Author: cw3e-web

Mesoscale Frontal Wave AR during CalWater-2014

CW3E Publication Notice

An Airborne and Ground-Based Study of a Long-Lived and Intense Atmospheric River with Mesoscale Frontal Waves Impacting California during CalWater-2014

May 10, 2016

Neiman, P.J., B.J. Moore, A.B. White, G.A. Wick, J. Aikins, D.L. Jackson, J.R Spackman, and F.M. Ralph, 2016: An Airborne and Ground-Based Study of a Long-Lived and Intense Atmospheric River with Mesoscale Frontal Waves Impacting California during CalWater-2014. Mon. Wea. Rev., 144, 1115-1144.

This study provides the most comprehensive observations to date of a mesoscale frontal wave associated with an atmospheric river, including its structure offshore, landfall characteristics and impacts on precipitation. It utilizes research aircraft, a unique array of coastal hydrometeorological measurements and inland data. This paper reflects the broader scientific collaboration between CW3E and NOAA/PSD, and adds to the knowledge of phenomena that are critical to creating extreme precipitation on the U.S. West Coast – a major thrust of CW3E. Dr. Ralph contributed to this paper by proposing the experiment (Ralph et al. 2016 BAMS), identifying the science objective for the flights (i.e., mapping out the structure of a mesoscale frontal wave with dropsondes and airborne radar), laying out the flight tracks, guiding the mission onboard, having been the PI of the major projects that created the unique land-based observing network (NOAA HMT- Ralph et al. 2013 BAMS, and the DWR-sponsored EFREP mesonet – White et al. 2013 JTech) used in the study and contributing to the analysis and interpretation of the measurements in this paper.

Contacts: Paul Neiman (paul.j.neiman@noaa.gov) and F. Martin Ralph (mralph@ucsd.edu)

Abstract

The wettest period during the CalWater-2014 winter field campaign occurred with a long-lived, intense atmospheric river (AR) that impacted California on 7–10 February. The AR was maintained in conjunction with the development and propagation of three successive mesoscale frontal waves. Based on Lagrangian trajectory analysis, moist air of tropical origin was tapped by the AR and was subsequently transported into California. Widespread heavy precipitation (200–400 mm) fell across the coastal mountain ranges northwest of San Francisco and across the northern Sierra Nevada, although only modest flooding ensued due to anomalously dry antecedent conditions. A NOAA G-IV aircraft flew through two of the frontal waves in the AR environment offshore during a ;24-h period. Parallel dropsonde curtains documented key three dimensional thermodynamic and kinematic characteristics across the AR and the frontal waves prior to landfall. The AR characteristics varied, depending on the location of the cross section through the frontal waves. A newly implemented tail-mounted Doppler radar on the G-IV simultaneously captured coherent precipitation features. Along the coast, a 449-MHz wind profiler and collocated global positioning system (GPS) receiver documented prolonged AR conditions linked to the propagation of the three frontal waves and highlighted the orographic character of the coastal-mountain rainfall with the waves’ landfall. Avertically pointing S-PROF radar in the coastal mountains provided detailed information on the bulk microphysical characteristics of the rainfall. Farther inland, a pair of 915-MHz wind profilers and GPS receivers quantified the orographic precipitation forcing as the AR ascended the Sierra Nevada, and as the terrain-induced Sierra barrier jet ascended the northern terminus of California’s Central Valley.

CW3E represented in recent policy and program meetings

CW3E Represented in Recent Policy and Program Meetings

June 8, 2017

During the last few weeks CW3E’s perspectives have been highlighted at three science policy-oriented meetings. The connection between CW3E’s scientific activities, practical applications and water policy implications is a common theme among them. The meetings and a brief synopsis are provided below:

1) AGU Congressional briefing on role of basic Geoscience in American Security May 2016

AGU invited three speakers to a Congressional briefing they organized to communicate to staff supporting a number of elected officials and policy committees. The goal was to make the connection between basic science advances (and the funding that has supported them), and benefits to American Security. CW3E’s Director, Dr. Ralph, represented the role of basic geoscience research in advancing water security in the Western U.S. His presentation emphasized the critical roles of key science funding strategies, from standard grants programs, to directed research efforts, cooperative agreements and federal labs. And in the end concluded that many breakthrough advances result not from a systems engineering approach to deciding what to do, but from ideas that are “outside the box.” He also highlighted that science, at its core, is fundamentally a creative endeavor that requires long-term support for people in their careers and for the organizations that host them. AGU has posted a video of the briefings here.

