Author: cw3e-web

CW3E AR Update: 13 December 2023 Outlook

CW3E AR Update: 13 December 2023 Outlook

December 13, 2023

Click here for a pdf of this information. Click here to provide feedback on these outlooks!

Cut Off Low Forecast to Bring Atmospheric River to California

  • A mid-level trough currently just south of the Aleutian Islands is forecast to propagate into the Northeast Pacific and continue to deepen, eventually becoming cut off.
  • The cut off low pressure system interacts with elevated moisture in the NE Pacific leading to the formation of an AR.
  • The low pressure system is forecast to progress toward the USWC and bring AR conditions to CA beginning Sun 16 Dec.
  • AR2 conditions (based on Ralph et al. 2019 AR scale) are forecast for this event.
  • There is uncertainty in the AR landfall timing and duration in the GEFS, ECMWF EPS and West-WRF Ensemble.
  • The NWS Weather Prediction Center (WPC) is currently forecasting 7-day precipitation totals ≥ 3” for much of the CA Coasts as well as the Sierras with isolated areas ≥ 6”.
  • The NWS Climate Prediction Center’s Day 8-14 Hazard Outlook shows slight risks of heavy precipitation and high winds for the CA coasts and heavy snow in the Sierras 12/20-12/21 and 12/23-12/26.

Click images to see loops of GFS IVT and IWV forecasts

Valid 0600 UTC 14 December 2023 – 0000 UTC 19 December 2023


 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Summary provided by M. Steen, S. Bartlett, C. Castellano and J. Kalansky; 13 December 2023

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*Outlook products are considered experimental

CW3E Subseasonal Outlook: 13 December 2023

CW3E Subseasonal Outlook: 13 December 2023

December 13, 2023

Click here for a pdf of this information.


 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Summary provided by C. Castellano, J. Wang, Z. Yang, M. DeFlorio, and J. Kalansky; 13 December 2023

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*Outlook products are considered experimental

CW3E Event Summary: 30 November-6 December 2023

CW3E Event Summary: 30 November-6 December 2023

11 December 2023

Click here for a pdf of this information.

Atmospheric Rivers Produce Heavy Precipitation and Flooding in Washington and Oregon

  • A series of low-pressure systems and three atmospheric rivers (ARs) brought heavy snow and rain to much of the Pacific Northwest during 30 Nov – 6 Dec.
  • While the first AR was associated with a cold system, the second and third ARs were characterized by the transport of very warm, moist air from the subtropical North Pacific into the midlatitudes.
  • The third and strongest AR produced AR3/AR4 conditions (based on the Ralph et al. 2019 AR Scale) over coastal WA/OR, as well as AR2 conditions in portions of the interior Pacific Northwest.
  • These storms produced 10–20 inches of total precipitation in the Olympic Mountains, Cascades, and OR Coast Ranges, as well as 4–8 inches of precipitation in the lowlands of western WA and OR.
  • The cold storms (including the first AR) produced 1–3 feet of snow in the Cascades during 30 Nov – 2 Dec.
  • Snow levels remained below 4,000 feet through the first AR, then rose above 7,000 feet during the second and third ARs, resulting in significant rain-on-snow.
  • High reservoir inflows prompted dam operators to increase releases to ~3,000 cfs at Howard Hanson Dam after the third AR.
  • Heavy rain falling on moist soils and fresh snowpack during the third AR led to widespread riverine flooding across western Washington and northwestern Oregon.
  • The Skagit and Stillaguamish Rivers reached major flood stage on 5 Dec.
  • Significant flooding was observed in multiple locations, requiring road closures, sandbagging, and multiple water rescues – to include a helicopter rescue by the US Coast Guard due to rapidly rising waters near Rosburg, WA.
  • There were also numerous landslides and debris flows in Washington and Oregon, requiring the shutdown of various roadways, including a post-fire debris flow within the boundaries of the 2020 Holiday Farm Fire in Oregon.

