Odds of Reaching 100% Water Year Precipitation – March Update

Odds of Reaching 100% of Normal Precipitation for Water Year 2016 in California (March update)

March 10, 2016

Contribution from Dr. M.D. Dettinger, USGS

The Febraury 2016 precipitation observations are now in, and have allowed for an update to the calculation of the odds of reaching 100% of normal for the water year across three key climate divisions of California and Nevada. These odds have decreased slightly across all of California and Nevada as a result of a very dry February. The odds of reaching 100% of normal Water Year precipitation in the key northern California climate division that encompasses the Sacramento River, and the State’s largest water supply reservoirs, decreased from 52% as of the end of January 2016, to 38% as of the end of February 2016. A series of Atmospheric Rivers have made landfall over Northern California and produced heavy precipitation throughout early March and will most likely cause changes in these odds when updated at the end of March.


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 (for all years, for only El Ninos, or for only La Ninas) 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. Contact mddettin@usgs.gov for more information.

[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 AR Update: 3 March 2016 Outlook

CW3E AR Update: 3 March 2016 Outlook

March 3, 2016

CW3E gives an outlook on current and upcoming Atmospheric River (AR) events along the U.S. West Coast. A moderate AR is currently impacting central California producing light precipitation over the northern Sierra Nevada and Central Valley. Two ARs are expected to make landfall over the Pacific Northwest in the next seven days, with both propagating south over California prior to dissipation. Long range forecasts also show the potential for another strong AR to make landfall in the Pacific Northwest next week.

For the latest river and precipitation forecasts and observations visit the California Nevada River Forecast Center (CNRFC) or the U.S. Geological Survey (USGS). For the latest AR forecasts visit the CW3E AR Portal.

Click here for a pdf file of this information.


 

Current Conditions: 3/3/2016
Northeast Pacific SSMI IWV: 1400 UTC 29 Feb 2016 – 1400 UTC 3 March 2016


 
GPS Integrated Water Vapor: 1515 UTC 3 March 2016
 
 
 
   
IWV values greater than 2 cm
throughout central California
-Current AR conditions

Current California Precipitation Conditions
The North Sierra 8-Station and Tulare Basin 6-Station Precipitation Indices are average for this time of year.


 

 
Forecasts
AR Landfall Probability Tool: Initialized 0000 UTC 3 March 2016
Hover mouse over description below to see forecast product or click to open. Images courtesy Jason Cordeira; Plymouth State University

IVT >250 kg m-1 s-1
IVT >500 kg m-1 s-1
Inland IVT >250 kg m-1 s-1
Inland IVT >500 kg m-1 s-1

  • Periods of AR conditions forecasted along most the U.S. West Coast on forecast days 0-1, 1-2, 2-5 and 4-5
  • Strong probability of AR event on forecast days 7-8
  • All forecasted ARs are expected to penetrate inland over Oregon and northern California


 


 
CNRFC River Forecasts
2000 UTC 3 March 2016
 
 

  • 1 river forecasted above flood stage
     -Navarro River
  • 7 rivers forecasted above monitor stage

    Russian River CNRFC Forecast


     
    GFS Ensemble MJO Index Forecast; 3 March 2016 – 17 March 2016

     

    • A continuation of MJO activity is expected
    • Propagation through Phases 8 and 1 and possibly 2
    • Significant decrease in amplitude

    GFS IWV: 0600 UTC 3 March 2016 – 1800 UTC 10 March 2016
     
      >

    • AR currently impacting northern and central California
    • AR to make landfall at 1800 UTC 4 March 2016 over NW Pacific
    • AR to make landfall at 0600 UTC 9 March 2016 over NW Pacific
    • All three ARs propagate south over California prior to dissipation

    GFS IVT: 0600 UTC 3 March 2016 – 1800 UTC 10 March 2016
     



     
    CNFRC Precipitation Forecasts: Produced 3 March 2016

    Max 72-h precip >6 inches over Northern Sierra Nevada and California Coastal Range
    Max 6-day precip ~11 inches over Northern Sierra Nevada and California Coastal Range

