scholarly journals Diagnosis of Anomalous Winter Temperatures over the Eastern United States during the 2002/03 El Niño

2006 ◽  
Vol 19 (21) ◽  
pp. 5624-5636 ◽  
Author(s):  
Lisa Goddard ◽  
Arun Kumar ◽  
Martin P. Hoerling ◽  
Anthony G. Barnston
Keyword(s):  
United States ◽  
El Niño ◽  
El Nino ◽  
Winter Season ◽  
Temperature Pattern ◽  
Eastern United States ◽  
Seasonal Forecasts ◽  
Temperature Anomalies ◽  
Winter Temperatures ◽  
The U.S

Abstract The eastern United States experienced an unusually cold winter season during the 2002/03 El Niño event. The U.S. seasonal forecasts did not suggest an enhanced likelihood for below-normal temperatures over the eastern United States in that season. A postmortem analysis examining the observed temperatures and the associated forecast is motivated by two fundamental questions: what are these temperature anomalies attributable to, and to what extent were these temperature anomalies predictable? The results suggest that the extreme seasonal temperatures experienced in the eastern United States during December–February (DJF) 2002/03 can be attributed to a combination of several constructively interfering factors that include El Niño conditions in the tropical Pacific, a persistent positive Pacific–North American (PNA) mode, a persistent negative North Atlantic Oscillation (NAO) mode, and persistent snow cover over the northeastern United States. According to the simulations and predictions from several dynamical atmospheric models, which were not rigorously included in the U.S. forecast, much of the observed temperature pattern was potentially predictable.

scholarly journals Predictable and Unpredictable Aspects of U.S. West Coast Rainfall and El Niño: Understanding the 2015/16 Event

2019 ◽  
Vol 32 (10) ◽  
pp. 2843-2868 ◽  
Author(s):  
Benjamin A. Cash ◽  
Natalie J. Burls
Keyword(s):  
Pacific Northwest ◽  
West Coast ◽  
El Niño ◽  
El Nino ◽  
Rainfall Variability ◽  
Winter Season ◽  
Seasonal Forecasts ◽  
The North ◽  
Dry Conditions ◽  
The Individual

AbstractCalifornia experienced record-setting drought from 2012 to 2017. Based on both seasonal forecast models and historical associations, there was widespread expectation that the major El Niño event of 2015/16 would result in increased winter-season precipitation and break the drought. However, the 2015/16 winter rainy season ultimately resulted in slightly below-average precipitation and the drought continued. In this work we analyze data from both observations and seasonal forecasts made as part of the North American Multi-Model Ensemble (NMME) to better understand the general relationship between El Niño and U.S. West Coast rainfall, focusing on Southern California (SOCAL) rainfall, Pacific Northwest (PNW) rainfall, and the 2015/16 event. We find that while there is a statistically significant positive correlation between El Niño events and the SOCAL and PNW rainfall anomalies, this relationship explains at most one-third of the observed variance. Examination of hindcasts from the NMME demonstrates that the models are capable of accurately reproducing this observed correlation between tropical Pacific sea surface temperatures and California rainfall when information from the individual ensemble members is retained. However, focusing on the multimodel ensemble mean, which deliberately reduces the influence of unpredicted variability, drastically overestimates the strength of this relationship. Our analysis demonstrates that much of the winter rainfall variability along the U.S. West Coast is dominated by unpredicted variations in the 200-hPa height field and that this same unpredicted variability was largely responsible for the unexpectedly dry conditions in 2015/16.

scholarly journals Pentad Evolution of Wintertime Impacts of the Madden–Julian Oscillation over the Contiguous United States

2014 ◽  
Vol 27 (19) ◽  
pp. 7356-7367 ◽  
Author(s):  
Stephen Baxter ◽  
Scott Weaver ◽  
Jon Gottschalck ◽  
Yan Xue
Keyword(s):  
United States ◽  
Velocity Potential ◽  
Function Analysis ◽  
Winter Season ◽  
Surface Air Temperature ◽  
Phase Identification ◽  
Positive Temperature ◽  
Madden Julian Oscillation ◽  
Eastern United States ◽  
Temperature Anomalies

Abstract Lagged pentad composites of surface air temperature and precipitation are analyzed for the winter season (December–February) to assess the influence of the Madden–Julian oscillation (MJO) on the climate of the contiguous United States. Composites are based on the Wheeler and Hendon MJO index as well as an index developed and maintained at NOAA’s Climate Prediction Center (CPC), which is based on extended empirical orthogonal function analysis of upper-level velocity potential. Significant positive temperature anomalies develop in the eastern United States 5–20 days following Wheeler and Hendon MJO index phase 3, which corresponds to enhanced convection centered over the eastern Indian Ocean. At the same lag, positive precipitation anomalies are observed from the southern Plains to the Great Lakes region. Negative temperature anomalies appear in the central and eastern United States 10–20 days following Wheeler and Hendon MJO phase 7. These impacts are supported by an analysis of the evolution of 200-hPa geopotential height and zonal wind anomalies. Composites based on the CPC velocity potential MJO index generally yield similar results; however, they capture more cases since the index contains both interannual and subseasonal variability. There are some cases where the CPC index differs from that of WH in both MJO phase identification and its North American impacts, especially near the West Coast. This analysis suggests that MJO-related velocity potential anomalies can be used without the Wheeler and Hendon MJO index to predict MJO impacts.

