CW3E AR Update: 15 January Outlook

CW3E AR Update: 15 January Outlook

January 15, 2019

Click here for a pdf of this information.

Two ARs forecast impact the US West Coast over the next six days

  • A moderate strength AR is expected to make landfall over the U.S. West Coast during 17-18 January.
  • This AR is expected to produce up to 10 inches of precipitation over the Sierra Nevada in 72 hours.
  • A second AR is expected to make landfall over the Pacific Northwest during 19-20 January.
  • An additional 1-2 inches of precipitation over CA and 4-5 inches of precipitation in WA and OR could be produced from the second AR.
  • Lake Mendocino storage levels are currently near the top of the Water Supply Pool and precipitation this week could push storage levels into the Flood Control Pool.

Click IVT or IWV image to see loop of 0-144 hour GFS forecasts

Valid 1200 UTC 15 January – 1200 UTC 21 January 2019


 

 

 

 

 

 

 

Summary provided by B. Kawzenuk, J. Kalansky, and F. M. Ralph; 3 PM PT 15 January 2019

CW3E AR Update: 10 January Summary and Outlook

CW3E AR Update: 10 January Summary and Outlook

January 10, 2019

Click here for a pdf of this information.

Several ARs have made landfall over the U.S. West Coast over the past week

  • A strong AR made landfall over the PNW on 3-4 January, followed by a short lived moderate strength AR over much of the U.S. West Coast on 4-5 Jan, and a third AR made landfall on 8-9 January with moderate strength.
  • The 7 day accumulated precipitation from the three systems was over 300 mm over the Olympic Mountains and over 200 mm over the Coastal and Sierra Nevada Mountains in CA.
  • These short lived ARs are part of an active pattern over the North Pacific Ocean that will continue to produce ARs for the next several days.

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

Valid 0000 UTC 3 January – 0000 UTC 10 January 2019

SSMI/SSMIS/AMSR2-derived Integrated Water Vapor (IWV)

Valid 1200 UTC 6 January – 1200 UTC 10 January 2019

Images from CIMSS/Univ. of Wisconsin

 

NEXRAD Radar Reflectivity

Valid 0000 UTC 5 January – 1200 UTC 10 January 2019

Multiple ARs forecast impact the US West Coast over the next several days

  • A weak-to-moderate AR is expected to make landfall over the U.S. West coast over the next two days.
  • This AR is expected to make landfall with a southerly orientation limiting precipitation accumulations.
  • A closed low system followed by a second AR are expected to produce up to 5 inches of precipitation over CA during 14-17 January.
  • Forecast confidence in the strength and timing of AR conditions during the second AR is currently low.
  • The GEFS is suggested additional AR activity over the U.S. West Coast in the long range forecast (19-20 January).

Click IVT or IWV image to see loop of 0-168 hour GFS forecasts

Valid 0600 UTC 10 January – 1800 UTC 17 January 2019

 

 

 

 

 

 

Summary provided by B. Kawzenuk, J. Kalansky, C. Hecht, and F. M. Ralph; 2 PM PT 10 January 2019

CW3E AR Update: 7 January Outlook

CW3E AR Update: 7 January Outlook

January 7, 2019

Click here for a pdf of this information.

Continued AR Activity Forecast for the USWC Over the next Several Days

  • A potentially moderate AR is forecast to make landfall over northern CA
  • AR conditions are currently forecast to last >24 hours over coastal locations north of 35˚N latitude
  • As much as 6 inches of precipitation could fall over the higher elevations of Northern California over the next 72-hours
  • Additional ARs forecast to make landfall between 11 and 14 January bringing more precipitation to the U.S. West Coast
  • The additional ARs could bring precipitation to Southern CA with the 6-day NWS CNRFC predicting .5-3 inches

Click IVT or IWV image to see loop of 0-168 hour GFS forecasts

Valid 0000 UTC 7 January – 0000 UTC 14 January 2019


 

 

 

 

 

Summary provided by C. Hecht, B. Kawzenuk, J. Kalansky, and F. M. Ralph; 3 PM PT 7 January 2019

CW3E AR Update: 4 January Outlook

CW3E AR Update: 4 January Outlook

January 4, 2019

Click here for a pdf of this information.

