scholarly journals Precipitation Prediction Skill for the West Coast United States: From Short to Extended Range

2018 ◽  
Vol 32 (1) ◽  
pp. 161-182 ◽  
Author(s):  
Baoxiang Pan ◽  
Kuolin Hsu ◽  
Amir AghaKouchak ◽  
Soroosh Sorooshian ◽  
Wayne Higgins
Keyword(s):  
United States ◽  
West Coast ◽  
El Niño ◽  
El Nino ◽  
The United States ◽  
Prediction Skill ◽  
Precipitation Prediction ◽  
Skill Scores ◽  
Extended Range ◽  
To Receive

Abstract Precipitation variability significantly influences the heavily populated West Coast of the United States, raising the need for reliable predictions. We investigate the region’s short- to extended-range precipitation prediction skill using the hindcast database of the Subseasonal-to-Seasonal Prediction Project (S2S). The prediction skill–lead time relationship is evaluated, using both deterministic and probabilistic skill scores. Results show that the S2S models display advantageous deterministic skill at week 1. For week 2, prediction is useful for the best-performing model, with a Pearson correlation coefficient larger than 0.6. Beyond week 2, predictions generally provide little useful deterministic skill. Sources of extended-range predictability are investigated, focusing on El Niño–Southern Oscillation (ENSO) and the Madden–Julian oscillation (MJO). We found that periods of heavy precipitation associated with ENSO are more predictable at the extended range period. During El Niño years, Southern California tends to receive more precipitation in late winter, and most models show better extended-range prediction skill. On the contrary, during La Niña years Oregon tends to receive more precipitation in winter, with most models showing better extended-range skill. We believe the excessive precipitation and improved extended-range prediction skill are caused by the meridional shift of baroclinic systems as modulated by ENSO. Through examining precipitation anomalies conditioned on the MJO, we verified that active MJO events systematically modulate the area’s precipitation distribution. Our results show that most models do not represent the MJO or its associated teleconnections, especially at phases 3–4. However, some models exhibit enhanced extended-range prediction skills under active MJO conditions.

Impact of Rossby Wave Breaking on U.S. West Coast Winter Precipitation during ENSO Events

2013 ◽  
Vol 26 (17) ◽  
pp. 6360-6382 ◽  
Author(s):  
Ju-Mee Ryoo ◽  
Yohai Kaspi ◽  
Darryn W. Waugh ◽  
George N. Kiladis ◽  
Duane E. Waliser ◽  
...  
Keyword(s):  
United States ◽  
West Coast ◽  
El Niño ◽  
Wave Breaking ◽  
El Nino ◽  
The United States ◽  
La Niña ◽  
The West ◽  
La Nina ◽  
Subtropical Jet

Abstract This study demonstrates that water vapor transport and precipitation are largely modulated by the intensity of the subtropical jet, transient eddies, and the location of wave breaking events during the different phases of ENSO. Clear differences are found in the potential vorticity (PV), meteorological fields, and trajectory pathways between the two different phases. Rossby wave breaking events have cyclonic and anticyclonic regimes, with associated differences in the frequency of occurrence and the dynamic response. During La Niña, there is a relatively weak subtropical jet allowing PV to intrude into lower latitudes over the western United States. This induces a large amount of moisture transport inland ahead of the PV intrusions, as well as northward transport to the west of a surface anticyclone. During El Niño, the subtropical jet is relatively strong and is associated with an enhanced cyclonic wave breaking. This is accompanied by a time-mean surface cyclone, which brings zonal moisture transport to the western United States. In both (El Niño and La Niña) phases, there is a high correlation (>0.3–0.7) between upper-level PV at 250 hPa and precipitation over the west coast of the United States with a time lag of 0–1 days. Vertically integrated water vapor fluxes during El Niño are up to 70 kg m−1 s−1 larger than those during La Niña along the west coast of the United States. The zonal and meridional moist static energy flux resembles wave vapor transport patterns, suggesting that they are closely controlled by the large-scale flows and location of wave breaking events during the different phase of ENSO.

