Author: cw3e-web

CW3E AR Update: 8 December 2021 Outlook

CW3E AR Update: 8 December 2021 Outlook

December 8, 2021

Click here for a pdf of this information.

Potential for Long-duration Atmospheric River and Heavy Precipitation in California

  • A weak system will bring AR conditions and light-to-moderate precipitation to Southern California and the Colorado River Basin tomorrow
  • A stronger and more complex system is forecasted to bring landfalling AR activity and heavy precipitation to much of California early next week
  • There is still considerable uncertainty in the timing, magnitude, and duration of AR conditions and precipitation, but the forecast models are starting to converge toward a similar outcome
  • The 00Z ECMWF EPS control run is forecasting AR 4 conditions over the San Francisco Bay Area, whereas the 00Z GEFS control run is only forecasting an AR 1 at this location
  • The NWS Weather Prediction Center is forecasting more than 5 inches of total precipitation over the Pacific Coast Ranges and the Sierra Nevada during the next 7 days
  • The 00Z GFS and ECMWF models were showing large differences in forecasted precipitation in association with the second AR over the Russian River watershed

Click images to see loops of GFS IVT & IWV forecasts

Valid 1200 UTC 8 December – 1200 UTC 15 December 2021


 

 

 

 

 

 

 

 

 

 

 

 

 

Summary provided by C. Castellano, C. Hecht, S. Roj, B. Kawzenuk, J. Kalansky, and F. M. Ralph; 8 December 2021

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*Outlook products are considered experimental

CW3E Publication Notice: Advances in the Application and Utility of Subseasonal-to-Seasonal Predictions

CW3E Publication Notice

Advances in the Application and Utility of Subseasonal-to-Seasonal Predictions

December 6, 2021

CW3E researcher Dr. Mike DeFlorio, along with co-authors Dr. F. Martin Ralph (CW3E Director), Dr. Luca Delle Monache (CW3E Deputy Director), Dr. Duane E. Waliser (NASA JPL/CalTech; Chief Scientist of the Earth Science and Technology Directorate), Dr. Peter B. Gibson (NIWA), and Dr. Michael L. Anderson (California Department of Water Resources) recently contributed as co-authors to an article in BAMS titled “Advances in the Application and Utility of Subseasonal-to-Seasonal Predictions”. The contributions of DeFlorio, Ralph, Delle Monache, and Gibson were supported by the California Department of Water Resources Atmospheric River Program Phase II and the United States Army Corps of Engineers Forecast Informed Reservoir Operations Program Phase II.

The purpose of this BAMS article is to provide a detailed description of an international community of researchers who are partners with specific end users in advancing the utility of subseasonal-to-seasonal (S2S; 2-week to 6-month lead time) forecasts. Twelve case studies are presented in the article and span the end user sectors of water resource management, public health, agriculture, renewable energy and utilities, and emergency management and response. A key component of the case studies presented in this article is the collaboration and partnership between researchers and end users in co-generating S2S forecasts of relevant quantities of interest (e.g., atmospheric rivers, precipitation, ridging, temperature, etc.). The organization and coalescence of this broad community of international researchers and end users was facilitated by the World Weather Research Programme (WWRP) / World Climate Research Programme (WCRP) S2S Prediction Project Real-time Pilot Initiative (http://www.s2sprediction.net/xwiki/bin/view/dtbs/RealtimePilot).

Figure 5 from the article is included below. It provides an overview of the CW3E/NASA JPL contribution to this effort, which includes week-3 AR activity and weeks 3-4 ridging outlooks.

