Application of Synoptic Weather Types in the Analysis of Evaporation in Southern Louisiana (Climatology).

An analysis of pan evaporation by synoptic weather types revealed that pan evaporation rates vary significantly by weather type conditions. Fair weather types are associated with the greatest evaporation rates as was expected, and stormy weather types with the least. These findings are primarily related to the variation of solar radiation by weather type. An investigation of the relationship of pan evaporation to solar radiation by synoptic weather types revealed that the ratio of pan evaporation, expressed in energy units, to incoming solar radiation, also varies considerably by synoptic weather types. In general it was found that stormy weather types are associated with the highest ratios of pan evaporation to solar radiation. Fair weather types are associated with lower ratios, with Continental High situations resulting in the lowest ratios of pan evaporation to solar radiation in general. An evaluation of potential evapotranspiration models by synoptic weather types revealed that models perform differently for varying weather type conditions. For example, temperature based models perform well during stormy weather conditions since they are unaffected by low levels of solar radiation, but do not perform as well for fair weather conditions. Models based on solar radiation perform well during fair weather, but performance is reduced when stormy weather conditions prevail. The results of this research have increased understanding of the variability of evaporation under different weather conditions and the variability of potential evapotranspiration model performance under varying weather conditions. Further research of the variability of pan evaporation and evapotranspiration by synoptic weather types will lead to improved potential evapotranspiration model evaluation, will aid potential evapotranspiration model selection and application and will permit potential evapotranspiration model modification for increased performance under certain weather conditions

A Hybrid Procedure for Classifying Synoptic Weather Types for Louisiana with an Application to Precipitation Variability

An automated synoptic weather classification system, based on the weather types devised by Robert Muller for Louisiana, is presented in this thesis and an application of the classification system to precipitation variability in Louisiana is demonstrated. The automated classification presented here is a hybrid classification system that uses sea level pressure composites for each Muller weather type as seeds in a correlation procedure to classify daily NCEP/NCAR Reanalysis sea level pressure patterns. The resulting hybrid classification is automated, objective, and has value in describing the surface weather variability in Louisiana. In the second part of this research project, the newly developed hybrid classification system is used to establish relationships between synoptic weather types and precipitation variability in Louisiana. Weather types that produce precipitation in Louisiana are identified and, using linear regression models, the frequency of rainy weather types is used to predict seasonal rainfall for each of the nine Louisiana climate divisions. Averaged among all climate divisions, synoptic weather type frequency accounts for 25% of the interannual precipitation variability in winter, 14% in spring, 19% in summer, and 25% in fall. While the models are better at predicting the decadal scale variability and trends during fall and winter, these results indicate that synoptic frequency alone is insufficient to describe precipitation variability in Louisiana. Future work will need to identify additional predictors. However, the automated hybrid classification system presented in this study can be used for many additional applications in historical and future climate research for Louisiana

Contribution of snowfall from diverse synoptic conditions in the Catskill/Delaware Watershed of New York State

Snowfall in the six basins of the Catskill/Delaware Watershed in south‐central New York State historically contributes roughly 20–30% of the water resources derived from the watershed for use in the New York City water supply. The watershed regularly experiences snowfall from three distinctive weather patterns: coastal mid‐latitude cyclones, overrunning systems, and lake‐effect or Great Lakes enhanced storms. Using synoptic weather classification techniques, these distinct regional atmospheric patterns impacting the watershed are isolated and analysed in conjunction with daily snowfall observations from 1960 to 2009 to allow the influence of each synoptic weather pattern on snowfall to be evaluated independently. Results indicate that snowfall‐producing events occur on average approximately 63 days/year, or once every 4 days during the October–May season, leading to an average of 213 cm/year of snowfall within the watershed. Snowfall from Great Lakes enhanced storms and overrunning systems contribute nearly equally to seasonal totals, representing 38 and 39%, respectively. Coastal mid‐latitude cyclones, while producing the highest amount of snowfall per event on average, contribute only 16% to the watershed average total snowfall. Predicted climate change is expected to impact snowfall differently depending on the specific atmospheric pattern producing the snow. As such, quantifying the contribution of snowfall to the watershed by synoptic pattern can inform future water management and reservoir operation practices for the New York City Water Supply Management System

Analysis of synoptic weather patterns of heatwave events

Altres ajuts: acords transformatius de la UABUnidad de excelencia María de Maeztu CEX2019-000940-MHeatwaves (HWs) are expected to increase both in duration and intensity in the next decades, but little is known about their synoptic and mesoscalar behavior, which is especially important in mid-latitude regions. Most climate research has focused on temperature analysis to characterize HWs. We propose that a combination of temperature and synoptic patterns is a better way to define and understand HWs because including atmospheric circulation patterns provides information about different HW structures that can irregularly affect the territory, and illustrate this approach at the regional and urban scales using the Iberian Peninsula and the Metropolitan Area of Barcelona as case studies. We first select HW events from 1950 to 2020 and apply a multivariate analysis to identify synoptic patterns based on mean sea level pressure, geopotential height at 500 hPa, and maximum daily 2 m temperature. The results indicate that four synoptic patterns reproduce at least 50% of the variance in HWs, namely, "stationary andstable", "dynamic and advective", "stationary and advective", and "dynamic, advective and undulated". Next, we apply the analysis to the Representative Concentration Pathway future scenarios (RCPs) 4.5 and 8.5 from the Coordinated Regional Climate Downscaling Experiment (CORDEX) to determine how these synoptic trends can change in the future. The analysis shows that the four synoptic patterns continue to explain 55 to 60% of the variance in HWs. Future HW events will be characterized by an increase in geopotential height at 500 hPa due to the northward shift of the anticyclonic ridge. This is especially true for RCP8.5, which simulates business as usual incrementing fossil fuel use and additionally shows an increase in atmospheric dynamism in north advections from all directions in comparison with RCP4.5. These findings point to the importance of considering the geopotential height in HW prediction, as well as the direction of advections

