cw3e-web - Center for Western Weather and Water Extremes

IARC 2016

The First International Conference on Atmospheric Rivers (IARC) is Being Hosted by the Center for Wester Weather and Water Extremes (CW3E) at the Scripps Seaside Forum from 8-11 August 2016

August 8, 2016

IARC is part of a multi-year effort led by CW3E’s Director F. Martin Ralph, Mike Dettinger of USGS and David Lavers of ECMWF to foster collaboration and exchange of ideas on atmospheric rivers (AR).

The first event was held in June 2015 and brought together about 30 key individuals in a workshop, with a special emphasis on identifying the relationships between ARs, warm conveyor belts, and tropical moisture exports, all phenomena involving horizontal water vapor transport. A brief workshop synopsis is available in EOS (Dettinger et al. 2015) and here. Two main directions emerged:
- 1) agreement that it was time to develop a comprehensive monograph on ARs, and
- 2) an atmospheric river focused conference should be organized.
The second event in this 3-year effort is the 2016 IARC conference held from 8-11 August (described below; agenda).
The third event is a summer colloquium intended for summer 2017 at Scripps. It is intended to bring together at Scripps authors of the AR Monograph Book Chapters and graduate students from around the world for roughly 3 weeks of lectures and mentored mini-research efforts.

Woven through this series of events over 3 years is the development of the AR Monograph, which has been funded by a grant, including publication by University of California Press. IARC brings together most of the Chapter authors, at a point in the writing where new ideas garnered during the conference can be incorporated into the Monograph. The goal is then to have the Monograph finalized and in print for the AR Summer Colloquium. A technical editor, Lauren Muscatine (and her experienced team from UC Davis), is supporting preparation of the Monograph.

IARC received 75 abstracts from people around the world studying ARs, their impacts and applications of AR information to decision making. Submissions represent work on 6 continents plus Greenland. It has been planned by an international steering committee of experts on the subject. 90 people have registered for the conference, which will include several invited presentations, oral sessions, a poster session, panels on “applications to decision making,” “converging on a definition of atmospheric rivers” and on “future directions.” Breakout sessions will be held on “AR Forecasting,” “AR Book Chapters” and on “ARs in future climates and subseasonal to seasonal prediction.”

Sessions are organized around the following themes, which represent sections in the AR Monograph:

AR Applications
Global and Regional Perspectives
Observing and detecting ARs
Impacts of ARs
Theory, Structure and Processes
Modeling methodologies

Contact: F. Martin Ralph (mralph@ucsd.edu)

Publication Notice: Extreme Daily Precipitation in the Northern California Upper Sacramento River Watershed Requires a Combination of a Landfalling Atmospheric River and a Sierra Barrier Jet

CW3E Publication Notice

Extreme Daily Precipitation in the Northern California Upper Sacramento River Watershed Requires a Combination of a Landfalling Atmospheric River and a Sierra Barrier Jet

July 18, 2016

Ralph, F.M., J.M. Cordeira, P.J. Neiman and M. Hughes, 2016: Extreme Daily Precipitation in the Northern California Upper Sacramento River Watershed Requires a Combination of a Landfalling Atmospheric River and a Sierra Barrier Jet. J. Hydrometeor., 17, 1904-1915.

The top 0.3% most extreme daily precipitation events in the key Sacramento River watershed all involved both a landfalling atmospheric river and a Sierra Barrier Jet. Thus, forecasts of extreme precipitation are related to the skill of forecasts of each of these key phenomena, and can be enhanced by evaluation of, and enhancement of, skill in predicting each of these key processes. This study was led by the CW3E Director, was supported by the California Department of Water Resources, used data from NOAA’s Hydrometeorology Testbed collected over a decade, and epitomizes the focus of the “Center for Western Weather and Water Extremes,” and its partnership with NOAA Research’s Physical Sciences Division and Plymouth State University.

Contact: F. Martin Ralph (mralph@ucsd.edu)

Abstract

The upper Sacramento River watershed is vital to California’s water supply and is susceptible to major floods. Orographic precipitation in this complex terrain involves both atmospheric rivers (ARs) and the Sierra barrier jet (SBJ). The south-southeasterly SBJ induces orographic precipitation along south-facing slopes in the Mt. Shasta–Trinity Alps, whereas landfalling ARs ascend up and over the statically stable SBJ and induce orographic precipitation along west-facing slopes in the northern Sierra Nevada. This paper explores the occurrence of extreme daily precipitation (EDP) in this region in association with landfalling ARs and the SBJ. The 50 wettest days (i.e., days with EDP) for water years (WYs) 2002–11 based on the average of daily precipitation from eight rain gauges known as the Northern Sierra 8-Station Index (NS8I) are compared to dates from an SSM/I satellite-based landfalling AR-detection method and dates with SBJ events identified from nearby wind profiler data. These 50 days with EDP accounted for 20% of all precipitation during the 10-WY period, or 5 days with EDP per year on average account for one-fifth of WY precipitation. In summary, 46 of 50 (92%) days with EDP are associated with landfalling ARs on either the day before or the day of precipitation, whereas 45 of 50 (90%) days with EDP are associated with SBJ conditions on the day of EDP. Forty-one of 50 (82%) days with EDP are associated with both a landfalling AR and an SBJ. The top 10 days with EDP were all associated with both a landfalling AR and an SBJ.

