR Update: 18-23 October 2017 Summary

October 26, 2017

Click here for a pdf of this information.

Two Early Season Atmospheric Rivers Make Landfall over the Pacific Northwest

  • The first AR made landfall over WA and OR ~1200 UTC 18 October 2017
  • This AR produced >300 mm of precipitation over the Olympic Mountains in 72 hours (R-Cat 2)
  • The second AR made landfall over OR ~0600 UTC 21 October 2017
  • This AR produced >400 mm of precipitation over the Cascade Mountains in OR in 72 hours (R-Cat 3)

Click IVT or IWV image to see loop of GFS analysis

Valid 0000 UTC 18 October – 0000 UTC 24 October 2017

SSMI/SSMIS/AMSR2-derived Integrated Water Vapor (IWV)

Valid 0000 UTC 18 October – 0000 UTC 24 October 2017

Images from CIMSS/Univ. of Wisconsin





Summary provided by B. Kawzenuk, C. Hecht, and F.M. Ralph; 1 PM PT Thursday 26 October 2017

CW3E Releases New Interactive Geospatial Observation and Forecast Maps

CW3E Releases New Interactive Geospatial Observation and Forecast Maps

Spetember 18, 2017

CW3E has released a new interactive mapping tool that takes advantage of “web mapping services”, GIS-based coding/thinking, and interactive technologies in order to provide dynamic weather analysis graphics in support of the CW3E mission. These interactive maps allow the user to display and interact with numerous variables from a synoptic to a watershed scale with the goal of providing insight into potential impacts of landfalling atmospheric rivers over California.

This interactive tool was developed as a means to geospatially visualize meteorological and hydrologic observations on a new platform and from a new perspective. This first set of maps/webpages illustrate the utility of the tool in displaying atmospheric river related forecast products and CW3E will continue to build upon the tool. As we continue to experiment in improving and expanding the tool, we encourage any feedback or suggestions. Please contact the website creator or the CW3E Webmaster with any questions or feedback you may have.

The development of the tool and maps/webpage is supported by the California Department of Water Resources. The page was created and developed by CW3E collaborator Dr. Jason Cordeira and CW3E Director Dr. F. Martin Ralph with input from CW3E researchers Brian Kawzenuk, Chad Hecht, and Dr. Julie Kalansky.

Click here to view the new interactive geospatial observation and forecast maps.

CW3E Publication Notice: The Chiricahua Gap and the Role of Easterly Water Vapor Transport in Southeastern Arizona Monsoon Precipitation

CW3E Publication Notice

The Chiricahua Gap and the Role of Easterly Water Vapor Transport in Southeastern Arizona Monsoon Precipitation

Spetember 13, 2017

Click here for personal use pdf file

This study is a collaborative effort between CW3E and University of Arizona that identifies a terrain feature along the Arizona-New Mexico border just north of Mexico that is potentially important to the weather and climate of the southeast Arizona summer monsoon. The terrain feature is a “gap” that is approximately 250 km across and 1 km deep and represents the lowest terrain elevation along the 3000-km length the Continental Divide from 16-45°N. The name “Chiricahua Gap” is introduced to identify this key terrain feature, which reflects the name of a nearby mountain range in southeast Arizona and the region’s Native American history. The importance of the Chiricahua Gap is that it represents the primary pathway in which low altitude atmospheric water vapor is transported across the Continental Divide.

