cw3e-web - Center for Western Weather and Water Extremes

Ranking Atmospheric Rivers: New Study Finds World of Potential

March 21, 2023

In a new study, titled Global Application of the Atmospheric River Scale, CW3E collaborators Bin Guan (UCLA) and Duane E. Waliser (JPL), along with CW3E director Marty Ralph explore a wider geographic application of the atmospheric river (AR) scale for characterizing strength and communicating potential impacts of ARs. This work contributes to the goals of CW3E’s 2019-2024 Strategic Plan to lead AR Research and Applications because the paper proposes the first globally uniform AR scale for facilitating communication about ARs and intercomparing across different regions.

CW3E Event Summary: 9-15 March 2023

20 March 2023

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Atmospheric Rivers Produce Heavy Precipitation and Flooding in California

Two atmospheric rivers (ARs) made landfall over California during 9–15 Mar
These ARs were characterized by the transport of very warm, moist air from the tropical North Pacific into the midlatitudes
The first AR brought AR3 conditions (based on the Ralph et al. 2019 AR Scale) and IVT magnitudes > 750 kg m^-1 s^-1 to Monterey and Santa Cruz Counties
The second AR brought AR2 conditions and IVT magnitudes > 500 kg m^-1 s^-1 to Central and Southern California
The heaviest precipitation fell during the first AR in the Central and Southern Sierra Nevada, with some locations recording > 12 inches in a 3-day period and sustained precipitation rates > 0.5 inches/hour
High freezing levels limited snowfall accumulations below 7,000 feet in both storms
Snow survey stations located above 7,000 feet recorded 7-day SWE increases > 12 inches
High reservoir inflows prompted dam operators to open the main spillway and increase releases to > 15,000 cfs at Oroville Dam after the first AR
The combination of heavy rainfall and melting snowpack led to widespread riverine flooding across Northern and Central California
The most destructive flooding occurred along the Pajaro River in the community of Pajaro, CA, and along the Kern River in Kernville, CA
An EF-1 tornado caused structural damage to mobile homes and farms in Tuolumne County

Click images to see loops of GFS IVT/IWV analyses Valid 0000 UTC 9 March – 0000 UTC 16 March 2023

Summary provided by C. Castellano, S. Bartlett, S. Roj, and J. Kalansky; 20 Mar 2023

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CW3E Welcomes Ali Wolman

March 20, 2023

Ali Wolman joined CW3E’s Field Team as a Lab Assistant in January 2023. She travels to field sites and launches weather balloons to collect profiles of temperature, pressure, wind & moisture data, which is used to better understand and predict atmospheric rivers (ARs). When she isn’t in the field, Ali is helping organize the field team’s equipment & spaces. Ali also is working to update hands-on climate science programming for K-12 classes.

Prior to SIO, Ali worked in ocean research and science education. After earning a BS in Biology at Cal Poly San Luis Obispo focused on marine biology & conservation, she continued to work around the Central Coast. Ali stayed involved at Cal Poly in research as a SCUBA tech and worked to develop video-data collection technology using artificial intelligence to identify organisms in videos of the ocean floor. Ali also worked for NOAA, teaching marine biology at an informal science teaching center in San Simeon, CA. Before joining CW3E, she taught hands-on, classroom science at the Elementary Institute of Science in San Diego, CA.

CW3E S2S Outlook: 17 March 2023

March 17, 2023

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Summary provided by J. Wang, C. Castellano, M. DeFlorio, and J. Kalansky; 17 March 2023

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CW3E AR Update: 17 March 2023 Outlook

March 17, 2023

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Atmospheric River Forecast to Bring Precipitation to Southern California

An atmospheric river (AR) developing in the Eastern Pacific is forecast to make landfall in Southern California on 20 March and persist in the region until 21 March
AR2 conditions (based on the Ralph et al. 2019 AR Scale) are forecast near San Diego, CA with AR1 conditions possible northward to San Luis Obispo, CA
AR3 conditions are forecast in Southern Arizona as a result of the inland penetration of this AR
There is still uncertainty between the GEFS and ECMWF EPS in the timing and intensity of AR conditions, including direction of IVT, which is leading to uncertainty in watershed precipitation forecasts over the next 7 days
The 00Z ECMWF is forecasting 3.10 inches of precipitation over the Santa Ana watershed over the next 7 days, while the 00Z GFS is forecasting 1.81 inches; a difference of 1.29 inches
The NWS Weather Prediction Center (WPC) is forecasting >1.5 inches of precipitation for Southern California coastal regions, >3 inches in the San Gabriel Mountains, and 1 inch over Central Arizona
Experimental excessive rainfall outlooks have been issued by the WPC for 21 March with a marginal risk (at least 5%) of rainfall exceeding flash flood guidance for much of Southern California and most of the Central Valley as well as Central Arizona

