CW3E AR Update: 10 November 2020 Outlook

CW3E AR Update: 10 November 2020 Outlook

November 10, 2020

Click here for a pdf of this information.

An active pattern is forecast to bring multiple landfalling atmospheric rivers to the Pacific Northwest and Northern California

  • The first AR is forecast to make landfall on 13 November, though there is currently large ensemble uncertainty in onset and overall duration of AR conditions
  • The second AR is forecast to make landfall over the Pacific Northwest on 15 November but is also associated with large ensemble and model-to-model uncertainty
  • The GEFS control member is currently suggesting that first AR could bring AR 2 conditions to Northern CA and Southern OR while the second AR could bring AR 4 conditions to Southern OR
  • The NOAA Weather Prediction Center is currently forecasting >10 inches of precipitation over the high elevations of the Coastal, Olympic, and Cascade Mountain Ranges during the next 7 days.

Click images to see loops of GFS IVT & IWV forecasts

Valid 0600 UTC 10 November – 0600 UTC 20 November 2020


 

 

 

 

 

 

 

 

Summary provided by C. Hecht, B. Kawzenuk, C. Castellano, J. Kalansky, and F. M. Ralph; 10 November 2020

*Outlook products are considered experimental

CW3E Hosts Fourth Yampa Basin Rendezvous Webinar of 2020: Exploring Uncertainty and Climate Change Impacts in the Yampa River Basin

CW3E Hosts Fourth Yampa Basin Rendezvous Webinar of 2020: Exploring Uncertainty and Climate Change Impacts in the Yampa River Basin

November 8, 2020

The Yampa River is one of the wildest remaining major tributaries of the Colorado River, and provides crucial water supplies to local stakeholders and to locations as far removed as Arizona and Southern California. A multitude of environmental and societal factors are expected to be affected by climate change in the Yampa River Basin, and are pertinent to other watersheds around the American West.

This summer, CW3E and our partners at Colorado Mountain College, Friends of the Yampa, Yampa Valley Sustainability Council, Steamboat Ski and Resort Corporation, and Vacasa, among others, have virtually come together for four webinars making up the third annual Yampa Basin Rendezvous (YBR). YBR 2020 is a series of four interactive webinars examining the Yampa River Basin through the lens of climate change and seasonal variability. The webinars include talks by regional experts and lively discussions.

The first webinar was held on June 4, 2020, introducing the series and providing an overview of the past year in the Yampa Basin with an eye to this year’s theme of Seasonal Variability. The panelists included Marty Ralph, CW3E Director; Kent Vertrees, with Friends of the Yampa and Steamboat Powdercats; and Nathan Stewart, Associate Professor of Sustainability Studies at Colorado Mountain College.

The second webinar of YBR 2020 was held on July 9, 2020. Webinar 2 was a panel discussion on Changes in Measurement with a Changing Climate, addressing what our measurement data are currently showing and ways we can adapt our strategies to be more effective. The panelists were Mike Dettinger, Visiting Researcher at Scripps Institution of Oceanography; Jeff Deems, Research Scientist with National Snow and Ice Data Center; and Gannet Hallar, Associate Professor of Atmospheric Science at University of Utah.

The third webinar of YBR 2020 was held on September 17th. Webinar 3 focused on the changes we are seeing from shifting seasons and precipitation and how these changes are impacting our local and statewide watershed and forest health. Our panelists were Russ Schumacher, Associate Professor of Atmospheric Science at Colorado State University, Director of the Colorado Climate Center, and Colorado’s State Climatologist; David Stahle, Distinguished Professor of Geosciences at University of Arkansas; and Courtney Peterson, Adaptive Silviculture for Climate Change (ASCC) Coordinator for the Northern Institute of Applied Climate Science.

The fourth webinar of YBR 2020 was held on October 22nd. This webinar delved into the uncertainty and impacts of seasonal variability on our economy, environment and way of life in the Yampa River Basin. Our panelists included David Anderson, Program Director for the Colorado Natural Heritage Program; Todd Hagenbuch, County Director and Agricultural Agent for CSU Extension; and Aneesh Subramanian, Assistant Professor of Atmospheric and Oceanic Sciences, UC Boulder.

The first, second, third and fourth webinars are now available to view online.

These four webinars were part of a larger effort to connect graduate students, post-doctoral scholars, researchers, staff, and faculty from CW3E to the local communities of river basins throughout the west, to share knowledge regarding climate variability and change that has impacts on the environment, people and the economy.

Panelists for Yampa Basin Rendezvous 2020 Webinar 4, held on October 22, 2020.

CW3E AR Update: 5 November 2020 Outlook

CW3E AR Update: 5 November 2020 Outlook

November 5, 2020

Click here for a pdf of this information.

