CW3E AR Update: 6 February 2017 Outlook

CW3E AR Update: 6 February 2017 Outlook

February 6, 2017

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Two ARs to Impact the West Coast

  • Two moderate to strong ARs are forecasted to make landfall in Northern CA and the Pacific Northwest
  • Due to the timing of both ARs, AR conditions could last over 90 hours in some locations
  • Weather Prediction Center forecast shows 1-5 Day precipitation amounts up to 17.5 inches over higher elevations in Sierras
  • 15 river gauges are currently forecast to rise above flood stage by the California Nevada River Forecast Center

Click IVT or IWV image to see loop of 0-126 hour GFS forecast

Valid 1200 UTC 6 Feb – 1800 UTC 11 Feb 2017


 

 

 

 

 

Summary provided by C. Hecht and F.M. Ralph; 3 PM PT Mon 06 Feb. 2017

CW3E AR Update: 1 February 2017 Outlook

CW3E AR Update: 1 February 2017 Outlook

February 1, 2017

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Precipitation forecast for Northern CA Pacific Northwest

  • A low pressure system is forecast to propagate toward Northern CA and Oregon
  • Up to 6 inches of precipitation are forecast to fall over higher elevations, while low elevations of N. CA could see as much as 2.5 inches
  • This event is not representative of an AR structure (long and narrow plumes IVT and IWV), though the IVT and IWV thresholds associated with an AR will be met at certain locations
  • Extended forecasts indicate the potential for an AR to make landfall in the next 5–7 days

Click IVT or IWV image to see loop of 0-126 hour GFS forecast

Valid 1200 UTC 6 Feb – 1800 UTC 11 Feb 2017


 

 

 

 

Summary provided by C. Hecht and F.M. Ralph; 12 PM PT Wed 01 Feb. 2017

Water year 2017 Precipitation

Water year 2017 Precipitation in California

January 24, 2017

The wetness of this winter in northern California has been truly exceptional. Only two past winters on record have had as much precipitation to date as this year has in the Sacramento River watershed, which is key to California water supply. And each of those was a major flood year.

CW3E AR Update: 19 January 2017 Outlook

CW3E AR Update: 19 January 2017 Outlook

January 19, 2017

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Update on 3 ARs Forecast to Impact the West Coast Over Next Several Days

  • AR 1 made landfall over the Pacific Northwest and propagated southward impacting the entire U.S. West Coast
  • 1–6 inches of precipitation have fallen over the last 48-h over portions of California
  • AR 2 and 3 are forecast to make landfall over Southern and Central CA, respectively, over the next 5 days
  • Forecast certainty is high for AR2 but still low for AR 3
  • NOAA Weather Prediction Center precipitation forecasts for the next 5 days in Southern CA are as high as 10 inches over the high elevations and 1–5 inches in the valleys


 

 

 

 

 

 

 

 

 

 

 

 

 

Summary provided by C. Hecht, and F.M. Ralph; 3 PM PT Thurs. 19 Jan. 2017

CW3E AR Update: 17 January 2017 Outlook

CW3E AR Update: 17 January 2017 Outlook

January 17, 2017

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Multiple ARs Forecast to Make Landfall Over Next Week

  • Three ARs are currently forecast to make landfall over the U.S. West Coast at different times over the next 5 days
  • The first AR is forecast to make landfall over the Pacific Northwest today and is associated with strong AR conditions (IVT 750–1000 kg/m/s)
  • The second AR is forecast to make landfall over Southern CA from 20 – 22 Jan and is associated with strong AR conditions (IVT 750–1000 kg/m/s)
  • The third AR is forecast to make landfall over Central CA and could potentially be associated with strong AR conditions (IVT 750–1000 kg/m/s)
  • Forecast uncertainty is currently high with both AR 2 and 3
  • Weather Prediction Center precipitation forecasts currently range from 3–9 inches with AR 1, 2–4 inches with AR 2, and 2–5 inches with AR 3


 

 

 

 

 

 

