0 - 2020 - Center for Western Weather and Water Extremes

CW3E Event Summary: 01-04 December 2020

December 4, 2020

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Southeast Alaska Pounded by Atmospheric River while California’s Fire Season Persists into December

A persistent high pressure and ridge has set up in the eastern Pacific and has directed all AR activity poleward towards Alaska and British Columbia
AR landfall over the Alaska Panhandle has resulted in AR 4 conditions, heavy precipitation, flooding, and debris flows
Several locations in southeastern Alaska broke daily and 48-hour precipitation records
The heavy precipitation triggered a landslide in Haines, AK leaving dozens of homes uninhabitable and prompting search and rescue efforts
On the opposite end of the spectrum, the offshore flow around the southeastern portion of the high pressure created a strong Santa Ana wind event over Southern California where wind gusts >80 mph were recorded and several fires were sparked during the dry and gusty conditions

MIMIC-TPW2 Total Precipitable Water

Valid 0000 UTC 30 November – 1600 UTC 04 December

Click images to see loops of GFS IVT/IWV analyses Valid 0000 UTC 30 November – 1200 UTC 04 December 2020

Summary provided by C. Hecht, C. Castellano, B. Kawzenuk, J. Kalansky, J. Cordeira, and F. M. Ralph; 04 December 2020

Past Yuba Water Agency General Manager Curt Aikens Honored with Association of California Water Agencies’ Lifetime Achievement Award

December 3, 2020

During the Association of California Water Agencies (ACWA) Annual Meeting this year, CW3E partner Curt Aikens was honored with ACWA’s Lifetime Achievement Award, acknowledging his many accomplishments throughout his career. His acceptance speech can be viewed here.

Each year since 2002, ACWA’s Lifetime Achievement Award recognizes individuals who, throughout the course of their career, have made remarkable and lasting contributions to the California water community. The award is presented at the discretion of the ACWA Executive Director in consultation with the ACWA President and Vice President.

CW3E offers our deepfelt congratulations on this well-deserved honor recognizing Curt’s many impactful accomplishments, including the Yuba Accord, Forecast Coordinated Operations, and playing a lead role to bring a FIRO viability assessment to New Bullards Bar. We are grateful for the opportunity to work with this visionary and collaborative leader, and the truly amazing team that he has created and nurtured during his years at Yuba Water Agency.

CW3E Field Team Installs New Meteorological Stations Ahead of WY2021

November 25, 2020

The CW3E Field Team installed two new observation sites and added additional instrumentation and performed maintenance on existing stations in the Yuba watershed between August-November 2020. The two new sites installed are soil meteorology (SMOIL) stations: North Star Meadow (NSM) and Lower Bath House (LBH). The sites are located near Strawberry Valley, CA and at San Francisco State University’s Sierra Nevada Field Campus near Bassetts, CA, respectively. These are two regions of the watershed previously lacking soil moisture observational data and add to the four existing CW3E stations installed for the Yuba-Feather Forecast Informed Reservoir Operations (FIRO) project,which researches opportunities at Lake Oroville and New Bullards Bar reservoir to improve reservoir operations and reduce flood risks by improving weather and runoff forecasts.

When conditions permit at the end of the winter season, a disdrometer will be installed at LBH to better observe the precipitation phase and understand the rain-snow transition during impactful atmospheric rivers (ARs) in the Sierra Nevada. Real-time communications will also be added at both new sites and data will be disseminated on CW3E’s website as well as MesoWest, NOAA HMT, and CDEC. The field team was also able to install GPS and conduct maintenance work at other CW3E sites in the Yuba to support Yuba/Feather FIRO activities before the wet season began. For more information on FIRO, visit the FIRO web page.

CW3E would especially like to thank SFSU’s Sierra Field Campus for their help and collaboration on the installation of LBH. We look forward to our continued partnership!

Figure 1: CW3E newest SMOIL stations: North Star Meadow (NSM) (left) near Strawberry Valley, CA on a smoke-free day in October, and Lower Bath House (LBH) (right) after the first snow of the season on 18 November.

