Odds of Reaching 100% Water Year Precipitation – Dec Update

Odds of Reaching 100% of Normal Precipitation for Water Year 2018 (December Update)

December 8, 2017

Contribution from Dr. M.D. Dettinger, USGS

The odds shown here are the odds of precipitation in the rest of the water year (after November 2017) totaling a large enough amount to bring the water-year total to equal or exceed the percentage of normal listed. “All Yrs” odds based on monthly divisional precipitation totals from water year 1896-2015. Numbers in parenthesis are the corresponding odds if precipitation through March had been precisely normal (1981-2010 baseline).

Click here for a pdf file of this information.

 

 

 

How these probabilities were estimated:

At the end of a given month, if we know how much precipitation has fallen to date (in the water year), the amount of precipitation that will be required to close out the water year (on Sept 30) with a water-year total equal to the long-term normal is just that normal amount minus the amount received to date. Thus the odds of reaching normal by the end of the water year are just the odds of precipitation during the remaining of the year equaling or exceeding that remaining amount.

To arrive at the probabilities shown, the precipitation totals for the remaining months of the water year were tabulated in the long-term historical record and the number of years in which that precipitation total equaled or exceeded the amount still needed to reach normal were counted. The fraction of years that at least reached that threshold is the probability estimate. This simple calculation was performed for a full range of possible starting months (from November thru September) and for a wide range of initial (year-to-date) precipitation conditions. The calculation was also made for the probabilities of reaching 75% of normal by end of water year, 125%, and 150%, to ensure that the resulting tables of probabilities cover almost the full range of situations that will come up in the future.

[One key simplifying assumption goes into estimating the probabilities this way: The assumption that the amount of precipitation that will fall in the remainder of a water year does not depend on the amount that has already fallen in that water year to date. This assumption was tested for each month of the year by correlating historical year-to-date amounts with the remainder-of-the-year amounts, and the resulting correlations were never statistically significantly different from zero, except possibly when the beginning month is March, for which there is a small positive correlation between Oct-Mar and Apr-Sept precipitation historically.]

Contact: Michael Dettinger (USGS)

CW3E Publication Notice: GPM Satellite Radar Measurements of Precipitation and Freezing Level in Atmospheric Rivers: Comparison with Ground-Based Radars and Reanalyses

CW3E Publication Notice

GPM Satellite Radar Measurements of Precipitation and Freezing Level in Atmospheric Rivers: Comparison with Ground-Based Radars and Reanalyses

December 6, 2017

Forest Cannon, postdoc at CW3E, along with CW3E director Marty Ralph, fellow postdoc Anna Wilson, and UCLA professor Dennis Lettenmaier, recently published a paper in the Journal of Geophysical Research – Atmospheres, titled: GPM Satellite Radar Measurements of Precipitation and Freezing Level in Atmospheric Rivers: Comparison with Ground-Based Radars and Reanalyses.

In their study, satellite radar reflectivity profiles from the Global Precipitation Measurement Dual-Frequency Precipitation Radar (GPM) were used to evaluate precipitation and temperature characteristics of Atmospheric Rivers (AR) over the western coast of North America and eastern North Pacific Ocean. Notably, their comparison of GPM bright band height with a network of ground-based vertically profiling radars along the West Coast demonstrated exceptional agreement, as did comparison with freezing level height from reanalyses over the eastern North Pacific Ocean (Figure 1; Figure 5 from the paper). These results indicate that GPM can be used to independently validate freezing level in models.

Additionally, the study identified significant differences in the frequency and intensity of precipitation between GPM and reanalyses over the eastern Pacific Ocean, indicating biases in both satellite-observed and modeled AR precipitation. Importantly, low-intensity precipitation rates accounted for a 20% increase in total precipitation in reanalyses compared to GPM-DPR, and AR conditions, specifically, contributed nearly 10% more to total GPM precipitation than reanalyses.

These results demonstrate that the advanced GPM satellite radar yields tremendous benefit for reducing the data gap over the global oceans and for supplementing the current understanding of precipitation processes in ARs.