2) NOAA Water Information “Listening Session” in Sacramento May 2016

NOAA invited water management stakeholders from across the West to hear about the National Water Center they are creating in Alabama and to listen to stakeholders interests and needs for weather and water information to support water supply, flood mitigation and endangered species restoration in the West. CW3E was represented by Dr. Ralph, who brought Scripps science into the discussion, and supported major points presented by water managers concerning the vital role of atmospheric rivers in western water decisions. NOAA held one other regional “listening session” – in Alabama, and is holding one more “National” session in July. They will be considering input from these meeting as they develop their agency’s strategies in the coming years to support water information needs for the nation.

3) WSWC S2S Workshop San Diego June 2016

The National Academies of Science recently released a report on the subject of science needed to enable subseasonal-to-seasonal predictions to support decisions. The Western States Water Council (a group supporting the Governors of 17 Western States) organized a regional Workshop in San Diego in early June to discuss both the user requirements for better forecasts and the science opportunities to achieve them. CW3E was represented well, including participation by Sasha Gerhunov, Tamara Shulgina and Marty Ralph, including a presentation by Marty on observing system needs to support the goals.

CW3E Welcomes Dr. Anna Wilson

CW3E welcomes Dr. Anna Wilson

June 1, 2016

Dr. Anna M. Wilson has joined CW3E at the Scripps Institution of Oceanography as a Postdoctoral Scholar after earning her Ph.D. in Civil and Environmental Engineering under the direction of Dr. Ana Barros at Duke University earlier this year. Her dissertation research focused on understanding the space-time structure of low level warm season precipitation processes in complex terrain, using an approach integrating numerical models and in situ and remote observations. During her Ph.D., Anna was able to amass extensive experience working with ground based instruments in the field through participation in a number of different NASA Global Precipitation Mission Ground Validation field campaigns. She is excited to work with her colleagues at CW3E and partner organizations to provide essential support to decision makers at all time scales through developing physically based, accurate representations of atmospheric rivers and other extreme events in forecasts and projections. In particular, she will be studying the origins of variance in the relationship between upslope water vapor flux in atmospheric rivers and precipitation in coastal northern California.

CW3E Welcomes Dr. Scott Sellars

CW3E welcomes Dr. Scott Sellars

April 25, 2016

Dr. Scott L. Sellars has joined CW3E at the Scripps Institution of Oceanography to work on improving the understanding and forecasting of hydrologic extremes and their impacts on water resource management in the Western United States. Scott’s previous research has been in the area of hydrometeorology and climate, with a particular focus on computational science methodologies applied to remote sensing information for understanding connections between weather and hydrological events. He has previously held appointments at the University of California, Irvine, Columbia University’s Columbia Water Center (CWC), Geophysical Fluid Dynamics Laboratory (GFDL) and the International Research Institute for Climate and Society (IRI). His Ph.D. is on seasonal hydrometeorological prediction, awarded in 2014, and was undertaken at the University of California, Irvine.

CW3E AR Update:Post-Event Summary: 7-10 April 2016

CW3E AR Update: 7-10 April 2016 Post Event Summary

April 13, 2016

CW3E and WRCC give a post-event storm summary about two cutoff lows that made landfall over Southern California during 7-10 April 2016. Precipitation was widespread throughout the Southeastern United States with 72-hr accumulations generally ~0.5-3 inches. While the low pressure system entrained moisture from the tropics, spatial characteristics of IWV >20 mm and IVT >250 kg m-1 s-1 did not meet the necesarry requirements to be considered an Atmospheric River.

Click here for a pdf file of this information.


 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Odds of Reaching 100% Water Year Precipitation – April Update

Odds of Reaching 100% of Normal Precipitation for Water Year 2016 in California (April update)

April 10, 2016

Contribution from Dr. M.D. Dettinger, USGS

March is over (and the precipitation totals are in), so here is the update to the historical odds of getting to normal (and other fractions of normal) precipitation this year. Notice that the odds from the March 1 situation (in parens; click here for March report) are included alongside the April 1 odds, so that you can see whether March wetness made much difference. In fact, the odds haven’t changed too much in most areas because, although March was wettish (except down south), those additions were balanced in these April odds by the fact that we have almost run out of time this year to get much more precipitation.

Bottom lines (both of which you probably already know): We’re not going to fill the precipitation deficits we accumulated over the past 5 years with this year’s precipitation (except, long-odds, maybe in eastern NV). In southern California, the precipitation situation is especially grim and even the odds of making it to 75% of normal this year are well less than even.


 

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 (for all years, for only El Ninos, or for only La Ninas) 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. Contact mddettin@usgs.gov for more information.

[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: 7-10 April 2016 Outlook

CW3E AR Update: 7-10 April 2016 Outlook

April 7, 2016

A weak low pressure system and high Integrated Water Vapor (IWV) values have brought light-to-moderate precipitation over Southern California this morning. A closed low is expected to develop off the coast over the next two days and will produce moderate precipitation over Southern California on 8-10 April 2016. IWV and Integrated Water Vapor Transport (IVT) values will be above AR thresholds but spatial characteristics of IWV/IVT will not meet the requirements of an AR. Coastal Southern California will experience AR conditions (IWV >20 mm and IVT >250 kg m-1 s-1) and light-to-moderate precipitaton, but this event is not considered an AR. For up to date AR forecasts visit the CW3E AR Portal.