Figure 2: Installation and maintenance of new and existing stations in the Yuba Watershed by CW3E Field Researchers. Top, From Left: Ava Cooper installs GPS at DLA; Carly Ellis digs a soil pit at NSM; Kerstin Paulsson digs hole for precip pole at LBH. Bottom, from Left: Kerstin Paulsson digs a trench for electrical at LBH; Ava Cooper connects soil sensors to the datalogger at NSM; Ava Cooper tests sensor connection at DLA; Kerstin Paulsson and Carly Ellis install GPS at NBB.

CW3E Welcomes Luke Odell

November 23, 2020

Luke Odell joined CW3E as a postdoctoral researcher, specializing in mesoscale dynamics and modeling, in November 2020. Luke received his Ph.D. in atmospheric science from the University of Wisconsin-Madison under the supervision of Professor Gregory Tripoli, and BSc. and MSc. in meteorology and environmental science from the University of Leeds in the U.K., under the supervision of Professor Peter Knippertz.

His Ph.D. research focused primarily on supercell thunderstorm dynamics, particularly processes involved in torrnadogenesis, from a theoretical and numerical modeling perspective. For his doctoral dissertation, Luke applied fluid dynamics theory to develop new parameters for describing and evaluating flow instabilities and vorticity evolution associated with tornadogenesis. Utilizing these parameters in the context of real-world and idealized mesoscale numerical model simulations of supercells, he developed new conceptual understanding of the physical process of tornadogenesis. Luke was an invited panelist at the ‘17^th cyclone workshop’ as a result of this work.

While his Ph.D. research focused on supercells, Luke has a comprehensive understanding of fluid dynamics, relating to turbulence and instability, and a broad range of atmospheric dynamics from the misoscale to the synoptic scale. His master’s research used the WRF model to investigate rapid cyclogenesis of the Braer storm over the North Atlantic in early 1993. This study culminated in the David Kay award for academic excellence of a master’s thesis and a first-author publication. Luke has recently applied his combined knowledge to a wide range of atmospheric scales, to study atmospheric instabilities and energy transfer associated with tropical cyclones, extra-tropical cyclogenesis and atmospheric river development.

Luke taught a number of undergraduate courses as a TA during his Ph.D., including ‘introduction to weather and climate’, ‘introduction to atmospheric physics’, and ‘mesoscale meteorology’. He also instructed graduate level thermodynamics and developed and ran a high-school ALP summer course in atmospheric science. Luke received several awards for his teaching, including the atmospheric and oceanic sciences ‘Wahl award’, the ‘university housing teaching award’ and was nominated for a school of Letters and Science teaching award.

At CW3E, Luke will focus on evaluating and improving mesoscale model performance of short- duration, high-intensity precipitation events in western North America alongside Drs. Nina Oakley and Forest Cannon. His work will involve theoretical advancements in our understanding of the atmospheric dynamics associated with atmospheric rivers, which will be applied to study model performance and sensitivities to these events, with the aim to improve forecasting accuracy of precipitation extremes in the western United States.

Besides science, Luke previously cofounded a financial start-up that led to $125,000 investment and a mobile payments application. Through this, he became heavily involved in the emerging cryptoasset space. Luke has an acute passion for storm chasing in the central Plains and has been featured on several storm chasing documentaries. He enjoys traveling, soccer and all forms of outdoor activity.

CW3E Publication Notice: Subseasonal‐to‐Seasonal Hindcast Skill Assessment of Ridging Events Related to Drought Over the Western United States

CW3E Publication Notice

Subseasonal‐to‐Seasonal Hindcast Skill Assessment of Ridging Events Related to Drought Over the Western United States

November 23, 2020

CW3E scientist Peter Gibson, along with researchers from CW3E (Michael DeFlorio and Luca Delle Monache), NASA’s Jet Propulsion Laboratory (Duane Waliser and Alexander Goodman) and NASA’s Global Modeling and Assimilation Office (Andrea Molod) recently published an article in the Journal of Geophysical Research: Atmospheres titled “Subseasonal‐to‐Seasonal Hindcast Skill Assessment of Ridging Events Related to Drought Over the Western United States”.

