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: 5-10 January 2017 Outlook

CW3E AR Update: 5-10 January 2017 Outlook

January 5, 2017

Click here for a pdf of this information.

Strong AR forecast to impact California this weekend

  • Forecasts continue to suggest the landfall of a strong AR over the weekend
  • Updated forecasts indicate that AR duration may decrease, which suggests lower precipitation amounts in some locations
  • Several more river gauges are expected to rise above flood stage
  • Extended forecasts predict another AR early next week potentially bringing more precipitation

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

Valid 1200 UTC 5 Jan – 1200 UTC 11 Jan 2017


 

 

 

 

Summary provided by C. Hecht, B. Kawzenuk, and F.M. Ralph; 3 PM PT Wed 5 Jan. 2017

CW3E AR Update: 4-10 January 2017 Outlook

CW3E AR Update: 4-10 January 2017 Outlook

January 4, 2017

Click here for a pdf of this information.
 

Strong AR forecast to impact California this weekend

  • A strong AR with IVT as high as 1000 kg m-1 s-1 is forecast make landfall over the West Coast this Weekend
  • Precipitation from an AR currently impacting CA combined with the precipitation from AR this weekend are producing 7-day precipitation forecasts as high as 20 inches in the higher elevations of the Sierra Nevada Mts.
  • The hydrologic impacts associated with an event of this magnitude could be numerous and several rivers are already forecast to rise above flood stage in portions of northern/central California and western Nevada

Click IVT or IWV image to see loop of 0-138 hour GFS forecast

Valid 1200 UTC 4 Jan – 0600 UTC 10 Jan 2017


 

 

 

 

 

 

 

Summary provided by C. Hecht, B. Kawzenuk, and F.M. Ralph; 3 PM PT Wed 4 Jan. 2017

CW3E AR Update: 13-17 December 2016 Outlook

CW3E AR Update: 13-17 December 2016 Outlook

December 13, 2016

Click here for a pdf of this information.

  • Current NWS precipitation forecasts predict higher precipitation amounts of over 10 inches in 3 days over the higher elevations of the Sierra Nevada Mts. with other locations in northern CA receiving 2-10 inches
  • Recent heavy precipitation has primed soil conditions and river flows to raise concern for flooding in some locations in northern California, as seen in NWS river forecasts

Landfalling AR to impact California

  • A moderate-strength AR is expected to make landfall in north/central California tonight, and could reach “strong” AR level
  • The AR propagates southward later in the week bringing AR conditions to portions of southern California

Click IVT or IWV image to see loop of 0-90 hour GFS forecast (Valid 1200 UTC 13 Dec – 0600 17 Dec)


 

 

 

 

Summary provided by C. Hecht, and F.M. Ralph; 12 PM PT Tue 13 Dec. 2016

Odds of Reaching 100% Water Year Precipitation – Dec Update

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

December 9, 2016

Contribution from Dr. M.D. Dettinger, USGS

The odds shown here are the odds of precipitation in the rest of the water year (after November 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 partners with California Department of Water Resources, California Geological Survey, US Geological Survey, and the Western Regional Climate Center to assess post-fire debris flow hazards in northern California

CW3E partners with California Department of Water Resources, California Geological Survey, US Geological Survey, and the Western Regional Climate Center to assess post-fire debris flow hazards in northern California

December 2, 2016

Highlights

Atmospheric River knowledge and tools support post-fire debris flow hazard mitigation and fast-response studies of debris flow-meteorology linkages

An important consequence of the recent record drought in parts of California is the occurrence of major wildfires. The Butte, Valley and Soberanes fires occurred in the last 18 months and have been some of the largest in California history. These tragic burns caused many adverse impacts at the time, and continue to create natural hazards due to the increased risk of damaging debris flows that can occur after the rains return.

California’s burned steeplands are prone to hazardous debris flows during winter storms. Wildfires remove vegetation and alter soil properties, increasing the likelihood of debris flows, even for relatively low intensity storms. When rainfall of sufficient intensity and duration impacts recently burned steeplands, landslides and surface runoff can mobilize ash, rocks, and other material into debris flows that devastate life and property.

California’s Department of Water Resources (DWR) is sponsoring work to examine the role of Atmospheric Rivers on flooding and landslide occurrence and magnitude. The project is led by the Center for Western Weather and Water Extremes (CW3E) at Scripps Institution of Oceanography and includes a team of experts from Scripps, California Geological Survey (CGS) and the U.S. Geological Survey (USGS) Landslide Hazards Team.

Within these burn areas, the geology team, led by Jeremy Lancaster of CGS, is deploying sensors and making measurements in the burn areas when conditions warrant. Doing so requires making decisions on whether to make observations at a study site following a storm event. In support of this, CW3E Graduate Student researchers Nina Oakley and Meredith Fish are using new knowledge of weather systems capable of producing intense precipitation, especially Atmospheric Rivers, to evaluate the potential for high-intensity precipitation over the Soberanes Fire, Butte Fire, and Valley Fire burn areas to advise Lancaster. Key to these preparations and day-to-day decisions are the new Atmospheric River forecasting tools at CW3E. Additionally, post-storm, CW3E scientists will compile meteorological data relevant to the storm event such as maximum precipitation intensity, storm total precipitation, radar imagery, an evaluation of Atmospheric River variables, and any information unique to that storm. For events that produce a debris flow response, a more in-depth case study will be conducted combining both geologic and atmospheric information.

