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Craig A. Clark

Abstract

Many high school students with a passion for meteorology visit college campuses each year, inquiring about program details and learning of the rigorous math requirements and somewhat daunting attrition risk. The natural question for many is, “Can I do it?” To address this question, the study herein has investigated the sensitivity of meteorology major outcomes at Valparaiso University to incoming test scores (based on 2008–14 first-year cohorts). These former students are classified as meteorology alumni (MET Degree), graduates of other programs (Other VU Degree), and those who left the University (Left VU). There is an additional performance classification, which indicates students who completed the program in good standing (On Track), students that completed the program with greater difficulty (Below Track), those who left the program in good academic standing (Left On Track), and those who left the program after not doing well (Left Below Track). Results indicate that incoming test scores are indeed indicative of student outcomes, with a substantially greater likelihood of being On Track and graduating with the MET Degree among students with higher incoming ACT scores. Among students who Left Below Track, signs of academic challenges typically appear within first semester calculus and/or the introductory meteorology course. Higher admission standards would increase retention and graduation rates, but at a cost of barring admission for some students who have been successful in the program.

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Craig A. Clark
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Craig A. Clark and Paymond W. Arritt

Abstract

A one-dimensional (column) version of a primitive equations model has been used to study the impact of soil moisture and vegetation cover on the development of deep cumulus convection in the absence of dynamical forcing. The model includes parameterizations of radiation, turbulent exchange, deep convection, shallow boundary layer convective clouds, vegetation, and soil temperature and moisture. Multiple one-dimensional experiments were performed using the average July sounding for Topeka, Kansas, as the initial condition. A range of volumetric soil moisture from one-half of the wilting point to saturation and vegetation cover ranging from bare soil to full cover were considered.

Vegetation cover was found to promote convection, both by extraction of soil moisture and by shading the soil so that conduction of heat into the soil was reduced (thereby increasing the available energy). The larger values of initial soil moisture were found to delay the onset of precipitation and to increase the precipitation amount. The greatest rainfall amounts were generally predicted to occur for moist, fully vegetated surfaces. Vegetation cover also had a pronounced moderating influence, decreasing the sensitivity of the results to the soil moisture content. The general nature of the results prevailed for modest variations in the initial summertime atmospheric profile and changes in the details of the surface parameterization. The inclusion of shading by shallow cumulus clouds tended to reduce the convection for moist, bare (or partly bare) soil. The nonlinearity of the interaction between the land surface and convective precipitation implies that the effects of subgrid landscape heterogeneity in climate models cannot accurately be represented by linear averages of the contributions from the different surface types.

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Raymond W. Arritt, Thomas D. Rink, Moti Segal, Dennis P. Todey, Craig A. Clark, Mark J. Mitchell, and Kenneth M. Labas

Abstract

Hourly wind profiler observations from the NOAA Profiler Network were used to develop a climatology of the low-level jet (LLJ) over the Great Plains of the central United States from April to September of 1993. The peak precipitation episode of the 1993 flood was associated with a sustained period of high incidence of strong low-level jets (over 20 m s−1). Consistent with previous studies, strong low-level jets were found to be promoted in the warm sector of an extratropical cyclone. Comparison of datasets formulated using velocity variance thresholds with unthresholded data similar to the operational hourly data suggests that the profiler observations often were contaminated by radar returns from migrating birds, especially during the months of April and May.

The strong low-level jets during the peak precipitation episode of the 1993 flood over the upper Mississippi River basin were associated with a high-amplitude upper-level wave pattern over and upstream of the continental United States. Separating the composite 850-mb wind for strong low-level jets into geostrophic and ageostrophic components showed that the magnitudes of the ageostrophic component and the anomalous geostrophic component were comparable.

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Craig A. Clark, Travis J. Elless, Anthony W. Lyza, Bharath Ganesh-Babu, Dana M. Koning, Alexander R. Carne, Holly A. Boney, Amanda M. Sink, Sarah K. Mustered, and Justin M. Barrick

Abstract

This study has investigated the spatiotemporal structure and changes in Lake Michigan snowfall for the period 1950–2013. With data quality caveats acknowledged, a larger envelope of stations was included than in previous studies to explore the data using time series analysis, principal component analysis, and geographic information systems. Results indicate warming in recent decades, a near-dearth of serial correlation, midwinter dependence on teleconnection patterns, strong sensitivity of snowfall to temperature, peak snowfall variability and dependence on temperature within the lake-effect belt, an increasing fraction of seasonal snowfall occurring from December to February, and temporal behavior consistent with the previously reported trend reversal in snowfall.

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Morris L. Weisman, Robert J. Trapp, Glen S. Romine, Chris Davis, Ryan Torn, Michael Baldwin, Lance Bosart, John Brown, Michael Coniglio, David Dowell, A. Clark Evans, Thomas J. Galarneau Jr., Julie Haggerty, Terry Hock, Kevin Manning, Paul Roebber, Pavel Romashkin, Russ Schumacher, Craig S. Schwartz, Ryan Sobash, David Stensrud, and Stanley B. Trier

Abstract

The Mesoscale Predictability Experiment (MPEX) was conducted from 15 May to 15 June 2013 in the central United States. MPEX was motivated by the basic question of whether experimental, subsynoptic observations can extend convective-scale predictability and otherwise enhance skill in short-term regional numerical weather prediction.

Observational tools for MPEX included the National Science Foundation (NSF)–National Center for Atmospheric Research (NCAR) Gulfstream V aircraft (GV), which featured the Airborne Vertical Atmospheric Profiling System mini-dropsonde system and a microwave temperature-profiling (MTP) system as well as several ground-based mobile upsonde systems. Basic operations involved two missions per day: an early morning mission with the GV, well upstream of anticipated convective storms, and an afternoon and early evening mission with the mobile sounding units to sample the initiation and upscale feedbacks of the convection.

A total of 18 intensive observing periods (IOPs) were completed during the field phase, representing a wide spectrum of synoptic regimes and convective events, including several major severe weather and/or tornado outbreak days. The novel observational strategy employed during MPEX is documented herein, as is the unique role of the ensemble modeling efforts—which included an ensemble sensitivity analysis—to both guide the observational strategies and help address the potential impacts of such enhanced observations on short-term convective forecasting. Preliminary results of retrospective data assimilation experiments are discussed, as are data analyses showing upscale convective feedbacks.

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