Subseasonal‐to‐Seasonal (S2S) forecasts of atmospheric rivers, precipitation and drought are scientifically challenging, yet are of immense value for stakeholders and decision makers in the water resource management sector. While forecasting precipitation directly on S2S timescales has proven difficult in past research, this study approaches the problem from a different angle – to focus on persistent atmospheric ridging events that are well known to cause drought across the Western United States. In prior research, the authors have developed a ridge detection algorithm that automatically tracks ridging events associated with drought, which can be applied seamlessly across very large observational, weather and climate model datasets.

By applying this ridge detection algorithm, the authors probed the extent to which drought relevant ridging events can be forecasted on S2S timescales (2-6 weeks ahead) in state-of-the-art dynamical forecast models. For certain models, and certain aspects of ridging, the authors found evidence of skillful ridging forecasts across Weeks 3 and 4, and more modest skill across Weeks 5 and 6 lead time. The authors also explored conditions in the climate system that tend to help extend prediction skill in the forecast models as well as conditions that tend to reduce skill. This information is valuable for future research and product development, for bias correcting known errors in the output from forecast models and improving S2S prediction skill.

Figure 1. Probabilistic Brier Skill score (BSS) for predicting above normal occurrence of ridge types (N, S, and W ridge types) across a 2-week period for lead times of weeks 1-2, weeks 3-4 and weeks 5-6. Skill scores above zero indicate model skill compared to a reference prediction. The left panels (a, c) show skill assessed relative to a reference climatology defined by the historical median ridge type frequency across the particular 2-week period. Panels (b,d) show skill assessed relative to randomly sampling (with replacement) from the reference distribution defined by the historical distribution of each ridge type frequency found in reanalysis.

Based on this research, experimental forecasts are being issued in real time by CW3E and are publicly available. This S2S forecast product, as well as the underpinning research, 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. This research received funding and support from the California Department of Water Resources.

Gibson, P. B., Waliser, D. E., Goodman, A., DeFlorio, M. J., Delle Monache, L., & Molod, A. (2020). Subseasonal‐to‐seasonal hindcast skill assessment of ridging events related to drought over the Western United States. Journal of Geophysical Research: Atmospheres, 125, https://doi.org/10.1029/2020JD033655.

CW3E Event Summary: 16-18 November 2020

November 20, 2020

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Powerful storm and AR bring rain, snow, and wind to the Western U.S.

A landfalling AR associated with a surface cyclone over the Northeast Pacific Ocean impacted the Pacific Northwest and Northern California during 16–18 Nov
Coastal Oregon and Washington experienced AR 3/AR 4 conditions (based on the Ralph et al. 2019 AR Scale)
About 2–5 inches of precipitation fell over the Pacific Coast Ranges, Cascades, and Northern Sierra Nevada, with locally higher amounts in the Olympic Mountains and North Cascades
Snowfall accumulations exceeded 12 inches in portions of the Cascades, Sierra Nevada, and Rocky Mountains
Strong winds caused minor coastal flooding and scattered power outages in Washington and Oregon

Click images to see loops of GFS IVT/IWV analyses Valid 0000 UTC 16 November – 1200 UTC 20 November 2020

Summary provided by C. Castellano, C. Hecht, B. Kawzenuk, N. Oakley, and F. M. Ralph; 20 November 2020

CW3E AR Update: 16 November 2020 Outlook

November 16, 2020

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Active pattern is forecast to continue as another atmospheric river makes landfall this evening

Multiple landfalling ARs have produced heavy rainfall and snowfall across the northwestern U.S. and Northern California over the past several days
A cyclone and an associated AR currently located over the Eastern Pacific are forecast to strengthen as they propagate towards the Pacific Northwest and southern British Columbia
Current forecasts suggest that this AR may bring AR 3–4 conditions (based on the Ralph et al. 2019 AR Scale) to the Pacific Northwest and AR 1–2 conditions to Northern CA
The WPC is forecasting as much as 3.5 inches of precipitation across numerous coastal and high elevation locations across the PNW and Northern CA
High wind speeds are forecast to impact coastal locations and high elevations from WA to Northern CA

