Water Year 2016 Summary

Water Year 2016 Summary

October 15, 2016

CW3E provides a summary of the top ten precipitation events based on the Northern Sierra 8-Station index during Water Year 2016 (Oct. 1 2015 – Sep. 30 2016). The top ten events occurred over a total of 27 days, and resulted in 30.09 inches of precipiation representing 51.89% of total water year precipitaiton and 60.2% of normal water year precipitation. All events were associated with an Atmospheric River (AR), with 6 considered strong ARs (IVT >750 kg m-1) s-1. For event specific reports refer to the CW3E News Page. For up to date AR forecasts and analysis visit the CW3E AR Portal.

Click here for a pdf file of this information.


 

 

 

 

 

Summary provided by B. Kawzenuk, and F.M. Ralph

CW3E AR Update: 4-9 November 2016 Outlook

CW3E AR Update: 4-9 November 2016 Post Event Summary

November 4, 2016

Two consecutive ARs are expected to make landfall over the Northwest U.S. and Southwest British Columbia. Current forecasts show both ARs with moderate strength, although there is high uncertainty in the forecast of the second AR. Despite high values of integrated vapor transport (IVT) forecasted precipitation values of the Northwest U.S. are modest due to the southwesterly orientation of the ARs. However, this orientation is favorable for precipitation production over Vancouver Island, where 5-day precipitation forecasts are >12 inches. For up to date AR forecasts visit the CW3E AR Portal.

Click here for a pdf file of this information.


 

 

Summary provided by C. Hecht, B. Kawzenuk, and F.M. Ralph; 3 PM PT Fri 05 Nov. 2016

CW3E AR Update: Post-Event Summary: 14-17 October 2016

CW3E AR Update: 14-17 October 2016 Post-Event Summary

October 20, 2016

CW3E gives a post-event storm summary about two Atmospheric Rivers that made landfall over the Pacific Northwest during 14-17 October 2016. This event was an R-Cat 3 event and produced over 15 inches of 72-hour precipitation.

Click here for a pdf file of this information.

NCEP GFS Analysis – Valid: 0000 UTC 12 Oct 2016 – 0600 UTC 17 Oct 2016

 

NEXRAD Radar: 0000 UTC 14-17 Oct 2016

  • Radar imagery shows widespread precipitation over the Pacific Northwest during 14-17 Oct 2016
  • Severe convection on 14 Oct produced multiple tornadoes in OR and high winds across the region
  • Throughout the period the PNW was impacted by several alternating periods of stratiform and convective precipiation


 

 

 

 

 

 

 

 

 

CW3E AR Update: 13-15 October 2016 Outlook

CW3E AR Update: 13-15 October 2016 Outlook

October 12, 2016

A series of ARs are expected to make landfall over the Northwest U.S., including Northern CA. The first AR is expected to make landfall on 13 October 2016 followed by a second AR on 15 October 2016. These systems have R-Cat 2 rainfall potential as some areas could see >12 inches of precipitation in 72 hours. For up to date AR forecasts visit the CW3E AR Portal.

Click here for a pdf file of this information.


 

 

Publication Notice: Extreme Daily Precipitation in the Northern California Upper Sacramento River Watershed Requires a Combination of a Landfalling Atmospheric River and a Sierra Barrier Jet

CW3E Publication Notice

Extreme Daily Precipitation in the Northern California Upper Sacramento River Watershed Requires a Combination of a Landfalling Atmospheric River and a Sierra Barrier Jet

July 18, 2016

Ralph, F.M., J.M. Cordeira, P.J. Neiman and M. Hughes, 2016: Extreme Daily Precipitation in the Northern California Upper Sacramento River Watershed Requires a Combination of a Landfalling Atmospheric River and a Sierra Barrier Jet. J. Hydrometeor., 17, 1904-1915.

The top 0.3% most extreme daily precipitation events in the key Sacramento River watershed all involved both a landfalling atmospheric river and a Sierra Barrier Jet. Thus, forecasts of extreme precipitation are related to the skill of forecasts of each of these key phenomena, and can be enhanced by evaluation of, and enhancement of, skill in predicting each of these key processes. This study was led by the CW3E Director, was supported by the California Department of Water Resources, used data from NOAA’s Hydrometeorology Testbed collected over a decade, and epitomizes the focus of the “Center for Western Weather and Water Extremes,” and its partnership with NOAA Research’s Physical Sciences Division and Plymouth State University.

