A 30-Yr Climatology of Meteorological Conditions Associated with Lightning Days in the Interior Western United States

AbstractA 30-yr climatology of lightning days and associated synoptic meteorological patterns are characterized across the interior western United States (WUS). Locally centered composite analyses show preferred synoptic meteorological patterns with positive 500-hPa geopotential height anomalies located to the northeast and negative sea level pressure anomalies to the northwest and collocated with local lightning days. Variations in preferred patterns for local lightning days are seen across the interior WUS. Areas not commonly affected by the North American monsoon system including the western Great Basin and northern Rocky Mountains show higher-amplitude anomalies of geopotential height, moisture, and midtropospheric instability patterns suggesting the importance of episodic midlatitude dynamics to lightning days in such locations. By contrast, locations closer to the core of the North American monsoon show weaker anomalies, likely reflecting the prevalence of favorable mesoscale dynamics key to lightning production during warm-season months in locations in the interior Southwest. Meteorological patterns for select locations are explored in more detail and two case studies of notably active lightning events are presented. Results from this observational analysis provide a foundation for evaluating meteorological conditions on lightning days in climate model simulations for the interior WUS.

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Relationships between Spring Snow Mass and Summer Precipitation in the Southwestern United States Associated with the North American Monsoon System

Journal of Climate ◽

10.1175/1520-0442(2002)015<1378:rbssma>2.0.co;2 ◽

2002 ◽

Vol 15 (11) ◽

pp. 1378-1385 ◽

Cited By ~ 35

Author(s):

Fiona Lo ◽

Martyn P. Clark

Keyword(s):

United States ◽

North American ◽

Summer Precipitation ◽

North American Monsoon ◽

Southwestern United States ◽

The North ◽

Monsoon System ◽

Snow Mass

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Simulations of the 2004 North American Monsoon: NAMAP2

Journal of Climate ◽

10.1175/2009jcli3138.1 ◽

2009 ◽

Vol 22 (24) ◽

pp. 6716-6740 ◽

Cited By ~ 27

Author(s):

D. S. Gutzler ◽

L. N. Long ◽

J. Schemm ◽

S. Baidya Roy ◽

M. Bosilovich ◽

...

Keyword(s):

Boundary Conditions ◽

North American ◽

Warm Season ◽

North American Monsoon ◽

Regional Models ◽

Global Models ◽

Low Level ◽

The Core ◽

The North ◽

Low Level Jet

Abstract The second phase of the North American Monsoon Experiment (NAME) Model Assessment Project (NAMAP2) was carried out to provide a coordinated set of simulations from global and regional models of the 2004 warm season across the North American monsoon domain. This project follows an earlier assessment, called NAMAP, that preceded the 2004 field season of the North American Monsoon Experiment. Six global and four regional models are all forced with prescribed, time-varying ocean surface temperatures. Metrics for model simulation of warm season precipitation processes developed in NAMAP are examined that pertain to the seasonal progression and diurnal cycle of precipitation, monsoon onset, surface turbulent fluxes, and simulation of the low-level jet circulation over the Gulf of California. Assessment of the metrics is shown to be limited by continuing uncertainties in spatially averaged observations, demonstrating that modeling and observational analysis capabilities need to be developed concurrently. Simulations of the core subregion (CORE) of monsoonal precipitation in global models have improved since NAMAP, despite the lack of a proper low-level jet circulation in these simulations. Some regional models run at higher resolution still exhibit the tendency observed in NAMAP to overestimate precipitation in the CORE subregion; this is shown to involve both convective and resolved components of the total precipitation. The variability of precipitation in the Arizona/New Mexico (AZNM) subregion is simulated much better by the regional models compared with the global models, illustrating the importance of transient circulation anomalies (prescribed as lateral boundary conditions) for simulating precipitation in the northern part of the monsoon domain. This suggests that seasonal predictability derivable from lower boundary conditions may be limited in the AZNM subregion.

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Variation of the North American Summer Monsoon Regimes and the Atlantic Multidecadal Oscillation

Journal of Climate ◽

10.1175/2007jcli2005.1 ◽

2008 ◽

Vol 21 (11) ◽

pp. 2371-2383 ◽

Cited By ~ 42

Author(s):

Qi Hu ◽

Song Feng

Keyword(s):