Click images to see loops of GFS IVT/IWV analyses and forecasts Valid 1200 UTC 16 November – 1200 UTC 26 November 2020

Summary provided by C. Castellano, C. Hecht, J. Kalansky, B. Kawzunek, and F. M. Ralph; 16 November 2020

*Outlook products are considered experimental

CW3E Publication Notice: The Observed Water Vapor Budget in an Atmospheric River over the Northeast Pacific

CW3E Publication Notice

The Observed Water Vapor Budget in an Atmospheric River over the Northeast Pacific

November 16, 2020

Joel Norris, Professor of Climate and Atmospheric Sciences at Scripps Institution of Oceanography and CW3E affiliate, recently published a paper in the Journal of Hydrometeorology along with co-authors including F. Martin Ralph, CW3E Director, Reuben Demirdjian, recently graduated CW3E PhD student, CW3E scientist Forest Cannon, and CW3E affiliate Duane E. Waliser of NASA’s Jet Propulsion Laboratory, among others (Norris et al., 2020). This study contributes to the goals of CW3E’s 2019-2024 Strategic Plan to support Atmospheric River (AR) Research and Applications by furthering our understanding of AR dynamics.

Observing and understanding the processes controlling the water budget of an AR offshore will help us better understand what factors lead to an increase in AR’s Integrated Water Vapor (IWV) content and how much water vapor will be available for precipitation when the AR makes landfall. This is particularly important for water supply and flood risk management, as substantial precipitation and flooding can occur when ARs make landfall in many regions across the world. Observational campaigns, such as those described in this study, are crucial to understanding the processes that modulate IWV. Specifically, lack of budget closure in reanalyses indicates that it is necessary to observationally quantify the magnitudes of precipitation and the dynamical convergence of water vapor and their offsetting contributions to IWV tendency in the AR core.

This study uses CalWater2 observations of an AR event on 5 February 2015 collected from the NOAA G-IV and the NOAA R/V Ron Brown (Fig 1) to derive a spatial estimate of precipitation over a ~24,000 km² oceanic domain off the coast of California. Calculating water vapor budget terms for subregions within the larger budget region allows additional physical insight into the processes controlling the AR’s IWV content. In this specific case, the IWV tendency over the entire domain was dominated by dynamical convergence, and evaporation was negligible. However, the results reveal the substantial spatial variability present in IWV convergence and precipitation at scales of ~50km (Fig 2).

The Norris et al. (2020) study was innovative in many ways. First, precipitation was observationally estimated by conversion of NOAA G-IV tail doppler radar reflectivity to rain rate using a Z-R relationship derived from shipboard disdrometer measurements on the same day. Second, this study documented precipitation, dynamical convergence, and advection for subregions of the main budget domain corresponding to different combinations of dropsonde subsets. And third, this study demonstrated that the water vapor budget of the main region could be observationally closed. The results have implications for our understanding of processes in the frontal sector of ARs, currently a primary source of uncertainty in IWV tendency.

Figure 1. Left: Flight tracks of NOAA G-IV (pink) and NOAA P-3 (yellow), locations of NOAA RHB (star) and dropsondes (circles), and boundary of water vapor budget region (black polygon), all overlaying MERRA-2 IWV for 1900 UTC 5 February 2015 (mm, color scale at bottom). Right: photos of the observing systems. (Figure 1 from Norris et al., 2020)

Figure 2. Kinematic diagnostic profiles derived from the G-IV dropsondes comprising the entire budget region (B00, black) and subregions with the most positive CIMC (R03, dashed blue) and most negative CIMC (R06, dotted red) , as defined in Fig. 10 and Table 4 (see publication): (a) mass-balanced horizontal moisture convergence (g kg^-1 day^-1), (b) mass-balanced change in moisture from horizontal dynamical convergence (g kg^-1 day^-1), © mass-balanced horizontal moisture advection (g kg^-1 day^-1), and (d) pressure vertical velocity (Pa s^-1). (Figure 11 from Norris et al., 2020).