Cannon, F. F.M. Ralph, A.M. Wilson, and D.P. Lettenmaier, 2017: GPM satellite radar measurements of precipitation and freezing level in atmospheric rivers: Comparison with ground-based radars and reanalyses. J. Geophys. Res. Atmos. DOI: 10.1002/2017JD027355

 

Click here for a personal pdf of the article

CW3E AR Update: 20 November 2017 Outlook

CW3E AR Update: 20 November 2017 Outlook and Summary

November 20, 2017

Click here for a pdf of this information.

A Potentially Extreme and Persistent AR is forecast to Impact the Pacific Northwest

  • A potentially extreme AR is forecast to impact the Pacific Northwest over the next 4 days
  • AR conditions could last over 50 hours in portions of Oregon and Northern California
  • As much as 15 inches of precipitation is forecast to fall over the Olympic Mountains over the next 5 days
  • Several rivers in Washington are currently forecast to rise above flood stage
  • Click IVT or IWV image to see loop of 0-180 hour GFS forecast

    Valid 1200 UTC 20 November – 0000 UTC 28 November 2017

     

     

     

     

     

     

    Summary provided by C. Hecht, B. Kawzenuk, J. Kalansky, and F.M. Ralph; 1 PM PT Friday 20 November 2017

    *Outlook products are considered experimental

CW3E AR Update: 17 November 2017 Outlook and Summary

CW3E AR Update: 17 November 2017 Outlook and Summary

November 17, 2017

Click here for a pdf of this information.

Strong AR recently made landfall over northern California

  • The AR reached its strongest magnitude of ~750 kg m-1 s-1 at ~6 PM PST over northern California making this a strong AR
  • IWV values within the AR ranged from 34–40 mm during the event
  • A second AR is forecast to make landfall over the USWC between 19 and 21 November 2017
  • The AR is currently over Southern California bringing precipitation to the Los Angeles area
  • Another AR is forecast to impact the USWC in the next several days

SSMI/SSMIS/AMSR2-derived Integrated Water Vapor (IWV)

Valid 0000 UTC 15 November – 1600 UTC 17 November 2017

Images from CIMSS/Univ. of Wisconsin

Click IVT or IWV image to see loop of GFS Analysis

Valid 0000 UTC 15 November – 1200 UTC 17 November 2017


 

 

A potentially extreme AR is forecasted to make landfall over the U.S. West Coast next week

  • The current AR impacting Southern California is forecast to end by later tonight
  • Multiple systems are forecast to bring potentially strong to extreme and prolonged AR conditions to the USWC
  • As much as 19 inches of precipitation could fall over the Olympic Mountains over the next week
  • Multiple rivers in Washington are currently forecast to rise above flood stage

Click IVT or IWV image to see loop of 0-180 hour GFS forecast

Valid 1200 UTC 17 November – 0000 UTC 25 November 2017

 

 

 

 

 

 

Summary provided by C. Hecht, B. Kawzenuk, J. Kalansky, and F.M. Ralph; 3 PM PT Friday 17 November 2017

*Outlook products are considered experimental

Lake Mendocino Forecast Informed Reservoir Operations Steering Committee Submit Major Deviation Request

Lake Mendocino Forecast Informed Reservoir Operations Steering Committee Submit Major Deviation Request

November 15, 2017

On November 2nd members of the Lake Mendocino Forecast Informed Reservoir Operations (FIRO) Steering Committee1 submitted a major deviation request to Lt. Colonel Travis Rayfield, Commander of the San Francisco District, US Army Corps of Engineers. The purpose of the request is to improve water supply reliability and environmental conditions while maintaining flood management capacity of Lake Mendocino.

The deviation request, based on the Lake Mendocino FIRO Preliminary Viability Assessment, represents the culmination of a three-year collaborative effort by the FIRO Steering Committee to produce a significant body of technical and scientific work including watershed and atmospheric observations, atmospheric and hydrologic forecast analyses, and parallel modeling applications. If approved, this deviation would result in a maximum additional storage of 11,650 acre-feet between November 1 and February 28. The figure below shows the existing guide curve for the Coyote Valley Dam Lake Mendocino Water Control Manual and the proposed guide curve with the requested changes.