United States ◽

North American ◽

Summer Rainfall ◽

Atlantic Multidecadal Oscillation ◽

North American Monsoon ◽

Western North America ◽

The North ◽

West Mexico ◽

Central United States ◽

Rainfall Variations

Abstract The North American summer monsoon holds the key to understanding warm season rainfall variations in the region from northern Mexico to the Southwest and the central United States. Studies of the monsoon have pictured mosaic submonsoonal regions and different processes influencing monsoon variations. Among the influencing processes is the “land memory,” showing primarily the influence of the antecedent winter season precipitation (snow) anomalies in the Northwest on summer rainfall anomalies in the Southwest. More intriguingly, the land memory has been found to vary at the multidecadal time scale. This memory change may actually reflect multidecadal variations of the atmospheric circulation in the North American monsoon region. This notion is examined in this study by first establishing the North American monsoon regimes from relationships of summer rainfall variations in central and western North America, and then quantifying their variations at the multidecadal scale in the twentieth century. Results of these analyses show two monsoon regimes: one featured with consistent variations in summer rainfall in west Mexico and the Southwest and an opposite variation pattern in the central United States, and the other with consistent rainfall variations in west Mexico and the central United States but different from the variations in the southwest United States. These regimes have alternated at multidecadal scales in the twentieth century. This alternation of the regimes is found to be in phase with the North Atlantic Multidecadal Oscillation (AMO). In warm and cold phases of the AMO, distinctive circulation anomalies are found in central and western North America, where lower than average pressure prevailed in the warm phase and the opposite anomaly in the cold phase. Associated wind anomalies configured different patterns for moisture transport and may have contributed to the development and variation of the monsoon regimes. These results indicate that investigations of the effects of AMO and its interaction with the North Pacific circulations could lead to a better understanding of the North American monsoon variations.

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Assessment of CMIP5 Model Simulations of the North American Monsoon System

Journal of Climate ◽

10.1175/jcli-d-13-00044.1 ◽

2013 ◽

Vol 26 (22) ◽

pp. 8787-8801 ◽

Cited By ~ 42

Author(s):

Kerrie L. Geil ◽

Yolande L. Serra ◽

Xubin Zeng

Keyword(s):

North American ◽

Geopotential Height ◽

General Circulation ◽

Large Scale ◽

North American Monsoon ◽

Monthly Precipitation ◽

Large Scale Circulation ◽

Low Level ◽

The North ◽

Monsoon System

Abstract Precipitation, geopotential height, and wind fields from 21 models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) are examined to determine how well this generation of general circulation models represents the North American monsoon system (NAMS). Results show no improvement since CMIP3 in the magnitude (root-mean-square error and bias) of the mean annual cycle of monthly precipitation over a core monsoon domain, but improvement in the phasing of the seasonal cycle in precipitation is notable. Monsoon onset is early for most models but is clearly visible in daily climatological precipitation, whereas monsoon retreat is highly variable and unclear in daily climatological precipitation. Models that best capture large-scale circulation patterns at a low level usually have realistic representations of the NAMS, but even the best models poorly represent monsoon retreat. Difficulty in reproducing monsoon retreat results from an inaccurate representation of gradients in low-level geopotential height across the larger region, which causes an unrealistic flux of low-level moisture from the tropics into the NAMS region that extends well into the postmonsoon season. Composites of the models with the best and worst representations of the NAMS indicate that adequate representation of the monsoon during the early to midseason can be achieved even with a large-scale circulation pattern bias, as long as the bias is spatially consistent over the larger region influencing monsoon development; in other words, as with monsoon retreat, it is the inaccuracy of the spatial gradients in geopotential height across the larger region that prevents some models from realistic representation of the early and midseason monsoon system.

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Multiscale Variability of the Flow during the North American Monsoon Experiment

Journal of Climate ◽

10.1175/jcli4087.1 ◽

2007 ◽

Vol 20 (9) ◽

pp. 1628-1648 ◽

Cited By ~ 53

Author(s):

Richard H. Johnson ◽

Paul E. Ciesielski ◽

Brian D. McNoldy ◽

Peter J. Rogers ◽

Richard K. Taft

Keyword(s):