Motivated by identification of the Chiricahua Gap, upper-air observations from a wind profiling radar in Tucson, model reanalyses (Climate Forecast System Reanalysis), and gridded daily precipitation data (NCEP Stage-IV) are used to construct a case study and 15-year climatology to link summer monsoon rainfall events in southeast Arizona to low-altitude water vapor transport within the Chiricahua Gap. The results show that 76% of the wettest summer monsoon days in southeast Arizona during 2002-2016 occurred in conditions of low-altitude easterly water vapor transport in the Chiricahua Gap on the previous day. This result highlights how low-altitude water vapor associated with the wettest summer monsoon days in southeast Arizona originates from the east side of the Continental Divide, which differs from previous studies published since the 1970s. Much of the recent scientific literature points to southwesterly surges of low-altitude water vapor from over the Gulf of California as the primary driver of rainfall over southern Arizona during the summer monsoon. The current study by F. M. Ralph and T. J. Galarneau shows that the source region of low-altitude water vapor in southeast Arizona during the summer monsoon is potentially more complex, and is significantly influenced by source regions east of the Divide.

The paper is an example of CW3E expanding its research to examine the dynamics of the North American monsoon. Because monsoon is an important source or water for the US southwest and can cause flooding events, particularly flash floods, better understanding and improving forecasts of the North American monsoon is and important component of CW3E achieving its goal of revolutionizing the physical understanding, observations, weather predictions, of extreme events in Western North America and their impacts on floods, droughts, hydropower, ecosystems and the economy.

Figure 1: Terrain height (shaded in m) over Arizona, New Mexico, western Texas, and northern Mexico. Key terrain features are labeled in black. The location of Tucson, Arizona, is labeled by the black-filled circle. Low-altitude easterly water vapor transport through the Chiricahua Gap is shown by the blue arrows. This figure is modified from Fig. 1b in Ralph and Galarneau (2017).

CW3E Field Team Beats the Heat, Installs Meteorology and Hydrology Instruments in Russian River Watershed

CW3E Field Team Beats the Heat, Installs Meteorology and Hydrology Instruments in Russian River Watershed

September 6, 2017

A group of CW3E graduate students, postdocs, and staff worked to install soil moisture, meteorology, and streamflow instruments in the Lake Mendocino watershed August 28 – September 1. Taking extra precautions and shifting work schedules due to California’s triple-digit heat wave, the team installed three soil moisture and surface meteorology arrays and a stream gauge on ranchlands representative of the hilly topography draining into Lake Mendocino. CW3E thanks the landowners who have volunteered to have instruments installed on their properties, as well as Steve Turnbull of the U.S. Army Corps of Engineers for participating in the installations. Two more soil moisture and meteorology arrays and three more stream gauges are planned to be installed in the watershed prior to the 2017-18 AR season for a total of six soil moisture and meteorology arrays and six stream gauges. The data from these sites will be used to better understand AR meteorological and hydrologic impacts in this region and improve streamflow forecasts on the Russian River.

The field team after completion of the Potter Valley North site: Lindsey Jasperse, Steve Turnbull, Will Chapman, Maryam Asgari-Lamjiri, Douglas Alden, Anna Wilson and Xin Zhang. Not pictured: Julie Kalansky and Brian Henn

CW3E Publication Notice: Hourly Storm Characteristics along the U.S. West Coast: Role of Atmospheric Rivers in Extreme Precipitation

CW3E Publication Notice

Hourly Storm Characteristics along the U.S. West Coast: Role of Atmospheric Rivers in Extreme Precipitation

July 10, 2017

Fifty-five years of gridded hourly precipitation observations (CPC Hourly U.S. Precipitation) are used in this study to identify storm characteristics which most strongly modulate extreme storms along the U.S. West Coast. By investigating storms at fine (hourly) time scales, we showed that U.S. West Coast storm total precipitation is more strongly modulated by storm durations than by storm intensities, whereas in the Southeast U.S., storm intensities more strongly dictate the storm total precipitation (Figure 1, presented as Figure 2 in Lamjiri et al. [2017]). This study also showed that the most extreme precipitation events along the U.S. West Coast are associated with the most persistent atmospheric rivers, rather than the high intensity ARs. Therefore, it is of high importance to improve forecast skill of the duration of storms over the U.S. West Coast, which provides valuable information that could be used to mitigate flood risks and enhance water reservoir management. More details are provided in the full manuscript, which was published in the AGU journal Geophysical Research Letters: Lamjiri, M. A., M. D. Dettinger, F. M. Ralph, and B. Guan, 2017: Hourly storm characteristics along the U.S. West Coast: Role of atmospheric rivers in extreme precipitation, Geophys. Res. Lett., 44, doi:10.1002/2017GL074193. click here for personal use pdf file

Figure 1 Correlation coefficient of storm-precipitation totals with storm durations (a), maximum intensities (b), and average intensities(c) based on hourly precipitation observations from 1948-2002.