Multiple ARs forecast impact the US West Coast over the next several days

  • An AR is currently impacting the Pacific Northwest, bringing heavy rain and strong winds
  • As much as 5 inches of precipitation has fallen over portions of the Pacific Northwest over the past 24 hours
  • Another system is forecast to develop along the cold front of the current AR, which will make landfall over Northern CA
  • As much as 9 inches of precipitation is forecast to fall over the higher elevations of Northern CA over the next 6 days
  • Forecast confidence in onset, duration, and magnitude of additional ARs (days 3+) is currently low

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

Valid 1200 UTC 4 January – 0000 UTC 12 January 2019


 

 

 

 

 

Summary provided by C. Hecht, B. Kawzenuk, and F. M. Ralph; 1 PM PT 4 January 2019

CW3E Publication Notice: Hourly Analyses of the Large Storms and Atmospheric Rivers that Provide Most of California’s Precipitation in Only 10-100 Hours per Year

CW3E Publication Notice

Hourly Analyses of the Large Storms and Atmospheric Rivers that Provide Most of California’s Precipitation in Only 10-100 Hours per Year

January 2, 2019

California is regularly affected by floods and droughts, primarily as a result of too many or too few atmospheric rivers (ARs). This study analyzes a 2-decade-long hourly precipitation data set from 176 California weather stations and a 3-hourly AR chronology to report variations in rainfall events across California and their association with ARs. On average, 10–40 and 60–120 hours of rainfall in southern and northern California, respectively, are responsible for more than half of annual rainfall accumulations. Approximately 10% to 30% of annual precipitation at locations across the state is from only one large storm (Figure 1).

Figure 1: (A) median number of hours generating 50% of annual total rainfall, 1995–2016, and (B) median fraction of annual total rainfall from the largest rainfall event, 1995–2016 (from Figure 2, Lamjiri et al., 2018).

On average, northern California receives 25 to 45 rainfall events annually (40% to 50% of which are AR-related). These events typically last longer and have higher event-precipitation totals than those in southern California. Northern California also receives more AR landfalls with longer durations and stronger Integrated Vapor Transport (IVT). On average, ARs contribute 79%, 76%, and 68% of extreme-rainfall accumulations (i.e., top 5% events annually) in the north coast, northern Sierra, and Transverse Ranges of southern California, respectively (Figure 2).

Figure 2: (A) Location of stations in the north coast, northern Sierra, and Transverse Ranges, where receive some of the most extreme rainfall events in California, (B) median contribution of ARs to total extreme rainfall accumulations and total number of extreme rainfall events (from Figure 8, Lamjiri et al., 2018).

The San Francisco Bay Area terrain gap in the California Coast Range allows more AR water vapor to reach inland over the Delta and Sacramento Valley, and thus influences precipitation in the Delta’s catchment. This is particularly important for extreme precipitation in the northern Sierra Nevada (Figure 3).

Figure 2: Composites of daily-averaged IVT (shading) and IWV (contours) for days of AR-related extreme rainfall events over the (A) north coast, and (B) northern Sierra (from Figure 9, Lamjiri et al., 2018) and (C) panel A subtracted from panel B (Difference in IVT composites associated with extreme rainfall in the north coast and northern Sierra Nevada; from figure 10, Lamjiri et al. 2018). The location of the San Francisco Bay Area gap is shown by the yellow star in panel C.

This study highlights differences between rainfall and AR characteristics in coastal versus inland northern California—differences that largely determine the regional geography of flood risks and water reliability. These analyses support water resource, flood, levee, wetland, and ecosystem management within the catchment of the San Francisco Estuary system by describing regional characteristics of ARs and their influence on rainfall on an hourly time-scale.