Existing Lake Mendocino guide curve (red dashed line) and the proposed guide curve with requested changes (blue solid line).

1 The Lake Mendocino FIRO Steering Committee consists of representatives from the Sonoma County Water Agency (SCWA), Scripps Institute of Oceanography (Scripps), U.S. Army Corps of Engineers (USACE), National Oceanic and Atmospheric Administration (NOAA), U.S. Geologic Survey (USGS), U.S. Bureau of Reclamation and the California Department of Water Resources. This deviation request is being submitted on behalf of steering committee members representing the following organizations: Sonoma County Water Agency, Scripps Institution of Oceanography, US Army Corps of Engineers, National Oceanic and Atmospheric Administration, and California Department of Water Resources.

CW3E AR Update: 14 November 2017 Outlook

CW3E AR Update: 14 November 2017 Outlook

November 14, 2017

Click here for a pdf of this information.

Two ARs Forecast to Impact the USWC over the Next Week

  • An AR currently impacting the Pacific Northwest is expected to end in the next several hours
  • A potentially strong AR (IVT >750 kg m-1 s-1) is forecast to impact California between 15 and 17 November
  • A second AR is forecast to make landfall over the USWC between 19 and 21 November 2017
  • Precipitation forecasts range from 5–8 inches over higher elevations associated with the first AR
  • Forecast uncertainty is currently high for the 19–21 November AR

Click IVT or IWV image to see loop of 0-168 hour GFS forecast

Valid 1200 UTC 14 November – 2100 UTC 21 November 2017


 

 

 

 

 

Summary provided by C.Hecht, B. Kawzenuk, J. Kalansky, and F.M. Ralph; 1 PM PT Wednesday 14 November 2017

*Outlook products are considered experimental

CW3E AR Update: 8 November 2017 Outlook

CW3E AR Update: 8 November 2017 Outlook

November 8, 2017

Click here for a pdf of this information.

Two ARs Forecasted to Make Landfall over the U.S. West Coast in the Next Week

  • A strong AR is currently making landfall over the U.S. West Coast
  • This AR is expected to produce up to 6 inches of precipitation over northern CA
  • The southerly orientation of this AR will result in the heaviest precipitation over the north Central Valley
  • A second, moderate strength, AR is forecasted to make landfall over northern CA, OR, and WA on 12 November 2017
  • The second AR is expected to make landfall further north resulting in the highest precipitation over the Olympic and Cascade

Click IVT or IWV image to see loop of 0-168 hour GFS forecast

Valid 1200 UTC 8 November – 1200 UTC 15 November 2017


 

 

 

 

 

Summary provided by B. Kawzenuk, J. Kalansky, and F.M. Ralph; 12 PM PT Wednesday 8 November 2017

*Outlook products are considered experimental

CW3E Hosts California DWR Winter Outlook Workshop

CW3E Hosts California DWR Winter Outlook Workshop

November 6, 2017

CW3E hosted the annual California Department of Water Resources Winter Outlook Workshop (WOW) from Nov. 1-3, at Scripps Institution of Oceanography. The purpose of the workshop is to highlight the latest science in seasonal to subseasonal (S2S), 1-month to 3-month, atmospheric forecasting. This timescale bridges the gap between weather and climate prediction. The meeting was organized by Jeanine Jones, ‎Interstate Resources Manager, and covered a variety of topics including paleoclimate, week three predictions, atmospheric rivers (ARs), summer North American monsoon, new forecasting tools, and drought.

