AR Recon Makes Headlines in New York Times and LA Times

AR Recon Makes Headlines in New York Times and LA Times

February 2, 2023

AR Recon, a CW3E led program in partnership with NCEP and Airforce, has made headlines in both the New York Times and the LA Times in recent weeks. Reporters from both papers had a chance to fly on NOAA’s G-IV and talk to CW3E Director, Marty Ralph (PI of AR Recon) and Anna Wilson (AR Recon Coordinator). For the full articles, please use the links below.

NY Times: Getting Inside California’s Wild Weather, 8 Miles Over the Pacific

LA Times: How do you track an atmospheric river? Climb aboard this highflying reconnaissance jet

Marty Ralph, center, watches as meteorologists Rich Henning, left, and Sofia de Solo track data while flying above an atmospheric river over the Pacific Ocean. (Ian James / Los Angeles Times)

CW3E Publication Notice: A 440-Year Blue-Oak Reconstruction of Heavy Precipitation in California

CW3E Publication Notice

A 440-Year Blue-Oak Reconstruction of Heavy Precipitation in California

February 2, 2023

Ian Howard, a post-doc from the University of Arkansas and CW3E collaborator, alongside co-authors David W. Stahle (University of Arkansas), Michael D. Dettinger (CW3E), Cody Poulsen (CW3E), F. Martin Ralph (CW3E), Max C.A. Torbenson (Johannes Gutenberg University), and Alexander Gershunov (CW3E), have published a paper titled “A 440-Year Reconstruction of Heavy Precipitation in California From Blue Oak Tree Rings” in the American Meteorological Society’s Journal of Hydrometeorology. This research advances the goals of CW3E’s 2019-20024 Strategic Plan by its contribution to Atmospheric Rivers Research and Applications, quantifying longer-than-instrument-period variations of extreme precipitation in Northern California through a novel analysis of blue-oak ring-width chronologies. The strong relationship between certain blue oak chronologies and total water year precipitation (correlation, r ≥ 0.90) has been known for years (Stahle et al. 2013). However, this study (Howard et al. 2023) advances our understanding of this relationship by discovering that some blue oak chronologies are equally well correlated (r = 0.82) with annual totals of just the heavy-precipitation fraction of precipitation (daily totals ≥ 1 in, ≈95th percentile of historical daily totals). In contrast, the correlation with non-heavy precipitation totals using the same chronologies is much weaker (daily totals < 1 inch; r = 0.55). On average, heavy precipitation accounts for only 39% of water year totals in the study region but largely determines year-to-year precipitation variations. Thus, as noted in previous studies of California heavy-precipitation variability (e.g., Dettinger and Cayan 2014), these days of heavy precipitation dictate most of the occurrence of our droughts and flood years.

The study developed a reconstruction of heavy-precipitation totals in northern California from 1582-2021 (Fig. 1), 440 years in all. The reconstruction identifies decadal to multi-decadal surges in extreme precipitation totals and volatility. Return-period estimates based on the 440-year heavy-precipitation reconstruction are quite close to recurrence estimates based on just the instrumental record. This suggests that the 73 yearlong instrumental record over the study area provides a good representative of the variance in heavy precipitation during the last 440 years (Fig. 2). Finally, a comparison of annual landfalling atmospheric river counts to the reconstructed and instrumental heavy precipitation records shows large contributions of atmospheric rivers to the variations of heavy precipitation and blue oak growth (Fig. 3).

Figure 1: (a) The tree-ring reconstruction of heavy precipitation totals in the northern California study area are plotted (gray) along with the sub-decadal smooth values (black) and the heavy instrumental totals (red). The reconstruction extends from 1582-2004 and the CPC instrumental observations are appended from 2005-2021. The mean and upper and lower 20th percentiles computed for the full period 1582-2021 are also plotted. The reconstruction and instrumental values are correlated from 1949-2004 at r = 0.82.

Figure 2: Return periods and probabilities are plotted for the instrumental and reconstruction heavy precipitation totals (daily amounts ≥25.4mm). The black line connects the discrete return periods computed for the full 440-year reconstruction (1582-2021) and the blue dots are return periods for non-overlapping 50-year intervals in the reconstruction. Instrumental return periods are plotted for 1949-1998 (orange circles) and 1949-2021 (squares). Reconstructed return periods restricted to 1949-1998 are also plotted for comparison (red circles).