Lake Mendocino Forecast-Informed Reservoir Operations (FIRO) Workshop Summary

July 5, 2016

Experts from multiple disciplines and organizations came together for the third annual FIRO workshop, which was held at UC San Diego/Scripps Institution of Oceanography (SIO) from 27-29 June 2016. This workshop was hosted jointly by the Sonoma County Water Agency (SCWA) and SIO’s Center for Western Weather and Water Extremes (CW3E). It was organized by the FIRO Steering Committee, co-chaired by CW3E’s Marty Ralph and SCWA’s Jay Jasperse. There were a total of 52 attendees from organizations including the US Army Corps of Engineers (USACE), California Department of Water Resources (CA DWR), National Oceanic and Atmospheric Administration (NOAA), US Geological Survey (USGS), US Bureau of Reclamation (USBR), SCWA and CW3E.

During the workshop, participants shared recent updates on FIRO activities, discussed reservoir conditions during water year 2016, summarized progress toward goals identified in the FIRO Workplan and identified issues to address regarding development of the Lake Mendocino FIRO “Preliminary Viability Assessment.” Progress was summarized on defining FIRO information requirements (e.g., forecast parameters and lead times), assessing current forecast skill, exploring the origins of forecast errors, advances in atmospheric river science, results of preliminary estimates of FIRO implications on Lake Mendocino water supply, and discussion of potential additional reservoirs for which FIRO may hold promise. Individual task groups (Preliminary Viability Assessment, Science, and Communications/Outreach) conducted break-out sessions in order to discuss progress and next steps towards meeting project goals (see photos below). In addition, the 11-member Lake Mendocino FIRO Steering Committee met afterward to review the workshop outcomes and plans. In short, the initial goals of year-1 of the 5-year FIRO Workplan are on track to be met, including development of the Preliminary Viability Assessment. Longer-term actions supporting the Full Viability Assessment are beginning and transferability is being discussed.

Lake Mendocino FIRO is summarized at /firo/.

Contacts: F. Martin Ralph (CW3E Director; mralph@ucsd.edu) and J. Jasperse (SCWA Chief Engineer; Jay.Jasperse@scwa.ca.gov)

Mesoscale Frontal Wave AR during CalWater-2014

CW3E Publication Notice

An Airborne and Ground-Based Study of a Long-Lived and Intense Atmospheric River with Mesoscale Frontal Waves Impacting California during CalWater-2014

May 10, 2016

Neiman, P.J., B.J. Moore, A.B. White, G.A. Wick, J. Aikins, D.L. Jackson, J.R Spackman, and F.M. Ralph, 2016: An Airborne and Ground-Based Study of a Long-Lived and Intense Atmospheric River with Mesoscale Frontal Waves Impacting California during CalWater-2014. Mon. Wea. Rev., 144, 1115-1144.

This study provides the most comprehensive observations to date of a mesoscale frontal wave associated with an atmospheric river, including its structure offshore, landfall characteristics and impacts on precipitation. It utilizes research aircraft, a unique array of coastal hydrometeorological measurements and inland data. This paper reflects the broader scientific collaboration between CW3E and NOAA/PSD, and adds to the knowledge of phenomena that are critical to creating extreme precipitation on the U.S. West Coast – a major thrust of CW3E. Dr. Ralph contributed to this paper by proposing the experiment (Ralph et al. 2016 BAMS), identifying the science objective for the flights (i.e., mapping out the structure of a mesoscale frontal wave with dropsondes and airborne radar), laying out the flight tracks, guiding the mission onboard, having been the PI of the major projects that created the unique land-based observing network (NOAA HMT- Ralph et al. 2013 BAMS, and the DWR-sponsored EFREP mesonet – White et al. 2013 JTech) used in the study and contributing to the analysis and interpretation of the measurements in this paper.