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).

scholarly journals Precipitation Characteristics of Warm Season Weather Types in the Southeastern United States of America

Atmosphere ◽  
2021 ◽  
Vol 12 (8) ◽  
pp. 1001
Author(s):  
Jian-Hua Qian ◽  
Brian Viner ◽  
Stephen Noble ◽  
David Werth
Keyword(s):  
United States ◽  
El Niño ◽  
Gulf Coast ◽  
El Nino ◽  
River Valley ◽  
Northern Great Plains ◽  
Ohio River ◽  
Fair Weather ◽  
Weather Types ◽  
Rainy Weather

Daily weather types (WTs) over the Southeast United States have been analyzed using 850 hPa winds from reanalysis data from March to October of 1979–2019. Six WTs were obtained. WTs 1–3 represent mid-latitude synoptic systems propagating eastward. WT4 is a summer-type pattern predominantly occurring in June–August, with the center of the North Atlantic Subtropical High (NASH) along the Gulf coast in the southern United States. WT5 is most frequent from August to middle October, with the NASH pushed further north and southerly winds over the northern Great Plains. An anticyclone centered at the Carolina coast characterizes WT6, which occurs in all months but is slightly more frequent in the spring and fall, especially in October, corresponding to fair weather in the region. WTs 1, 2 and 3 can persist for only a few days. WTs 4, 5 and 6 can have long spells of persistence. Besides self-persistence, the most observed progression loop is WT1 to WT2, to WT3, and then back to WT1, corresponding to eastward-propagating waves. WTs 4 and 5 are likely to show persistence, with long periods of consecutive days. WT6 usually persists but can also transfer to WT3, i.e., a change from fair weather in the Southeast U.S. to rainy weather in the Mississippi River Valley. A diurnal cycle of precipitation is apparent for each WT, especially over coastal plains. The nocturnal precipitation in central U.S. is associated with WT3. WTs 1–3 are more frequent in El Niño years, corresponding to stronger westerly wave activities and above normal rainfall in the Southeast U.S. in the spring. The positive rainfall anomaly in the Mississippi and Ohio River valley in El Niño years is also associated with more frequent WT3.

scholarly journals ENSO’s Modulation of Water Vapor Transport over the Pacific–North American Region

2015 ◽  
Vol 28 (9) ◽  
pp. 3846-3856 ◽  
Author(s):  
Hye-Mi Kim ◽  
Michael A. Alexander
Keyword(s):  
United States ◽  
El Niño ◽  
North Pacific ◽  
Moisture Transport ◽  
El Nino ◽  
Tropical Pacific ◽  
Vapor Transport ◽  
Water Vapor Transport ◽  
Southwestern United States ◽  
The Pacific

Abstract The vertically integrated water vapor transport (IVT) over the Pacific–North American sector during three phases of ENSO in boreal winter (December–February) is investigated using IVT values calculated from the Climate Forecast System Reanalysis (CFSR) during 1979–2010. The shift of the location and sign of sea surface temperature (SST) anomalies in the tropical Pacific Ocean leads to different atmospheric responses and thereby changes the seasonal mean moisture transport into North America. During eastern Pacific El Niño (EPEN) events, large positive IVT anomalies extend northeastward from the subtropical Pacific into the northwestern United States following the anomalous cyclonic flow around a deeper Aleutian low, while a southward shift of the cyclonic circulation during central Pacific El Niño (CPEN) events induces the transport of moisture into the southwestern United States. In addition, moisture from the eastern tropical Pacific is transported from the deep tropical eastern Pacific into Mexico and the southwestern United States during CPEN. During La Niña (NINA), the seasonal mean IVT anomaly is opposite to that of two El Niño phases. Analyses of 6-hourly IVT anomalies indicate that there is strong moisture transport from the North Pacific into the northwestern and southwestern United States during EPEN and CPEN, respectively. The IVT is maximized on the southeastern side of a low located over the eastern North Pacific, where the low is weaker but located farther south and closer to shore during CPEN than during EPEN. Moisture enters the southwestern United States from the eastern tropical Pacific during NINA via anticyclonic circulation associated with a ridge over the southern United States.

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