Figure 5: Water management in western U.S., showing: a) CW3E/JPL week 3 AR activity outlook. Forecast initialized September 21, 2020 and verified October 06-12, 2020. Top panel shows the forecasted number of AR days to occur during the week 3 verification period; middle panel shows the NCEP hindcast climatology of AR days during the October 06-12 week in the hindcast record; bottom panel shows the anomaly forecast field (top minus middle panels). Hindcast skill assessment provided in DeFlorio et al. (2019a,b); b) CW3E/JPL weeks 3-4 experimental ridging outlook. Forecast initialized on September 21, 2020 and verified October 05-19, 2020. Left column shows the occurrence frequency of each ridge type (bars) compared to climatology (horizontal line) for each of the model ensemble members. The top, middle, and bottom row display the North, South, and West ridge forecasts, respectively. If over 50% of the ensemble members predict more ridging than expected (for this time of year), then the right column maps indicate the likelihood of wetter or drier conditions based on how each ridge type typically influences precipitation. Methodology for calculating ridge types is provided in Gibson et al. (2020a); hindcast skill assessment is provided in Gibson et al. (2020b).

White, C.J., Domeisen, D.I.V., Acharya, N., Adefisan, E.A., Anderson, M.L., Aura, S., Balogun, A.A., Bertram, D., Bluhm, S., Brayshaw, D.J., Browell, J., Büeler, D., Charlton-Perez, A., Chourio, X., Christel, I., Coelho, C.A.S., DeFlorio, M.J., Delle Monache, L., Di Giuseppe, F., García-Solórzano, A.M., Gibson, P.B., Goddard, L., González Romero, C., Graham, R.J., Graham, R. M., Grams, C.M., Halford, A., Katty Huang, W.T., Jensen, K., Kilavi, M., Lawal, K.A., Lee, R.W., MacLeod, D., Manrique-Suñén, A., Martins, E.S.P.R., Maxwell, C.J., Merryfield, W.J., Muñoz, Á.G., Olaniyan, E., Otieno, G., Oyedepo, J.A., Palma, L., Pechlivanidis, I.G., Pons, D., Ralph, F.M., Reis, D.S., Jr., Remenyi, T.A., Risbey, J.S., Robertson, D.J.C., Robertson, A.W., Smith, S., Soret, A., Sun, T., Todd, M.C., Tozer, C.R., Vasconcelos, F.C., Jr., Vigo, I., Waliser, D.E., Wetterhall, F., & Wilson, R.G. (2021). Advances in the application and utility of subseasonal-to-seasonal predictions. Bulletin of the American Meteorological Society, 1(aop), 157. https://doi.org/10.1175/BAMS-D-20-0224.1.

CW3E AR Update: 3 December 2021 Outlook

CW3E AR Update: 3 December 2021 Outlook

December 3, 2021

Click here for a pdf of this information.

Multiple atmospheric rivers are forecast to make landfall over the US West Coast

  • Two ARs and their parent lows are forecast to bring rain to the Pacific Northwest and parts of California over the next week
  • These ARs are primarily being steered by persistent high pressure in the Eastern Pacific, which is resulting in a northwesterly orientation as the ARs make it to California
  • Due to the northwesterly orientation of the IVT, the precipitation from these ARs will likely be much less than an AR of similar magnitude but a southwesterly orientation
  • The parent lows of these ARs are forecast to move inland over the Pacific Northwest, which may result in very low freezing levels and snow showers at low elevations
  • The WPC is currently forecasting ~3–5 inches of precipitation over the Cascades in Washington and 0.5 – 1.5 inches over the Sierra Nevada and Southern California Mountains

Click images to see loops of GFS IVT & IWV forecasts

Valid 1200 UTC 3 December – 0000 UTC 13 December 2021


 

 

 

 

 

 

 

 

Summary provided by C. Hecht, S. Roj, J. Cordeira, C. Castellano, B. Kawzenuk, J. Kalansky, and F. M. Ralph; 3 December 2021

To sign up for email alerts when CW3E post new AR updates click here.

*Outlook products are considered experimental

CW3E AR Update: 29 November 2021 Outlook

CW3E AR Update: 29 November 2021 Outlook

November 29, 2021

Click here for a pdf of this information.