First significant precipitation event of the season likely in California and the Four Corners Region

  • A shortwave trough and an associated AR are forecast to bring significant precipitation to portions of California and the Four Corners Region over the next several days
  • AR 2/AR 3 conditions (based on the Ralph et al. 2019 AR Scale) are possible in south-central Arizona
  • The highest precipitation amounts (1–3 inches) are forecast over far northern California, the Sierra Nevada, coastal Southern California, and across the higher terrain in central Arizona, Utah, and western Colorado
  • Significant snowfall is also possible in the Sierra Nevada and San Juan Mountains

Click images to see loops of GFS 500-hPa Absolute Vorticity & IVT forecasts

Valid 1200 UTC 5 November – 1200 UTC 9 November 2020


 

 

 

 

 

 

 

 

Summary provided by C. Castellano, C. Hecht, J. Kalansky, B. Kawzenuk, and F. M. Ralph; 5 November 2020

*Outlook products are considered experimental

Four CW3E Researchers Honored with CA DWR’s Award For Climate Science Service

Four CW3E Researchers Honored with CA DWR’s Award For Climate Science Service

November 5, 2020

During the annual Winter Outlook Workshop (WOW), sponsored by the California Department of Water Resources (DWR) and hosted virtually by CW3E on Nov 3-5, 2020, CW3E’s early career researchers, Dr. Anna Wilson, Dr. Julie Kalansky, Dr. Michael DeFlorio, and Dr. Peter Gibson, were recognized for their Climate Science Service. The awards were a tribute to their continued contribution and collaboration with DWR on subseasonal to seasonal forecasting and climate science related research and innovations. It is an honor to have the work of our scientists recognized for their role in the development of new technologies for water and flood-risk management. Thank you, DWR! Read the full press release here.

From Top Left: Dr. Anna Wilson, Dr. Julie Kalansky, Dr. Mike DeFlorio and Dr. Peter Gibson.

CW3E Launches Public Subseasonal-to-Seasonal (S2S) Experimental Forecast Webpage for Winter 2020-2021

CW3E Launches Public Subseasonal-to-Seasonal (S2S) Experimental Forecast Webpage for Winter 2020-2021

November 3, 2020

Demand for subseasonal-to-seasonal (S2S; 2-week to 6-month lead time) forecasts of precipitation and other meteorological variables is historically high in the stakeholder and applications communities. In particular, water managers, energy and insurance companies, agriculture producers, and other end users are keenly interested in improved prediction of precipitation, atmospheric river (AR) activity, and circulation patterns that may serve as precursor patterns for future wet or dry conditions relative to normal.

In response to this demand, California Department of Water Resources (DWR) has funded a partnership between the Center for Western Weather and Water Extremes (CW3E) and the National Aeronautics and Space Administration Jet Propulsion Laboratory (NASA JPL) to create S2S experimental forecast products supported by peer-reviewed literature assessing the skill of model(s) used to make a prediction. This effort is focused on precipitation over California, but also includes predictions of ARs and ridging events (extended periods of high atmospheric pressure) that influence precipitation amount during wintertime. These S2S experimental forecast products and their associated research supports CW3E’s Strategic Plan by producing experimental S2S outlooks of ARs, total precipitation, and ridges and by improving understanding of S2S predictability of these quantities through research studies.

The URL for the newly-launched CW3E S2S experimental forecast product website is /s2s_forecasts/.

Support from California DWR for this effort has spawned the creation of a number of experimental S2S forecast products and their associated peer reviewed journal articles providing hindcast skill assessments of the prediction systems used to make the experimental forecasts. There are currently four experimental S2S outlooks displayed on the public S2S website: weeks 1-3 AR activity outlooks; weeks 1-6 ridging outlooks; seasonal precipitation outlooks based on Canonical Correlation Analysis (CCA); and Odds of Water Year Normal precipitation outlooks. The following papers provide hindcast skill assessments for each of the products:

DeFlorio et al. 2019b (weeks 1-3 AR activity outlooks)

Gibson et al. 2020b (weeks 1-6 ridging outlooks)

Gershunov and Cayan 2003 (seasonal CCA outlooks)

The Odds of Water Year Normal Precipitation outlooks are calculated based on only historical data and are not considered a dynamic prediction system. Future S2S experimental prediction products will be added to the public S2S website, contingent upon the publication of their associated hindcast skill assessment (if needed) and the approval of CW3E Director F. Martin Ralph.

DeFlorio, M. J., D. E. Waliser, F. M. Ralph, B. Guan, A. Goodman, P. B. Gibson, S. Kumar (2019b), Experimental subseasonal-to-seasonal (S2S) forecasting of atmospheric rivers over the Western United States. Journal of Geophysical Research – Atmospheres (S2S Special Issue), 124, 11,242-11,265. https://doi.org/10.1029/2019JD031200.