Figure 1: Map of three burn areas that we propose to assess: Soberanes, Valley, and Butte wildfires.

Synthesis of the information collected through these storm and debris flow response logs will provide insight to post-fire debris flow triggering rainfall thresholds across northern California and the meteorological conditions that produce such rainfall. This integrated approach of meteorologists and geologists working together to address the post-fire debris flow issue will help advance our knowledge of these potentially hazardous events. This knowledge will be incorporated into landslide/debris flow hazard outlooks that factor in both landscape conditions (e.g., fire) and meteorology (e.g., extreme precipitation from Atmospheric Rivers)

Figure 2: Debris flow deposits stopped by cement barriers outside the Big Sur Lodge in California. This event was triggered by rain falling on burned steeplands in 2009, near an area now burned again by the Soberanes wildfire. (credit: David Longstreth, CGS).


Figure 3: During Fall 2016, USGS and CGS researchers install a rain near Pfeiffer Falls in the Soberanes Fire burn area to measure the rainfall intensities that trigger post-fire debris flows.

Contacts: Jeremy Lancaster (CGS), Nina Oakley (DRI and CW3E), John Stock (USGS), F.M. Ralph (CW3E)

Congressional Briefing on “A New Frontier in Water Operations: Atmospheric Rivers, Subseasonal-to-Seasonal Predictions and Weather Forecasting Technology”

Congressional Briefing on “A New Frontier in Water Operations: Atmospheric Rivers, Subseasonal-to-Seasonal Predictions and Weather Forecasting Technology”

July 27, 2016

An interagency, cross-disciplinary team of experts recently convened in Washington to provide Congressional staff with a briefing on atmospheric rivers, subseasonal-to-seasonal precipitation prediction needs, and the benefits of enhanced predictive forecasting technology to the future of water management.

Attendees heard from a diverse panel of experts representing a broad spectrum of perspectives, including government engagement by the National Weather Service and the U.S. Army Corps of Engineers, scientific findings presented by the Scripps Institution of Oceanography, and regional impacts to stakeholders represented by the Western States Water Council.

This briefing highlighted CW3E’s major effforts on atmospheric river science, monitoring and predictions, and their application to possible new water management strategies, such as Forecast-Informed Reservoir Operations (FIRO; http://cw3e.ucsd.edu/FIRO/), which is co-led by CW3E’s Director, F. Martin Ralph. Roughly 40 people attended, including representatives of congressional offices, committees, ACWA, federal agencies and other groups.

Click here for a summary.

Contact: F. Martin Ralph (mralph@ucsd.edu)

Publication Notice: CalWater Field Studies Designed to Quantify the Roles of Atmospheric Rivers and Aerosols in Modulating U.S. West Coast Precipitation in a Changing Climate

CW3E Publication Notice

CalWater Field Studies Designed to Quantify the Roles of Atmospheric Rivers and Aerosols in Modulating U.S. West Coast Precipitation in a Changing Climate

November 28, 2016

Ralph F.M., K. A. Prather, D. Cayan, J.R. Spackman, P. DeMott, M. Dettinger, C. Fairall, R. Leung, D. Rosenfeld, S. Rutledge, D. Waliser, A. B. White, J. Cordeira, A. Martin, J. Helly, and J. Intrieri, 2016: CalWater Field Studies Designed to Quantify the Roles of Atmospheric Rivers and Aerosols in Modulating U.S. West Coast Precipitation in a Changing Climate. Bull. Amer. Meteor. Soc. 97, yyy-zzz. doi: 10.1175/BAMS-D-14-00043.1.

This paper summarizes the 8-year-long CalWater program of field studies, from planning to field operations and analysis efforts. It also summarizes the major motivations for the program as well as science gaps addressed, and serves as the standard reference for future CalWater analysis papers.

Contact: F. Martin Ralph (mralph@ucsd.edu)

Abstract

Quantifying the roles of atmospheric rivers and aerosols in modulating U.S. West Coast precipitation, water supply, flood risks and drought in a changing climate.

The variability of precipitation and water supply along the U.S. West Coast creates major challenges to the region’s economy and environment, as evidenced by the recent California drought. This variability is strongly influenced by atmospheric rivers (AR), which deliver much of the precipitation along the U.S. West Coast and can cause flooding, and by aerosols (from local sources and transported from remote continents and oceans) that modulate clouds and precipitation. A better understanding of these processes is needed to reduce uncertainties in weather predictions and climate projections of droughts and floods, both now and under changing climate conditions.

To address these gaps a group of meteorologists, hydrologists, climate scientists, atmospheric chemists, and oceanographers have created an interdisciplinary research effort, with support from multiple agencies. From 2009-2011 a series of field campaigns (CalWater 1) collected atmospheric chemistry, cloud microphysics and meteorological measurements in California and associated modeling and diagnostic studies were carried out. Based on remaining gaps, a vision was developed to extend these studies offshore over the Eastern North Pacific and to enhance land-based measurements from 2014-2018 (CalWater 2). The data set and selected results from CalWater 1 are summarized here. The goals of CalWater-2, and measurements to date, are then described.

CalWater is producing new findings and exploring new technologies to evaluate and improve global climate models and their regional performance and to develop tools supporting water and hydropower management. These advances also have potential to enhance hazard mitigation by improving near-term weather prediction and subseasonal and seasonal outlooks.