Contacts: Paul Neiman (paul.j.neiman@noaa.gov) and F. Martin Ralph (mralph@ucsd.edu)

Abstract

The wettest period during the CalWater-2014 winter field campaign occurred with a long-lived, intense atmospheric river (AR) that impacted California on 7–10 February. The AR was maintained in conjunction with the development and propagation of three successive mesoscale frontal waves. Based on Lagrangian trajectory analysis, moist air of tropical origin was tapped by the AR and was subsequently transported into California. Widespread heavy precipitation (200–400 mm) fell across the coastal mountain ranges northwest of San Francisco and across the northern Sierra Nevada, although only modest flooding ensued due to anomalously dry antecedent conditions. A NOAA G-IV aircraft flew through two of the frontal waves in the AR environment offshore during a ;24-h period. Parallel dropsonde curtains documented key three dimensional thermodynamic and kinematic characteristics across the AR and the frontal waves prior to landfall. The AR characteristics varied, depending on the location of the cross section through the frontal waves. A newly implemented tail-mounted Doppler radar on the G-IV simultaneously captured coherent precipitation features. Along the coast, a 449-MHz wind profiler and collocated global positioning system (GPS) receiver documented prolonged AR conditions linked to the propagation of the three frontal waves and highlighted the orographic character of the coastal-mountain rainfall with the waves’ landfall. Avertically pointing S-PROF radar in the coastal mountains provided detailed information on the bulk microphysical characteristics of the rainfall. Farther inland, a pair of 915-MHz wind profilers and GPS receivers quantified the orographic precipitation forcing as the AR ascended the Sierra Nevada, and as the terrain-induced Sierra barrier jet ascended the northern terminus of California’s Central Valley.

CW3E represented in recent policy and program meetings

CW3E Represented in Recent Policy and Program Meetings

June 8, 2017

During the last few weeks CW3E’s perspectives have been highlighted at three science policy-oriented meetings. The connection between CW3E’s scientific activities, practical applications and water policy implications is a common theme among them. The meetings and a brief synopsis are provided below:

1) AGU Congressional briefing on role of basic Geoscience in American Security May 2016

AGU invited three speakers to a Congressional briefing they organized to communicate to staff supporting a number of elected officials and policy committees. The goal was to make the connection between basic science advances (and the funding that has supported them), and benefits to American Security. CW3E’s Director, Dr. Ralph, represented the role of basic geoscience research in advancing water security in the Western U.S. His presentation emphasized the critical roles of key science funding strategies, from standard grants programs, to directed research efforts, cooperative agreements and federal labs. And in the end concluded that many breakthrough advances result not from a systems engineering approach to deciding what to do, but from ideas that are “outside the box.” He also highlighted that science, at its core, is fundamentally a creative endeavor that requires long-term support for people in their careers and for the organizations that host them. AGU has posted a video of the briefings here.

2) NOAA Water Information “Listening Session” in Sacramento May 2016

NOAA invited water management stakeholders from across the West to hear about the National Water Center they are creating in Alabama and to listen to stakeholders interests and needs for weather and water information to support water supply, flood mitigation and endangered species restoration in the West. CW3E was represented by Dr. Ralph, who brought Scripps science into the discussion, and supported major points presented by water managers concerning the vital role of atmospheric rivers in western water decisions. NOAA held one other regional “listening session” – in Alabama, and is holding one more “National” session in July. They will be considering input from these meeting as they develop their agency’s strategies in the coming years to support water information needs for the nation.

3) WSWC S2S Workshop San Diego June 2016

The National Academies of Science recently released a report on the subject of science needed to enable subseasonal-to-seasonal predictions to support decisions. The Western States Water Council (a group supporting the Governors of 17 Western States) organized a regional Workshop in San Diego in early June to discuss both the user requirements for better forecasts and the science opportunities to achieve them. CW3E was represented well, including participation by Sasha Gerhunov, Tamara Shulgina and Marty Ralph, including a presentation by Marty on observing system needs to support the goals.

CW3E Welcomes Dr. Anna Wilson

CW3E welcomes Dr. Anna Wilson

June 1, 2016

Dr. Anna M. Wilson has joined CW3E at the Scripps Institution of Oceanography as a Postdoctoral Scholar after earning her Ph.D. in Civil and Environmental Engineering under the direction of Dr. Ana Barros at Duke University earlier this year. Her dissertation research focused on understanding the space-time structure of low level warm season precipitation processes in complex terrain, using an approach integrating numerical models and in situ and remote observations. During her Ph.D., Anna was able to amass extensive experience working with ground based instruments in the field through participation in a number of different NASA Global Precipitation Mission Ground Validation field campaigns. She is excited to work with her colleagues at CW3E and partner organizations to provide essential support to decision makers at all time scales through developing physically based, accurate representations of atmospheric rivers and other extreme events in forecasts and projections. In particular, she will be studying the origins of variance in the relationship between upslope water vapor flux in atmospheric rivers and precipitation in coastal northern California.

