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.

    The Washington Post Capital Weather Gang features CW3E and Atmospheric River Field Mission

    The Washington Post Capital Weather Gang features CW3E and Atmospheric River Field Mission

    February 18, 2016

    The Washington Post Capital Weather Gang today (18 February 2016) featured the current observing missions happening over the eastern Pacific as coordinated by CW3E director Dr. F. Martin Ralph. Current missions are starting from Hickam Air Force Base in Hawaii and include some 800-mile transects. Critical information about water vapor distribution and winds are gathered during these flights and are used as initial conditions in global forecast models. The article highlights several quotes from CW3E director Ralph including the importance of pin-pointing the landfall of an Atmospheric River. Regarding forecast uncertainty: “Where it hits is off by an average of plus or minus 500 kilometers,” Ralph said. “An atmospheric river is 500 kilometers wide, so the error can mean the difference of whether you’re hit or not.”

    Find the full article at The Washington Post Capital Weather Gang page: here.

    State-of-the-art WC-130J aircraft for weather reconnaissance missions. The aircraft is a C-130J transport configured with palletized weather instrumentation for penetration of tropical disturbances and storms, hurricanes and winter storms to obtain data on movement, size and intensity.The WC-130J carries a minimal crew of five: pilot, co-pilot, navigator, aerial reconnaissance weather officer and weather reconnaissance loadmaster. (U.S. Air Force photo/Tech. Sgt. Ryan Labadens)

    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.


    AR storms impact northern California: January 12-15

    AR storms impact northern California: January 12-15

    January 15, 2016

    DRI/CW3E researcher Nina Oakley, CW3E researcher Scott Sellars and other CW3E team members evaluate two storms that had an impact on northern California as well as the Pacific Northwest from 12-15 January 2016. Fresh Sierra snow can be seen in the cover satellite image from Friday, January 15 (courtesy NWS Sacramento). The approaching clouds from the next series of storms can be seen approaching the coast as well as valley fog in the Sacramento region. The first storm event leading to this fresh snow was a moderate atmospheric river (AR) storm with 1 to over 4 inches of precipitation from northern California to the Canadian border. The second storm event was weaker and ahead of a larger scale AR that will impact the same region from 15-18 January 2016. The weaker event spun off the Aleutian Low and produced some areas of heavy snowfall in the Sierra Nevada. An outlook for the upcoming AR event for 15-18 January is also briefly examined.

    Click here for a pdf file of this information.

     

     

     

     

     

     

     

    Above is a sequence of SSMI water vapor imagery from 10-13 January 2016 which shows the AR propagating towards northern California and making landfall.


     

     

     

     

     

     

    Above is a sequence of SSMI water vapor imagery from 12-15 January 2016 which shows the first AR making landfall and the dissipation of the second AR as it approaches land.

     

     

     

     

     

     

     

     

     

     

     

     

     

     

    Recent Rainy Week in San Diego County

    Recent Rainy Week in San Diego County

    January 8, 2016

    El Nino-fueled storms over the last few days, including a land-falling atmospheric river on 5 January (see cw3e.ucsd.edu for more details), have brought San Diego county’s accumulated winter precipitation to well above normal for this time of year. These numbers are tracked by the California-Nevada Applications program (cnap.ucsd.edu) and the Center for Western Weather and Water Extremes (cw3e.ucsd.edu) at UCSD’s Scripps Institution of Oceanography, in association with KPBS. The precipitation tracking tool shows the impact of the recent storms on the accumulated winter precipitation:

    In the last three days, San Diego county has received almost 17% of the amount of precipitation it receives in an entire year, on average.

    Precipitation gauge records compiled by the California Nevada River Forecast Center show accumulations of 3-5″ over much of the Los Angeles basin in the 72 hour period, reaching 7″ in some locations in the surrounding mountains. San Diego county accumulations are 1-3″ over much of the city, and 4-5″ in the North County interior:

    These storms bring San Diego county’s running total accumulated precipitation so far this winter to 42% of the total typically received over an entire average year. This is an above-average value for the first time since the winter started; typically, by this point in the winter, San Diego will have accumulated 32% of the average year-end total precipitation.

    Before the recent storms hit, the accumulated precipitation in the Los Angeles region since the winter started was only 11% of the typical end-of-winter total, far below the average value of 29%. In three days the accumulation has jumped to 27%. This rapid increase is more than is experienced in 95 out of 100 wet periods of 3-day duration in the region, leading to strong flows in the normally quiescent Los Angeles river and localized flooding in Southern California coastal areas.

    Precipitation during the week was widespread, with rain and snow delivered from Washington to Northern Mexico. California statewide totals also were boosted during the Jan 4-7 period (cnap.ucsd.edu), although amounts were not as heavy in Northern California as they were in Southern California.

    These accumulated precipitation totals can be tracked in real time from the California-Nevada Applications Project (CNAP) and Center for Western Weather and Water Extremes (CW3E)’s “San Diego Precipitation Page”. This includes monitoring of how current winter precipitation compares to that during the last 5 strongest El Nino winters (1982-83, 1997-98, 1957-58, 1972-73, and 1965-66), shown as the colored lines in the upper panels:

    The current El Nino event is is one of the three strongest in records that go back to 1950, with a broad area of unusually warm ocean surface waters in the tropical Pacific ocean and highly anomalous winds and other atmospheric conditions in the region. El Nino events can alter the North Pacific winter storm track, producing unusually wet winters in Southern California about 60% of the time, compared to about 11% of the time during years when no El Nino or its opposite, La Nina, is present. Forecasts indicate that El Nino conditions are likely to persist through the spring of 2016, before fading in the early summer of 2016.

    Points of contact: David Pierce (dpierce@ucsd.edu), Dan Cayan (dcayan@ucsd.edu), and Marty Ralph (mralph@ucsd.edu) at the Scripps Institution of Oceanography, UCSD.

    For a PDF version of this information click here.

    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.


     

     

     

     

     

     

    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

    Test Beds Linking Research and Forecasting

    Test Beds Linking Research and Forecasting

    September 10, 2013

    TestBeds Linking Research and Forecasting

    A new article written by Marty Ralph and colleagues was recently published in the Bulletin of the American Meteorological Society focusing on the emergence of weather-related test beds. The paper provides a brief background on how these test beds successfully bridged the gap between research and forecasting operations; summarizes test bed origins, methods and selected accomplishments; and provides a perspective on the future of test beds. A personal use copy of the paper can be obtained here.