Lamjiri, M. A, Dettinger, M. D, Ralph, F. M, Oakley, N. S, & Rutz, J. J. (2018). Hourly Analyses of the Large Storms and Atmospheric Rivers that Provide Most of California’s Precipitation in Only 10 to 100 Hours per Year. San Francisco Estuary and Watershed Science. 16(4). Retrieved from https://escholarship.org/uc/item/3jr7z162 .

CW3E AR Update: 5-7 December 2018 Summary

CW3E AR Update: 5-7 December 2018 Summary

December 11, 2018

Click here for a pdf of this information.

Summary of Atmospheric River that impacted Southern California on 5-7 Dec. 2018

  • An AR associated with a cutoff low made landfall near Point Concepcion, CA around 00 UTC 05 December 2018
  • The AR propagated southward bringing AR conditions to a larger portion of Coastal Southern California
  • The cutoff low also propagated over extreme Southern California, resulting in more precipitation for Los Angeles, Orange, and San Diego Counties on the 7th
  • Click IVT or IWV image to see loop of GFS Analsyis

    Valid 0000 UTC 03 December – 0000 UTC 07 December 2018


     

     

     

     

    Summary provided by M. Lamjiri, F. M. Ralph, B. Kawzenuk, C. Hecht; 10 AM PT 11 December 2018

CW3E participates in California Department of Water Resources (DWR) Workshop: Water Year 2019: Feast or Famine?

CW3E participates in California Department of Water Resources (DWR) Workshop: Water Year 2019: Feast or Famine?

December 10, 2018

The California Department of Water Resources (DWR) sponsored the “Water Year 2019: Feast or Famine?” workshop on December 5, 2018 at the UC-Irvine Beckman Center. The workshop was organized by the Water Education Foundation, in partnership with CW3E/UCSD-Scripps Institution of Oceanography and the NASA Jet Propulsion Laboratory (JPL). The goal of the workshop was to communicate the importance of Subseasonal-to-Seasonal (S2S) forecasting of atmospheric rivers and their associated precipitation over the Western U.S. region. The information that was presented at the meeting was largely funded by DWR.

The workshop began with a presentation by Jeanine Jones, the Interstate Resources Manager at California DWR, who gave an overview of the challenges associated with S2S forecasting of precipitation, the potential impacts of prolonged drought if WY 2019 has a similar dry signal to WY 2018. Dr. Duane Waliser, Chief Scientist and Senior Research Scientist at NASA JPL, followed this with a presentation describing national and international research on predicting precipitation weeks to months in advance. Dr. Ben Hatchett (Western Regional Climate Center) and Dr. Jon Rutz (Western Region Headquarters, National Weather Service) then gave presentations detailing the challenges and substantial variability associated with using the El Niño-Southern Oscillation (ENSO) as a predictor for western U.S. precipitation, and the skill of present National Weather Service outlooks, respectively. Dr. Hatchett also gave a presentation later in the day on preliminary work in forecasting precipitation in the Colorado River Basin region.

Dr. Mike Anderson, the state climatologist at DWR, gave a thorough overview of the investments DWR has made in improving forecasts of precipitation at all time scales. Dr. Mike DeFlorio, researcher at CW3E/UCSD-Scripps and former postdoctoral researcher at NASA JPL, then described one such investment, an effort to produce experimental S2S forecasts of atmospheric river activity (a joint effort between CW3E-UCSD Scripps and NASA JPL). Dr. Peter Gibson, postdoctoral researcher at NASA JPL, followed this with an overview of another such investment to study experimental forecasts of winter blocking/ridging conditions at S2S leads over the North Pacific/Western U.S. region.

The workshop concluded with final thoughts from Dr. Mike Anderson on what we can say going forward regarding Water Year 2019, and the uncertainties associated with forecasts of precipitation on S2S timescales in this region.

From left: Dr. Peter Gibson (NASA JPL), Dr. Duane Waliser (NASA JPL), Jeanine Jones (California DWR), Dr. Bin Guan (NASA JPL), and Dr. Mike Deflorio (CW3E).