Click images to see loops of GFS IVT and IWV forecasts Valid 0000 UTC 17 March – 1200 UTC 22 March 2023

Summary provided by M. Steen, S. Roj, and S. Bartlett; 17 March 2023

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CW3E AR Update: 13 March 2023 Outlook

March 13, 2023

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Strong Atmospheric River to Bring Additional Heavy Precipitation and Flooding to California

Another atmospheric river (AR) will impact California this evening into Wednesday
AR3 conditions (based on the Ralph et al. 2019 AR Scale) are forecast near Santa Cruz, CA, while AR2 conditions are forecast over much of the remainder of coastal California between Sonoma County and San Diego County
Strong upslope moisture flux will support heavy precipitation over the Sierra Nevada, Central California Coast Ranges, and Transverse Ranges
The NWS Weather Prediction Center (WPC) is forecasting at least 3–7 inches of precipitation in these areas over the next 3 days, as well as 1–3 inches of precipitation in the lower elevations of coastal Southern California
Moderate precipitation amounts of 1–3 inches are also forecast in the higher terrain of the Colorado River Basin due to inland penetration of the AR
Heavy rain falling in areas with saturated soil conditions and high river/stream levels will likely produce major hydrologic impacts throughout California
The NWS WPC has issued a moderate-to-high risk of rainfall exceeding flash flood guidance in the vicinity of the Sierra Nevada, Coast Ranges, and Transverse Ranges through Wednesday morning
The California–Nevada River Forecast Center is currently forecasting 13 stream gages to rise above flood stage over the next 5 days
Similar to the previous storm, freezing levels will be relatively high, and a majority of the precipitation is forecast to fall as rain in watersheds along the Sierra Nevada
Extreme winter storm impacts are expected in the higher terrain of the Sierra Nevada, where up to 5 feet of snow are possible

Click images to see loops of GFS IVT and IWV forecasts Valid 1200 UTC 13 March – 1200 UTC 16 March 2023

Summary provided by C. Castellano, S. Bartlett, J. Kalansky, and S. Roj; 13 March 2023

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CW3E AR Update: 10 March 2023 Outlook

March 10, 2023

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Atmospheric River Continues to Bring Moisture and High Snow Levels to California with another Atmospheric River Forecast to Make Landfall in Northern California Shortly After

Current atmospheric river (AR) made landfall in Northern California around 10am PT 9 March and will continue to push moisture into California over the next couple days
IVT will values remain above 250 kg m^-1 s^-1 off the US West Coast ahead of the next AR which is forecast to make landfall on 14 March and bring AR2/3 conditions (based on the Ralph et al. 2019 AR Scale) to the majority of coastal Central California
There is substantial uncertainty between the GFS and ECMWF global models in the timing and location of AR conditions, including direction of IVT, which is mostly due to how each model handles the location of a pair of mid-level troughs
As compared to the GEFS, the ECMWF EPS has more confidence in a broader area of AR3 conditions for coastal areas around the San Francisco Bay area
The NWS Weather Prediction Center (WPC) has forecast 48-hour precipitation totals >2 inches over the Coast Ranges of Northern and Central California, >3 inches for the Western Transverse Range of Southern California and >5 inches over the Sierra
Experimental excessive rainfall outlooks have been issued by the WPC for Monday through Wednesday with a moderate risk (at least 40%) of rainfall exceeding flash flood guidance in the Northern Sierra and parts of the Northern California coast for Monday-Tuesday, and a moderate risk for the Sierra Nevada and Big Sur coast for Tuesday-Wednesday
The 00Z GFS is forecasting 11.31 inches of mean areal precipitation in the Upper Yuba watershed over the next 7 days, while the 00Z ECMWF is forecasting 8.11 inches over the same watershed, however, these totals include precipitation forecasted to fall during the current AR
Forecast freezing levels are expected to remain quite high (~2,000m) in the Sierra Nevada. This may lead to high fractions of most Sierra watersheds exposed to rain-on-snow