Click here for a pdf file of this information.


 

 

Publication Notice: Predictability of Horizontal Water Vapor Transport Relative to Precipitation

CW3E Publication Notice

Predictability of Horizontal Water Vapor Transport Relative to Precipitation: Enhancing Situational Awareness for Forecasting Western U.S. Extreme Precipitation and Flooding

March, 2016

Lavers, D.A., D.E. Waliser, F.M. Ralph and M.D. Dettinger, 2016: Predictability of horizontal water vapor transport relative to precipitation: Enhancing situational awareness for forecasting western U.S. extreme precipitation and flooding. Geophysical Research Letters, 43, doi:10.1002/2016GL067765 (Please click here for personal use pdf file)

The following paper has just appeared in Geophysical Research Letters. It was motivated by the critical role of horizontal vapor transport in determining the strength and distribution of extreme precipitation in the Western U.S., and by the fact that this transport is the defining characteristic of atmospheric rivers, which are key to many extreme events in the region. The work was carried out primarily at CW3E in response to interest from State and local water agencies to explore new methods to predict extreme precipitation events. While the findings are based on U.S. West Coast domains, the results are applicable to other west coasts of mid latitude continents where cool season orographic precipitation is a key process. The results support the use of water vapor transport as a variable to monitor for earlier awareness of extreme hydrometeorological events.

(e) The average interannual predictability (r2) across the 30°N–50°N, 125°W–120°W region. (f) The predictability throughout the forecast horizon calculated using all winter forecasts (n = 2796) at 38°N, 122°W. From Lavers et al. (2016).

Contacts: David Lavers (david.lavers@ecmwf.int) and F. Martin Ralph (mralph@ucsd.edu)

Abstract

The western United States is vulnerable to socioeconomic disruption due to extreme winter precipitation and floods. Traditionally, forecasts of precipitation and river discharge provide the basis for preparations. Herein we show that earlier event awareness may be possible through use of horizontal water vapor transport (integrated vapor transport (IVT)) forecasts. Applying the potential predictability concept to the National Centers for Environmental Prediction global ensemble reforecasts, across 31 winters, IVT is found to be more predictable than precipitation. IVT ensemble forecasts with the smallest spreads (least forecast uncertainty) are associated with initiation states with anomalously high geopotential heights south of Alaska, a setup conducive for anticyclonic conditions and weak IVT into the western United States. IVT ensemble forecasts with the greatest spreads (most forecast uncertainty) have initiation states with anomalously low geopotential heights south of Alaska and correspond to atmospheric rivers. The greater IVT predictability could provide warnings of impending storminess with additional lead times for hydrometeorological applications.

CW3E AR Update: Post-Event Summary: 5-6 March 2016

CW3E AR Update: 5-6 March 2016 Post-Event Summary

March 10, 2016

CW3E gives a post-event storm summary about a moderate strength Atmospheric River that made landfall over Northern California on 5 March 2016. The AR was an R-Cat 1 event and produced over 10 inches of 72-hour precipitation.

Click here for a pdf file of this information.


 

 

 

 

Northern Sierra Precipitaiton: 8-Station Index

~7.5 inches of precipitation measured by the 8-Station Index

Increased water-year-to-date accummulation from average to ~115% of average

Lake Mendocino Storage

Increase in storage of ~8000 af

Storage remains above the Target Water Supply Storage Curve

SSMI Integrated Water Vapor: 0000 UTC 3 March – 0000 UTC 7 March

  • AR developed over the Central North Pacific and made landfall over Northern California
  • AR entrained moisture from previous decaying AR off California coast prior to landfall

GFS IVT Analysis: 0000 UTC 3 March – 1200 UTC 7 March 2016

Cazadero, Ca Snow Level Radar

Heavy bright-band precipitation began ~0600 UTC 5 March

Large drop in snow level post-frontal

Bodega Bay 0200 UTC Sounding

  • Saturated atmosphere up to ~550 hPa
  • IWV = 31.9 mm
  • IVT = 878.3 kg m-1s-1
  • Winds >50 knots throughout the troposphere
  • Majority of water vapor flux between 950-700 hPa

Event Summary

  • A moderate strength Atmospheric River made landfall over Northern California during 5-6 March 2016
  • Maximum 48-h precipitation of >10 inches occurred over the Sierra Nevada
  • Widespread precipitation >6 inches occurred over the Coastaland Sierra Nevada Ranges
  • Several rivers reached above flood stage in Northern California

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.