CW3E AR Update: 18 October 2017 Outlook

CW3E AR Update: 18 October 2017 Outlook

October 18, 2017

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Multiple ARs forecast to Impact U.S. West Coast

  • A potentially extreme AR is forecast to make landfall over the Pacific Northwest today
  • NWS precipitation forecasts show accumulations of ~10 inches for the Olympic Mountains in northwest Washington
  • A second AR is forecast to make landfall on Saturday, though forecast uncertainty is currently high
  • Total 5-day precipitation accumulations could be as high as 15.5 inches
  • Current soil conditions are dry which could lead to less runoff and lower flooding potential

Click IVT or IWV image to see loop of 0-141 hour GFS forecast

Valid 0600 UTC 18 October – 0300 UTC 24 October 2017

For more information on the satellite imagery and the configuration click here

 

 

 

 

 

 

Summary provided by C. Hecht, B. Kawzenuk, and F.M. Ralph; 1 PM PT Wednesday 18 October 2017

*Outlook products are considered experimental

CW3E AR Update: 06 June 2017 Outlook

CW3E AR Update: 06 June 2017 Outlook

June 06, 2017

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Update on Late Season AR Forecast to Impact West Coast This Week

  • Little change from yesterday’s forecast
  • Ensemble GFS members are still in good agreement of the onset, duration, and maximum magnitude of coastal IVT
  • NOAA WPC precipitation forecasts are predicting as much as 4.2 inches over the Coastal Mountains of Northern CA and OR
  • A few rivers in the Cascade Range of WA and OR are forecast to rise to action or flood stage due to melting snow and the landfalling AR

Click IVT or IWV image to see loop of 0-114 hour GFS forecast

Valid 1200 UTC 06 June – 0600 UTC 11 June 2017


 

 

 

 

 

 

Summary provided by C. Hecht and F.M. Ralph; 12 PM PT Tuesday 06 June 2017

CW3E AR Update: 05 June 2017 Outlook

CW3E AR Update: 05 June 2017 Outlook

June 05, 2017

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Late Season AR Forecast to Impact West Coast

  • An unseasonably strong AR is forecast to impact the Pacific Northwest and Northern CA over the next couple of days
  • As much as 4.1 inches of precipitation is forecast to fall over the higher elevations of the Coastal Mountains in CA and OR over the next week
  • With higher freezing levels forecast during landfall, there is a potential for rain on snow and increased runoff
  • Due to the combination of snowmelt and the landfalling AR, several rivers in the Pacific Northwest are forecast to rise above flood stage

Click IVT or IWV image to see loop of 0-114 hour GFS forecast

Valid 1200 UTC 05 June – 0600 UTC 10 June 2017


 

 

 

 

 

 

Summary provided by C. Hecht and F.M. Ralph; 1 PM PT Monday 05 June 2017

CW3E AR Update: 11 April 2017 Outlook

CW3E AR Update: 11 April 2017 Outlook

April 11, 2017

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AR Currently Impacting West Coast

  • An AR is currently impacting Northern CA producing widespread precipitation over the region
  • A second AR is forecast to merge with the current AR, prolonging AR conditions over Northern CA
  • .25 to .88 inches of precipitation has already fallen across portions of Northern CA with >2.5 inches forecasted for higher elevations
  • This event could produce enough precipitation to make water year 2017 the wettest year recorded by the Northern Sierra 8-station index

SSMI Integrated Water Vapor (IWV)

Valid 10-11 April 2017

Click IVT or IWV image to see loop of 0-51 hour GFS forecast

Valid 1200 UTC 11 April – 1500 UTC 11 April 2017

A second AR with a separate parent low-pressure system is forecast to merge with the current AR, which could prolong AR conditions over portions of Northern CA


 

 

 

 

Summary provided by C. Hecht and F.M. Ralph; 1 PM PT Tuesday 11 April 2017

How Many Atmospheric Rivers Have Hit the U.S. West Coast During the Remarkably Wet Water Year 2017?

How Many Atmospheric Rivers Have Hit the U.S. West Coast During the Remarkably Wet Water Year 2017?