     
    7-day Precipitation Forecasts: Ending 4:00 am PST 10 March 2016

    Max 7-day precip ~290 mm over Northern Sierra Nevada, Olympic Mountains and Vancouver Island
    Max 7-day precip ~270 mm over Northern Sierra Nevada, Olympic Mountains and Vancouver Island


     

     
     

    Summary

    • Current dissipating AR impacting central California
    • Two moderate strength ARs expected to make landfall along the U.S. West Coast over the next five days
    • Another AR may potentially make landfall late next week
    • 7-day precipitation totals up to 300 mm in multiple locations over the U.S. West Coast


    For more information about AR updates or forecast products visit the CW3E Home Page or contact Brian Kawzenuk, Marty Ralph, or Scott Sellars at CW3E.

    Odds of Reaching 100% Water Year Precipitation – February Update

    Odds of Reaching 100% of Normal Precipitation for Water Year 2016 in California (February update)

    February 8, 2016

    Contribution from Dr. M.D. Dettinger, USGS

    The January 2016 precipitation observations are now in, and have allowed calculation of the odds of reaching 100% of normal for the water year across three key climate divisions of California. These odds have increased slightly in Northern California, and decreased slightly in Southern California. The previous estimate had been based on observations only through December 2015. The state was affected by a series of storms in January, including atmospheric river events, such as the one highlighted in an earlier CW3E storm summary (see the storm summaries posted on 5, 8 and 15 January 2016 under “What’s New” on the CW3E web page – cw3e.ucsd.edu). The odds of reaching 100% of normal Water Year precipitation in the key northern California climate division that encompasses the Sacramento River, and the State’s largest water supply reservoirs, increased from 32% as of the end of December 2015, to 52% as of the end of January 2016.


    California Storm of 5 January 2016: A Preliminary Synopsis of a Marginal Landfalling Atmospheric River

    California Storm of 5 January 2016: A Preliminary Synopsis of a Marginal Landfalling Atmospheric River

    January 5, 2016

    CW3E researchers Brian Kawzenuk and Scott Sellars and DRI researcher Nina Oakley provide a preliminary analysis and synopsis of a weak Atmospheric River that made landfall over southern California on 5 January 2016. The AR was the first event in what will be an active week over the North Pacific and brought significant precipitation throughout central and southern California. The AR initially developed near Japan and propagated across the entire North Pacific Ocean before making landfall. A brief forecast for the rest of the week is also provided by the San Diego National Weather Service Forecast Office, courtesy Roger Pierce.

    Click here for a pdf file of this information.

     

     

     

     

     

     

    Above is a sequence of SSMI water vapor imagery from 01-05 January 2016 which shows the Atmospheric River propagating towards California and making landfall.

    -Atmospheric River intially developed over the northwestern Pacific Ocean
    -AR propagated eastward and strengthened
    -AR became disconnected with its parent low and began to dissipate prior to landfall
    -Secondary cyclogenesis occurred just off the California/Oregon coast north of the AR shortly before landfall
    -AR made landfall over southern California at ~0600 UTC 5 January 2016

     

    Above is a sequence of integrated vapor transport (IVT) from the GFS analysis during 31 December 2015 to 5 January 2016 which shows the Atmospheric River propagating towards California and making landfall.


     

     

     

    Above is a sequence of Jason Cordeira’s AR Landfall tool initialized between 0600 UTC 29 Dec 2015 and 0600 UTC 5 Jan 2016. The sequence shows how the forecast developed over the previous eight days and shows the skill this tool had in forecasting the AR. For more information on this product visit the AR Forecast page.