CW3E Postdoctoral Scholar Mike DeFlorio discusses his research focused on experimental S2S forecasts of atmospheric river activity.

CW3E Publication Notice: Atmospheric Rivers impacting Northern California and their modulation by a variable climate

CW3E Publication Notice

Atmospheric Rivers Impacting Northern California and their Modulation by a Variable Climate

December 10, 2018

CW3E project scientist Kristen Guirguis and co-authors Alexander Gershunov, Tamara Shulgina, Rachel Clemesha, along with CW3E director Marty Ralph, have recently published a paper in Climate Dynamics entitled “Atmospheric Rivers impacting Northern California and their modulation by a variable climate” (Guirguis et al. 2018).

The researchers examined daily activity of atmospheric rivers (ARs) targeting the Northern California coast over six decades using observations of synoptic-scale circulation, high-resolution precipitation, and a long-term AR detection catalog. Using self-organizing maps (Figure 1), they classified ARs making landfall in Northern California in the vicinity of the Russian River watershed based on atmospheric circulation, and then examined the role of large-scale climate modes in determining different characteristics of ARs. They demonstrate how dramatically different atmospheric states evolve into landfalling ARs along distinct pathways that are modulated by interannual (El Niño/Southern Oscillation and the Pacific Decadal Oscillation) and subseasonal (Arctic Oscillation, Pacific North American Pattern, West Pacific Oscillation, and the Eastern Pacific Oscillation) modes of large-scale climate variability. Different configurations of climate variability modes are shown to favor ARs having different characteristics in terms of synoptic evolution, integrated vapor transport and landfall orientation, resulting in different patterns of precipitation over the landscape. In particular, the results show that while ENSO plays an important role in modulating the synoptic evolution of ARs and their orientation at landfall, subseasonal regional climate modes, which also influence landfall orientation as well as the position of the storm track, appear to be more influential than ENSO in modulating precipitation variability in California (Figure 2). This could have implications for subseasonal to seasonal (S2S) forecasting. The researchers also examined AR activity over the most recent and highly anomalous winter 2016-17 and showed how the unprecedented wet conditions in Northern California were at least partly due to the persistence of ARs characterized by a southward storm track and southerly orientation, which represent the type of ARs associated with heavy rainfall in California, and which are associated with the negative phase of subseasonal regional teleconnection patterns.

Figure 1: Self-Organizing Maps trained on 500 mb geopotential height anomalies for peak AR days at 40°N along with the number of days (N) assigned to each node. The nine SOM patterns represent different types of ARs classified by their synoptic circulation. Circulation differences seen in the top versus bottom rows are due to the phase of regional climate modes (Arctic Oscillation, Eastern Pacific Oscillations, Western Pacific Oscillation). Circulation differences seen in the left versus the right columns are due to the phase of ENSO/PDO, where Types 1, 4, and 7 occur during El Niño/PDO+ and Types 3, 6, and 9 occur during La Niño/PDO-.

Figure 2: Anomaly difference maps highlighting the effect of ENSO/PDO and the regional modes in modulating precipitation variability. Panel (a) shows the difference in precipitation between the left nodes (Types 1, 4, and 7) and the right nodes (Types 3, 6, and 9). Therefore, Panel (a) shows El Niño precipitation minus La Niña precipitation at the peak AR day. Panel (b) shows difference in precipitation between the top nodes (Types 1-3) and the bottom nodes (Types 7-9). Therefore, panel (b) shows precipitation occurring when the regional modes are negative minus precipitation occurring when they are positive. Heavier precipitation (green-blue-purple) in (a) means there is more precipitation during El Niño/PDO+. Heavier precipitation in (b) means there is more precipitation when the regional modes are negative. Only values that are statistically significant are colored (95% level using bootstrapping).

Guirguis, K., Gershunov, A., Shulgina, T., Clemesha, R.E.S., Ralph, F.M., 2018: Atmospheric rivers impacting Northern California and their modulation by a variable climate. Climate Dynamics, https://doi.org/10.1007/s00382-018-4532-5.