Contact: F. Martin Ralph (mralph@ucsd.edu)

Abstract

The upper Sacramento River watershed is vital to California’s water supply and is susceptible to major floods. Orographic precipitation in this complex terrain involves both atmospheric rivers (ARs) and the Sierra barrier jet (SBJ). The south-southeasterly SBJ induces orographic precipitation along south-facing slopes in the Mt. Shasta–Trinity Alps, whereas landfalling ARs ascend up and over the statically stable SBJ and induce orographic precipitation along west-facing slopes in the northern Sierra Nevada. This paper explores the occurrence of extreme daily precipitation (EDP) in this region in association with landfalling ARs and the SBJ. The 50 wettest days (i.e., days with EDP) for water years (WYs) 2002–11 based on the average of daily precipitation from eight rain gauges known as the Northern Sierra 8-Station Index (NS8I) are compared to dates from an SSM/I satellite-based landfalling AR-detection method and dates with SBJ events identified from nearby wind profiler data. These 50 days with EDP accounted for 20% of all precipitation during the 10-WY period, or 5 days with EDP per year on average account for one-fifth of WY precipitation. In summary, 46 of 50 (92%) days with EDP are associated with landfalling ARs on either the day before or the day of precipitation, whereas 45 of 50 (90%) days with EDP are associated with SBJ conditions on the day of EDP. Forty-one of 50 (82%) days with EDP are associated with both a landfalling AR and an SBJ. The top 10 days with EDP were all associated with both a landfalling AR and an SBJ.

Lake Mendocino Forecast-Informed Reservoir Operations (FIRO) Workshop Summary

Lake Mendocino Forecast-Informed Reservoir Operations (FIRO) Workshop Summary

July 5, 2016

Experts from multiple disciplines and organizations came together for the third annual FIRO workshop, which was held at UC San Diego/Scripps Institution of Oceanography (SIO) from 27-29 June 2016. This workshop was hosted jointly by the Sonoma County Water Agency (SCWA) and SIO’s Center for Western Weather and Water Extremes (CW3E). It was organized by the FIRO Steering Committee, co-chaired by CW3E’s Marty Ralph and SCWA’s Jay Jasperse. There were a total of 52 attendees from organizations including the US Army Corps of Engineers (USACE), California Department of Water Resources (CA DWR), National Oceanic and Atmospheric Administration (NOAA), US Geological Survey (USGS), US Bureau of Reclamation (USBR), SCWA and CW3E.

During the workshop, participants shared recent updates on FIRO activities, discussed reservoir conditions during water year 2016, summarized progress toward goals identified in the FIRO Workplan and identified issues to address regarding development of the Lake Mendocino FIRO “Preliminary Viability Assessment.” Progress was summarized on defining FIRO information requirements (e.g., forecast parameters and lead times), assessing current forecast skill, exploring the origins of forecast errors, advances in atmospheric river science, results of preliminary estimates of FIRO implications on Lake Mendocino water supply, and discussion of potential additional reservoirs for which FIRO may hold promise. Individual task groups (Preliminary Viability Assessment, Science, and Communications/Outreach) conducted break-out sessions in order to discuss progress and next steps towards meeting project goals (see photos below). In addition, the 11-member Lake Mendocino FIRO Steering Committee met afterward to review the workshop outcomes and plans. In short, the initial goals of year-1 of the 5-year FIRO Workplan are on track to be met, including development of the Preliminary Viability Assessment. Longer-term actions supporting the Full Viability Assessment are beginning and transferability is being discussed.

Lake Mendocino FIRO is summarized at http://cw3e.ucsd.edu/firo/.

Contacts: F. Martin Ralph (CW3E Director; mralph@ucsd.edu) and J. Jasperse (SCWA Chief Engineer; Jay.Jasperse@scwa.ca.gov)

Mesoscale Frontal Wave AR during CalWater-2014

CW3E Publication Notice

An Airborne and Ground-Based Study of a Long-Lived and Intense Atmospheric River with Mesoscale Frontal Waves Impacting California during CalWater-2014

May 10, 2016

Neiman, P.J., B.J. Moore, A.B. White, G.A. Wick, J. Aikins, D.L. Jackson, J.R Spackman, and F.M. Ralph, 2016: An Airborne and Ground-Based Study of a Long-Lived and Intense Atmospheric River with Mesoscale Frontal Waves Impacting California during CalWater-2014. Mon. Wea. Rev., 144, 1115-1144.

This study provides the most comprehensive observations to date of a mesoscale frontal wave associated with an atmospheric river, including its structure offshore, landfall characteristics and impacts on precipitation. It utilizes research aircraft, a unique array of coastal hydrometeorological measurements and inland data. This paper reflects the broader scientific collaboration between CW3E and NOAA/PSD, and adds to the knowledge of phenomena that are critical to creating extreme precipitation on the U.S. West Coast – a major thrust of CW3E. Dr. Ralph contributed to this paper by proposing the experiment (Ralph et al. 2016 BAMS), identifying the science objective for the flights (i.e., mapping out the structure of a mesoscale frontal wave with dropsondes and airborne radar), laying out the flight tracks, guiding the mission onboard, having been the PI of the major projects that created the unique land-based observing network (NOAA HMT- Ralph et al. 2013 BAMS, and the DWR-sponsored EFREP mesonet – White et al. 2013 JTech) used in the study and contributing to the analysis and interpretation of the measurements in this paper.