Figure 3: (a) Instrumental heavy precipitation (a) was correlated with gridded AR counts (Gershunov et al. 2017) on the specific days each year when heavy precipitation (≥25.4mm) was measured for the study area in northern California. These days of heavy precipitation vary from 2 to 28 days (1949 and 2017, respectively). (b) Non-heavy precipitation was also correlated with gridded AR counts on the corresponding non-heavy days also defined for northern California. The regional blue oak chronology was correlated with gridded AR count on the days with (c) heavy and (d) non-heavy precipitation in the study area [p <0.05 for all correlations mapped, 1949-2004, contour intervals plotted above 0.80 in (a), above 0.60 in (c)]. Note the area of highest correlations (>0.95) near Monterey Bay in (a). (e) A photomicrograph of ring porous annual rings in blue oak from Mt. Diablo is reproduced for 1980-1995, along with the count of landfalling ARs near the Golden Gate to illustrate the proportionality between oak growth and AR-delivered heavy precipitation. The annual rings are oriented vertically, and two medullary rays run horizontally through the ring sequence.

Dettinger, M., & Cayan, D. R. (2014). Drought and the California delta – A matter of extremes. San Francisco Estuary and Watershed Science, 12,, 1-6. https://doi.org/10.15447/sfews.2014v12iss2art4

Howard, I. M., Stahle, D. W., Dettinger, M. D., Poulsen, C., Ralph, F. M., Torbenson, M. C. A., & Gershunov, A. (2023). A 440-Year Reconstruction of Heavy Precipitation in California from Blue Oak Tree Rings*. Journal of Hydrometeorology (published online ahead of print). https://doi.org/10.1175/JHM-D-22-0062.1

Stahle, D. W., Griffin, R. D., Meko, D. M., Therrell, M. D., Edmondson, J. R., Cleaveland, M. K., Stahle, L. N., Burnette, D. J., Abatzoglou, J. T., Redmond, K. T., Dettinger, M. D., & Cayan, D. R. (2013). The Ancient Blue Oak Woodlands of California: Longevity and Hydroclimatic History. Earth Interactions, 17, 1-23. https://doi.org/10.1175/2013EI000518.1

CW3E AR Update: 1 February 2023 Outlook

CW3E AR Update: 1 February 2023 Outlook

February 1, 2023

Click here for a pdf of this information.

Multiple Atmospheric Rivers Forecast to Bring Precipitation to the US West Coast

  • Two atmospheric rivers (ARs) are forecast to make landfall along the US West Coast over the next several days
  • An AR 2 (based on the Ralph et al. 2019 AR Scale) is currently forecast in southern coastal Oregon, where weak AR conditions may persist for more than 48 hours across both storms
  • The NWS Weather Prediction Center is forecasting 2–4 inches of total precipitation in the Pacific Coast Ranges, Cascades, and Sierra Nevada during the next 5 days, with higher amounts possible in the Olympic Mountains
  • Significant snowfall accumulations are possible in the Olympic Mountains and North Cascades during the first storm, as well as in the Sierra Nevada during the second storm
  • Freezing levels in the Sierra Nevada are forecast to drop during the second AR, allowing for accumulating snowfall below 5,000 feet

Click images to see loops of GFS IVT and IWV forecasts

Valid 1200 UTC 1 February – 1200 UTC 6 February 2023


 

 

 

 

 

 

Summary provided by C. Castellano, S. Bartlett, J. Kalansky, and S. Roj; 1 February 2023

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

*Outlook products are considered experimental

AR Recon Milestones – Flight Plans for the Gulf of Mexico and Atlantic Ocean

AR Recon Milestones – Flight Plans for the Gulf of Mexico and Atlantic Ocean

January 25, 2023

The Atmospheric River Reconnaissance (AR Recon) field campaign recently achieved a milestone by having designed and received official tasking for observational flights over the Gulf of Mexico and the Atlantic Ocean along the U.S. East Coast. These flights were scheduled to be centered at 00Z 25 Jan and 00Z 26 Jan, respectively, tracking an intense AR as it develops over the western Gulf of Mexico and moves rapidly eastward in association with a deepening low pressure system over the Eastern U.S. (requested flight tracks shown below).