Changes in Observed Daily Precipitation over the United States between 1950–79 and 1980–2009

2013 ◽  
Vol 14 (1) ◽  
pp. 105-121 ◽  
Author(s):  
R. W. Higgins ◽  
V. E. Kousky
Keyword(s):  
United States ◽  
Great Plains ◽  
El Niño ◽  
Daily Precipitation ◽  
El Nino ◽  
Southern Oscillation ◽  
Heavy Precipitation ◽  
The United States ◽  
Enso Cycle ◽  
Precipitation Events

Abstract Changes in observed daily precipitation over the conterminous United States between two 30-yr periods (1950–79 and 1980–2009) are examined using a 60-yr daily precipitation analysis obtained from the Climate Prediction Center (CPC) Unified Raingauge Database. Several simple measures are used to characterize the changes, including mean, frequency, intensity, and return period. Seasonality is accounted for by examining each measure for four nonoverlapping seasons. The possible role of the El Niño–Southern Oscillation (ENSO) cycle as an explanation for differences between the two periods is also examined. There have been more light (1 mm ≤ P < 10 mm), moderate (10 mm ≤ P < 25 mm), and heavy (P ≥ 25 mm) daily precipitation events (P) in many regions of the country during the more recent 30-yr period with some of the largest and most spatially coherent increases over the Great Plains and lower Mississippi Valley during autumn and winter. Some regions, such as portions of the Southeast and the Pacific Northwest, have seen decreases, especially during the winter. Increases in multiday heavy precipitation events have been observed in the more recent period, especially over portions of the Great Plains, Great Lakes, and Northeast. These changes are associated with changes in the mean and frequency of daily precipitation during the more recent 30-yr period. Difference patterns are strongly related to the ENSO cycle and are consistent with the stronger El Niño events during the more recent 30-yr period. Return periods for both heavy and light daily precipitation events during 1950–79 are shorter during 1980–2009 at most locations, with some notable regional exceptions.

What Made El Niño 1997-1998 Famous?: The Key Events Associated with a Unique Climatic Event

2000 ◽  
Author(s):  
Stanley A. Changnon
Keyword(s):  
United States ◽  
News Media ◽  
El Niño ◽  
El Nino ◽  
The United States ◽  
Climate Conditions ◽  
The Pacific ◽  
Climate Event ◽  
The Media ◽  
Key Events

El Niño 97-98 provided one of the most interesting and widely known climatic events of this century. It garnered enormous attention not only in the scientific community but also in the media and from the American public. El Niño developed rapidly in the tropical Pacific during May 1997, and by October “El Niño “had become a household phrase across America. Television and radio, newspapers and magazines pummeled America with the dire tales of El Niño during the fall of 1997 as the climate disruption battered the West Coast and the southern United States with storm after storm. Worried families changed vacation plans, and insurance executives pondered losses and raised rates. Victims of every type of severe weather blamed El Niño . After a winter filled with unusual weather, the head of the National Oceanic and Atmospheric Administration (NOAA) declared, “This winter’s El Niño ranks as one of the major climatic events of this century.” It was the first El Niño observed and forecast from start to finish. The event was noteworthy from several perspectives. • First, it became the largest and warmest El Niño to develop in the Pacific Ocean during the past 100 years. • Second, the news media gave great attention to the event, and El Niño received more attention at all levels than had any previous climate event. • Third, scientists were able to use El Niño conditions to successfully predict the climate conditions of the winter six months in advance. • Fourth, the predictive successes brought new credibility to the science of long-range prediction and, in general, acted to increase the public’s understanding of the climate and oceanic sciences. • Fifth, there were notable differences in how weather-sensitive decision makers reacted to the predictions, some used them for great gain, while others, fearing failure, did not. • Sixth, the great strength of El Niño brought forth claims that the phenomenon was the result of anthropogenic-induced global warming. This possibility was debated and added to the scientific-policy debates surrounding climate change. • Seventh, the net effect of the El Niño -influenced weather on the United States was an economic benefit, after early fears and predictions of great damages.

