cw3e-web - Center for Western Weather and Water Extremes

CW3E Welcomes Jiabao Wang

January 25, 2021

Dr. Jiabao Wang joined CW3E as a postdoctoral research scholar in January 2021. She received her B.S. (2013) and M.S. (2015) degrees in Meteorology from Sun Yat-sen University in China. She earned her Ph.D. degree in December 2020 from the School of Marine and Atmospheric Sciences at Stony Brook University under the advisement of Dr. Hyemi Kim.

Jiabao’s prior research work includes investigations of midlatitude storm tracks and their interactions with Arctic amplification and the Quasi-biennial oscillation, as well as intraseasonal oscillations (e.g., the Madden-Julian oscillation, MJO) and their teleconnections to the midlatitudes. She has published five first-author journal articles during her time as a Ph.D. student. She also led the development of a set of standardized MJO teleconnection diagnostics as a joint effort between the Working Group on Numerical Experimentation (WGNE) MJO Task Force and the WMO Subseasonal-to-Seasonal (S2S) teleconnection subproject, which enables a consistent investigation of MJO teleconnection variations and impacts, and objective assessment and comparison of teleconnection performance among different models and across model generations. Jiabao’s Ph.D. research detailed the observational MJO teleconnection characteristics and evaluated its reproduction by CMIP models. She also used a linear baroclinic model to explore the dynamical processes controlling the teleconnection variations, simulation fidelity, and future changes in a warming climate.

At CW3E, Jiabao will be working with the S2S group under the supervision of Dr. Mike DeFlorio. Her research will focus on improving the understanding of S2S variability of extreme precipitation and atmospheric rivers (ARs) over the Western US., such as their intrinsic characteristics, simulation capability by global climate models (CMIP6), and S2S predictability in the hindcast experiments of multimodel ensemble projects (S2S, SubX, or CESM S2S hindcasts). Particularly, she will apply her MJO teleconnection metrics for a quantitative examination of the MJO impacts on extreme precipitation and ARs and help evaluate and improve their prediction in ensemble prediction systems at S2S lead times.

CW3E AR Update: 22 January 2021 Outlook

January 22, 2021

Click here for a pdf of this information.

Active Weather Pattern Forecast Across the Western U.S. this Weekend through Next Week

A series of upper-level shortwave disturbances will bring multiple episodes of precipitation to the southwestern U.S. this weekend into early next week
At least 1–3 inches of precipitation are forecasted in the Southern Sierra, coastal Southern California, and Central Arizona in association with these shortwave disturbances
Significant snowfall accumulations are possible over the higher terrain in the southwestern U.S.
There is increasing forecast confidence in a landfalling AR and major precipitation event next week over California
However, there is still considerable uncertainty in the location, duration, and intensity of this landfalling AR
More than 5 inches of total precipitation are possible over the California Coast Ranges, Sierra Nevada, and Southern California Transverse Ranges during the next 7 days

Click images to see loops of ECMWF IVT & IWV forecasts Valid 0000 UTC 22 January – 0000 UTC 30 January 2021

Probability of AR Conditions Along Coast: dProg/dt

Model Runs: 00Z 17 Jan – 00Z 22 Jan 2021 (every 12 h)

Summary provided by C. Castellano, C. Hecht, J. Kalansky, and F. M. Ralph; 22 January 2021

*Outlook products are considered experimental

CW3E Event Summary: 11-13 January 2021

January 14, 2021

Click here for a pdf of this information.

An Extreme Atmospheric River brought AR 5 Conditions and Widespread Hydrologic Impacts to the Pacific Northwest

The AR initially made landfall at ~00 UTC 12 January and brought an initial pulse of IVT magnitudes >750 kg m^–1 s^–1
A mesoscale frontal wave developed along the northern periphery of the initial AR, strengthened and moved onshore at ~00 UTC 13 January
The secondary pulse of AR conditions was much stronger than the first (>1000 kg m^–1 s^–1) and helped to prolong the overall duration of the event, resulting in AR 5 conditions
More than 5 inches of precipitation fell in portions of the Pacific Coast Ranges and Cascades, with the highest amounts (locally > 10 inches) in the Olympic Peninsula and extreme northwestern Oregon
Heavy rainfall on saturated/nearly saturated soils produced widespread flooding and landslides
High winds also caused significant tree damage and power outages in western WA and northwestern OR

MIMIC-TPW2 Total Precipitable Water

Valid 0000 UTC 10 January – 0800 UTC 14 January

Images from CIMSS/University of Wisconsin

Click images to see loops of GFS IVT/IWV analyses Valid 0000 UTC 10 January – 1200 UTC 14 January

Summary provided by C. Castellano, C. Hecht, J. Kalansky, B. Kawzenuk, and F. M. Ralph; 14 January 2021

CW3E AR Update: 12 January 2021 Outlook

January 12, 2021

Click here for a pdf of this information.