Contacts: Paul Neiman (paul.j.neiman@noaa.gov) and F. Martin Ralph (mralph@ucsd.edu)

Abstract

The wettest period during the CalWater-2014 winter field campaign occurred with a long-lived, intense atmospheric river (AR) that impacted California on 7–10 February. The AR was maintained in conjunction with the development and propagation of three successive mesoscale frontal waves. Based on Lagrangian trajectory analysis, moist air of tropical origin was tapped by the AR and was subsequently transported into California. Widespread heavy precipitation (200–400 mm) fell across the coastal mountain ranges northwest of San Francisco and across the northern Sierra Nevada, although only modest flooding ensued due to anomalously dry antecedent conditions. A NOAA G-IV aircraft flew through two of the frontal waves in the AR environment offshore during a ;24-h period. Parallel dropsonde curtains documented key three dimensional thermodynamic and kinematic characteristics across the AR and the frontal waves prior to landfall. The AR characteristics varied, depending on the location of the cross section through the frontal waves. A newly implemented tail-mounted Doppler radar on the G-IV simultaneously captured coherent precipitation features. Along the coast, a 449-MHz wind profiler and collocated global positioning system (GPS) receiver documented prolonged AR conditions linked to the propagation of the three frontal waves and highlighted the orographic character of the coastal-mountain rainfall with the waves’ landfall. Avertically pointing S-PROF radar in the coastal mountains provided detailed information on the bulk microphysical characteristics of the rainfall. Farther inland, a pair of 915-MHz wind profilers and GPS receivers quantified the orographic precipitation forcing as the AR ascended the Sierra Nevada, and as the terrain-induced Sierra barrier jet ascended the northern terminus of California’s Central Valley.

Publication Notice: Predictability of Horizontal Water Vapor Transport Relative to Precipitation

CW3E Publication Notice

Predictability of Horizontal Water Vapor Transport Relative to Precipitation: Enhancing Situational Awareness for Forecasting Western U.S. Extreme Precipitation and Flooding

March, 2016

Lavers, D.A., D.E. Waliser, F.M. Ralph and M.D. Dettinger, 2016: Predictability of horizontal water vapor transport relative to precipitation: Enhancing situational awareness for forecasting western U.S. extreme precipitation and flooding. Geophysical Research Letters, 43, doi:10.1002/2016GL067765 (Please click here for personal use pdf file)

The following paper has just appeared in Geophysical Research Letters. It was motivated by the critical role of horizontal vapor transport in determining the strength and distribution of extreme precipitation in the Western U.S., and by the fact that this transport is the defining characteristic of atmospheric rivers, which are key to many extreme events in the region. The work was carried out primarily at CW3E in response to interest from State and local water agencies to explore new methods to predict extreme precipitation events. While the findings are based on U.S. West Coast domains, the results are applicable to other west coasts of mid latitude continents where cool season orographic precipitation is a key process. The results support the use of water vapor transport as a variable to monitor for earlier awareness of extreme hydrometeorological events.

(e) The average interannual predictability (r2) across the 30°N–50°N, 125°W–120°W region. (f) The predictability throughout the forecast horizon calculated using all winter forecasts (n = 2796) at 38°N, 122°W. From Lavers et al. (2016).

Contacts: David Lavers (david.lavers@ecmwf.int) and F. Martin Ralph (mralph@ucsd.edu)

Abstract

The western United States is vulnerable to socioeconomic disruption due to extreme winter precipitation and floods. Traditionally, forecasts of precipitation and river discharge provide the basis for preparations. Herein we show that earlier event awareness may be possible through use of horizontal water vapor transport (integrated vapor transport (IVT)) forecasts. Applying the potential predictability concept to the National Centers for Environmental Prediction global ensemble reforecasts, across 31 winters, IVT is found to be more predictable than precipitation. IVT ensemble forecasts with the smallest spreads (least forecast uncertainty) are associated with initiation states with anomalously high geopotential heights south of Alaska, a setup conducive for anticyclonic conditions and weak IVT into the western United States. IVT ensemble forecasts with the greatest spreads (most forecast uncertainty) have initiation states with anomalously low geopotential heights south of Alaska and correspond to atmospheric rivers. The greater IVT predictability could provide warnings of impending storminess with additional lead times for hydrometeorological applications.