Atmospheric Rivers Produce Heavy Rainfall and Flooding in the Pacific Northwest

  • The first two atmospheric rivers (ARs) in a sequence of three ARs impacted the Pacific Northwest between 24 Nov and 29 Nov
  • The first AR produced AR 2 conditions (based on the Ralph et al. 2019 AR Scale) in coastal Oregon and Washington
  • The second AR produced AR 3/AR 4 conditions in northern coastal Oregon and coastal Washington
  • Some locations in the Olympic Peninsula and North Cascades received more than 10 inches of total precipitation from the first two ARs
  • Heavy rain falling on moist soils resulted in flooding and mudslides in northern Washington and southern British Columbia
  • This sequence of storms, which began less than two weeks after a series of destructive storms earlier this month, led Environment and Climate Change Canada to declare a “red alert” for British Columbia


 

 

 

 

Unsettled Weather to Continue through the End of November in Pacific Northwest

  • The third AR in a sequence of ARs is forecasted to make landfall over British Columbia and Washington today
  • AR 4 conditions are possible across portions of coastal British Columbia, whereas AR 3 conditions are currently forecasted across coastal Washington
  • An additional 2–4 inches of precipitation are forecasted over the Olympic Peninsula and North Cascades during the next 3 days, with higher amounts (> 5 inches) possible in coastal British Columbia
  • The British Columbia River Forecast Center has issued Flood Watches and Flood Warnings ahead of the third AR

Click images to see loops of GFS IVT & IWV forecasts

Valid 1200 UTC 29 November – 0000 UTC 2 December 2021


 

 

 

Summary provided by C. Castellano, C. Hecht, B. Kawzenuk, S. Roj, and F. M. Ralph; 29 November 2021

To sign up for email alerts when CW3E post new AR updates click here.

*Outlook products are considered experimental

CW3E AR Update: 24 November 2021 Outlook

CW3E AR Update: 24 November 2021 Outlook

November 24, 2021

Click here for a pdf of this information.

Another family of atmospheric rivers is forecast to impact the Pacific Northwest and British Columbia over the next week

  • Three atmospheric rivers (ARs) are forecast to bring enhanced precipitation to much of the PNW and BC over the next week after a family of ARs brought record-breaking rains and flooding to the region during 10–16 November
  • Currently, the GEFS is forecasting the first 2 ARs to bring AR 3 conditions to southern Vancouver Island and the Olympic Peninsula
  • The third AR may bring another round of AR 3 conditions, but ensemble spread is considerably large due to the extended forecast lead time
  • The NWS Weather Prediction Center is currently forecasting 15–20 inches of precipitation over the next 7 days across portions of the PNW
  • Due to high forecasted freezing levels and moist soil conditions caused by the multiple ARs during 10–16 November, a large portion of the precipitation could lead to runoff, exacerbating hydrologic impacts

Click images to see loops of GFS IVT & IWV forecasts

Valid 1200 UTC 24 November – 0000 UTC 2 December 2021


 

 

 

 

 

 

 

 

 

Summary provided by C. Hecht, S. Roj, C. Castellano, and F. M. Ralph; 24 November 2021

To sign up for email alerts when CW3E post new AR updates click here.

*Outlook products are considered experimental

Bibliography of AR-Focused Publications

Bibliography of AR-Focused Publications

November 23, 2021

The Center for Western Weather and Water Extremes (CW3E) recently developed a bibliography of scientific journal articles focused on atmospheric rivers (ARs). This AR bibliography includes 350 journal articles directly focused on ARs from 1991 through 2020. It is developed for use by CW3E, its collaborators, and to share with other interested people. Meanwhile, it provides a resource that allows people new to the AR topic to find key relevant articles and increases the ease of keeping up to date on the growing literature.

The scientific journal articles focused on ARs in this bibliography were identified as the articles with the words “atmospheric river” or “atmospheric rivers” (tropospheric rivers) in their title from peer-reviewed journals according to the search results from Google Scholar. Other journal articles focused on ARs are not included currently but may be added in the future. Books, or book chapters, including “Atmospheric Rivers” published in 2020, are also not included.

Figure 1. Annual count of AR publications in 1991-2020. The AR publications here were identified as the publications with “atmospheric river” or “atmospheric rivers” in the title from peer-reviewed journals according to Google Scholar.

