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New Forecast Tool Looks Three Weeks Ahead for Chances of Atmospheric Rivers

New Forecast Tool Looks Three Weeks Ahead for Chances of Atmospheric Rivers – The Storm Type Key to Water Supply and Flooding, that Can Break U.S. West Coast Droughts, and Douse Wildfires

March 12, 2020

While the Pacific Northwest experienced serious flooding in January and February, areas farther south are bracing for drought after an extremely dry winter. People in these dry regions are hoping for a “Miracle March” to deliver substantial rain and snow to alleviate drought risk. However, a new experimental forecast tool looking out as far as three weeks shows little chance of this happening. The tool focuses on the odds of atmospheric rivers hitting the region over the next three weeks. Atmospheric river storms can deliver up to half of California’s total annual precipitation and cause 90 percent of flooding in the state, while a lack of enough of these storms can lead to drought.

The forecast tool has just been made available online at the Center for Western Weather and Water Extremes (CW3E) at Scripps Institution of Oceanography at UC San DIego. Developed in partnership with the NASA Jet Propulsion Laboratory, the tool displays forecasted atmospheric river (AR) occurrence at weeks 1-3 lead time. The public release of this product, and the underlying research supporting it, is part of a joint partnership between CW3E and NASA JPL, sponsored by the California Department of Water Resources, to improve the two-week to two-month lead time of forecasts, known as subseasonal-to-seasonal (S2S) forecasts. The aim of these improved forecasts of atmospheric rivers and precipitation is to benefit western U.S. water resource management.

This is the first CW3E subseasonal-to-seasonal (S2S) prediction product to be released to the public, and is based on the National Centers for Environmental Prediction (NCEP) Climate Forecast System (CFS) data. For weeks 1-2 (days 1-14 lead time), the daily probability of forecasted AR occurrence based on the fraction of CFS ensemble members that predict an AR occurring is displayed; for week-3, the forecasted anomaly of the number of AR days to occur during week-3 (days 15-21 lead time) is displayed. Forecasts are updated each Friday on the CW3E website, and the hindcast skill assessment associated with these forecast products is provided in DeFlorio et al. 2019b (JGR-Atmospheres, S2S Special Issue).

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. An example of the weeks 1-3 forecast products are shown below.

The product can be accessed at /iwv-and-ivt-forecasts/#S2S. An example of the outlook is included below.

Plain Language Summary of Weeks 1-3 AR Occurrence Outlook

This is a new forecast tool that makes a prediction of the likelihood of an AR occurring over the North Pacific/Western U.S. domain at weeks 1-3 lead time. For Week-1 and Week-2, the color shading represents the percentage chance of AR occurrence on each day into the future, from 1 to 15 day lead time. For Week-3, the bottom plot depicts the chances of above (blue) or below (red) average AR conditions based on long-term statistics in a given forecast model. Historical skill of these forecasts are very good during week-1, modestly higher than a prediction based on climatology at week-2, and no better than climatology (i.e. not very skillful) at week-3 over much of the entire region.

Figure 1: CW3E/JPL Weeks 1-3 AR occurrence outlook, issued February 10, 2020 and based on NCEP CFS forecast data. For weeks 1-2 (left and middle panels), the daily probability of AR occurrence is shaded based on the fraction of ensemble members that predict the occurrence on an AR at 00Z each day. For week-3 (right panel), the top plot shows the forecasted number of AR days during the week-3 (15-21 day lead) period; the middle plot shows the hindcast climatology of AR occurrence in the NCEP hindcast database; and the bottom plot shows the AR occurrence forecast anomaly for week-3 (top minus bottom plot).

DeFlorio, M. J., D. E. Waliser, F. M. Ralph, B. Guan, A. Goodman, P. B. Gibson, S. Asharaf, L. Delle Monache, Z. Zhang, A. C. Subramanian, F. Vitart, H. Lin, and A. 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, 11242-11265. https://doi.org/10.1029/2019JD031200

CW3E AR Update: 11 March 2020 Outlook

March 11, 2020

Click here for a pdf of this information.

