On the synoptic and mesoscale organization of mid-latitude, continental convective snow events

The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file.Title from title screen of research.pdf file (viewed on June 10, 2009)Vita.Includes bibliographical references.Thesis (Ph. D.) University of Missouri-Columbia 2008.Dissertations, Academic -- University of Missouri--Columbia -- Soil, environmental and atmospheric sciences.An ingredients-based methodology was pursued in order to evaluate the likelihood of thunderstorms occurring in the presence of snowfall (i.e. thundersnow; TSSN). In order to properly distinguish from typical snowstorms (i.e. non-TSSN), the detailed examination focused on stability characteristics of wintertime convection across the central United States immediately leading up to the onset of the event. More specifically, the research primarily analyzed the value of the seldom applied growth rate parameter ([sigma]²). Identification of a separate collection of non- TSSN events helped to highlight the differences, and ultimately, the significance in the findings for the TSSN subset. The current work substantiated the premise that atmospheres were more unstable in episodes of convective snow with the analyses also revealing pronounced forcing mechanisms. The development of TSSN and any associated banding was correctly and most accurately predicted from trends in plots of [sigma]² analyzed at the level at which the highest significant growth rates occurred. An outlook can be more accurately issued by identifying regions where reduced values of equivalent potential vorticity (i.e. small symmetric stability or instability) are collocated with estimates of high [sigma]² (i.e. where small-scale slantwise perturbations will grow). Given the overall success, it is hoped that some of the conclusions established by this work will be implemented routinely in an operational environment and provide forecasters an additional, essential tool in dealing with snowcasting situations of hazardous winter weather events

Calculated Height Tendencies in Two Southern Hemisphere Blocking and Cyclone Events: The Contribution of Diabatic Heating to Block Intensification

The Zwack-Okossi vorticity tendency equation was used to calculate 500-hPa height tendencies in two intensifying Southern Hemisphere blocking events. The National Centers for Environmental Prediction- National Center for Atmospheric Research gridded reanalyses were used to make each of these calculations. The block intensification period for each event was associated with a deepening surface cyclone during a 48-h period beginning at 1200 UTC 28 July and 1200 UTC 8 August 1986, respectively. These results demonstrate that the diabatic heating forces height rises through the sensible and latent heating terms in these two Southern Hemisphere blocking events. The sensible heating was the larger contributor, second only to (about the same as) the vorticity advection term in the first (second) event. The vorticity advection term has been shown by several studies to be associated with block intensification

The Interannual variability of hurricane activity in the Atlantic and east pacific regions

The investigation of the interannual and interdecadal variations in hurricane activity has been an important topic of study lately, especially with regard to their implications for climate change issues. On the interannual time-scale, the El Niño and Southern Oscillation (ENSO) phase has been correlated with hurricane activity in the Atlantic and Eastern Pacific Ocean Basins. For example, various atmospheric and oceanic parameters that influence hurricane development become significantly altered during an El Niño event, leading to suppressed easterly wave development and growth in the Atlantic, but more activity in the Eastern Pacific Ocean Basin. This study examined the interannual variability of hurricane intensity (measured as wind speed and interpreted through the Saffir-Simpson Scale) from 1938 through 2007 in the Atlantic and 1970 through 2007 in the Pacific basins, respectively. These data were then compared with the occurrence of El Niño/La Niña events as defined using the Japan Meteorological Association (JMA) index. El Niño/La Niña variability superimposed on variability associated with the Pacific Decadal Oscillation (PDO) was also examined here. Not surprisingly, during an El Niño year the intensity of Atlantic hurricanes was found to be weaker than during a neutral year or a La Niña year, but these conclusions were opposite in the Eastern Pacific Ocean Basin. There were also significant differences found in hurricane intensity between El Niño and La Niña years when the PDO was in phase 1 (warm phase), rather than when the PDO was in phase 2 (cool phase). This study also examined the interannual variation in hurricane intensity by genesis region (i.e. Atlantic: the eastern and western Atlantic Ocean Basins, the Caribbean, and the Gulf of Mexico; Eastern Pacific: divided into quadrants using 20o N and 125o W as the quadrant intersection point). Finally, the utility of this information in a long-range forecast application is demonstrated

A comparison of two cases of low-latitude thundersnow

http://solberg.snr.missouri.edu/gcc/Two cases of low-latitude snow with lightning are studied to determine their characteristics. Both cases had synoptic-scale origins, but also featured smaller-scale influences (e. g. orographic lift and elevated instability).The first event occurred in the Southern Hemisphere and was a late winter case that developed under the influence of underlying orography. Lightning was plentiful in that event (94 cloud-to-ground flashes in the region), but snow accumulations were not significant. Lightning flashes of negative polarity dominated this case, with a mean peak amplitude of -43.2 kA. The second event was a Northern Hemisphere case of elevated convection, with frontogenesis beneath an extended layer of potential instability. Appreciable lightning occurred with this event as well (706 cloud-to-ground flashes in the region), and snow accumulations were significant over a broad area. Lightning flashes of negative polarity dominated this case also, with a mean peak amplitude of -23.7 kA. Each of these events is worthy of further scrutiny, as studies of such storms do not appear often in the literature. Indeed, such warm, subtropical regions are often unprepared for the effects of just a little snow or ice accumulation. Future forecasters can anticipate better such anomalous events by looking for these broad features: 1) significant and well-defined synoptic-scale weather systems at low latitudes, 2) a strong baroclinic zone with a well-defined (≥60 ms-1) jet structure aloft, 3) cold air of appreciable depth and areal extent drawn much closer to the equator than is typical, and 4) a moist neutral to conditionally unstable layer above the frontal zone