Figure 2. Same as Figure 1 but for the publications from CW3E (blue) and the others (green). The red
arrows label the important time points for AR research.

The concept of ARs first appeared in the peer-reviewed literature in the early 1990s. Newell and Zhu found a long and narrow region of intense water vapor flux in the troposphere and named it atmospheric/tropospheric river (Newell et al, 1992; Newell and Zhu 1994; Zhu and Newell 1994). Through the 1990s, there were only seven AR-focused journal articles published (Figure 1). During the 2000s the number of AR-focused studies increased slights to 10, these included Ralph et al. (2004, 2005, and 2006), which investigated the structure of ARs using observations, the influence of ARs on extreme precipitation, and the role of ARs in flooding, respectively. Then, in the last decade (the 2010s) the interest in ARs grew quickly, which was highlighted by the rapid increase in AR publications from three in 2010 to 67 in 2019 and a total number of AR journal articles of 248 during that decade. The Center for Western Weather and Water Extremes (CW3E) was established in 2013 and contributed about 25% of the 350 publications in 1991-2020 (Figure 2). Several significant events led by CW3E occurred during the 2010s, including the 1st International Atmospheric Rivers Conference in 2016, the addition of the AR definition to the AMS Glossary of Meteorology in 2018, and the launch (publication in BAMS in 2019) of the AR Scale based on AR intensity and duration. The number of AR-focused articles has continued to increase during the current decade. The selection criteria in this bibliography are different from the criteria used in Wilson et al. 2020, which includes journal and conference papers with “atmospheric rivers” anywhere in the paper.

Figure 3. Pie plot showing the peer-reviewed journals of the AR publications in 1991-2020.

The 350 AR-focused articles in 1991-2020 were published in 73 different peer-reviewed academic journals (Figure 3). Eight peer-reviewed journals had at least 10 AR-focused articles during this period, four of which published nearly half of the 350 studies: Geophysical Research Letters, Journal of Hydrometeorology, Journal of Geophysical Research – Atmosphere, and Monthly Weather Review.

Although it is not included in this AR bibliography, the Atmospheric Rivers Book, published in August 2020, contains roughly 20 years of research on ARs (Figure 4). Led by F. Martin Ralph, Mike Dettinger, Jon Rutz, and Duane Waliser, a global team of 34 authors who have conducted and published the majority of critical research on ARs contributed to this book. It emphasizes the progress made on science, applications, and remaining knowledge gaps, providing a comprehensive review of the AR publications in this bibliography.

Figure 4. Summary of the Atmospheric River Book.

Currently, this AR bibliography includes 350 AR-focused articles from 1991 through 2020 with detailed information (year of publication, authors, paper titles, and journal names). These articles were selected based on Google Scholar; thus, some relevant publications might be missed. Please send any comments, suggestions, or additions to Zhenhai Zhang. To view the bibliography or learn more about it click here.


Newell, R. E., Newell, N. E., Zhu, Y., & Scott, C. (1992). Tropospheric Rivers – A pilot study. Geophysical Research Letters, 19(24), 2401-2404.

Newell, R. E., & Zhu, Y. (1994). Tropospheric rivers: A one‐year record and a possible application to ice core data. Geophysical Research Letters, 21(2), 113-116.

Ralph, F. M., Neiman, P. J., & Wick, G. A. (2004). Satellite and CALJET aircraft observations of atmospheric rivers over the eastern North Pacific Ocean during the winter of 1997/98. Monthly Weather Review, 132(7), 1721-1745.

Ralph, F. M., Neiman, P. J., & Rotunno, R. (2005). Dropsonde observations in low-level jets over the northeastern Pacific Ocean from CALJET-1998 and PACJET-2001: Mean vertical-profile and atmospheric-river characteristics. Monthly Weather Review, 133(4), 889-910.

Ralph, F. M., Neiman, P. J., Wick, G. A., Gutman, S. I., Dettinger, M. D., Cayan, D. R., & White, A. B. (2006). Flooding on California's Russian River: Role of atmospheric rivers. Geophysical Research Letters, 33(13).