Click images to see loops of GFS IVT and IWV forecasts Valid 0000 UTC 10 March – 1200 UTC 16 March 2023

Summary provided by S. Roj, S. Bartlett, J. Cordeira, and J. Kalansky; 10 March 2023

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CW3E Winter 2022-23 Recap

CW3E 2022-23 Winter (Dec – Feb) Recap

March 8, 2023

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Wet Winter Helped Alleviate Drought Conditions and Produced Massive Snowpack

A family of 9 ARs made landfall between 26 Dec and 19 Jan and brought about half the of California’s precipitation during these three weeks.
Parts of the Central and Southern Sierras and some transverse ranges received 60+ inches.
Much of Central California received 100-150% of water year normal precipitation. Northeast and southeast California have received 50% or less of water year normal precipitation.
According to the US drought monitor there has been 3-5 class improvement in drought conditions over Central California and at least a class drought improvement over much of California.
Winter precipitation eliminated the 3-year drought deficit in 13% of the state.
SWE in the Southern Sierra went from 14% of April 1st at the beginning of December to 198% of April 1st SWE at the end of February.
By Mar 1, 9 reservoirs exceeded the historical average capacity, up from 1 on Dec 1 2022.
Water storage (reservoir +snowpack) in the Western Sierras increased from four-fold, with the greatest gains in the Southern Sierras.
As part of AR Recon there were 33 Intensive Observing Period (IOPs) which included 25 C130 flights, 18 GIV flights and the release of 1,186 dropsondes.
Precipitation and SWE totals during this winter are similar to Dec 2016– Feb 2017, with differences in the spatial patterns. In particular, northern CA received more precipitation in 2017 than this current winter.

CW3E Welcomes Laura Martin

March 7, 2023

Laura Martin joined CW3E as the Deputy Director of Administration in March 2023. She has previously worked in a wide variety of administration positions at UC San Diego that include Chief Administrative Officer of the Department of Visual Arts, Strategic Program Manager in the Office of the Dean of Arts and Humanities, and Program Manager at the Institute on Global Conflict and Cooperation. Before she worked at UC San Diego, she was a Conference Coordinator in Detroit, Michigan. Laura is an experienced manager with strong financial analysis, grant management, event and conference planning, writing, budgeting, and relationship-building skills. She received a Bachelors and Masters Degree in English from Oakland University in Rochester, Michigan.

As the Deputy Director of Administration Laura will be an executive member of the CW3E team focusing on the oversight of finance, human resources, facilities, and logistics and will serve as CW3E’s Chief Financial Officer. She is delighted to be able to support the important research occurring at CW3E.

CW3E AR Update: 6 March 2023 Outlook

March 6, 2023

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Warm Atmospheric River to Bring Heavy Precipitation, Potential Flooding to California Later This Week

An atmospheric river (AR) is forecast to make landfall in California later Thursday, bringing with it considerable rainfall to the region through Saturday
IVT > 750 kg m-1 s-1 is forecast during AR landfall along the coast of California, bringing AR 3/AR 4 conditions (based on the Ralph et al. 2019 AR Scale) to Central and Northern California
This AR is forecast to be a warm storm, with a broad region of 850-hPa temperatures > 0° C forecast over California during this storm period
The 00Z ECMWF is forecasting a stronger AR at coastal locations in Central California as compared to the GFS, while the GFS is forecasting a slightly longer duration of AR conditions along the coast
Models are showing low-to-moderate confidence in a second AR landfall in California early next week
The NWS Weather Prediction Center (WPC) has forecast 48-hour precipitation totals > 3 inches over the Coast Ranges of Northern and Central California and > 5 inches over the Sierra Nevada in association with the first AR
The 00Z ECMWF is forecasting considerably more precipitation (5.06 in) for the Russian River Watershed as compared to the 00Z GFS (1.32 in), highlighting significant model-to-model uncertainty with this event
GEFS ensemble has forecast freezing levels to rise rapidly, to nearly 6,000 feet across Northern California and the Sierra Nevada ahead of this AR
The combination of high freezing levels, heavy precipitation, and existing snowpack conditions will likely result in a substantial amount of rain-on-snow, thereby increasing runoff and the potential for flooding