Proximity soundings of thundersnow in the central United States

[1] Proximity balloon soundings for snow events with lightning and thunder during the period 1961 through 1990 reveal a less statically stable environment than similar nonthundering snow events. When thundersnow is present, a less stable environment (and in some cases subsequent upright convection) is found aloft in all of the thundering cases examined here; all of the events feature their most unstable parcel originating above a frontal inversion. In fact, only events in the cold air north of an extratropical cyclone are included in this study. Events with a lake effect or orographic enhancement are eliminated from the sample. The basic composite derived by averaging temperatures at an established interval reveals a nearly saturated lower atmosphere, below 0°C throughout its depth, with the frontal inversion present and its most unstable parcel occurring just above the top of the inversion. The feature-preserving composite approach of R

THE COMMUNITY LEVERAGED UNIFIED ENSEMBLE (CLUE) IN THE 2016 NOAA/HAZARDOUS WEATHER TESTBED SPRING FORECASTING EXPERIMENT

One primary goal of annual Spring Forecasting Experiments (SFEs), which are coorganized by NOAA’s National Severe Storms Laboratory and Storm Prediction Center and conducted in the National Oceanic and Atmospheric Administration’s (NOAA) Hazardous Weather Testbed, is documenting performance characteristics of experimental, convection-allowing modeling systems (CAMs). Since 2007, the number of CAMs (including CAM ensembles) examined in the SFEs has increased dramatically, peaking at six different CAM ensembles in 2015. Meanwhile, major advances have been made in creating, importing, processing, verifying, and developing tools for analyzing and visualizing these large and complex datasets. However, progress toward identifying optimal CAM ensemble configurations has been inhibited because the different CAM systems have been independently designed, making it difficult to attribute differences in performance characteristics. Thus, for the 2016 SFE, a much more coordinated effort among many collaborators was made by agreeing on a set of model specifications (e.g., model version, grid spacing, domain size, and physics) so that the simulations contributed by each collaborator could be combined to form one large, carefully designed ensemble known as the Community Leveraged Unified Ensemble (CLUE). The 2016 CLUE was composed of 65 members contributed by five research institutions and represents an unprecedented effort to enable an evidence-driven decision process to help guide NOAA’s operational modeling efforts. Eight unique experiments were designed within the CLUE framework to examine issues directly relevant to the design of NOAA’s future operational CAM-based ensembles. This article will highlight the CLUE design and present results from one of the experiments examining the impact of single versus multicore CAM ensemble configurations

THE COMMUNITY LEVERAGED UNIFIED ENSEMBLE (CLUE) IN THE 2016 NOAA/HAZARDOUS WEATHER TESTBED SPRING FORECASTING EXPERIMENT

One primary goal of annual Spring Forecasting Experiments (SFEs), which are coorganized by NOAA’s National Severe Storms Laboratory and Storm Prediction Center and conducted in the National Oceanic and Atmospheric Administration’s (NOAA) Hazardous Weather Testbed, is documenting performance characteristics of experimental, convection-allowing modeling systems (CAMs). Since 2007, the number of CAMs (including CAM ensembles) examined in the SFEs has increased dramatically, peaking at six different CAM ensembles in 2015. Meanwhile, major advances have been made in creating, importing, processing, verifying, and developing tools for analyzing and visualizing these large and complex datasets. However, progress toward identifying optimal CAM ensemble configurations has been inhibited because the different CAM systems have been independently designed, making it difficult to attribute differences in performance characteristics. Thus, for the 2016 SFE, a much more coordinated effort among many collaborators was made by agreeing on a set of model specifications (e.g., model version, grid spacing, domain size, and physics) so that the simulations contributed by each collaborator could be combined to form one large, carefully designed ensemble known as the Community Leveraged Unified Ensemble (CLUE). The 2016 CLUE was composed of 65 members contributed by five research institutions and represents an unprecedented effort to enable an evidence-driven decision process to help guide NOAA’s operational modeling efforts. Eight unique experiments were designed within the CLUE framework to examine issues directly relevant to the design of NOAA’s future operational CAM-based ensembles. This article will highlight the CLUE design and present results from one of the experiments examining the impact of single versus multicore CAM ensemble configurations

The Storm Prediction Center (SPC) and

Objective forecast verification was conducted for the second year in near real-time during the 2013 Hazardous Weather Testbed (HWT) Spring Forecasting Experiment (2013 SFE). As part of the daily activities, experimental probabilistic forecasts for severe thunderstorms were created. These forecasts were then evaluated the next day via webpages with preliminary local storm reports (LSR) serving as the verification dataset. The idea was to further explore the value of incorporating verification metrics by comparing various scores to subjective evaluations from the participants. In addition to the forecast verification metrics examined in the 2012 SFE, the relative skill score was introduced since it was designed with a baseline reference capable of measuring skill of rare-event forecasts (i.e. severe thunderstorms). Results suggested that the relative skill scores were generally better on days with more severe weather reports. Further, the participants generated skillful forecasts at the lower probability thresholds, as the relative skill scores were predominately positive in accordance with favorable subjective ratings. ______________