Summary provided by C. Hecht, and F.M. Ralph; 3 PM PT Mon 17 Jan. 2017

CW3E AR Update: 11 January 2017 Outlook

CW3E AR Update: 11 January 2017 Outlook

January 11, 2017

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A look back at how the forecasts changed ahead of and during the active AR landfall period from 8-11 January (dProg/dT) and for next possible AR landfall next week

Forecasts initialized 0600 UTC 4 Jan – 0600 UTC 11 Jan


 

 

 

Summary provided by B. Kawzenuk, C. Hecht, and F.M. Ralph; 3 PM PT Wed 11 Jan. 2017

CW3E in the News

CW3E in the News

January 10, 2017

Due to several recent landfalling Atmospheric Rivers (ARs), the media has been contacting CW3E for their expert commentary. We share some recent examples below.

Director of CW3E, Marty Ralph, recently joined Here & Now’s Meghna Chakrabarti on National Public Radio to discuss ARs and their impact on California’s water supply. He described how ARs form and generate precipitation and how their annual variability largely impact the annual precipitation in California. The interview can be heard here.

Dr. Ralph also discussed the importance of ARs with Alex Cohen on Take Two, this interview can he heard here

Given the importance of water supply to California, Forecast Informed Reservoir Operations (FIRO) has also gained media attention. The most recent volume of the Flood Risk Management Newsletter highlights the potential of FIRO to improve resiliency to droughts and floods by improving water supply and decreasing flood risk. The newsletter can be found here.

The impacts of the most recent AR caused widespread damages and hazardous conditions from the extreme precipitation (see CW3E AR Update: 9 January 2017 Outlook and Summary). Prior to the event as forecast confidence grew several CW3E forecast tools were featured in various news outlets. One example can be seen here, as the Capital Weather Gang highlighted the Time Integrated Water Vapor Transport maps produced by CW3E. After the event Marty Ralph describes the large variability in California’s annual precipitation and the importance of flood management strategies. Article found here.

Click here for more CW3E news.

CW3E AR Update: 9 January 2017 Outlook and Summary

CW3E AR Update: 9 January 2017 Outlook

January 9, 2017

Click here for a pdf of this information.


 

 

 

Strong AR forecast to impact California this weekend

  • Another AR is forecast to make landfall over Central California tonight and last until Wednesday evening
  • As much as 10 more inches of rain could fall over already saturated soil
  • Lower freezing levels may cause most of the higher elevations to receive snow instead of rain
  • Several river gauges are forecast to rise back above flood stage with little time to recover back to normal after this past weekends AR

Click IVT or IWV image to see loop of 0-72 hour GFS forecast

Valid 1800 UTC 9 Jan – 1800 UTC 12 Jan 2017

 

 

 

 

 

Summary provided by C. Hecht, B. Kawzenuk, and F.M. Ralph; 3 PM PT Mon 9 Jan. 2017

Odds of Reaching 100% Water Year Precipitation – Jan Update

Odds of Reaching 100% of Normal Precipitation for Water Year 2017 (January Update)

January 9, 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 December 2016) 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 October 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 AR Update: 6 January 2017 Outlook

CW3E AR Update: 6 January 2017 Outlook

January 6, 2017

Click here for a pdf of this information.
 

Update on Strong AR over the weekend

  • Forecast confidence of AR conditions have improved since yesterday’s update
  • Moderate AR conditions could last over 24-hrs over some locations in Central CA
  • 1–3 Day Precipitation forecasts by the Weather Predication Center are as high as 15.5 inches over high elevations of Sierras
  • 19 river gauges are currently forecast to rise above flood stage by the California Nevada River Forecast Center
  • Extended forecasts show another AR making landfall next week, though the forecasts are more uncertain

Click IVT or IWV image to see loop of 0-132 hour GFS forecast

Valid 1200 UTC 6 Jan – 0000 UTC 12 Jan 2017


 

 

 

 

 

 

Summary provided by C. Hecht, B. Kawzenuk, and F.M. Ralph; 5 PM PT Fri 6 Jan. 2017

Products presented in this outlook are meant for informational purposes and are not intended to support decision making operations