CW3E AR Update: 27 November 2018 Outlook

CW3E AR Update: 27 November Outlook

November 27, 2018

Click here for a pdf of this information.

Update on ARs Forecast to Impact SoCal Later This Week and Over the Weekend

  • An AR that is currently impacting Northern California is forecast to propagate southward and bring AR conditions to SoCal
  • A secondary low is forecast to develop along the cold front of the current AR and propagate eastward over CA
  • The development of this secondary low is forecast to extend AR conditions over SoCal and bring additional precipitation
  • Additional AR activity is also forecast over SoCal for the weekend, which could lead to more precipitation
  • NOAA CNRFC is currently forecasting as 3+ inches of precipitation over the mountains of SoCal for the next 6 days

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

Valid 1200 UTC 27 November – 0000 UTC 05 December 2018


 

 

 

 

 

Summary provided by C. Hecht, F. M. Ralph, B. Kawzenuk; 2:15 PM PT 27 November 2018

*Outlook products are considered experimental

CW3E AR Update: 21 November 2018 Outlook

CW3E AR Update: 21 November Outlook

November 21, 2018

Click here for a pdf of this information.

Update on the ARs Currently Impacting and Forecast to Impact the U.S. West Coast

  • Precip. has begun in association with AR 1, where as much as 0.5 to 2 in. has fallen over North-Coastal CA
  • AR 2 is forecast to bring strong AR conditions (IVT 750–1000 kg m–1 s–1) to Southern OR and moderate AR conditions to CA tomorrow
  • The National Weather Service has issued numerous Flash Flood watches across the Northern CA and Southern OR
  • Forecast Confidence for another period of AR activity from 26 to 28 November has increased

SSMI/SSMIS/AMSR2-derived Integrated Water Vapor (IWV)

Valid 0000 UTC 18 November – 1600 UTC 21 November 2018

Images from CIMSS/Univ. of Wisconsin

 

 

  • The current AR (AR 1) is forecast to end over Southern California at ~12Z (4 AM PST) on 22 November
  • AR conditions over Southern California will be weak and impacts will liekly be minimal
  • AR 2 is forecast to make landfall over Coastal Oregon at ~15Z (7 AM PST) 22 November
  • AR conditions associated with AR 2 are forecast to end at ~6 UTC 24 November (11 PM PST 23 November) over Central CA
  • Additional ARs are forecast to make landfall in the extended forecast (5 days+) but uncertainty is currently high

Click IVT or IWV image to see loop of 0-240 hour GFS forecast

Valid 1200 UTC 21 November – 1200 UTC 26 November 2018


 

 

 

 

 

 

 

 

Summary provided by C. Hecht, F. M. Ralph, F. Cannon, J. Kalansky; 1:30 PM PST 21 November 2018

*Outlook products are considered experimental

CW3E AR Update: 20 November 2018 Outlook

CW3E AR Update: 20 November Outlook

November 20, 2018

Click here for a pdf of this information.

Update on the ARs forecast to Impact California this Week

  • Forecast confidence within the GEFS has continued to increase for the two ARs forecast to impact CA over next few days
  • There is potential for development of a mesoscale frontal wave associated with AR 2, which could lead to stalling of the AR
  • NOAA WPC 1–3 day precipitation forecasts are as high as 5–7 inches over the N. CA Coastal Mountains and N. Sierra
  • The precipitation may bring much needed relief to the currently active fires and smoky conditions over CA
  • While precipitation will bring relief from the currently active fires and smoke across California, there is the potential for high precipitation rates, which are conducive to the triggering of debris flows

Click IVT or IWV image to see loop of 0-102 hour GFS forecast

Valid 1200 UTC 20 November – 1800 UTC 24 November 2018

 

 

 

 

 

 

 

 

 

Summary provided by C. Hecht, F. M. Ralph, B. Kawzenuk, J. Kalansky; 3 PM PT 20 November 2018

*Outlook products are considered experimental

CW3E AR Update: 19 November 2018 Outlook

CW3E AR Update: 19 November Outlook

November 19, 2018

Click here for a pdf of this information.