United States ◽

North American ◽

Gulf Of California ◽

Large Scale ◽

Regional Scale ◽

North American Monsoon ◽

Return Flow ◽

Southwestern United States ◽

The North ◽

Upper Level

Abstract The 2004 North American Monsoon Experiment (NAME) provided an unprecedented observing network for studying the structure and evolution of the North American monsoon. This paper focuses on multiscale characteristics of the flow during NAME from the large scale to the mesoscale using atmospheric sounding data from the enhanced observing network. The onset of the 2004 summer monsoon over the NAME region accompanied the typical northward shift of the upper-level anticyclone or monsoon high over northern Mexico into the southwestern United States, but in 2004 this shift occurred slightly later than normal and the monsoon high did not extend as far north as usual. Consequently, precipitation over the southwestern United States was slightly below normal, although increased troughiness over the Great Plains contributed to increased rainfall over eastern New Mexico and western Texas. The first major pulse of moisture into the Southwest occurred around 13 July in association with a strong Gulf of California surge. This surge was linked to the westward passages of Tropical Storm Blas to the south and an upper-level inverted trough over northern Texas. The development of Blas appeared to be favored as an easterly wave moved into the eastern Pacific during the active phase of a Madden–Julian oscillation. On the regional scale, sounding data reveal a prominent sea breeze along the east shore of the Gulf of California, with a deep return flow as a consequence of the elevated Sierra Madre Occidental (SMO) immediately to the east. Subsidence produced a dry layer over the gulf, whereas a deep moist layer existed over the west slopes of the SMO. A prominent nocturnal low-level jet was present on most days over the northern gulf. The diurnal cycle of heating and moistening (Q1 and Q2) over the SMO was characterized by deep convective profiles in the mid- to upper troposphere at 1800 LT, followed by stratiform-like profiles at midnight, consistent with the observed diurnal evolution of precipitation over this coastal mountainous region. The analyses in the core NAME domain are based on a gridded dataset derived from atmospheric soundings only and, therefore, should prove useful in validating reanalyses and regional models.

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Applications of Monsoon Research: Opportunities to Inform Decision Making and Reduce Regional Vulnerability

Journal of Climate ◽

10.1175/jcli4098.1 ◽

2007 ◽

Vol 20 (9) ◽

pp. 1608-1627 ◽

Cited By ~ 54

Author(s):

Andrea J. Ray ◽

Gregg M. Garfin ◽

Margaret Wilder ◽

Marcela Vásquez-León ◽

Melanie Lenart ◽

...

Keyword(s):

United States ◽

Decision Making ◽

North American ◽

Knowledge Exchange ◽

The United States ◽

North American Monsoon ◽

Precipitation Regime ◽

The North ◽

Integrated Assessments ◽

Inform Decision Making

Abstract This article presents ongoing efforts to understand interactions between the North American monsoon and society in order to develop applications for monsoon research in a highly complex, multicultural, and binational region. The North American monsoon is an annual precipitation regime that begins in early June in Mexico and progresses northward to the southwestern United States. The region includes stakeholders in large urban complexes, productive agricultural areas, and sparsely populated arid and semiarid ecosystems. The political, cultural, and socioeconomic divisions between the United States and Mexico create a broad range of sensitivities to climate variability as well as capacities to use forecasts and other information to cope with climate. This paper highlights methodologies to link climate science with society and to analyze opportunities for monsoon science to benefit society in four sectors: natural hazards management, agriculture, public health, and water management. A list of stakeholder needs and a calendar of decisions is synthesized to help scientists link user needs to potential forecasts and products. To ensure usability of forecasts and other research products, iterative scientist–stakeholder interactions, through integrated assessments, are recommended. These knowledge-exchange interactions can improve the capacity for stakeholders to use forecasts thoughtfully and inform the development of research, and for the research community to obtain feedback on climate-related products and receive insights to guide research direction. It is expected that integrated assessments can capitalize on the opportunities for monsoon science to inform decision making and, in the best instances, reduce regional climate vulnerabilities and enhance regional sustainability.

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Long-Term Changes in the Climatology of Transient Inverted Troughs over the North American Monsoon Region and Their Effects on Precipitation

Journal of Climate ◽

10.1175/jcli-d-15-0726.1 ◽

2016 ◽

Vol 29 (17) ◽

pp. 6037-6064 ◽

Cited By ~ 18

Author(s):

Timothy M. Lahmers ◽

Christopher L. Castro ◽

David K. Adams ◽

Yolande L. Serra ◽

John J. Brost ◽

...

Keyword(s):

North American ◽

Climate Model ◽

Regional Climate ◽

Track Density ◽

North American Monsoon ◽

Northwest Mexico ◽

The North ◽

Simulated Precipitation ◽

Precipitation Estimates ◽

Resolution Model

Abstract Transient inverted troughs (IVs) are a trigger for severe weather during the North American monsoon (NAM) in the southwest contiguous United States (CONUS) and northwest Mexico. These upper-tropospheric disturbances enhance the synoptic-scale and mesoscale environment for organized convection, increasing the chances for microbursts, straight-line winds, blowing dust, and flash flooding. This work considers changes in the track density climatology of IVs between 1951 and 2010. IVs are tracked as potential vorticity (PV) anomalies on the 250-hPa surface from a regional climate model that dynamically downscales the NCEP–NCAR Reanalysis 1. Late in the NAM season, a significant increase in IV track density over the 60-yr period is observed over Southern California and western Arizona, coupled with a slight decrease over northwest Mexico. Changes in precipitation are evaluated on days when an IV is observed and days without an IV, using high-resolution model-simulated precipitation estimates and CPC gridded precipitation observations. Because of changes in the spatial distribution of IVs during the 1951–2010 analysis period, which are associated with a strengthening of the monsoon ridge, it is suggested that IVs have played a lesser role in the initiation and organization of monsoon convection in the southwest CONUS during recent warm seasons.