During the first day, Dave Meko, from University of Arizona, discussed paleodrought in Southern California and how this compared to paleodrought in Northern California and in the Colorado River Basin. The second day of the workshop highlighted recent accomplishments in subseasonal to seasonal forecasting. Dr. David DeWitt, NCEP CPC Director, presented on the S2S activities on-going at the National Weather Service (NWS) Climate Prediction Center (CPC). Dr. Marty Ralph, Director of CW3E, gave an overview of the activities at CW3E related to observations, modeling and S2S prediction ARs. This was followed by a session chaired by Dr. Duane Waliser and Dr. Aneesh Subramanian on current S2S activities at CW3E and an experimental CW3E week-3 AR outlook product. The session had three talks presented by Dr. Alexander Gershunov, Dr. Michael DeFlorio, and Dr. Aneesh Subramanian on the experimental CW3E week-3 AR outlooks and the multi-pronged effort to design and evaluate the product. The day ended with presentation by Yolande Serra, from the University of Washington, on the dynamics and predictability of the summer monsoon. The third and final day began with a presentation on the influence of ARs in the Colorado River Basin as well an historical perspective on atmospheric river maps by Jon Rutz, National Weather Service. The last presentation of the day was by Dan Cayan on how various atmospheric patterns can lead to drought in the western U.S. WOW provided an opportunity for CW3E researchers and collaborators to share their latest advancements in subseasonal to seasonal forecasting and discuss future research collaboration and needs.

CW3E Director, Marty Ralph, discusses the research and activities at CW3E during the DWR WOW.

During the workshop Jeanine Jones also presented Department of Water Resources Climate Service Awards to Dr. Jason Cordeira, Plymouth State University, Dr. Duane Waliser, NASA JPL and Dr. Dave Meko, University of Arizona. The awards highlight the three individuals’ contribution to climate science as it applies to DWR operations. Jason Cordiera, a close collaborator of CW3E spoke of the honor, “My collaboration with CW3E has led to the synergistic development of many weather forecast tools that have benefited and informed water resource management and related impact-based decision support. Receipt of the CA DWR Climate Science Service Award reflects the dedication of many individuals at CW3E and Plymouth State who support and provide invaluable resources to maintain a productive research and application environment. Thank you to the CA DWR for the honor and I look forward to continued collaboration in pursuit of improving our ability to understand and forecast hydrological extremes”.

Recipients of the Department of Water Resources Climate Service Awards, presented at the WOW. From left, Dr. Duane Waliser, NASA JPL, Dr. Dave Meko, University of Arizona, and Dr. Jason Cordeira, Plymouth State University.

Atmospheric Rivers Highlighted in the U.S. Fourth National Climate Assessment

Atmospheric Rivers Highlighted in the U.S. Fourth National Climate Assessment

November 6, 2017

Click here for a pdf of this information.

The Fourth National Climate Assessment, released last week, highlights atmospheric rivers as a key topic of its chapter on “Extreme Storms.” The other storm types addressed in this section are “tropical storms (hurricanes and typhoons),” “severe convective storms (thunderstorms)” and “winter storms.

The “Key findings” on atmospheric rivers are: “The frequency and severity of landfalling “atmospheric rivers” on the U.S. West Coast (narrow streams of moisture that account for 30%–40% of the typical snowpack and annual precipitation in the region and are associated with severe flooding events) will increase as a result of increasing evaporation and resulting higher atmospheric water vapor that occurs with increasing temperature. (Medium confidence).”

This major report further highlighted the atmospheric river topic by using a satellite image of an atmospheric river hitting the U.S. West Coast in February 2017 for the cover page of the entire report.


 

 

Contacts: Duane Waliser, F. Martin Ralph

CW3E AR Update: 3 November 2017 Outlook

CW3E AR Update: 3 November 2017 Outlook

November 3, 2017

Click here for a pdf of this information.

Two systems expected to produce precipitation over the U.S. West Coast in the next week

  • AR conditions (IVT >250 kg m-1 s-1 and IWV >20 mm) are expected over most of CA over the next four days
  • While AR conditions are forecast for some locations of the USWC, this event is not necessarily an AR due to geometric and spatial structure, but could produce up to 5 inches of precipitation and some snow over the Sierra Nevada
  • A potentially strong AR is expected to make landfall over CA, OR, and WA on 8 November 2017
  • The highest amounts of precipitation are expected over the coastal ranges of CA and OR
  • The AR is currently expected to have a southerly orientation which will result in less extreme precipitation

Click IVT or IWV image to see loop of 0-180 hour GFS forecast

Valid 1200 UTC 3 November – 0000 UTC 11 November 2017


 

 

 

 

 

 

 

Summary provided by B. Kawzenuk, J. Kalansky, C. Hecht, and F.M. Ralph; 3 PM PT Friday 3 November 2017

*Outlook products are considered experimental