CW3E Welcomes Dr. Scott Sellars

CW3E welcomes Dr. Scott Sellars

April 25, 2016

Dr. Scott L. Sellars has joined CW3E at the Scripps Institution of Oceanography to work on improving the understanding and forecasting of hydrologic extremes and their impacts on water resource management in the Western United States. Scott’s previous research has been in the area of hydrometeorology and climate, with a particular focus on computational science methodologies applied to remote sensing information for understanding connections between weather and hydrological events. He has previously held appointments at the University of California, Irvine, Columbia University’s Columbia Water Center (CWC), Geophysical Fluid Dynamics Laboratory (GFDL) and the International Research Institute for Climate and Society (IRI). His Ph.D. is on seasonal hydrometeorological prediction, awarded in 2014, and was undertaken at the University of California, Irvine.

CW3E AR Update:Post-Event Summary: 7-10 April 2016

CW3E AR Update: 7-10 April 2016 Post Event Summary

April 13, 2016

CW3E and WRCC give a post-event storm summary about two cutoff lows that made landfall over Southern California during 7-10 April 2016. Precipitation was widespread throughout the Southeastern United States with 72-hr accumulations generally ~0.5-3 inches. While the low pressure system entrained moisture from the tropics, spatial characteristics of IWV >20 mm and IVT >250 kg m^-1 s^-1 did not meet the necesarry requirements to be considered an Atmospheric River.

Click here for a pdf file of this information.

Odds of Reaching 100% Water Year Precipitation – April Update

Odds of Reaching 100% of Normal Precipitation for Water Year 2016 in California (April update)

April 10, 2016

Contribution from Dr. M.D. Dettinger, USGS

March is over (and the precipitation totals are in), so here is the update to the historical odds of getting to normal (and other fractions of normal) precipitation this year. Notice that the odds from the March 1 situation (in parens; click here for March report) are included alongside the April 1 odds, so that you can see whether March wetness made much difference. In fact, the odds haven’t changed too much in most areas because, although March was wettish (except down south), those additions were balanced in these April odds by the fact that we have almost run out of time this year to get much more precipitation.

Bottom lines (both of which you probably already know): We’re not going to fill the precipitation deficits we accumulated over the past 5 years with this year’s precipitation (except, long-odds, maybe in eastern NV). In southern California, the precipitation situation is especially grim and even the odds of making it to 75% of normal this year are well less than even.

How these probabilities were estimated:

At the end of a given month, if we know how much precipitation has fallen to date (in the water year), the amount of precipitation that will be required to close out the water year (on Sept 30) with a water-year total equal to the long-term normal is just that normal amount minus the amount received to date. Thus the odds of reaching normal by the end of the water year are just the odds of precipitation during the remaining of the year equaling or exceeding that remaining amount.

To arrive at the probabilities shown, the precipitation totals for the remaining months of the water year were tabulated (for all years, for only El Ninos, or for only La Ninas) and the number of years in which that precipitation total equaled or exceeded the amount still needed to reach normal were counted. The fraction of years that at least reached that threshold is the probability estimate. This simple calculation was performed for a full range of possible starting months (from November thru September) and for a wide range of initial (year-to-date) precipitation conditions. The calculation was also made for the probabilities of reaching 75% of normal by end of water year, 125%, and 150%, to ensure that the resulting tables of probabilities cover almost the full range of situations that will come up in the future. Contact mddettin@usgs.gov for more information.

[One key simplifying assumption goes into estimating the probabilities this way: The assumption that the amount of precipitation that will fall in the remainder of a water year does not depend on the amount that has already fallen in that water year to date. This assumption was tested for each month of the year by correlating historical year-to-date amounts with the remainder-of-the-year amounts, and the resulting correlations were never statistically significantly different from zero, except possibly when the beginning month is March, for which there is a small positive correlation between Oct-Mar and Apr-Sept precipitation historically.]

Contact: Michael Dettinger (USGS)

CW3E AR Update: 7-10 April 2016 Outlook

April 7, 2016

A weak low pressure system and high Integrated Water Vapor (IWV) values have brought light-to-moderate precipitation over Southern California this morning. A closed low is expected to develop off the coast over the next two days and will produce moderate precipitation over Southern California on 8-10 April 2016. IWV and Integrated Water Vapor Transport (IVT) values will be above AR thresholds but spatial characteristics of IWV/IVT will not meet the requirements of an AR. Coastal Southern California will experience AR conditions (IWV >20 mm and IVT >250 kg m^-1 s^-1) and light-to-moderate precipitaton, but this event is not considered an AR. For up to date AR forecasts visit the CW3E AR Portal.

Click here for a pdf file of this information.