This storm is predicted to produce severe weather across portions of the Southeastern U.S., as well as a broad swath of ~6″ snowfall across the Central and Eastern U.S.

The planning process for these flights included evaluation of scientific objectives within different geographic environments, consideration of a more complex network of flight avoidance zones, and coordination amongst the CW3E AR Recon Team, US Air Force Reserve Command, NCEP, WPC, and other NWS offices. In order to prepare for this event, the team used a weaker storm system taking a similar track on 22 and 23 Jan as a test case — mocking up flight paths and running through the process for gaining approval. In addition, a Pacific flight was also planned for the same day (00Z 26 Jan) as the Atlantic flight, another first for AR Recon.

The significance of this achievement is that formerly, AR Recon operations were limited to the Northeast Pacific Ocean, where ARs impacting the Western U.S. typically originate. The ability to sample storms developing in the Gulf of Mexico or just off the U.S. East Coast means that portions of the Central and Eastern U.S. can also benefit from increased forecast skill as a result of additional observations provided by AR Recon.

AR Recon is led by PI Marty Ralph (CW3E) and Co-PI Vijay Tallapragada (NCEP).

CW3E Welcomes Dr. Vesta Afzali Gorooh

CW3E Welcomes Dr. Vesta Afzali Gorooh

January 10, 2023

Vesta is a Postdoctoral Scholar-Employee at the Center for Western Weather and Water Extremes (CW3E) at Scripps Institution of Oceanography, the University of California San Diego, where she joined in January 2023. Her research interest lies at the intersection of hydrometeorology and remote sensing disciplines with an emphasis on the application of machine learning methods in satellite retrieval systems.

At CW3E, Vesta’s research activities will involve developing quantitative precipitation estimation algorithms and short-term precipitation forecasts at high spatiotemporal resolution using machine learning techniques. This research aligns with her Ph.D. work, which she completed in Civil and Environmental Engineering in December 2022 at the Civil and Environmental Engineering Ph.D. program at UC Irvine, under the supervision of Prof. Soroosh Sorooshian in the Center for Hydrometeorology and Remote Sensing. Since her Ph.D. time, she has been working on fusing multispectral images derived from geostationary satellites with Low-Earth-Orbit active and passive microwave measurements to retrieve surface precipitation rates at high spatiotemporal resolution.

During her Ph.D., Vesta was named Future Investigator by NASA Earth and Space Science and Technology to implement deep learning architectures for cloud type classification and precipitation estimation using CloudSat Cloud Profiling Radar and the new generation of NOAA and NASA’s geostationary platforms. She interned at NASA Ames Research Center in 2018 and Earth System Science Interdisciplinary Center (ESSIC) in 2022 while completing her graduate degree. To date, she has produced over a dozen scientific articles, which have been disseminated in peer-reviewed scientific and technical journals. She will continue her work through widespread collaboration, peer-reviewed journal publications, and conference presentations.

CW3E 2023 Undergraduate Summer Internship Program Now Accepting Applications

CW3E 2023 Undergraduate Summer Internship Program Now Accepting Applications

January 10, 2023

Interested in developing your research skills while working on cutting-edge water cycle science? Our summer internship program provides summer research opportunities to undergraduate students on projects regarding U.S. West Coast weather phenomena such as atmospheric rivers, hands-on field science, and the impacts of climate change. In addition to research, the internship program offers professional development programming designed to help prepare our interns for whatever lies beyond their undergraduate experience. No prior research experience is required, so all undergraduate students with an interest in CW3E’s research areas are invited to apply!

Our paid 9-week program is expected to run from June 20th to August 18th, 2023 (exact dates are tentative). Interns can expect to be paid $18/hour for 35-40 hours/week during the 9-week period. In addition, paid dormitory housing will be provided on the UC San Diego campus.

For more details about the 2023 CW3E Summer Internship Program, please see our webpage. To apply, click here. The last day to apply is Feb 12th, and applicants can expect to hear back by the end of March.

To see a list of previous years’ interns and research projects, click here.

Please contact Weiming Hu for additional information at weiminghu@ucsd.edu.