Summary

2000 ◽  
Author(s):  
Stanley A. Changnon ◽  
Roger A., Jr. Pielke
Keyword(s):  
United States ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Climate Extremes ◽  
The United States ◽  
Rapid Onset ◽  
Global Scale ◽  
Lessons Learned ◽  
Decision Makers

Much has been said about El Niño 97-98, some of it profound and some not. Several of the key findings from this assessment are reflected in an excellent short summary published by the World Meteorological Organization (WMO) in January 1999. . . . The 1997/1998 El Niño was probably the strongest in recorded history; it disrupted the lives of millions of people on all the Earth’s inhabited continents. Not all climate extremes and severe weather events of the period, however, can be directly attributed to the El Niño event. Further, not all its impacts were negative, and some regions that were expected to suffer were not seriously affected. (Obasi, 1999) . . . As the WMO found on a global scale, we have documented the profound impacts of El Niño 97-98 in the United States. But, perhaps contrary to conventional wisdom, the impacts in the United States were, in the aggregate, positive. Because El Niño shifted the geographical distribution of seasonal anomalies and because scientists were able to anticipate these shifts, many decision makers were able to profit from the early warnings to take compensatory actions. The accuracy of the predictions, and the successful use by decision makers of those predictions, offers the promise of the development of a more robust climate service in the United States. The remainder of this chapter summarizes the surprises, the lessons learned, and the legacy of El Niño 97-98. Once the rapid onset of El Niño conditions was detected late in the spring of 1997, forecasters successfully predicted the event’s strength and duration. The oceanic predictions reinforced the ensuing seasonal climate forecasts. The official seasonal outlooks issued by the National Oceanic and Atmospheric Administration (NOAA) in the summer of 1997 skillfully predicted the fall, winter, and early spring 1997-1998 conditions in many parts of the United States many months in advance. The seasonal forecasts had an accuracy of greater than 50 percent for temperatures and of between 30 percent and 50 percent for precipitation, the highest levels of accuracy ever attained, a reflection of the benefits of the considerable research and ocean-monitoring efforts directed at the El Niño Southern Oscillation (ENSO) over the past twenty years.

Who Used and Benefited from the El Niño Forecasts?

2000 ◽  
Author(s):  
David Changnon
Keyword(s):  
United States ◽  
Water Resources ◽  
El Niño ◽  
El Nino ◽  
The United States ◽  
Decision Makers ◽  
Seasonal Forecasts ◽  
Public And Private ◽  
Climate Forecasts ◽  
Great Confidence

The long-range seasonal climate forecasts based on El Niño 97-98 conditions and issued from June through August 1997 for the fall, winter, and early spring conditions across the United States were accurate for many parts of the nation (see chapter 2). An important question concerns whether decision makers in weather-sensitive public and private organizations used these El Niño -derived seasonal forecasts. Most seasonal forecasters viewed with great confidence the predictions of a strong El Niño and associated precipitation, temperature, and storm anomalies expected across the United States. From their perspective, it was an opportune time to use and, presumably, to benefit from the forecasts. Our assessment of a large group of potential users of the seasonal forecasts sought to identify who used and did not use the forecasts, the reasons for their use or non use, and the applications and potential value of the forecasts derived from their use. Sector differences were assessed by sampling decision makers in agribusiness, water resources, utilities, and other sectors. Results of such use and non use investigations will help develop better, more effective strategies for disseminating climate forecasts (Pfaff et al, 1999). Another objective of this study was to understand the perceptions decision makers had of seasonal forecasts and how the successful predictions based on El Niño 97-98 may have modified those perceptions. Figure 5-1 presents a typical humorous media view of the forecasts. A survey of individuals was conducted to gather the desired information about how the seasonal forecasts based on El Niño 97-98 were obtained, evaluated, and incorporated into decisions. The study was designed to focus on decision makers in weather-sensitive positions and to employ sampling techniques tested and developed in prior surveys. These previous studies had developed, tested, and used questionnaires as the tool by which to gather information about the use of climate information by weather-sensitive users in water resources, agribusiness, and utilities (Changnon, 1982, 1991, 1992; Changnon and Changnon, 1990; Changnon etal, 1988, 1995; Sonka etal, 1992).

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