Click images to see loops of GFS IVT/IWV analyses

Valid: 1200 UTC 2 December – 1200 UTC 6 December 2023

GOES West GEOCOLOR Composite:NOAA/NESDIS/STAR



 

Total Precipitable Water: NOAA CIMSS – UW Madison



 


 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Summary provided by C. Castellano, S. Bartlett, P. Iñiguez, and J. Kalansky; 11 Dec 2023

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CW3E Publication Notice: Antecedent Snowpack Cold Content Alters the Hydrologic Response to Extreme Rain-on-Snow Events

CW3E Publication Notice

Antecedent Snowpack Cold Content Alters the Hydrologic Response to Extreme Rain-on-Snow Events

December 4, 2023

A new paper titled “Antecedent Snowpack Cold Content Alters the Hydrologic Response to Extreme Rain-on-Snow Events” by Lisa Katz (University of Nevada, and now CW3E), Gabriel Lewis (University of Nevada, and now CW3E), Sebastian Krogh (University of Concepción), Stephen Drake (University of Nevada), Erin Hanan (University of Nevada), Benjamin Hatchett (University of Nevada/Desert Research Institute), and Adrian Harpold (University of Nevada) was recently published in the Journal of Hydrometeorology. This paper examines rain-on-snow (ROS) events in California’s Sierra Nevada, focusing on the controls that antecedent snowpack conditions, namely snowpack cold content, snow density, snow water equivalent (SWE), and liquid water content, have on the timing and magnitude of liquid drainage from the snowpack onto the land surface. By furthering our understanding of how hydrometeorological models interpret meteorological and watershed interactions during complex events such as ROS, this work advances CW3E’s 2019–2024 Strategic Plan goal to improve modeling capabilities to better serve water supply management programs in the western U.S., such as Forecast Informed Reservoir Operations (FIRO) and flood warning systems.

The researchers modeled 71 ‘historical’ ROS events between 1981 and 2019 true to the record, and created ‘scenario’ events for modeling, by exposing a set of 40 unique snowpack states to meteorological conditions from the most extreme ROS. The model used was the physically based, 1-dimensional SNOWPACK, initiated with the Richards Equation. Results from this study agreed with previous studies that rainfall is the dominant control on TWI during ROS (R2 = 0.95, p < 0.01), and found that terrestrial water input (TWI) is largely generated at higher elevations, where rainfall amount is greatest. This study adds that snowpacks with more negative cold content reduce the ratio of TWI to rain over the event duration. Scenario event TWI to rain ratio responses spanned the range from ≤ 1 to > 1, providing evidence for snowpacks storing rain or meltwater, depending on antecedent snowpack conditions.

An analysis of antecedent snowpack conditions by multiple linear regression (R2 = 0.92, p < 0.01) determined that cold content, over snow density, liquid water content, or SWE, produced the highest Pearson correlation with TWI (0.75, p < 0.01), and even stronger relationships were found for cold content–liquid water content (0.89, p < 0.01) and cold content–density (0.81, p < 0.01). These results suggest that refreezing from higher cold content and slower unsaturated flow from higher snow density lead to more liquid water retention during ROS events.

Antecedent cold content is a rarely measured snowpack state that is the result of several interconnected snowpack processes and could lead to useful observations for streamflow forecasting. A combination of refreezing, matric forces, or reductions in hydraulic conductivity from dense vertical layering may cause the larger retention of rainfall and/or TWI than would be predicted by a simple refreezing of the snowpack in a single snow layer. This retention may be partially due to rainfall and cold content being larger at the higher elevations, affecting the catchment average. Results from this study highlight the importance of hydraulic limitations in dense snowpacks and energy limitations in warm snowpacks for retaining liquid water that would otherwise be available as TWI for flooding.

Figure 1: (Figure 6 from Katz et al. 2023) Scenario analysis of 1986 ROS event at High falling (top) on the cold and dry antecedent snowpack conditions from 26 Jan 2005 and (middle) the warm and wet antecedent snowpack conditions from 26 Jan 2000. The upper panels show hourly rain and precipitation (bars) as well as resulting TWI (black). (bottom) Cumulative TWI from 2000 (blue) and 2005 (red) antecedent conditions. Dashed vertical lines indicate the ROS event start and end.