CW3E AR Update: 10 January 2023 Outlook

CW3E AR Update: 10 January 2023 Outlook

January 10, 2023

Click here for a pdf of this information.

Increased Atmospheric River Activity Forecast to Continue over California during the next 7–10 days

  • A strong atmospheric river (AR) made landfall Sunday night, resulting in very heavy rainfall and flooding in portions of Central and Southern California
  • This episode of increased AR activity across the Western U.S. is forecast to continue with four additional ARs predicted to make landfall over the next week
  • The first AR will bring long duration and southerly AR conditions to a portion of the North-Coast tomorrow into Friday
  • The storm track is forecast to shift southward as two additional ARs are forecast to make landfall over Central California on Saturday and Sunday
  • A fourth AR is then forecast to make landfall next week over Northern California, though there is large forecast uncertainty associated with this fourth AR
  • The NOAA Weather Prediction Center has issued a slight risk for precipitation to exceed flash flood guidance where the first AR is forecast to extend inland for several days
  • Large model-to-model uncertainty in precipitation forecasts currently exists over the Russian River watershed as any slight shift in the location of the first AR will result in large differences in AR magnitude and duration
  • Stay alert to official NWS forecasts, watches, and warnings at weather.gov and follow guidance from local emergency management officials

Click images to see loops of GFS IVT and IWV forecasts

Valid 1200 UTC 10 January – 1200 UTC 18 January 2023


 

 

 

 

 

 

 

 

 

 

Summary provided by C. Hecht, C. Castellano, S. Bartlett, J. Kalansky, and F. M. Ralph; 10 January 2023

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

*Outlook products are considered experimental

CW3E AR Update: 5 January 2023 Outlook

CW3E AR Update: 5 January 2023 Outlook

January 5, 2023

Click here for a pdf of this information.

Atmospheric Rivers Forecast to Continue to Bring Additional Precipitation to Northern and Central California

  • A family of ARs (Fish et al. 2019) is forecast to make landfall beginning Friday, continuing into early next week
  • The first AR is forecast to make landfall late in the day Friday 6 Jan and bring a period of IVT > 400 kg/ms into Northern and Central California
  • Before AR conditions from the first AR completely dissipate, a second AR associated with a surface low-pressure system is forecast to bring a stronger pulse of IVT > 600 kg/ms to the same areas, resulting in AR 2 conditions (based on the Ralph et al. 2019 AR Scale)
  • The third and strongest AR is forecast to make landfall along the coast of Northern California with IVT exceeding 750 kg/ms resulting in AR 3/AR 4 conditions in the region, although considerable uncertainty remains in the exact timing, intensity, duration, and position of this system
  • The NWS Weather Prediction Center is forecasting more than 7 inches of precipitation for a broad area over coastal Northern and Central California, the Southern Cascades, and Sierra Nevada
  • NWS WPC has also issued excessive rainfall outlooks for multiple days during this period, highlighting the hazard posed by additional rainfall on soils which are currently saturated
  • Precipitation forecast for watersheds across Northern and Central California currently exceed 8 inches over a 7-day period, with the North Fork Feather > 10 inches over this forecast period
  • The NWS California Nevada River Forecast Center has forecast streamflow to exceed flood stage at multiple locations in California in association with the precipitation from this sequence of ARs
  • A period of active weather will continue for the US West Coast next week, stay tuned to CW3E for future AR Outlooks and Quick Looks
  • Stay alert to official NWS forecasts, watches, and warnings at weather.gov and follow guidance from local emergency management officials

Click images to see loops of GFS IVT and IWV forecasts

Valid 0000 UTC 6 January – 0900 UTC 11 January 2023


 

 

 

 

 

 

 

 

 

Summary provided by S. Bartlett, S. Roj, C. Castellano, J. Kalansky, and F. M. Ralph; 5 January 2023

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

*Outlook products are considered experimental

CW3E Event Summary: 29 December 2022 – 1 January 2023

CW3E Event Summary: 29 December 2022 – 1 January 2023

January 4, 2023

Click here for a pdf of this information.