A cutoff low and landfalling AR will bring heavy rainfall to the Desert Southwest

A cutoff low that has been impacting California since Monday will strengthen and interact with a remnant atmospheric river (AR) over the Baja Peninsula
This interaction will result in heavy rainfall across Southern California, southern Nevada, and west-central Arizona
Some areas in southern Arizona may experience another round of AR1 conditions
An additional 3+ inches of precipitation are possible over the eastern Transverse Ranges
Portions of the Sonoran and Mojave Deserts may receive 15–30% of average annual rainfall over the next 48 hours

Click IVT or IWV image to see loop of GFS analyses/forecasts Valid 1200 UTC 11 March – 1200 UTC 13 March 2020

Summary provided by C. Castellano and F. M. Ralph; 11 March 2020

*Outlook products are considered experimental

CW3E AR Update: 9 March 2020 Outlook

March 9, 2020

Click here for a pdf of this information.

A cutoff low and landfalling AR will bring moderate-to-heavy rainfall to portions of the southwestern U.S.

The interaction between a cutoff low off the California coast and tropical moisture over the Eastern Pacific will result in a landfalling atmospheric river (AR) over Baja California, Southern California, and Southern Arizona
Some areas in southern Arizona may experience 48 hours of AR conditions
The highest precipitation amounts (1–3 inches) are expected in Southern California and the Lower Colorado River Basin
More than 3 inches of precipitation are possible over the Transverse Ranges, Peninsular Ranges, and higher terrain in central Arizona

Click IVT or IWV image to see loop of GFS analyses/forecasts Valid 0000 UTC 9 March – 0000 UTC 14 March 2020

Summary provided by C. Castellano, C. Hecht, F. M. Ralph, and A. Wilson; 9 March 2020

*Outlook products are considered experimental

CW3E AR Update: 6 March 2020 Outlook

March 6, 2020

Click here for a pdf of this information.

A cutoff low and landfalling AR is forecast to bring moderate-to-heavy rainfall to portions of the southwestern U.S.

The interaction between a cutoff low off the California coast and tropical moisture over the Eastern Pacific is expected to result in a landfalling atmospheric river (AR) over Southern California and Arizona early next week
Some areas in coastal Southern California may experience at least AR2 conditions
The highest precipitation amounts are expected in Southern California, with 1–2 inches forecast over coastal and inland valley areas, and more than 2.5 inches possible over the Transverse and Peninsular Ranges

Click IVT or IWV image to see loop of GFS analyses/forecasts Valid 1200 UTC 8 March – 0000 UTC 12 March 2020

GEFS AR Landfall Probabilities: dProg/dt

Initialization Period: 1200 UTC 1 March – 1200 UTC 6 March 2020

Confidence in the probability of AR conditions along the Southern California coast has increased substantially over the past 5 days
As the loop demonstrates, run-to-run differences in forecast AR landfall probability were quite large until ~ 12Z 5 Mar
High uncertainty in AR conditions was driven primarily by uncertainty in the evolution of a cutoff low that will form over the Northeast Pacific Ocean during the next 48 hours

Summary provided by C. Castellano, L. Delle Monache, B. Kawzenuk, and F. M. Ralph; 6 March 2020

*Outlook products are considered experimental

CW3E Event Summary: 21-23 February 2020

February 25, 2020

Click here for a pdf of this information.

Cutoff low and landfalling AR bring heavy rainfall and mountain snowfall to southwestern U.S.