Katz, L., Lewis, G., Krogh, S., Drake, S., Hanan, E., Hatchett, B., & Harpold, A. (2023). Antecedent Snowpack Cold Content Alters the Hydrologic Response to Extreme Rain-on-Snow Events. Journal of Hydrometeorology, 24(10), 1825-1846. https://doi.org/10.1175/JHM-D-22-0090.1

CW3E AR Update: 1 December 2023 Outlook

CW3E AR Update: 1 December 2023 Outlook

December 1, 2023

Click here for a pdf of this information. Click here to provide feedback on these outlooks!

Trio of Atmospheric Rivers Forecast to Impact Pacific Northwest

  • An AR associated with a cold storm will bring a brief period of AR conditions tonight into Saturday
  • Two stronger ARs are forecast to make landfall late Sat 2 Dec and early Mon 4 Dec
  • AR1 conditions (based on Ralph et al. 2019 AR scale) are forecast during the first AR
  • Nearly all GEFS ensemble members are forecasting an AR4 over northern coastal OR due to a prolonged period (> 72 hours) of continuous AR conditions during the second and third ARs
  • A majority of ECMWF EPS members are forecasting a break in AR conditions between the second and third ARs, with AR2/3 conditions likely during the second AR, and AR3/4 conditions likely during the third AR
  • The NWS Weather Prediction Center (WPC) is currently forecasting 7-day precipitation totals ≥ 10 inches in the vicinity of the Olympic Mountains, Cascades, and Coast Ranges
  • The NWS WPC Extreme Rainfall Outlook highlights a Marginal Risk for flooding for western OR/WA Dec 2-6 with a Slight Risk for the Olympic Peninsula on Dec 5
  • Heavy rain, particularly during the second and third ARs, is expected to cause flooding on rivers in western WA and northwestern OR
  • Rain falling on fresh snowpack will likely increase flood risk near the Olympic Mountains and WA Cascades
  • NWS Seattle and Portland are forecasting at least 1-3 feet of snow in the Olympic Mountains and the Cascades through late Saturday evening
  • High snowfall totals in the forecast have led to major to extreme conditions forecast within the NWS Winter Storm Severity Index along the Cascades between 1-3 December

Click images to see loops of GFS IVT and IWV forecasts

Valid 1200 UTC 01 December 2023 – 1800 UTC 6 December 2023


 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Summary provided by M. Steen, S. Bartlett, C. Castellano and P. Iniguez; 1 December 2023

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

*Outlook products are considered experimental

Breaking Ground to Expand Climate Monitoring Network in Upper Yampa River Basin

Breaking Ground to Expand Climate Monitoring Network in Upper Yampa River Basin

November, 28 2023

Building on a successful pilot study, two new climate monitoring stations will expand the coverage of the monitoring network and improve understanding of climate and water resources in the Yampa River Basin.

Steamboat Springs, Co., (November 27, 2023) – In early November 2023, two new climate monitoring stations were installed in the Upper Yampa River Basin. The first is on private property at the Howe Ranch, roughly 10 miles North of Hayden, CO, and the second is on private property roughly 7 miles northwest of Steamboat Springs, CO. The installations represent the breaking of ground for a new phase of collaboration between Yampa Valley Sustainability Council (YVSC), Colorado Mountain College (CMC), and the Center for Western Weather and Water Extremes (CW3E) at Scripps Institution of Oceanography at the University of California San Diego. The project team conducted a successful pilot installation near Stagecoach Reservoir in 2022 and is now working on expanding the network of monitoring stations thanks to additional funding from the Upper Yampa Water Conservancy District (UYWCD), the Colorado River District’s (CRD) Community Funding Partnership, and the Colorado Water Conservation Board’s (CWCB) Water Plan Grant.

Left: The newly installed ELK station overlooking Elk Mountain, near Steamboat Springs, amid a light snow flurry. Right: The ELK soil pit prior to backfilling, showing the soil temperature/moisture sensors.

The climate monitoring network is motivated by increasing uncertainty in“snow-to-flow” predictions of water availability in the Colorado River Basin. Water managers are finding it harder to predict how much snowmelt runoff will enter rivers and reservoirs in the Colorado River Basin, and one theory is that drier soils are absorbing snow melt like a sponge. The hypothesis is that warming temperatures in recent years are causing soils to dry out and winter snowfall to sublimate or evaporate away, leading to reduced springtime run-off. Unfortunately, without reliable measurements of soil moisture and meteorological conditions throughout the basin, the “soil drying” hypothesis has been difficult to test. “Soil moisture is an under-observed reservoir of water in the basin” says Dr. Marty Ralph, the Director of CW3E and principal investigator on the project. The new monitoring stations were designed to rectify this problem by providing the much-needed observations of soil moisture and a baseline for long-term monitoring in the basin. Ralph’s vision for the project is to “develop methods to comprehensively reduce the uncertainty in that knowledge gap” by integrating the new data into forecasting and water management decision-making.