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Can a Regional Climate Model Improve the Ability to Forecast the North American Monsoon?

Journal of Climate ◽

10.1175/jcli-d-11-00441.1 ◽

2012 ◽

Vol 25 (23) ◽

pp. 8212-8237 ◽

Cited By ~ 48

Author(s):

Christopher L. Castro ◽

Hsin-I Chang ◽

Francina Dominguez ◽

Carlos Carrillo ◽

Jae-Kyung Schemm ◽

...

Keyword(s):

North American ◽

Large Scale ◽

Dynamical Downscaling ◽

Warm Season ◽

Regional Model ◽

Precipitation Anomaly ◽

Early Summer ◽

North American Monsoon ◽

The North ◽

Temperature And Precipitation

Abstract Global climate models are challenged to represent the North American monsoon, in terms of its climatology and interannual variability. To investigate whether a regional atmospheric model can improve warm season forecasts in North America, a retrospective Climate Forecast System (CFS) model reforecast (1982–2000) and the corresponding NCEP–NCAR reanalysis are dynamically downscaled with the Weather Research and Forecasting model (WRF), with similar parameterization options as used for high-resolution numerical weather prediction and a new spectral nudging capability. The regional model improves the climatological representation of monsoon precipitation because of its more realistic representation of the diurnal cycle of convection. However, it is challenged to capture organized, propagating convection at a distance from terrain, regardless of the boundary forcing data used. Dynamical downscaling of CFS generally yields modest improvement in surface temperature and precipitation anomaly correlations in those regions where it is already positive in the global model. For the North American monsoon region, WRF adds value to the seasonally forecast temperature only in early summer and does not add value to the seasonally forecast precipitation. CFS has a greater ability to represent the large-scale atmospheric circulation in early summer because of the influence of Pacific SST forcing. The temperature and precipitation anomaly correlations in both the global and regional model are thus relatively higher in early summer than late summer. As the dominant modes of early warm season precipitation are better represented in the regional model, given reasonable large-scale atmospheric forcing, dynamical downscaling will add value to warm season seasonal forecasts. CFS performance appears to be inconsistent in this regard.

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Impact of Tropical Easterly Waves on the North American Monsoon

Journal of Climate ◽

10.1175/jcli4071.1 ◽

2007 ◽

Vol 20 (7) ◽

pp. 1219-1238 ◽

Cited By ~ 21

Author(s):

Jennifer L. Adams ◽

David J. Stensrud

Keyword(s):

United States ◽

Boundary Conditions ◽

North American ◽

Moisture Flux ◽

North American Monsoon ◽

Southern Plains ◽

The North ◽

Gulf Surges ◽

Northwestern Mexico ◽

The Impact

Abstract The North American monsoon (NAM) is a prominent summertime feature over northwestern Mexico and the southwestern United States. It is characterized by a distinct shift in midlevel winds from westerly to easterly as well as a sharp, marked increase in rainfall. This maximum in rainfall accounts for 60%–80% of the annual precipitation in northwestern Mexico and nearly 40% of the yearly rainfall over the southwestern United States. Gulf surges, or coastally trapped disturbances that occur over the Gulf of California, are important mechanisms in supplying the necessary moisture for the monsoon and are hypothesized in previous studies to be initiated by the passage of a tropical easterly wave (TEW). Since the actual number of TEWs varies from year to year, it is possible that TEWs are responsible for producing some of the interannual variability in the moisture flux and rainfall seen in the NAM. To explore the impact of TEWs on the NAM, four 1-month periods are chosen for study that represent a reasonable variability in TEW activity. Two continuous month-long simulations are produced for each of the selected months using the Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model. One simulation is a control run that uses the complete boundary condition data, whereas a harmonic analysis is used to remove TEWs with periods of approximately 3.5 to 7.5 days from the model boundary conditions in the second simulation. These simulations with and without TEWs in the boundary conditions are compared to determine the impact of the waves on the NAM. Fields such as meridional moisture flux, rainfall totals, and surge occurrences are examined to define similarities and differences between the model runs. Results suggest that the removal of TEWs not only reduces the strength of gulf surges, but also rearranges rainfall over the monsoon region. Results further suggest that TEWs influence rainfall over the Southern Plains of the United States, with TEWs leading to less rainfall in this region. While these results are only suggestive, since rainfall is the most difficult model forecast parameter, it may be that TEWs alone can explain part of the inverse relationship between NAM and Southern Plains rainfall.

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