Strong atmospheric river will continue to impact the U.S. West Coast today

A strong atmospheric river (AR) made landfall across Washington, Oregon, and Northern California late yesterday
Forecasts of maximum IVT magnitude have increased substantially since yesterdays outlook and the GEFS control is now forecasting AR 5 conditions (based on the Ralph et al. 2019 AR Scale) over portions of coastal Oregon
Some areas in western Washington and northwestern Oregon have already received 3–5 inches of precipitation
An additional 3–7 inches of precipitation are forecast in the Pacific Coast Ranges and Cascades, with the heaviest amounts expected in extreme southwestern Oregon and northwestern California
Widespread riverine flooding and landslides are possible in western Washington and Oregon

Click images to see loops of GFS IVT & IWV forecasts Valid 1200 UTC 12 January – 1200 UTC 16 January 2021

Summary provided by C. Castellano, C. Hecht, J. Kalansky, N. Oakley, and F. M. Ralph; 12 January 2021

*Outlook products are considered experimental

CW3E AR Update: 11 January 2021 Outlook

January 11, 2021

Click here for a pdf of this information.

Strong atmospheric river to impact the Pacific Northwest this week

A strong and zonally elongated atmospheric river (AR) is forecast to make landfall across Washington, Oregon, and Northern California today
AR 4 conditions (based on the Ralph et al. 2019 AR Scale) are possible over coastal Oregon and Washington
At least 3–7 inches of precipitation are expected in the Pacific Coast Ranges and Cascades
More than 2 feet of snow is forecast in the higher terrain of the Olympic Mountains and Washington Cascades
Intense precipitation falling in areas with saturated soils and existing burn scars from the 2020 wildfires may result in flooding and debris flows in western Washington and Oregon

Click images to see loops of GFS IVT & IWV forecasts Valid 0600 UTC 11 January – 0600 UTC 15 January 2021

Summary provided by C. Castellano, C. Hecht, J. Kalansky, N. Oakley, and F. M. Ralph; 11 January 2021

*Outlook products are considered experimental

CW3E Event Summary: 1-7 January 2021

January 8, 2021

Click here for a pdf of this information.

Active weather pattern produces an extremely wet start to 2021 in the Pacific Northwest

Several ARs associated with a series of storms over the Northeast Pacific Ocean impacted the Pacific Northwest during the first week of 2021
These storms produced at least 2–7 inches of total precipitation in northwestern California, western Oregon, and western Washington, with the highest amounts (> 10 inches) in the Olympic Mountains and North Cascades
More than 5 feet of snow fell in parts of the Olympic Mountains and Washington Cascades
Total water-year-to-date precipitation remains well-below normal across much of the western U.S.

MIMIC-TPW2 Total Precipitable Water

Valid 0000 UTC 1 January – 0000 UTC 7 January

Images from CIMSS/University of Wisconsin

Click images to see loops of GFS IVT/IWV analyses Valid 0000 UTC 1 January – 0000 UTC 7 January

Summary provided by C. Castellano, J. Kalansky, N. Oakley, and F. M. Ralph; 8 January 2021

CW3E Event Summary: 17-22 December 2020

December 23, 2020

Click here for a pdf of this information.

Multiple storms impacted the Pacific Northwest over the Weekend and into Monday

The first event brought AR 1 conditions to far northwestern Washington as a decaying AR propagated down the coast from British Columbia
The second AR was stronger and lasted several days, bringing AR 3 conditions to Coastal Oregon
A mesoscale frontal wave developed along the second AR and resulted in an additional pulse of enhanced IVT and extended the overall duration of AR conditions
Several daily precipitation records were broken across the Seattle Metropolitan area where several both urban and river flooding was observed

MIMIC-TPW2 Total Precipitable Water

Valid 1200 UTC 17 December – 1700 UTC 22 December

Images from CIMSS/Univ. of Wisconsin

Click images to see loops of GFS IVT/IWV analyses Valid 1200 UTC 17 December – 1200 UTC 22 December 2020

Summary provided by C. Hecht, C. Castellano, J. Kalansky, and F. M. Ralph; 23 December 2020

CW3E Publication Notice: Atmospheric river sectors: Definition and characteristics observed using dropsondes from 2014-2020 CalWater and AR Recon

CW3E Publication Notice

Atmospheric river sectors: Definition and characteristics observed using dropsondes from 2014-2020 CalWater and AR Recon

December 23, 2020

Alison Cobb, a postdoctoral scholar at CW3E, recently published a paper in Monthly Weather Review, along with CW3E co-authors Allison Michaelis, Sam Iacobellis, Luca Delle Monache and F. Martin Ralph, titled “Atmospheric river sectors: Definition and characteristics observed using dropsondes from 2014-2020 CalWater and AR Recon” (Cobb 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 out understanding of AR dynamics. In particular, this work examines atmospheric measurements over the Pacific.