Gridded hourly precipitation observations over the conterminous US, from 1948 to 2002, are analyzed to determine climatological characteristics of storm precipitation totals. Despite generally lower hourly intensities, precipitation totals along the U.S. West Coast (USWC) are comparable to those in Southeast U.S. (SEUS). Storm durations, more so than hourly intensities, strongly modulate precipitation-total variability over the USWC, where the correlation coefficients between storm durations and storm totals range from 0.7 to 0.9. Atmospheric rivers (ARs) contribute 30-50% of annual precipitation on the USWC, and make such large contributions to extreme storms that 60-100% of the most extreme storms, i.e. storms with precipitation-total return intervals longer than two years, are associated with ARs. These extreme storm totals are more strongly tied to storm durations than to storm hourly or average intensities, emphasizing the importance of AR persistence to extreme storms on the USWC.

CW3E Undergraduate Researcher, Cody Poulsen, Awarded a SDEP Excellence Award

CW3E Undergraduate Researcher, Cody Poulsen, Awarded a SDEP Excellence Award

June 28, 2017

Cody Poulsen, an undergraduate student at UC San Diego pursuing a degree in Environmental Chemistry in the Environmental Systems (ESYS) Department and a minor in Digital Media, has collaborated on a research project with CW3E post-doc Scott Sellars. The project began during the summer of 2016 and was focused on using a program created by the Monterey Bay Aquarium Research Institute (MBARI) named Video Annotation Reference Systems (VARS) to produce useable meteorological metadata. VARS was created by MBARI to aid researchers in cataloguing the occurrences of biological species and geological formations in the large amounts of underwater footage collected by their ROVs. The research continued as part of Cody’s senior thesis during which he created an Atmospheric River metadata set with VARS. During the process, he learned more about the system and its capabilities. The metadata set is comprised of annotations for the location of AR landfall and center of AR events during the Water Years (WYs) 2001 and 2011. In addition, annotations for ARs with an associated Lower Level Jet (LLJ) structure where produced for both WYs. In the case study of WYs 2001 and 2011, the metadata depicted an anomalously high amount of landfalling AR events in California/Oregon for December 2010 juxtaposed to zero landfalling events along the North American West Coast excluding Alaska for December 2000. 500-hPa average wind speeds, heights, & direction plots for the two months where created to discern the general first principal flow that might explain the different AR trajectories. With these plots, it was found that a high-pressure ridge at 180° and low pressure trough at 140°W funneled ARs onto the California/Oregon coast for December 2010. Where December 2000 had a slight high pressure ridge along the coast to produce an insignificant blocking action leading to the assumption that some other synoptic features must be at play to produce the zero-event period.

For his senior thesis, Cody produced a poster on the VARS research project and presented it at the ESYS senior symposium. The symposium was comprised of poster presentations from each of the ESYS seniors that participated in research projects/ internships over their senior year. Cody and his research were selected by San Diego Environmental Professionals (SDEP) as one of the two projects to win an excellence award.

CW3E undergraduate researcher, Cody Poulsen, presents his research using VARS at the ESYS senior symposium.

Atmospheric Rivers: Recent Developments and Applications in California

Atmospheric Rivers: Recent Developments and Applications in California

May 19, 2017

In Sacramento on Tuesday, May 23rd, CW3E director, F. Martin Ralph will be presenting a seminar about atmospheric rivers and their impacts to California legislative and agency staff. The seminar, Atmospheric Rivers: Recent Developments and Applications in California, will provide updates on the impacts of ARs on the current water year and the ongoing research to better understand and better forecast ARs. Dr. Ralph is looking forward to sharing all of the exciting research being done at CW3E with the group.