Update on the Multiple ARs forecast to Impact California this Week

  • Forecast confidence in the onset, duration, and magnitude of AR conditions has increased since the last update on 16 Nov.
  • The GEFS is currently suggesting that the 2nd AR could bring moderate AR conditions (IVT 500–750 kg m–1 s–1 ) to coastal CA
  • NOAA WPC 1-5 precipitation accumulations have increased to ~6 inches over portions of Northern California
  • The precipitation may bring much needed relief to the currently active fires and smoky conditions over CA
  • The GEFS is also suggesting the potential for AR activity in the extended forecast (8–13 days) but uncertainty is currently high
  • Click IVT or IWV image to see loop of 0-138 hour GFS forecast

    Valid 1200 UTC 19 November – 1200 UTC 25 November 2018

     

     

     

     

     

     

     

     

    Summary provided by C. Hecht, F. M. Ralph, B. Kawzenuk, J. Kalansky; 3 PM PT 19 November 2018

    *Outlook products are considered experimental

    CW3E AR Update: 16 November 2018 Outlook

    CW3E AR Update: 16 November Outlook

    November 16, 2018

    Click here for a pdf of this information.

    Potential for Atmospheric River Activity over California Next Week

    • Multiple systems are currently forecast to potentially bring AR conditions and much needed precip. to California next week
    • Each of the 3 ARs are currently forecast to bring weak AR conditions (IVT magnitudes of 250–500 kg m–1 s–1) to portions of CA
    • These ARs could bring much needed relief to currently active fires in California
    • The precipitation could also reduce the extremely smoky conditions across most of California
  • Since these ARs are in the extended forecast (5–8 days), forecast uncertainty in onset, duration, and magnitude of AR conditions and precipitation is currently very high (stay tuned as time progresses closer to landfall)
  • Click IVT or IWV image to see loop of 0-240 hour GFS forecast

    Valid 1200 UTC 16 November – 1200 UTC 26 November 2018

     

     

    For information on how these experimental forecast products are created, click here

    For questions regarding these experimental ensemble forecast products, contact Mike Deflorio

     

     

     

     

     

    Summary provided by C. Hecht, F. M. Ralph, B. Kawzenuk, M. Deflorio; 3 PM PT Friday 16 November 2018

    *Outlook products are considered experimental

    FIRO Highlighted at Kansas Governor’s Conference on the Future of Water in Kansas

    FIRO Highlighted at Kansas Governor’s Conference on the Future of Water in Kansas

    November 15, 2018

    CW3E’s Anna Wilson recently attended the Kansas Governor’s Conference on the Future of Water in Kansas, held in Manhattan, Kansas on November 13-14, 2018. The annual conference is meant to bring together scientists, water managers, state and federal officials and legislators, city and county administrators, environmental organizations, irrigators, and citizens who share an interest in Kansas water resources.

    Based on a visit to the US Army Corps of Engineers Engineer Research and Development Center (ERDC) in Vicksburg, MS from a delegation from the Kansas Water Office and Corps of Engineers Kansas City District, Steve Turnbull from ERDC was invited, along with Dr. Wilson from CW3E and Chris Delaney from Sonoma Water, to be on a panel describing the Forecast Informed Reservoir Operations (FIRO) project. Panel presentations covered FIRO’s purpose and background; data collection and monitoring and modeling efforts in support of FIRO; and an update on current results and status of FIRO at Lake Mendocino, including the major deviation approval for WY2019. Cara Hendricks from the Kansas Water Office served as panel moderator. Transferability potential was discussed in the context of extreme event predictability and the framework developed by the FIRO Steering Committee to assess viability.

    From left, Steve Turnbull (ERDC), Cara Hendricks (Kansas Water Office), Anna Wilson (CW3E), and Chris Delaney (Sonoma Water) outside the panel conference room at the Governor’s Conference on the Future of Water in Kansas.