October 2016 Summary

October 2016 Summary

November 23, 2016

CW3E provides a summary of October 2016, one of the wettest Octobers on record for the Western United States. Several Atmospheric Rivers (ARs) made landfall along the U.S. West Coast and led to record setting precipitation production. For specific details on AR events refer to the CW3E AR Summaries, found on the CW3E News page.

Click here for a pdf file of this information.



 

 

 

 

 

 

 

 

 

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

Publication Notice: Forecasting Atmospheric Rivers during CalWater 2015

CW3E Publication Notice

Forecasting Atmospheric Rivers during CalWater 2015

November 22, 2016

Cordeira, J., F. Ralph, A. Martin, N. Gaggini, R. Spackman, P. Neiman, J. Rutz, and R. Pierce, 0: Forecasting Atmospheric Rivers during CalWater 2015. Bull. Amer. Meteor. Soc., 0, doi: 10.1175/BAMS-D-15-00245.1.

As part of CW3E’s mission and goals a new set of atmospheric river (AR)-focused diagnostic and prediction tools have been created, in close partnership with Plymouth State University’s Prof. Jason Cordeira, and building upon work done earlier at NOAA under the HMT Program (see Ralph et al. 2013 BAMS, Wick et al. 2013 Wea. Forecasting). These developments were accelerated and focused by the needs for specialized AR forecast displays to support the CalWater field campaigns in 2014 and 2015 (see Ralph et al. 2016, BAMS). CalWater used research aircraft to observe atmospheric rivers and carried out aerosol science. These developments are summarized in a paper on the forecasting tools that were used in the CalWater field campaign by CW3E researchers and collaborators (Cordeira et al.) that was recently published in Bulletin of the American Meteorological Society (BAMS). The paper details some of the new AR forecasting tools developed using NCEP Global Forecast System and Global Ensemble Forecast System. A novel AR landfall detection forecast tool illustrates the probability of AR conditions at different locations along the western coast of the US. Another new forecast tool that used the various ensemble members illustrates the possible range of integrated water vapor transport (IVT) at a specific location using each of the ensemble members. In addition, the high quality plots of forecasted IVT and observed integrated water vapor supported the CalWater field campaign. Beyond supporting the CalWater Field Campaign, these new forecasting tools will likely improve AR forecasting throughout the West Coast. All these and more of the new forecasting tools can be found on the CW3E website under “Atmospheric River Resources.”

84-h NCEP GFS gridded forecast of IVT magnitude (kg m-1s-1 and direction; initialized at 1200 UTC on 3 February 2015; (b) as in (a), except for the verifying analysis of IVT magnitude and direction at 0000 UTC 7 February 2015 with overlaid draft flight track of the NOAA G-IV aircraft (c) GPS-derived IWV (mm) at 0015 UTC 7 February 2015.


Abstract

Atmospheric Rivers (ARs) are long and narrow corridors of enhanced vertically integrated water vapor (IWV) and IWV transport (IVT) within the warm sector of extratropical cyclones that can produce heavy precipitation and flooding in regions of complex terrain, especially along the U.S. West Coast. Several field campaigns have investigated ARs under the “CalWater” program of field studies. The first field phase of CalWater during 2009–2011 increased the number of observations of precipitation and aerosols, among other parameters, across California and sampled ARs in the coastal and near-coastal environment, whereas the second field phase of CalWater during 2014–2015 observed the structure and intensity of ARs and aerosols in the coastal and offshore environment over the Northeast Pacific. This manuscript highlights the forecasts that were prepared for the CalWater field campaign in 2015 and the development and use of an “AR portal” that was used to inform these forecasts. The AR portal contains archived and real-time deterministic and probabilistic gridded forecast tools related to ARs that emphasize water vapor concentrations and water vapor flux distributions over the eastern North Pacific, among other parameters, in a variety of formats derived from the NCEP Global Forecast System and Global Ensemble Forecast System. The tools created for the CalWater 2015 field campaign provided valuable guidance for flight planning and field activity purposes, and may prove useful in forecasting ARs and better anticipating hydrometeorological extremes along the U.S. West Coast.

Click here for personal use PDF file

Points of contact: Jason Cordeira, F. Martin Ralph, Brian Kawzenuk

CW3E Hosts Winter Outlook Workshop with California DWR

CW3E Hosts Winter Outlook Workshop with California DWR

November 18, 2016

The California Department of Water Resources (CDWR) and CW3E led a working meeting with researchers at the Scripps Institution of Oceanography in La Jolla, November 16-18, 2016. The workshop focused on efforts to improve sub-seasonal to seasonal prediction of precipitation, which could help agencies better manage water resources.

“We’d all like to know if 2017 will be wet or dry, but determining that is scientifically difficult. We’re trying to emphasize the need for prioritizing this research in the science community,” said Jeanine Jones, Interstate Resources Manager at CDWR.

Participants from the following agencies were in attendance: CW3E/Scripps, CDWR, Sonoma County Water Agency (SCWA), National Center for Atmospheric Research (NCAR), Natonal Weather Service (NWS), Western States Federal Agency Support Team (WestFAST), National Oceanic and Atmospheric Administration (NOAA), Plymouth State University (PSU), Oregon State University (OSU), University of California, Los Angeles (UCLA), Salt River Project (SRP), Climate Assessment for the Southwest (CLIMAS), Desert Research Institute (DRI), and Metropolitan Water District of Southern California (MWD).

Images courtesy DWR Photography – Florence Low

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.