April 6, 2017

It has been well established that much of the west coast receives roughly 30-50% of its annual precipitation from landfalling atmospheric rivers. One of the goals of CW3E is to provide timely information on atmospheric rivers and their impacts on water in the West. The analysis presented here is based upon examination of AR conditions on each day from 1 October 2016 through 31 March 2017. Research-based criteria for AR identification have been used, especially the strength of integrated vapor transport (IVT). ARs are also ranked according to a simple scale introduced in 2016 (see inset in the graphic for the scaling).

As would be expected, one reason this winter has been so wet in the west is the large number of landfalling ARs. In addition, a large fraction of these events has been strong, or even extreme, in magnitude, and have caused serious flooding, and incidents like the Oroville Dam spillway issue.

Contacts: F. Martin Ralph, Chad Hecht, Brian Kawzenuk

There have been 45 total atmospheric rivers that have made landfall over the U.S. West coast from 1 October to 31 March 2017. Of the 45 total ARs, 10 have been Weak, 20 have been Moderate, 12 have been Strong, and 3 have been Extreme (Based on IVT magnitude). 1/3 of the landfalling ARs have been “strong” or “extreme”.

The large number of ARs that have made landfall over the U.S. West Coast have produced large amounts of precipitation. The Northern Sierra 8-station index is currently at 83.4 inches, which is just 5.1 inches below the wettest year on record with seven months remaining in the water year. The graphic below, from the California Department of Water Resources, highlights this information.

CW3E AR Update: 04 April 2017 Outlook

CW3E AR Update: 04 April 2017 Outlook

April 04, 2017

Click here for a pdf of this information.

AR conditions Forecast for Entire U.S. West Coast

  • An AR is currently impacting the Pacific Northwest while another AR is forecast to make landfall over Northern CA on Thursday
  • A mesoscale frontal wave that develops during the second AR could prolong the duration of AR conditions but uncertainty is currently high
  • 1–5 day precipitation forecasts are >6 inches over the high elevations of the Coastal Mts., Northern Sierra Mts., and Trinity Alps
  • Freezing levels are forecast to start at ~7,000 feet before dropping to ~3,000 feet, causing this to be a snow event for higher elevations
  • Wet soil and the potential for rain on snow at lower elevations raises the concern for flooding in eastern California and northern Nevada

Click IVT or IWV image to see loop of 0-114 hour GFS forecast

Valid 1200 UTC 04 April – 0600 UTC 09 April 2017


 

 

 

 

 

Summary provided by C. Hecht and F.M. Ralph; 1 PM PT Tuesday 04 April 2017

CW3E AR Update: 16 March 2017 Outlook

CW3E AR Update: 16 March 2017 Outlook

March 16, 2017

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Two ARs Forecast to Impact West Coast Over the Next Week

  • First AR to make landfall over Oregon Friday morning and primarily impact the Pacific Northwest and Northern CA
  • Second AR is forecast to impact Oregon and Northern CA beginning Monday Morning
  • Coastal Oregon could potentially experience strong AR conditions around 8 PM PDT Friday associated with first AR
  • Second AR could bring moderate AR conditions to Northern California but forecast confidence is currently low
  • Precipitation forecasts range from 2 to 4.8 inches over the high elevations of Northern California and the Pacific Northwest

Click IVT or IWV image to see loop of 0-150 hour GFS forecast

Valid 1200 UTC 16 March – 1800 UTC 22 March 2017


 

 

 

 

 

Summary provided by C. Hecht and F.M. Ralph; 1 PM PT Thurs 16 March 2017

CW3E AR Update: 28 February 2017 Post Event Summary and Outlook

CW3E AR Update: 28 February 2017 Post Event Summary and Outlook

February 28, 2017

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Summary of the ARs that impacted the U.S. West Coast over the past week

  • Landfalling AR brought weak-to-moderate AR conditions to portions of Southern CA for ~24 hours between 27 and 28 February
  • >6 inches of precipitation fell over the high elevations of San Diego County with lower elevations receiving 1.5–4 in.
  • The San Diego River rose to ~14.15 feet at 2 am 28 Feb, 2.8 feet above flood stage, and the 3rd highest peak all time
  • The heavy precipitation led to several road closures, multiple mudslides, hotel evacuations, and flooded businesses

Click IVT or IWV image to see loop of GFS analysis

Valid 0000 UTC 26 Feb – 0600 UTC 28 Feb 2017


 