Southern Arizona experienced weak-to-moderate AR conditions for more than 24 hours [AR1/AR2 based on the Ralph et al. (2019) AR Scale]
Some locations in central AZ received more than 2 inches of total precipitation from this event
Significant snowfall (> 8 inches) also occurred over the higher terrain in south-central UT and central CO

MIMIC-TPW2 Total Precipitable Water

Valid 1200 UTC 20 February – 1200 UTC 23 February

Images from CIMSS/Univ. of Wisconsin

GOES-West GeoColor

Valid 2201 UTC 21 February – 0001 UTC 22 February

Images from NOAA/NESDIS/STAR and CIRA/NOAA

Summary provided by C. Castellano, C. Hecht, B. Kawzenuk, N. Oakley, and F. M. Ralph; 25 February 2020

CW3E Fosters Closer Connections at the Head of the Yampa River in Steamboat Springs, CO

February 24, 2020

Early this February, CW3E Ph.D. students Kara Voss and Mike Sierks visited Steamboat Springs, Colorado to learn more about the headwaters of the Colorado River, meet with key stakeholders in the area, and share information about the connections between the work of CW3E and water issues in the region. This coming June CW3E is set to co-host the annual Yampa Basin Rendezvous (YBR) for the third consecutive year. The YBR is an annual conference held at Colorado Mountain College where members of the Steamboat community, including commercial, agricultural and recreational users of water from the Yampa River, gather with other organizations including CW3E to learn and share information about how to use climate and meteorological information to improve the resilience of their community. YBR is an effort to connect graduate students, post-doctoral scholars, researchers, staff and faculty from CW3E to river basins throughout the west, to pursue the mission and goals of this new center. CW3E is based at the University of California San Diego’s (UCSD) Scripps Institution of Oceanography and is building a regional community of scientists and engineers to work on western weather and climate problems.

Two members of the YBR Steering committee — Sarah Jones, the former director of the Yampa Valley Sustainability Council and current Sustainability and Community Engagement Director for Steamboat Ski Resort, and Nathan Stewart, Professor at Colorado Mountain College, graciously hosted Kara and Mike’s visit allowing them to connect with individuals from a variety of sectors. Mike and Kara met with local water managers, the Colorado State Forest Service, Steamboat Ski Resort, and local government officials responsible for Steamboat’s climate action plan. The goal of these meetings was to learn about the different groups’ planning and operations and understand how CW3E’s expertise could overlap with their work in the future. Mike and Kara gave several guest lectures at Colorado Mountain College and at the local high school, sharing CW3E’s work with an audience of enthusiastic students, and gave Steamboat Ski Resort’s first science ‘Brown Bag’ talk discussing how changing climate has been observed to influence snowpack in the western U.S. over recent decades. Mike and Kara also met with scientists at Storm Peak Laboratory, a cloud and aerosol microphysics observing laboratory located at the top of Steamboat Ski Resort, to discuss future collaboration and research directions. Between skiing to meetings, talking about cool science, and engaging with fascinating and warm members of the Steamboat Springs community, the Ph.D. candidates expressed that they never thought a work trip could be this good!

This meeting represents a continuing connection between Steamboat Springs, home of the Yampa River (headwaters of the Colorado River), and CW3E, based in San Diego (which gets a significant amount of water via the Colorado River).

CW3E AR Update: 20 February 2020 Outlook

February 20, 2020

Click here for a pdf of this information.

A cutoff low and landfalling AR will bring moderate-to-heavy rainfall to portions of the southwestern U.S.

The interaction between a cutoff low off the California coast and tropical moisture over the Eastern Pacific will result in a landfalling AR over Baja California
As time progresses, the AR will intensify and move northeastward across Arizona and New Mexico
Some areas in southern AZ are forecast to experience AR2 conditions
More than 0.5 inches of precipitation are forecast over portions of the southwestern U.S., with the highest amounts (> 1.5 inches) expected over the higher terrain in central and eastern AZ, as well as the San Juan Mountains in CO

Click IVT or IWV image to see loop of GFS analyses/forecasts Valid 1200 UTC 20 February – 1200 UTC 23 February 2020

Summary provided by C. Castellano and F. M. Ralph; 20 February 2020

*Outlook products are considered experimental

CW3E Welcomes Dr. Peter Gibson

February 20, 2020

Dr. Peter Gibson joined CW3E in February 2020. Originally from New Zealand, he earned a B.S. with a double major in Mathematics and Physical Geography from the University of Otago (2012). His MS thesis (2014), also from the University of Otago, focused on how synoptic weather types influence regional variability and reliability in New Zealand’s wind energy resource. Peter then moved to Australia to complete his doctoral thesis (2017) at the University of New South Wales, where his research focused on better understanding the large-scale drivers of Australian heatwaves in a changing climate. After completing his PhD, Peter moved further abroad to California and worked as a postdoctoral researcher at NASA’s Jet Propulsion Laboratory under supervision of Duane Waliser (2017-2020). During this time, his research focused primarily on drought and atmospheric ridging/blocking across the western United States, including examining sources of predictability and model skill on subseasonal-to-seasonal (S2S) timescales.