Hazardous Weather and Human Response in the Southeastern United States

Effectively mitigating the human costs of future hazardous weather events requires examining meteorological threats, their long-term patterns, and human response to these events. The southeastern United States is a region that has both a high climatological risk and a high societal vulnerability to many different meteorological hazards. In this dissertation, I study hazardous weather and human response in the Southeast through three different lenses: identifying uniquely simultaneous hazards posed by tropical cyclones, assessing precipitation and synoptic weather patterns on hazardous weather days, and examining patterns in intended response to tornado watches. I find that simultaneous and collocated tornado and flash flood warnings are common in strong tropical cyclones, particularly those that move slowly after landfall. Additionally, hazardous weather days are common on days dominated by Moist Moderate and Moist Tropical airmasses and airmass transition days. Finally, factors including age, income, self-efficacy beliefs, and knowledge of and experience with tornadoes affect one’s intended response to a tornado watch. These studies produce new contributions to the state of knowledge on both the natural and social elements of hazards studies

Interpretation of remote sensing data in the Bayou Lafourche Delta of south Louisiana

There are no author-identified significant results in this report

The Formation and Geographic Relocation of January Diurnal Precipitation Patterns in Louisiana and Southeastern Texas (Rainfall, Meteorology, Cyclogenesis, Synoptic Climatology).

The diurnal patterns of hourly precipitation events in Louisiana and southeastern Texas in January have varied over space and time. Distinct spatial patterns were observed so that southern Texas had morning maximums throughout the study period while a southwest to northeast band of morning precipitation shifted south and east from eastern Texas in the 1950\u27s into central Louisiana in the 1960\u27s and 1970\u27s. Southeastern Louisiana maintained an afternoon pattern throughout the period. The morning precipitation in southern Texas is the result of the diurnal variation in cyclogenesis, especially off the Texas-Gulf coast. A southwest to northeast band of mid-morning precipitation peaks is the result of the northeastward migration of weak disturbances which move to the northeast with the southwesterly flow aloft, well in advance of the Texas-West Gulf cyclone. The band of mid-morning precipitation and its associated transition zone to afternoon peaks shifted to the south and east in the 1960\u27s and 1970\u27s due to the more southerly displacement of the polar front. There is much evidence to support this more southerly position of the polar front, including colder temperatures across the study region, a much greater frequency of frontal overrunning rainfall events at Lake Charles in the 1960\u27s and 1970\u27s, and stronger winds and lower pressures aloft at Brownsville since 1958. The transition zone between morning and afternoon precipitation maximums shift to the Florida panhandle in February according to other researchers. This shift takes place because the mean position of the arctic high shifts eastward as does the axis of the arctic air outbreaks across the eastern United States. Storm tracks in the south and eastern parts of the United States are also displaced eastward in late winter and spring. This research is of interest to weather forecasters, not just in Texas and Louisiana, but also throughout much of the southern and eastern United States. Previous research of diurnal precipitation patterns has not focused on changes in diurnal patterns over time. This study indicates that diurnal patterns can shift markedly with climatic fluctuations

Urban Effects on Precipitation in the Southern United States of America.

Of the many weather conditions influenced by urban areas, precipitation is one of the most controversial and unsolved elements in characterizing the urban climate. The purpose of this dissertation was to identify anomalies in precipitation totals and frequencies due to urban effects and to evaluate whether certain meteorological conditions or seasons have more apparent effects. The five largest cities in the south-central United States were selected: Houston; Dallas; San Antonio; New Orleans; and Memphis. It was assumed that simple spatial analysis can detect urban effects on precipitation over and downwind of the city with a localized maximum. Trend surface analysis was used to evaluate a natural precipitation gradient over the study area. Residual maps were used to detect whether a maximum in the simple spatial analysis is present after eliminating the regional effect. To evaluate the magnitude of precipitation enhancements, differences between the city (or downwind) and the upwind control areas were calculated. This research showed that Houston revealed the most distinct precipitation enhancement due to urban effects in summer with a 15.5% increase during the 1961-1990 period when examining precipitation totals. Dallas had a 5% increase of precipitation totals in spring and a 7% increase in summer. Precipitation frequencies showed more apparent enhancements than precipitation totals with a higher magnitude of enhancements. Houston showed distinct urban effects on extreme rainfall events producing 1-inch or higher rainfall in summer (23%) while the other four cities revealed apparent increases on the light precipitation-days in the colder seasons (20-60%). Rainfall frequency relations of extreme 24-hour rainfall did not show apparent precipitation enhancements due to urban effects because the magnitude of storms was too large. Airmass type storms showed more apparent precipitation enhancements due to urban effects than the other types and the three Texas cities showed more distinct effects than New Orleans and Memphis. The magnitude of precipitation enhancements might be closely related to the size of the city