Norris, J.R., F.M. Ralph, R. Demirdjian, F. Cannon, B. Blomquist, C.W. Fairall, J.R. Spackman, S. Tanelli, and D.E. Waliser, 2020: The Observed Water Vapor Budget in an Atmospheric River over the Northeast Pacific. J. Hydrometeor., 21, 2655-2673, https://doi.org/10.1175/JHM-D-20-0048.1.

CW3E Publication Notice: Hydrometeorological Characteristics of Ice Jams on the Pemigewasset River in Central New Hampshire

CW3E Publication Notice

Hydrometeorological Characteristics of Ice Jams on the Pemigewasset River in Central New Hampshire

November 15, 2020

Matthew Sanders, M.S., of Plymouth State University, has published a paper in the Journal of Hydrometeorology, along with his advisor, CW3E affiliate Jason M. Cordeira of Plymouth State University, and Nicholas D. Metz of Hobart and William Smith Colleges (Sanders et al., 2021). This study contributes to the goals of CW3E’s 2019-2024 Strategic Plan to support monitoring and projections of climate variability and change by advancing understanding and projections of extreme precipitation events.

The study considers two impactful ice jams, both of which resulted in flooding, in order to illustrate the hydrometeorological characteristics of ice jam events on the Pemigewasset River in central New Hampshire. The two case studies show the importance of short term antecedent conditions to the ultimate impacts of the ice jams. Antecedent conditions from each event, one which included a long melting period with low precipitation and the other which included a short melting period with high precipitation, contributed to the formation of the ice jams, along with the presence of an atmospheric river (AR). In addition to the case studies highlighted, a longer period of record (>25 years) with composite analysis is employed in order to understand the circulation patterns associated with these events. Composite analysis of 20 ice jam events during 1981–2019 allows for the construction of a schematic summarizing common synoptic-scale characteristics (Figure 1). All but one of the events were preceded by environments characterized by ARs along the U.S. East Coast. Five general phases associated with ice jams and flooding were identified and described in order to support situational awareness, beginning 1-2 weeks before the event with cold temperatures and periodic snow accumulations, and continuing through a few days before the event with warming temperatures and some melting of existing snowpack. Directly before the event, a midlatitude cyclone almost always associated with an AR brings periods of heavy precipitation. At the event, the ice aggregates and blocks rising river flow; and just after the event, there is potential for freezing in place especially if a cold front passes. This work provides an important assessment of the synoptic-scale characteristics and effect of short term antecedent conditions before ice jams that cause significant local impacts in the Northeast United States.

Figure 1: Figure 13 in Sanders et al., 2020: Overview schematic for meteorological features associated with ice jams on the Pemigewasset River in Plymouth, New Hampshire. The schematic highlights 1) the location of Plymouth (yellow star), 2) upper-level (e.g., 300-hPa) jet streaks (“J”; purple shading with dashed contours), 3) upstream trough in mid-level (e.g., 500-hPa) geopotential height contours (solid black lines), 4) warm-period temperature anomaly (red oval and shading), 5) tropospheric moisture (green shading for IWV values >25 mm) and moisture transport (black arrow representing AR and corridor of IVT values >600 kg m−1s−1), 6) surface frontal features, and 7) surface cyclone and anticyclone locations (red “L” and blue “H” symbols, respectively) and associated lower-tropospheric flow (red arrows).

Sanders, M. C., J. M. Cordeira, and N. D. Metz, 2020: Hydrometeorological Characteristics of Ice Jams on the Pemigewasset River in Central New Hampshire. J. Hydrometeorology, 21, 2923-2942 https://doi.org/10.1175/JHM-D-20-0027.1 .

CW3E AR Update: 12 November 2020 Outlook

November 12, 2020

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Active weather pattern expected to bring heavy rainfall and snowfall to portions of the Western U.S.

A series of storms and landfalling ARs are forecast to bring significant precipitation to portions of Northern California and the Pacific Northwest over the next 7 days
AR 4/AR 5 conditions (based on the Ralph et al. 2019 AR Scale) are possible over coastal Oregon and Washington in association with the second landfalling AR
The highest 7-day precipitation amounts (5–10 inches) are forecast over the Pacific Coast Ranges and Cascade Mountains
More than 2 feet of snow is possible in the higher elevations of the Washington Cascades during the next 48 hours