    – Greater than 50% of ensemble members predicted the landfall of the AR ~8 days in advance
    – Greater than 85% of ensemble members predicted the landfall of the AR ~3 days in advance
    – AR conditions were not forecasted over southern CA until ~5 days in – advance
    – Between days 8 and 3 duration of AR conditions forecasted ranged from ~18–48 hours
    – Duration and location of AR conditions remained constant and accurate during days 0–3 forecasts

    The following forecast is from the San Diego National Weather Service Forecast Office

    The weather pattern in SoCal will be very active this week with several storm systems moving through the region. This afternoon through Wednesday morning will bring moderate to heavy rainfall over the coast, valleys, foothills and deserts, with heavy snowfall occurring in the mountains above 5,500 ft. Total snowfall for the through Wednesday morning will be around a foot for elevations above 5,500 ft, with lesser amounts between 4,500 and 5,500 ft. Rainfall totals through Wednesday morning will be 1 to 1.5 inches west of the mountains with local amounts near 2 inches in the foothills. If you have travel plans at anytime during the week, especially in the mountains, check local conditions and be prepared for inclement weather. Another storm with moderate to high impacts will affect the region Wednesday afternoon through Wednesday night. A third system on Thursday will bring additional rain and mountains snow, but it appears to be less intense than the first two.

    Pacific Northwest Storm of 13-15 November 2015: A Synopsis of Landfalling Atmospheric River Conditions

    Pacific Northwest Storm of 13-15 November 2015: A Synopsis of Landfalling Atmospheric River Conditions

    November 25, 2015

    CW3E researcher Brian Kawzenuk provides an analysis and synopsis of an Atmospheric River that made landfall along the U.S. Pacific Northwest over the 13-15 November 2015 period. The AR made initial landfall along the Washington coast and lead to significant precipitation for nearly three days throughout western Oregon, Washington, and British Columbia. The AR initially developed near Japan and propagated across the entire North Pacific Ocean before making landfall.


     

    Above is a sequence of 30-minute NEXRAD radar composite imagery from 12-15 November 2015 which shows precipitation throughout the Pacific Northwest during nearly the entire period.


     

     

    The above loop shows SSMI Integrated Water Vapor during 10-15 November 2015.


     

     

     

     

     

     

    A Preliminary Summary of Highway 58 and I-5 Flooding Event of October 15, 2015

    A Preliminary Summary of Highway 58 and I-5 Flooding Event of October 15, 2015

    October 27, 2015

    Nina Oakley (WRCC/DRI), Jeremy Lancaster (CGS), John Stock (USGS), Brian Kawzenuk (CW3E), and Mike Kaplan (DRI) provide an analysis and synopsis of the meteorological and geological conditions that produced alluvial fan flooding over portions of Highway 58 and Interstate 5 in southern California. A weakening cutoff low that had entrained subtropical moisture moved onshore over southern California, initiating convection and localized heavy precipitation. Hillslope runoff concentrated in steep valleys where it entrained debris. The debris then flowed onto steep alluvial fans at the base of these valleys, inundating portions of I-5 and State Hwy 58.

    Click here for pdf file of this information.


     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

    Click here for pdf file of this information.

    Improving Understanding of Atmospheric Rivers: Legislation Authorized by California Governor Brown

    Improving Understanding of Atmospheric Rivers: Legislation Authorized by California Governor Brown

    October 12, 2015

    The Center for Western Weather and Water Extremes (CW3E) is grateful for the approval of legislation that will improve California’s ability to respond to major precipitation episodes. This legislation, recently approved, will aim to allow the state of California to better manage water supplies by expanding climate and weather research that is focused on the causes of drought and flood.