Atmospheric River Brings Record-Breaking Precipitation to California

  • A strong atmospheric river (AR) made landfall over Northern California on 29 Dec
  • AR 1/AR 2 conditions (based on the Ralph et al. 2019 AR Scale) were observed across much of coastal California
  • While the initial pulse of moisture transport produced little precipitation, two additional stronger pulses produced heavy precipitation across portions of Northern and Central California on 30–31 Dec
  • More than 5 inches of storm-total precipitation fell across the San Francisco Bay Area, while more than 10 inches fell over portions of the Sierra Nevada
  • More than 3 feet of snow fell in the higher terrain of the Central and Southern Sierra Nevada
  • Warm air associated with this AR limited snowfall accumulations in the Northern Sierra Nevada
  • The combination of heavy rainfall and high antecedent soil moisture and streamflow conditions led to riverine and urban flooding
  • Multiple levee breaks along the Cosumnes River caused major flooding on Highway 99 and led to water rescues and at least one fatality
  • Heavy rain falling on nearly saturated soils triggered mudslides and rockslides in Northern and Central California
  • Strong winds downed trees and power lines, resulting in numerous power outages in the Sacramento area
  • The severe flooding along the Cosumnes River was poorly forecast at lead times < 48 hours due to large errors in precipitation forecasts, which substantially underestimated the observed precipitation in the Upper Cosumnes watershed

MIMIC-TPW2 Total Precipitable Water

Valid 0000 UTC 29 December 2022 – 0600 UTC 1 January 2023

Click images to see loops of NAM IVT/IWV analyses

Valid 0000 UTC 29 December 2022 – 0000 UTC 2 January 2023


 

 

 

 

 

 

 

 

 

 

Summary provided by C. Castellano, S. Bartlett, J. Kalansky, S. Roj, and F.M. Ralph; 4 January 2023

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

*Summary products are considered experimental

CW3E AR Update: 3 January 2023 Outlook

CW3E AR Update: 3 January 2023 Outlook

January 3, 2023

Click here for a pdf of this information.

Atmospheric River to Bring Significant Rainfall to Northern and Central California

  • An atmospheric river in association with a strong low-pressure system over the North Pacific will bring significant precipitation to Northern California between Wednesday morning and Thursday afternoon
  • IVT associated with this AR will exceed 750 kg m-1 s-1 along the coast of Northern California, making this an AR 3 based on the Ralph et al. 2019 AR Scale
  • This AR will be the first of three landfalling ARs over the next 7 days, with the following two ARs also forecast to impact Northern and Central California with additional precipitation over the weekend and into early next week
  • The NWS Weather Prediction Center (WPC) has forecast 7-day precipitation totals to exceed 15 inches along the coast of Central California and the Northern Sierra Nevada
  • NWS WPC has issued a moderate risk for excessive rainfall with the potential for flash flooding along much of coastal California over the coming days, highlighting the enhanced risk due to saturated antecedent soil conditions
  • Precipitation forecasts over the next 7 days for watersheds in northern California and the Northern Sierra are between 6–8 inches, with the ECMWF forecasting higher precipitation totals along the coast and less in the Sierra Nevada compared to the GFS
  • NWS Weather Forecast Offices have begun issuing watches and warnings for flood, high wind, and winter weather hazards in association with this AR
  • The NWS California Nevada River Forecast Center (CNRFC) has forecast multiple rivers to exceed flood stage in association with the precipitation from this AR
  • Stay alert to official NWS forecasts, watches, and warnings at weather.gov and follow guidance from local emergency management officials

Click images to see loops of GFS IVT and IWV forecasts

Valid 1200 UTC 3 January – 1200 UTC 10 January 2023


 

 

 

 

 

 

 

 

 

 

 

 

 

Summary provided by S. Bartlett, S. Roj, C. Castellano, J. Kalansky, and F. M. Ralph; 03 January 2023

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

*Outlook products are considered experimental

CW3E AR Update: 28 December 2022 Outlook

CW3E AR Update: 28 December 2022 Outlook

December 28, 2022

Click here for a pdf of this information.

Click images to see loops of GFS IVT & IWV forecasts

Valid 1200 UTC 28 December – 1200 UTC 07 January 2022


 

 

 

 

 

 

 

 

 

 

 

 

 

Summary provided by J. Cordeira & C. Hecht; 28 December 2022

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

*Outlook products are considered experimental