In this study, a unique set of 858 dropsondes deployed in lines transecting 33 ARs during CalWater and AR Recon field campaigns (2014-2020) are analyzed. Integrated vapor transport (IVT) is used to define five regions: core, cold and warm sectors, and non-AR cold and warm sides. The core is defined as having at least 80% of the maximum IVT in the transect. Remaining dropsondes with IVT > 250 kg m^-1 s^-1 are assigned to cold or warm sectors, and those outside of this threshold form non-AR sides. The mean widths of the three AR sectors are approximately 280 km. However, the core contains roughly 50% of all the water vapor transport (i.e., the total IVT), while the others each contain roughly 25%. A low-level jet occurs most often in the core and warm sector with mean maximum wind speeds of 28.3 and 21.7 m s^-1, comparable to previous studies, although with heights approximately 300 m lower than previously reported. The core exhibits characteristics most favorable for adiabatic lifting to saturation by the California coastal range. On average, stability in the core is moist neutral, with considerable variability around the mean. A relaxed squared moist Brunt Väisälä frequency threshold shows ~8–12 % of core profiles exhibiting near-moist neutrality. The vertical distribution of IVT, which modulates orographic precipitation, varied across AR sectors, with 75% of IVT residing below 3115 m in the core.

The Cobb et al. (2020) study was the first of its kind to composite such a large dataset into different sectors of the AR. This analysis using only observations has revealed distinct characteristics across ARs when categorized into sectors based on IVT. There is symmetry across the AR in terms of TIVT, low-level jet wind speed, and lifting condensation level, but asymmetry in other diagnostics, including height of low-level jet and height below which 75 IVT is contained. Analyzing a large sample (858 dropsondes) has allowed for examination of the variability that is apparent in the ARs, rather than simply presenting mean characteristics, which have been reported in previous studies.

An important goal of AR observational campaigns is to retrieve data that will reduce forecast error and uncertainty in real-time. This study has shown the value of these observations to pure research, furthering the understanding of characteristics of ARs from observations. This simple technique for identifying sectors within an AR can be applied across a variety of studies, for example in forecast diagnostics and assessing model performance. Improvement in the forecast models would allow for better prediction of landfalling ARs that bring both beneficial and damaging precipitation to the U.S. West Coast. Results from this study can help to inform the sampling strategy of ARs, by further analyzing the sensitivity of forecasts to assimilation of dropsondes in different sectors, therefore helping to bridge the gap between observations and models. Following work also examines dropsondes in the sectors defined in this study to assess atmospheric reanalysis products, which is important as these are the closest we get to spatially homogeneous observations. This work supports ongoing collaborations involving CW3E, NOAA, NRL, U.S. Army Corps of Engineers, NCAR, and ECMWF.

Figure 1. Locations of dropsondes deployed during IOP5 2020, centered around 00 UTC 5th February. Color of dots reflects sector of dropsonde (see legend). Non-AR cold side (NCS), AR cold sector (CS), AR core (C), AR warm sector (WS), non-AR warm side (NWS). ERA5 IVT at central time shown in colored contours and mean sea level pressure shown in grey contour lines.

Figure 2. a) Composite vertical profiles of water vapor flux using 154 non-AR cold side, 197 cold sector, 247 core, 207 warm sector, 53 non-AR warm side dropsondes. 95% confidence interval shown at 500 m increments. b) Fraction of IVT for AR sectors (cold sector: CS, core: C, warm sector: WS). Mean shown in solid line and one standard deviation shown in shading. 0.5 and 0.75 fractions are shown in dashed vertical lines with the corresponding height value marked in triangles and stars on the y axis. c) Cumulative IVT with mean in solid line and one standard deviation in shading for all sectors.

Cobb, A., A. Michaelis, S. Iacobellis, F.M. Ralph, and L. Delle Monache, 2020: Atmospheric river sectors: Definition and characteristics observed using dropsondes from 2014-2020 CalWater and AR Recon. Mon. Wea. Rev., https://doi.org/10.1175/MWR-D-20-0177.1.

CW3E AR Update: 22 December 2020 Outlook

December 22, 2020

Click here for a pdf of this information.