Ralph, F. M., Dettinger, M. D., Cairns, M. M., Galarneau, T. J., & Eylander, J. (2018). Defining “atmospheric river”: How the Glossary of Meteorology helped resolve a debate. Bulletin of the American Meteorological Society, 99(4), 837-839.

Ralph, F. M., Rutz, J. J., Cordeira, J. M., Dettinger, M., Anderson, M., Reynolds, D., … & Smallcomb, C. (2019). A scale to characterize the strength and impacts of atmospheric rivers. Bulletin of the American Meteorological Society, 100(2), 269-289.

Wilson, A. M., Chapman, W., Payne, A., Ramos, A. M., Boehm, C., Campos, D., … & Ralph, F. M. (2020). Training the next generation of researchers in the science and application of atmospheric rivers. Bulletin of the American Meteorological Society, 101(6), E738-E743.

Zhu, Y., & Newell, R. E. (1994). Atmospheric rivers and bombs. Geophysical Research Letters, 21(18), 1999-2002.

Congratulations to Dr. Chapman – CW3E Graduate Student Successfully Defends Dissertation

Congratulations to Dr. Chapman – CW3E Graduate Student Successfully Defends Dissertation

November 23, 2021

The sixth CW3E PhD student has successfully defended his dissertation. Dr. Will Chapman’s defense was held on Friday, November 19, 2021. His dissertation title is “Improved Earth System Prediction with Deep Learning and Large Ensembles” and includes three chapters published in peer reviewed journals (Chapman et al., 2019, 2021a, 2021b), with an additional publication in preparation. Will’s committee members were Shang-Ping Xie and Marty Ralph (Co-Chairs), Ian Eisenman, Amato Evan, Jan Kleissl, and Aneesh Subramanian. Funding for Will’s dissertation came from FIRO and the AR Program, both under PI Marty Ralph.

Will is moving on with a joint post-doctoral appointment in Boulder Colorado, with half of his funding coming as an Advance Studies Program (ASP) post-doctoral scholar at the National Center for Atmospheric Research, and additionally working for the m2lines project on correcting CESM model biases.

Due to the ongoing COVID-19 health crisis, Will defended his dissertation virtually. CW3E is incredibly proud of Will’s accomplishment today and all that he has accomplished throughout his PhD. We are so grateful to have had the opportunity to work with Will throughout his graduate school career.

Dr. Chapman summarizing answers a question from the audience during his defense.

Dr. Chapman thanks his committee at the close of his defense.

Chapman, W. E., Subramanian, A. C., Delle Monache, L., Xie, S. P., & Ralph, F. M. (2019). Improving Atmospheric River Forecasts with Machine Learning. Geophysical Research Letters, 46, 10627-10635, https://doi.org/10.1029/2019GL083662

Chapman, W. E., Delle Monache, L., Alessandrini, S., Subramanian, A. C., Ralph, F. M., Xie, S., Lerch, S., & Hayatbini, N. (2021a). Probabilistic Predictions from Deterministic Atmospheric River Forecasts with Deep Learning, Monthly Weather Review (published online ahead of print), https://doi.org/10.1175/MWR-D-21-0106.1

Chapman, W. E., Subramanian, A. C., Xie, S., Sierks, M. D., Ralph, F. M., & Kamae, Y. (2021b). Monthly Modulations of ENSO Teleconnections: Implications for Potential Predictability in North America, Journal of Climate, 34, 5899-5921. https://doi.org/10.1175/JCLI-D-20-0391.1

CW3E Launches New AR Scale Ensemble Forecast Tool

CW3E Launches New AR Scale Ensemble Forecast Tool

November 19, 2021

CW3E recently launched a new forecast tool using ensemble models to forecast the AR Scale. The AR scale is determined based on the duration of AR conditions (IVT >250 kg m-1 s-1) and maximum IVT during the AR as described in Ralph et al. 2019. The new tool uses ensemble members from the NCEP Global Ensemble Forecast System (GEFS) or the European Centre for Medium-Range Weather Forecasts Ensemble Prediction System (ECMWF EPS) to forecast the AR Scale for locations in the western U.S. over the next seven days. The tool illustrates the uncertainty in the timing and magnitude of AR conditions and AR scale ranking among the ensemble models. The development of the AR Scale Ensemble Forecast product was supported by California Department of Water Resources via the AR Program. NWS service has used this in developing the forecasts for the AR 5 that made landfall on 24 October 2021.