Left: CW3E, CMC, and YVSC team members assemble the tower for the meteorological sensors at ELK station.
Center: Team members work to install the meteorological sensors on the HOW station tower, with soil from the soil pit laid out in foreground. Right: Team members work to install the HOW soil sensors and backfill the soil pit.

The new stations record soil temperature and moisture at six different depths down to 40 inches in the soil profile. The stations also include meteorological sensors measuring wind speed and direction, precipitation, snow depth, temperature, relative humidity, pressure, and solar radiation. Thanks to cellular communications, the data are available in near-real-time. Site locations were identified using a comprehensive geospatial analysis designed to maximize the impact of their observations and capture basin land surface complexity. First, the team analyzed spatial patterns in the various characteristics that drive soil moisture variability such as precipitation, topography, and vegetation cover. They then compiled records of all the existing soil and meteorological observations in the watershed to identify observational gaps in the basin. Gaps in the existing observations were confirmed by input from local stakeholders, water managers, forecasting agencies, and researchers and site locations were finalized. The newly installed and existing stations will be complemented by an additional six stations to be installed through 2026, resulting in a comprehensive network spanning the entire basin.

Widespread enthusiasm for the project is evident in the Yampa Valley. Executive Director of YVSC, Dr. Michelle Stewart, says “the Yampa Valley Sustainability Council sees this ground-breaking for the climate monitoring network expansion as critical in enhancing our ability to accurately monitor and respond to climate change in the Yampa Valley. YVSC greatly appreciates the investment and support from our funding partners to further this type of science-driven, decision-support project for the benefit of water and land use in the Yampa River Basin.”

Andy Rossi, the General Manager of UYWCD, adds that “the continued expansion of a soil moisture monitoring network across the Upper Yampa River Basin is critical to understanding spring runoff, especially as our climate becomes hotter and drier.” He also sees potential for benefits outside the basin, explaining that “the data collected from these stations will not only assist local water managers like UYWCD, but could lead to a more collaborative approach to water management decisions downstream.” The support from UYWCD, CRD and CWCB has been critical in continuing this effort to increase observational monitoring in the Upper Yampa.

Amy Moyer, Director of Strategic Partnerships at the Colorado River District, also recognizes the importance of the project. “In coordination with related efforts across our District, we see this climate and soil monitoring effort as an important piece of an overall strategy to better understand how water resources are changing in the Colorado River Basin, both from near-term operations and to long term planning perspectives.” She also praised the project for its commitment to community-oriented science, adding that “the project aligns well with our Community Funding Partnership Program goals, and we are proud to financially support this cooperative initiative that will achieve multiple benefits.”

To maximize the impact of the knowledge generated by the monitoring network, the project team is committed to collaborating with the residents and water interests of the Yampa River Basin. This involves partnering with local private landowners to host the stations, inviting students and volunteers from Colorado Mountain College to participate in the installations, and co-organizing the Yampa Basin Rendezvous–a conference dedicated to water and weather in the Yampa River Basin held at Colorado Mountain College in late spring each year, as well as coordinating with related regional and federal soil monitoring efforts.

Local partners Emily Howe and Jeremiah Psiropoulos described their motivation for participating in the project and the benefits they see for the community: “We are hosting this station to help provide a better understanding of how water behaves in the Elkhead watershed. As biologists ourselves, we’re excited to contribute data to scientists working to understand hydrology and climate change in our community, and we love the idea of helping to maintain a long-term dataset. We manage the Howe Ranch to conserve the land, water, flora, and fauna in our community. As water scarcity and drought accelerate in the Yampa Valley along with a warmer future, we hope that water use in our valley will be data informed and sustainable, and we hope our weather station will benefit efforts to ensure that.”

