CW3E R-Cat Alerts

CW3E R-Cat Alerts: Automated Notification of Heavy Precipitation Events

March 10, 2016

The Center for Western Weather and Water Extremes (CW3E) has set up an automated e-mail notification service that informs users of heavy precipitation events in near real-time. Along the West Coast, such events are often the result of land-falling atmospheric rivers, which transport substantial moisture into the area. Tracking, analyzing, improving the forecasting, and anticipating the impacts of such extreme events are a core element of CW3E’s mission.

The “Rainfall Category” or “R-Cat” 3-day precipitation classification of Ralph and Dettinger (2012) is a simple, effective measure of strong precipitation events, which can have a large impact on the Western U.S.:

R-Cat 1: 200-299 mm (roughly 8-12 inches) / 3 days

R-Cat 2: 300-399 mm (roughly 12-16 inches) / 3 days

R-Cat 3: 400-499 mm (roughly 16-20 inches) / 3 days

R-Cat 4: more than 500 mm (more than roughly 20 inches) / 3 days

An R-cat email alert includes a short summary of the 3-day total precipitation, location of the event (based on sources such as the Global Historical Climatology Network [GHCN] and the National Weather Service’s co-op precipitation stations), and a map showing the location of the event(s). Here is a recent example:

————————————————————————————————————
Station: BRUSH CREEK RS USC00041130
Location: (39.695, -121.345)
Date: 2016/03/07 (third day of event)
Event strength: R-Cat 1
3-day total precip (mm): 206.3
Individual days precip (mm): 76.5 102.1 27.7
 
————————————————————————————————————
Station: QUINCY USC00047195
Location: (39.937, -120.948)
Date: 2016/03/07 (third day of event)
Event strength: R-Cat 1
3-day total precip (mm): 202.7
Individual days precip (mm): 59.7 119.9 23.1

The email R-Cat alert service can be subscribed to by sending a message with the subject line “subscribe” to rcatalert@cirrus.ucsd.edu.

For more information, please contact David Pierce, dpierce@ucsd.edu.

CW3E AR Update: 10-11 March 2016 Outlook

CW3E AR Update – 10-11 March 2016 Outlook

March 10, 2016

A storm predicted to make landfall over northern California on 10 March 2016 has characteristics of an Atmospheric River. The AR is showing weak-to-moderate strength with an average landfall duration of 12-24 hours. This AR is about 75% as strong as the last significant AR landfall over northern California (March 5-6, 2016). The storm has the slight potential for R-Cat 1 rainfall in favored mountain areas. For up to date AR forecasts visit the CW3E AR Portal.



CW3E AR Update: 5-7 March 2016 Outlook

CW3E AR Update – 5-7 March 2016 Outlook

March 4, 2016

A storm predicted to make landfall over northern California on 5 March 2016 has characteristics of an Atmospheric River. The AR is showing moderate strength with an average landfall duration of 12-24 hours. The storm has the potential for R-Cat 1 rainfall in favored mountain areas. For up to date AR forecasts visit the CW3E AR Portal.


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.

    Reconnaissance Flights Into Atmospheric Rivers Aim To Improve West Coast Storm Predictions

    Reconnaissance Flights Into Atmospheric Rivers Aim To Improve West Coast Storm Predictions

    February 13, 2016

    Scripps Oceanography, NOAA, U.S. Air Force team up on flights through atmospheric rivers this month, starting with flights on Saturday 13 February into a moderate strength AR between Hawaii, Alaska and the Pacific Northwest. Although of only moderate strength, this AR is likely to stall somewhere in the WA-OR area, creating a long-duration AR landfall. The long duration of landfall is key to determining whether the AR produces extreme rainfall and possibly flooding, or is more of a benefit to water supply and snow pack. Details in the AR conditions offshore, that are not represented accurately in the “initial conditions” needed for weather prediction limit the skill of forecasts of AR landfall duration and intensity. The flights today, one from Hawaii, and one from Tacoma WA, are aimed at reducing that uncertainty.

    Researchers at Scripps Institution of Oceanography, UC San Diego have developed a new method for improving atmospheric river (AR) forecasts that is being used for the first time in National Weather Service-directed flights over the Pacific Ocean.

    Scientist F. Martin Ralph, director of the Center for Western Weather and Water Extremes at Scripps, said the observations made aboard two U.S. Air Force C-130 aircraft later this month are aimed at improving forecasters’ ability to say exactly where storms will make landfall. Current forecasts of landfall location of ARs made one to three days in advance are typically off by 300 kilometers (200 miles).

    Contact: F. Martin Ralph (CW3E Director, and PI of the C-130 AR Recon Mission)

    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.


     

     

     

     

     

     

    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.