“The ensembles of the AR scale were extremely helpful for us to establish confidence in a major event coming. Seeing how many members had AR4-5 several days out gave me confidence to be more bullish on our “wet scenario” projections and to really hit the potential rain impacts during our briefings.”

-Chris Smallcomb, Warning Coordination Meteorologist for the National Weather Service’s Reno Forecast Office

The top left panel represents the integrated water vapor transport (IVT) forecast for each of the individual ensemble models (thin gray lines), the unperturbed GFS or ECMWF control forecast (black line), the ensemble mean (green line), and plus or minus one standard deviation from the ensemble mean (red line (+), blue line (-), and gray shading). Colored shading represents the AR scale forecast for the given time, shaded according to scale, calculated using the model control forecast. The bottom left panel shows the probability of AR Scale rankings at the given location calculated by the number of ensemble members predicting a given AR Scale ranking at each forecast lead time. The top right panel shows the maximum AR Scale forecast from the GFS or ECMWF control member at each grid point for the next seven days (colored dots), and the 7-day accumulated precipitation forecast from the GFS or ECMWF control forecast. The bottom right panel shows the AR Scale magnitude and timing calculated for each GEFS or ECMWF EPS ensemble member, with values representing the magnitude and timing of the maximum IVT during each forecasted AR. Gray shading in each panel represents IVT >250 (kg m-1s-1 for a duration less than 24 hours.

This tool will be updated four times daily for the GEFS model (00, 06, 12, and 18 UTC) and twice daily for the ECMWF EPS model (00 and 12 UTC) and is available at /arscale/.

Example forecast from the GEFS initialized 00 UTC 22 October 2021 near San Francisco. This forecast showed a nearly 80% chance of an AR5 making landfall on 23-25 October.


CW3E Event Summary: 10-16 November 2021

CW3E Event Summary: 10-16 November 2021

November 17, 2021

Click here for a pdf of this information.

Atmospheric Rivers Produce Heavy Rainfall, Flooding, and Landslides in the Pacific Northwest

  • Multiple strong atmospheric rivers (ARs) impacted the Pacific Northwest between 10 Nov and 15 Nov
  • The first AR produced AR 3/AR 4 conditions (based on the Ralph et al. 2019 AR Scale) in coastal Oregon and southern coastal Washington
  • The second AR produced AR 4 conditions in coastal Washington and northern coastal Oregon
  • The intensification of a mesoscale frontal wave (MFW) led to a secondary pulse in moisture transport that prolonged the duration of the 2nd AR and brought borderline AR 5 conditions (max IVT > 1000 kg m−1 s−1; AR duration > 48 hours) to Tillamook County, OR
  • Parts of the Olympic Peninsula and Washington Cascades received more than 15 inches of total precipitation from these ARs
  • Heavy rain falling on moist soils led to widespread flooding and mudslides, particularly in northern Washington and southern British Columbia following the second AR landfall
  • Strong winds and flooding during the second AR also created dangerous travel conditions, downed numerous trees, and caused widespread power outages in western Washington

Click images to see loops of GFS IVT/IWV analyses

Valid 0000 UTC 10 November – 0000 UTC 16 November 2021

MIMIC-TPW2 Total Precipitable Water

Valid 0000 UTC 10 November – 0000 UTC 16 November 2021


 

 

 

 

 

 

 

 

 

 

 

Summary provided by Chad Hecht, Chris Castellano, Shawn Roj, Brian Kawzenuk, Jay Cordeira, F.M. Ralph; 17 November 2021

To sign up for email alerts when CW3E post new AR updates click here.

*Outlook products are considered experimental