Nathan Stewart, Professor of Ecosystem Science at CMC and project collaborator, recognizes the value of the Climate Monitoring Network to undergraduate training in STEM: “our students participate in station installation alongside technical experts from CW3E, colleagues from YVSC, and local Yampa Valley landowners and witness dynamic community-engaged science first hand. Immediate benefits include mentorship in tower, sensor, and soil pit establishment; long term benefits include training in station maintenance, data analysis and visualization, and science communication. The network provides our basin with an unparalleled outdoor laboratory for student career training in meteorology and watershed science.”

This season’s station installations represent the groundbreaking of the newly funded expansion of the monitoring network. Expanding the network will generate additional observations and sample a wider range of soil and hydrological conditions, helping water managers to better determine exactly what is happening to snowpack in the basin and improve predictions of springtime reservoir inflows.

The data collected by the stations will be publicly available on the CW3E website, MesoWest, and the NOAA Physical Science Laboratory.

Contact:

El Knappe

Center for Western Weather and Water Extremes

Phone: 805-708-7472

Email: eknappe@ucsd.edu

Madison Muxworthy

Yampa Valley Sustainability Council

Phone: 970-871-9299, ext. 107

Email: madison@yvsc.org

Nathan Stewart

Colorado Mountain College

Phone: 970-870-4562

Email: nlstewart@coloradomtn.edu

CW3E AR Update: 28 November 2023 Outlook

CW3E AR Update: 28 November 2023 Outlook

November 28, 2023

Click here for a pdf of this information. Click here to provide feedback on these outlooks!

Multiple Atmospheric Rivers Forecast to Impact Pacific Northwest and Northern California

  • Several low pressure systems will spin out of the Asian continent and into the Northeast Pacific Ocean heading into the weekend.
  • As these systems approach the West Coast of North America, multiple atmospheric rivers (ARs) are forecast to develop and make landfall over the Pacific Northwest.
  • The first AR is forecast to arrive by Sat Dec 2, with two stronger ARs to follow on Sun Dec 3 possibly through Wed Dec 6. IVT values may exceed 750 kg/(ms) with the third AR.
  • While there is high confidence on the development of the ARs, large uncertainty in the timing, duration, and intensity remain.
  • Moderate/heavy precipitation is very likely from far northwest CA into southern BC.
  • Rises on area rivers could push them above action stage or even flood stage.
  • Freezing levels may initially fall to ~2000’ in northern WA and to 5000’ in central CA during the first (weak) AR before rising with subsequent ARs.
  • Significant mountain snow is possible.

Click images to see loops of GFS IVT and IWV forecasts

Valid 1200 UTC 28 November 2023 – 0000 UTC 6 December 2023


 

 

 

 

 

 

 

 

 

 

 

 

 

 

Summary provided by P. Iniguez, C. Castellano, and S. Bartlett; 28 November 2023

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

*Outlook products are considered experimental

CW3E Welcomes Lu Su

CW3E Welcomes Lu Su

November 20, 2023

Lu Su joined CW3E in November 2023 as a postdoctoral research scholar. Prior to joining the Center, Lu Su earned her PhD in Geography from University of California, Los Angeles, under the supervision of Dr. Dennis P. Lettenmaier. Lu’s doctoral dissertation explored the evaluation and improvement of hydrological simulation and forecast in the western U.S..Her work primarily focused on three areas: improving subseasonal drought onset and termination forecast accuracy using NOAA’s Climate Testbed Subseasonal Experiment (SubX) reforecasts, evaluating and improving flood forecasting capabilities of the Noah-MP model and comparing with the the existing river forecast center predictions, and developing finely calibrated parameters for two prominent land surface models – the VIC model and Noah-MP.

Additionally, Lu’s research extends to historical drought analysis over the past century in the contiguous United States, and the creation of a gridded forcing dataset and conducting over ten high-resolution climate simulations using the VIC model in California.

At CW3E, Lu will be working with the hydrology group under the supervision of Dr. Ming Pan. Her work will involve supporting the development and operation of CW3E’s hydrologic monitoring and seasonal forecasting system; performing hydrologic modeling experiments and analysis for the verification and improvement of forecast skills; and conducting climate-scale modeling to investigate the hydrologic consequences of climate change in the California region and its impact on regional water resources and other sectors.