    The two images below show an example of research aimed at improving forecasting ability. The two maps show the integrated water vapor (IWV) forecast from February 9, 2014. The top panel shows a CW3E simulation by a regional model (called West-WRF). The bottom panel shows a national forecast by the Global Forecasting System (GFS). The CW3E simulation offers a resolution of 9km while the national forecast is at 0.5 degrees (approximately 100km). This improved model forecast horizontal resolution will allow forecasters to better pinpoint heavy precipitation events aimed at the west coast.

    westwrf_forecast_comparison

    Please find more at the Scripps Institution of Oceanography news page: https://scripps.ucsd.edu/news/legislation-improve-understanding-atmospheric-rivers-authorized-governor

    Resilience in a Changing Climate: Sonoma County Adaptation Forum

    Resilience in a Changing Climate: Sonoma County Adaptation Forum

    April 15, 2015

    CW3E director Marty Ralph and scientist Julie Kalansky presented at the Sonoma County Adaptation Forum on April 8th. The forum was modeled after state forums, but was the first regional adaptation forum in California. The forum focused on information and approaches to help mitigate the impacts of climate change in Sonoma County and surrounding areas. The audience of over 200 people included city and county leaders, utility managers, environmental groups and the public.

    Both Marty and Julie presented in the first session of the morning entitled “Extreme Weather Science; Drought and Deluge in Sonoma County.” Jay Jasperse, Chief Engineer and Director of Groundwater Management at Sonoma County Water Agency, moderated the session. The other panelists included Tim Doherty, from NOAA’s Office for Coastal Management, who discussed the impacts of sea level rise on the region, and Dr. Lisa Micheli, Executive Director of Pepperwood Preserve, who presented on the importance of downscaling climate models to understand the regional response to climate change. Marty Ralph discussed the importance of atmospheric rivers (ARs) to the water supply as well as the potential flooding risk associated with ARs. This led into an explanation of the FIRO, forecast informed reservoir operations, project for improving the water supply resilience of Lake Mendocino. At the end of his presentation he introduced the first part of an ongoing NOAA-NIDIS and Sonoma County Water Agency funded project to examine how the frequency and intensity of ARs may change in future. The link below is to an interview with Marty Ralph about atmospheric rivers and the forum that was broadcasted on North Bay Public Radio.

    http://radio.krcb.org/post/charting-local-adaptations-climate-change

    After Marty’s presentation, Julie presented on the second part of the study including the development of a “mega-drought” stress test for the region and working with the community to understand the all the different dimensions of drought. During Julie’s presentation, she was able to involve the audience and received feedback on the vulnerabilities to drought and the difficult decisions that surround drought. The day was a great success in bringing together scientists, decisions makers and the public to discuss how to make the community more resilient to climate change.

    Sonoma County Water Agency video posted about Atmospheric Rivers

    Sonoma County Water Agency (SWCA) Video posted about Atmospheric Rivers (ARs)

    March 4, 2015

    CW3E is pleased to be part of a recent video produced by our partners at the Sonoma County Water Agency (SCWA) and hosted by SCWA Director Shirlee Zane. This video focuses on the importance of Atmospheric Rivers (ARs) to California’s precipitation. Extremes of both drought and flood are examined for their link to ARs and impact on the Sonoma region. Emphasis is placed on the importance of understanding ARs and applying that knowledge to create better forecast information to help SCWA prepare for drought and potential flood conditions. Shirlee points out a key goal of our collaboration: “retain water without increasing flood risk”.

    California Drought: 2013/14 4th driest water year on record

    California Drought: 4th driest water year depletes reservoirs

    October 1, 2014

    CW3E partners at the Sonoma County Water Agency (SCWA) are quoted in a recent article in the Santa Rosa Press Democrat marking water year 2013/14 as the 4th driest on record.

    lake_mendocino_30sep2014

    The baked lakebed of Lake Mendocino shows a carp head (photo taken 30 September 2014 by Press Democrat photographer Kent Porter)

    Dwindling reservoir levels are one of the main concerns due to the drought – Lake Mendocino is only 27% full. The article mentions the research partnership between SCWA and CW3E. Understanding the key role of atmospheric rivers in the area’s water supply is a focus of the research agreement. Please find the full article (including additional photos and a video) at: http://www.pressdemocrat.com/news/2909680-181/north-coast-water-woes-reflected