Gershunov, A., and D. R. Cayan (2003): Heavy daily precipitation frequency over the contiguous United States: sources of climatic variability and seasonal predictability. Journal of Climate, 16, 2752–2765, https://doi.org/10.1175/1520-0442(2003)016<2752:HDPFOT>2.0.CO;2.

Gibson, P. B., D. E. Waliser, A. Goodman, M. J. DeFlorio, L. Delle Monache, and A. Molod (2020b), Subseasonal-to-seasonal hindcast skill assessment of ridging events related to drought over the Western United States. Journal of Geophysical Research – Atmospheres, in press.

CW3E Launches New Forecast Tools for the Atmospheric River Scale

CW3E Launches New Forecast Tools for the Atmospheric River Scale

November 2, 2020

CW3E has recently launched new tools focused on forecasting the Atmospheric River Scale. The new tools (available here), offer a 7-day forecast and review of the past 7 days for the Atmospheric River (AR) Scale. The AR Scale was originally launched in 2019 (overview video to the right). Similar to the Saffir-Simpson Hurricane Scale, it categorizes atmospheric rivers 1-5. Storms are characterized by the maximum strength, determined by the amount of water vapor they carry, and the winds, and their duration in a given location. Category is assigned based on if the storm will potentially be weak (AR 1), moderate (AR 2), strong (AR 3), extreme (AR 4), or exceptional (AR 5). The scale also indicates if the storm will be beneficial, by relieving drought and refilling water supply, or hazardous, causing flooding and dangerous conditions.

There are two new forecast tools on the page:

1. A forecast of incoming atmospheric rivers and the potential corresponding AR scale ranking at various latitude grid points along the West Coast. Also looks at the past 7 days.

2. A measure of integrated vapor transport (the mix of water vapor and wind that is a signature of atmospheric river storms) at grid points along the West, to give more detail on the magnitude of the storm. Colored shading represents the AR scale observed or forecast for the given time, calculated using the control forecast or ensemble mean.

Interested parties can sign up to get AR Scale alerts via text or email on this page: /arscale_alerts/. Alerts can be customized by locations, frequency, and various thresholds on the AR Scale.

The Center expects the new AR Scale forecast tool to be useful to water agencies that rely on forecasts for reservoir management, as well as broadcast meteorologists. Additional AR forecast tools created by CW3E can be found here: /iwv-and-ivt-forecasts/.

To learn more about atmospheric rivers and the AR Scale, please see the video below:


New Forecast Tool Looks Out to Six Weeks for Early Signs of Ridging Conditions – A Phenomenon Key to Diverting Winter Storms and Promoting U.S. West Coast Drought

New Forecast Tool Looks Out to Six Weeks for Early Signs of Ridging Conditions – A Phenomenon Key to Diverting Winter Storms and Promoting U.S. West Coast Drought

November 2, 2020

October 2020 has seen the continuation of abnormally dry conditions across much of California and the Western United States. As of the end of October, a considerable area of the Western United States is in Severe Drought or Extreme Drought, as classified by the United States Drought Monitor. On top of these severely dry conditions, downslope foehn winds have fanned multiple wildfires across the states of Washington, Oregon, California and Colorado throughout September and October. Ridging conditions, defined as extended regions of persistent high pressure in the atmosphere, play an important role in amplifying the likelihood of dry conditions across the Western United States. When ridging conditions are situated in certain key locations, the likelihood of the presence of atmospheric rivers to deliver a vital source of precipitation to the West is diminished, allowing dry conditions to persist across the water year (Gibson et al., 2020a). Forecasting when these ridging events are likely to setup and persist can therefore provide valuable information for water resource management. A new experimental forecast tool provides an extended outlook for when ridges are likely to be present in these key regions.

The new experimental forecast tool was developed by researchers at at the Center for Western Weather and Water Extremes (CW3E) at Scripps Institution of Oceanography at UC San Diego in partnership with the NASA Jet Propulsion Laboratory. The tool displays the likelihood of ridge occurrence in three different key regions, termed the North-Ridge type, the South-Ridge type, and West-Ridge type, as defined by the positioning of the ridge and associated regional precipitation anomalies. For each of these three ridge types, the forecast tool quantifies the likelihood of ridging at lead times of weeks 1 & 2, weeks 3 & 4, weeks 5 & 6, and maps the expected precipitation anomalies associated with ridging. A comprehensive hindcast skill assessment related to these forecasts is detailed in Gibson et al. (2020b).

This subseasonal-to-seasonal (S2S) product is based on input data from the National Centers for Environmental Prediction (NCEP) Climate Forecast System (CFS). The public release of the product was approved by an internal CW3E S2S Advisory Panel, co-chaired by CW3E Director Dr. F. Martin Ralph and NASA JPL Chief Scientist for Earth Sciences Dr. Duane E. Waliser. This S2S product, as well as the research that underpins the product, supports CW3E’s Strategic Plan goals for revolutionizing seasonal outlooks of extreme events in North America and their impacts on floods, drought, hydropower, and the economy.