 

 

 

 

 

 

Three ARs expected to make landfall over the U.S. West Coast over the next ten days

  • The first AR is expected to make landfall over the Pac NW ~1800 UTC 2 March 2017 with weak strength (IVT=250–500 kg m-1s-1). Weak AR conditions may propagate over N CA. prior to dissipation.
  • A second AR is expected to make landfall over N CA. at ~0000 UTC 5 March 2017. Coastal areas of N CA may see several hours of moderate strength AR conditions.
  • Long range forecasts indicate the potential for a third weak AR during 8-10 March 2017, however there is large uncertainty in the models beyond forecast day 5.
  • Large scale pattern beyond forecast day 9 indicates the potential for a return to active AR landfall conditions over the Pac NW
    Highest precipitation and impacts from these events is predicted to be over the Olympic and Cascade Mtns. in WA and Coastal Mtns. In NW CA.

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

Valid 0600 UTC 28 Feb – 1800 UTC 7 Mar 2017


 

 

 

 

 

 

Summary provided by C. Hecht, B. Kawzenuk, and F.M. Ralph; 1 PM PT Tues 28 Feb. 2017

CW3E AR Update: 22 February 2017 Post Event Summary

CW3E AR Update: 22 February 2017 Post Event Summary

February 22, 2017

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Summary of the ARs that impacted the U.S. West Coast over the past week

  • Three separate ARs made landfall and impacted the U.S. West from 14–21 February 2017
  • Over 20 inches of precipitation fell over some of the high elevations of the West Coast
  • There were 291 total storms reports made to NOAA NWS during the three ARs
  • A summary of the ARs and their impacts are discussed in this post event summary

SSMI Integrated Water Vapor (IWV)

Valid 14-21 Feb 2017

  • The first AR made landfall between 18 UTC (10 AM PST) 14 February and 00 UTC 15 February (4 PM PST 14 Feb) over the Pacific Northwest before propagating southward over California
  • Maximum IVT at the Coast was between 800 and 1000 kg/m/s, which is considered a strong AR
  • Some locations experienced AR conditions for up to 42 hours during this event
  • Note: The strength of AR conditions noted on this summary was determined based on 6-hourly NCEP GFS analysis periods and observed IVT magnitudes may have been higher at specific locations along the coast
  • The second AR, which developed in conjunction with a mesoscale frontal wave, made landfall ~6 UTC on 17 February (4 PM PST 16 Feb) over Southern CA
  • Some locations experienced AR conditions for up to 24 hours during this event
  • Note: The strength of AR conditions noted on this summary was determined based on 6-hourly NCEP GFS analysis periods and observed IVT magnitudes may have been higher at specific locations along the coast
  • The third AR made landfall at ~6 UTC on 20 February (4 PM PST 19 Feb) over the Northern Ca
  • Maximum IVT at the Coast was between 700 and 800 kg/m/s, which is considered a moderate strength AR
  • Some locations experienced AR conditions for up to 42 hours during this event
  • Note: The strength of AR conditions noted on this summary was determined based on 6-hourly NCEP GFS analysis periods and observed IVT magnitudes may have been higher at specific locations along the coast


 

 

 

 

 

 

Summary provided by C. Hecht, B. Kawzenuk, and F.M. Ralph; 3 PM PT Wed. 22 Feb. 2017

CW3E AR Update: 17 February 2017 Outlook

CW3E AR Update: 17 February 2017 Outlook

February 17, 2017

Click here for a pdf of this information.

Update on ARs Currently Impacting and Forecast to Impact West Coast

  • Precipitation continues to fall over a majority of California
  • The Transverse Mountains (north of Santa Barbara) have received over 3.5 inches in the last 24-hours
  • SoCal is forecast to receive another 2 – 6 inches in the next 24-hours, raising concerns for flooding and landslides
  • Forecast confidence for this weekends landfalling AR has increased over Northern California

NOAA NWS NEXRAD Pacific Southwest Radar Loop

Valid 10:08 AM – 11:18 AM PST 17 Feb 2017




 

 

 

 

 

 

 

Summary provided by C. Hecht and F.M. Ralph; 1 PM PT Fri 17 Feb. 2017