May 31 – June 2 Big Data and The Earth Sciences: Grand Challenges Workshop

May 31 – June 2 Big Data and The Earth Sciences: Grand Challenges Workshop

April 17, 2017

Abstract deadline extended to April 21st

The Center for Western Weather and Water Extremes (CW3E) of UC San Diego’s Scripps Institution of Oceanography and the Pacific Research Platform (PRP) is excited to announce the organization of a workshop focused on earth sciences and information technology at the University of California San Diego. The workshop is a three-day Grand Challenges workshop May 31 to June 2 in La Jolla, Calif., on the topic of “Big Data and the Earth Sciences”.

CW3E is focused on advancing science and technology to support the unique information needs related to western U.S. extreme weather and water events, such as California’s recent flooding and multi-year drought and associated potential for subseasonal-to-seasonal forecasting. PRP is a consortium of universities in the western U.S. that is building a “science-driven, high-capacity data-centric freeway system on a large regional scale.” Funded by the National Science Foundation, PRP is based in the California Institute for Telecommunications and Information Technology (Calit2), a partnership of UC San Diego and UC Irvine. The workshop will take place in UC San Diego’s Atkinson Hall, headquarters of the Qualcomm Institute (the UCSD division of Calit2).

The goal of the The Big Data and Earth Sciences: Grand Challenges Workshop is to bring thought leaders in Big Data and Earth Sciences together for a three day, intensive workshop to discuss what is needed to advance our understanding and predictability of the Earth systems and to highlight key technological advances and methods that are readily available or in the final stages of development.

Sessions will include:

  • Big data collaborations;
  • Big data research platforms, networks, technologies and visualization;
  • Big data and predictability challenges in earth science data;
  • Pattern detection, segmentation and object recognition for earth sciences;
  • Structuring unstructured data in the earth sciences; as well as
  • Data mining and discovery, machine learning and predictive modeling.

For more information please visit:


Official workshop website:

Please send abstracts to

Abstracts are restricted to one page. Please include the abstract title, authors’ names and affiliations. A word document or .pdf is preferred.

CW3E Launches Radiosonde with Potter Valley Elementary School Students

CW3E Launches Radiosonde with Potter Valley Elementary School Students

April 16, 2017

CW3E’s Reuben Demirdjian and Anna Wilson recently conducted a demonstration radiosonde launch at the Potter Valley Fire Department for the Potter Valley Elementary School in the Russian River Watershed. The 5th and 6th grade classes, taught by Lori Clark and Merri Emerson respectively, were very enthusiastic participants in the demonstration launch. During the event the students showed their interest while asking a seemingly endless supply of questions about how the information is collected and why it it is useful. The students wrote a message on the to be launched radiosonde’s plastic exterior (Go Bearcats!), and released the balloon. Topics covered included the research done with the collected data, how the information gained from our experiments might help their strong agricultural community, why the balloon expands as it rises, what the sensors attached to the balloon measure, and how far the balloon might go (atmospheric layers were discussed!). Reuben and Anna, along with CW3E’s Douglas Alden, were also able to interact with the same classes at the start of the 2017 field season in January, when they deployed ground instrumentation including a vertically pointing radar, optical disdrometers, rain gauges, and more instrumentation at the Potter Valley Fire Department. The instrumentation at the Potter Valley Fire Department site has collected a valuable dataset over this historic winter season and CW3E is grateful for the support and collaboration and looks forward to a strong relationship going forward.

CW3E graduate student Reuben Demirdjian gets ready to hand off the radiosonde and balloon to two capable Potter Valley Elementary School students to sample a vertical profile of the atmosphere; Potter Valley Elementary School students watch the balloon ascend.