At CW3E, Peter will serve as a Senior Researcher on S2S projects. He will research S2S skill of operational hindcast systems in terms of probabilistic forecasts of atmospheric ridging/blocking and atmospheric rivers. Informed by these skill assessments, he will continue to develop the suite of S2S operational products for the Center. Peter will also test and implement novel machine learning approaches for longer-lead seasonal prediction of drought and atmospheric rivers.

Three Aircraft Set to Sample Atmospheric River This Afternoon

February 14, 2020

As part of Atmospheric River Reconnaissance, in collaboration with the US Air Force 53^rd Weather Reconnaissance Squadron and the National Oceanic and Atmospheric Administration (NOAA) Aircraft Operations Center, there will be three reconnaissance aircraft sampling an Atmospheric River over the northwest Pacific Ocean this afternoon. Flights will be centered on 0000 UTC 15 February 2020 in an effort to increase data assimilated into the global weather models. Planned flight tracks are shown below where 80 dropsondes (25 from each Air Force C-130 and 30 from the NOAA G-IV) will be released to measure temperature, humidity, pressure, and winds throughout the atmosphere. This will be the eighth intensive observing period (IOP) flown this winter as part of AR Recon, and the third with three aircraft.

Planned flight tracks of two USAF C-130 and NOAA G-IV aircraft over NCEP GFS 42-hour forecast of integrated vapor transport (kg m^-1 s^-1; shaded and vectors) and sea level pressure (hPa; contours) valid at 000 UTC 15 February 2020.

These data will be assimilated into the global atmospheric models in an effort to improve what has been a very uncertain forecast. Over the past several days various weather models have shown a great deal of uncertainty in forecasting the strength and timing of this AR, as well as the precipitation associated with it (more information below). Although this AR is not very strong (currently forecasted to be an AR 1 according to the AR Scale; Ralph et al. 2019, it will make landfall over the Pacific Northwest following a very wet period that resulted in the current high soil moisture, which increases the likelihood of runoff with several rivers already at an elevated stage.

NOAA G-IV taking off out of Portland International Airport on 6 February 2020 for AR Recon IOP 6 (Photo credit: Jack Parrish; NOAA).

CW3E researcher Forest Cannon practices using a survival suit as part of pre-flight protocol.

For more information about Atmospheric River Reconnaissance visit /arrecon_overview/.

For AR forecasts visit the CW3E AR forecasts webpage, and for precipitation and streamflow forecasts visit the Northwest River Forecast Center or the Weather Prediction Center.

CW3E Welcomes Marian de Orla-Barile

February 12, 2020

Marian de Orla-Barile joined CW3E as a lab assistant in January 2020. He completed his B.S. in electrical engineering at California State University, Long Beach in 2018. While an undergraduate, Marian received funding from the NIH diversity research initiative, BUILD, to work as a student researcher where he performed water quality testing of various contaminants
within the Los Angeles River watershed to study storm drain contributions during the dry weather season.

After graduating, Marian worked as a summer intern in 2019 for CW3E with Dr. Forest Cannon on a project focused on documenting the occurrence of narrow cold-frontal rainband (NCFR) episodes within Southern California using archived NEXRAD radar imagery.

As a newly hired lab assistant, Marian’s focus is to continue to expand the work on NCFR impacts within Southern California, as well as to lead radiosonde launches in the Yuba watershed to support the objectives of the Forecast Informed Reservoir Operations program.

Marian hopes to continue to grow his knowledge base in meteorology through his work at CW3E and is excited to continue to contribute meaningful work to his home state of California.