A recent example of the weeks 3 & 4 forecast product is shown below. Forecasts are updated twice weekly on the CW3E website.

Figure: Example of the weeks 3 & 4 ridging outlook generated on October 26th 2020 and valid from November 9th to November 23rd. Across this forecast time period the West-ridge type is expected to be particularly active, with 75% of the ensemble members (grey bars) showing a higher occurrence of ridging compared to climatology (horizontal blue dashed lined). The associated precipitation pattern anomaly is shown on the right-hand side and indicates a preference for drier-than-normal conditions across southern California and wetter-than-normal conditions across Washington State.

Gibson, P. B., D. E. Waliser, B. Guan, M. J. DeFlorio, F. M. Ralph, and D. L. Swain, 2020a: Ridging associated with drought in western and southwestern United States: characteristics, trends and predictability sources. J. Climate, 33, 2485-2508, doi: https://doi.org/10.1175/JCLI-D-19-0439.1.

Gibson, P. B., Waliser, D. E., Goodman, A., DeFlorio, M. J., Delle Monache, L., and Molod, A. (2020b). Subseasonal-to-seasonal (S2S) hindcast skill assessment of ridging events related to drought over the Western United States. Journal of Geophysical Research: Atmospheres (accepted for publication).

CW3E AR Update: 30 October 2020 Outlook

CW3E AR Update: 30 October 2020 Outlook

October 30, 2020

Click here for a pdf of this information.

Active weather pattern to bring landfalling AR activity and precipitation to the Pacific Northwest

  • A series of storms is forecast to produce a prolonged period of AR conditions across portions of Oregon and Washington next week
  • Current forecasts suggest that AR 3/AR 4 conditions (based on the Ralph et al. 2019 AR Scale) are possible over coastal Oregon and Washington
  • AR 2/AR 3 conditions are also possible over portions of interior Oregon and Washington
  • 7-day precipitation totals may exceed 5 inches in the Olympic Mountains and North Cascades

Click images to see loops of GFS IVT/IWV analyses and forecasts

Valid 1200 UTC 30 October – 1200 UTC 7 November 2020


 

 

 

 

 

Summary provided by C. Castellano, C. Hecht, J. Kalansky, and F. M. Ralph; 30 October 2020

*Outlook products are considered experimental

Distribution of Landfalling Atmospheric Rivers over the U.S. West Coast During Water Year 2020: End of Water Year Summary

Distribution of Landfalling Atmospheric Rivers over the U.S. West Coast During Water Year 2020: End of Water Year Summary

October 28, 2020

For a pdf of this information click here.

Link to a post-event summary of the 26 January to 02 February 2020 AR here

Link to a post-event summary of the 04 to 08 February 2020 AR here

Analysis by Chad Hecht, Jason Cordeira, Julie Kalansky, & F. Martin Ralph. This analysis is considered experimental. For questions regarding the data or methodology please contact Chad Hecht

CW3E Director gives virtual talks for UCLA and Stony Brook University

CW3E Director gives virtual talks for UCLA and Stony Brook University

October 26, 2020

As many universities’ Fall Seminar series have kicked off virtually this year, travelling to different departments to share research has been easier than ever! CW3E’s director, Dr. Marty Ralph, recently gave a virtual seminar on the topic of “Atmospheric Rivers: Recent developments in science, impacts and policies” for UCLA’s Department of Atmospheric and Oceanic Science on Wednesday, October 21, 2020, and for Stony Brook University’s School of Marine and Atmospheric Sciences (SoMAS) Ocean, Sustainability, Atmosphere Colloquium on Friday October 23, 2020.

In the presentation, Dr. Ralph reviewed recent developments in the study of atmospheric rivers (ARs), including creation of the formal definition of an AR, the scale for AR intensity and impacts, the operational airborne AR Reconnaissance program, and AR-focused forecast tools. He then discussed the role of ARs in extreme precipitation, including examples from the US East Coast and trends in the occurrence of extreme 3-day-total precipitation events. Lastly, Dr. Ralph described how the AR topic has related to recent public policy developments at state and federal levels, focusing on the potential for better AR forecasts to support water management.

The full seminar delivered to Stony Brook is available here, and the recording delivered to UCLA is available here. If you would like to inquire about CW3E participation in upcoming seminars or outreach opportunities, please don’t hesitate to get in touch directly or sign up for our mailing list!

Screenshot from the seminar given to Stony Brook; outline slide of Marty Ralph’s virtual talk.

Screenshot from seminar given to Stony Brook; results from recently published work.