Multiple storms forecast to bring precipitation to the Western U.S. over the next 7 days

An atmospheric river (AR) associated with a surface cyclone is forecast to make landfall along the U.S. West Coast on 25–26 Dec
A cutoff low may bring additional impacts to the southwestern U.S. on 28–29 Dec, but forecast uncertainty is currently high
The GFS and ECMWF are forecasting more than 2 inches of precipitation over portions of the Pacific Coast Ranges and Cascades during the next 7 days

Click images to see loops of GFS IVT & IWV forecasts Valid 0000 UTC 22 December – 0000 UTC 30 December 2020

Probability of AR Conditions Along Coast: dProg/dt

Model Runs: 00Z 18 Dec 2020 – 00Z 22 Dec 2020 (every 12 h)

Summary provided by C. Castellano, J. Kalansky, and F. M. Ralph; 22 December 2020

*Outlook products are considered experimental

CW3E Publication Notice: A soil moisture monitoring network to assess controls on runoff generation during atmospheric river events

CW3E Publication Notice

A soil moisture monitoring network to assess controls on runoff generation during atmospheric river events

December 22, 2020

CW3E hydrologist Edwin Sumargo, CW3E affiliate Hilary McMillan, CW3E mesoscale modeler Rachel Weihs, CW3E field researcher Carly Ellis, CW3E field research manager Anna Wilson, and CW3E Director F. Martin Ralph published a paper in the Hydrological Processes, titled “A soil moisture monitoring network to assess controls on runoff generation during atmospheric river events” (Sumargo et al. 2020). As part of CW3E’s 2019-2024 Strategic Plan to support Forecast Informed Reservoir Operations (FIRO), CW3E researches the impacts of atmospheric rivers (ARs) on water management and public safety in order to improve the prediction capability. This study highlights the role of soil moisture in runoff generation from precipitation during AR events and the value-added for hydrologic model design and calibration. Ultimately, this work supports ongoing collaborations involving CW3E, California Department of Water Resources, NOAA, Sonoma Water, and the U.S. Army Corps of Engineers to improve streamflow predictions and develop situational awareness tools for FIRO at Lake Mendocino.

Soil moisture is a key modifier of runoff generation from rainfall excess. This paper presents a new and publicly available dataset from a soil moisture monitoring network in Northern California’s Russian River Basin (Fig. 1), designed to assess soil moisture controls on runoff generation under AR conditions. The observations consist of 2‐minute volumetric soil moisture at 19 sites and 6 depths (5, 10, 15, 20, 50, and 100 cm). We present short analyses of these data to demonstrate their capability to characterize soil moisture responses to precipitation across sites and depths, including time series analysis, correlation analysis, and identification of soil saturation thresholds that induce runoff. Our results show strong inter‐site Pearson’s correlations at the seasonal timescale (Fig. 2). Correlations are strong (>0.8) during events with wet antecedent soil moisture and during drydown periods, and weak (<0.5) otherwise. High event runoff ratios are observed when certain antecedent soil moisture thresholds are exceeded, and when antecedent runoff is high. Our analyses also indicate three ways in which soil moisture data are valuable for model design: (1) with multi‐depth sensors, statistical tests can be used to identify which depths show differences in soil moisture dynamics and, therefore, should be used by modelers to define distinct model layers; (2) time series analysis indicates the role of soil moisture processes in controlling runoff ratio during precipitation, which hydrologic models should replicate; and (3) analysis of decreases in soil moisture spatial correlation helps identify which areas of the watershed would benefit from a distributed calibration of model parameters related to soil moisture.

Figure 1. Terrain base maps showing the locations of RHONET soil moisture observations (left), including the HMT and CW3E stations within the Lake Mendocino sub‐basin (right). Also shown is a California map with pointers on Russian River basin and Bodega Bay ARO site (top left inset). The CW3E and United States geological survey (USGS) stream gauges are also shown, which are parts of the RHONET in the greater Russian River basin as well as within the Lake Mendocino sub‐basin. Orange contours delineate areas that drain into five CW3E stream gauges.

Figure 2. Pearson’s correlation maps of 2‐min soil moisture VWCn with BCC site at 10‐cm depth for (a) autumn (Oct–Dec), (b) winter (Jan–mar), (c) spring (Apr–Jun), and (d) summer (Jul–Sep) of WYs 2018–2019. The thick black contours demarcate the Lake Mendocino sub‐basin. The sites where the correlations are statistically significant at 99% significance level are outlined in black.

Sumargo, E., McMillan, H., Weihs, R., Ellis, C. J., Wilson, A. M., and Ralph, F. M. (2020). A soil moisture monitoring network to assess controls on runoff generation during atmospheric river events. Hydrologic Processes, e13998, https://doi.org/10.1002/hyp.13998.