James T. Moore

Bio: James T. Moore is an academic researcher from Saint Louis University. The author has contributed to research in topics: Mesoscale meteorology & Equivalent potential temperature. The author has an hindex of 10, co-authored 19 publications receiving 506 citations.

The Environment of Warm-Season Elevated Thunderstorms Associated with Heavy Rainfall over the Central United States

Abstract: Twenty-one warm-season heavy-rainfall events in the central United States produced by mesoscale convective systems (MCSs) that developed above and north of a surface boundary are examined to define the environmental conditions and physical processes associated with these phenomena. Storm-relative composites of numerous kinematic and thermodynamic fields are computed by centering on the heavy-rain-producing region of the parent elevated MCS. Results reveal that the heavy-rain region of elevated MCSs is located on average about 160 km north of a quasi-stationary frontal zone, in a region of low-level moisture convergence that is elongated westward on the cool side of the boundary. The MCS is located within the left-exit region of a south-southwesterly lowlevel jet (LLJ) and the right-entrance region of an upper-level jet positioned well north of the MCS site. The LLJ is directed toward a divergence maximum at 250 hPa that is coincident with the MCS site. Near-surface winds are light and from the southeast within a boundary layer that is statically stable and cool. Winds veer considerably with height (about 1408) from 850 to 250 hPa, a layer associated with warm-air advection. The MCS is located in a maximum of positive equivalent potential temperature ue advection, moisture convergence, and positive thermal advection at 850 hPa. Composite fields at 500 hPa show that the MCS forms in a region of weak anticyclonic curvature in the height field with marginal positive vorticity advection. Even though surfacebased stability fields indicate stable low-level air, there is a layer of convectively unstable air with maximumue CAPE values of more than 1000 J kg21 in the vicinity of the MCS site and higher values upstream. Maximumue convective inhibition (CIN) values over the MCS centroid site are small (less than 40 J kg 21) while to the south convection is limited by large values of CIN (greater than 60 J kg 21). Surface-to-500-hPa composite average relative humidity values are about 70%, and composite precipitable water values average about 3.18 cm (1.25 in.). The representativeness of the composite analysis is also examined. Last, a schematic conceptual model based upon the composite fields is presented that depicts the typical environment favorable for the development of elevated thunderstorms that lead to heavy rainfall.

A Climatology of Snow-to-Liquid Ratio for the Contiguous United States

Abstract: A 30-yr climatology of the snow-to-liquid-equivalent ratio (SLR) using the National Weather Service (NWS) Cooperative Summary of the Day (COOP) data is presented. Descriptive statistics are presented for 96 NWS county warning areas (CWAs), along with a discussion of selected histograms of interest. The results of the climatology indicate that a mean SLR value of 13 appears more appropriate for much of the country rather than the often-assumed value of 10, although considerable spatial variation in the mean exists. The distribution for the entire dataset exhibits positive skewness. Histograms for individual CWAs are both positively and negatively skewed, depending upon the variability of the in-cloud, subcloud, and ground conditions.

The Effect of Jet-Streak Curvature on Kinematic Fields

Abstract: A simple two-layer primitive equation (PE) model is used to study the effect of curvature on jet-streak kinematics, specifically vertical motion. Three types of vertical motion are studied: kinematic (PE) vertical motion, quasigeostrophic (QG) vertical motion, and vertical motion associated with an unbalanced component of the flow, partially due to inertial-gravity waves (IGW). The latter vertical motion is computed as the difference between the PE vertical motion and “balanced” vertical motion derived from Krishnamurti's balanced omega equation. In addition, the upper-level ageostrophic flow is discussed as it relates to the patterns of divergence associated with various jet curvatures. The PE model was run out to 12 h to we how straight-line (SL), cyclonic (CY), and anticyclonic (AC) curvature affects jet-streak kinematics. At the initial time, a two-cell pattern of vertical motion was found for the CY and AC jet streaks as opposed to the four-cell pattern associated with the SL jet streak. Als...

The Use of Equivalent Potential Vorticity to Diagnose Regions of Conditional Symmetric Instability

Abstract: Conditional symmetric instability (CSI) is an important property of the atmosphere when diagnosing and predicting mesoscale bands of moderate to heavy precipitation within winter cyclones. Within regions of CSI, slantwise convection can increase snow totals over narrow regions. Typically, CSI is evaluated in a cross-sectional plane chosen normal to the middle-tropospheric thermal wind using Mg, the absolute geostrophic momentum, and θ e, the equivalent potential temperature. Regions where Mg, surfaces slope less than θe, surfaces are subject to CSI. We describe an objective measure of CSI, called the equivalent potential vorticity (EPV), that makes evaluating CSI quick and effective. Cross sections of Mg, versus θe, and EPV are compared for two cases to demonstrate the effectiveness of using EPV cross sections to diagnose CSI. The distinction between slantwise convection and upright convection is also demonstrated by these case studies.

Initiation of an Elevated Mesoscale Convective System Associated with Heavy Rainfall

Abstract: A mesoscale convective system (MCS) developed during the morning hours of 6 June 1993 and moved across northern and central Missouri, resulting in a narrow swath of excessive rainfall (>150 mm). The MCS developed well north of a surface warm front above a cool, stable boundary layer and moved east–southeast across the state. Although some features of the synoptic environment agree with the frontal flash flood composite model, predicting the elevated thunderstorms that composed the MCS posed a unique forecasting challenge. This paper first describes the diagnostic parameters of the prestorm environment that would have been helpful to predict the initiation of the MCS and the resultant locally excessive precipitation. Attention is then drawn to the MCS itself via IR satellite and WSR-88D imagery. Finally, the similarities and differences of this episode to previous studies of flash flooding and elevated thunderstorms are noted, and a summary of key parameters useful in the anticipation of this type...

The Kain–Fritsch Convective Parameterization: An Update

Abstract: Numerous modifications to the Kain‐Fritsch convective parameterization have been implemented over the last decade. These modifications are described, and the motivating factors for the changes are discussed. Most changes were inspired by feedback from users of the scheme (primarily numerical modelers) and interpreters of the model output (mainly operational forecasters). The specific formulation of the modifications evolved from an effort to produce desired effects in numerical weather prediction while also rendering the scheme more faithful to observations and cloud-resolving modeling studies.

Severe Local Storms Forecasting

Abstract: Knowledge of severe local storms has been increasing rapidly in recent years as a result of both observational studies and numerical modeling experiments. This paper reviews that knowledge as it relates to development of new applications for forecasting of severe local storms. Many of these new applications are based on physical understanding of processes taking place on the storm scale and thus allow forecasters to become less dependent on empirical relationships. Refinements in pattern recognition and severe weather climatology continue to be of value to the operational severe local storms forecasters, however. Current methodology for forecasting severe local storms at the National Severe Storms Forecast Center is described. Operational uses of new forecast applications, new “real-time” data sources (such as wind profilers and Doppler radars), and improved numerical model products are discussed.

Organization and Environmental Properties of Extreme-Rain-Producing Mesoscale Convective Systems

Abstract: This study examines the radar-indicated structures and other features of extreme rain events in the United States over a 3-yr period. A rainfall event is defined as “extreme” when the 24-h precipitation total at one or more stations surpasses the 50-yr recurrence interval amount for that location. This definition yields 116 such cases from 1999 to 2001 in the area east of the Rocky Mountains, excluding Florida. Two-kilometer national composite radar reflectivity data are then used to examine the structure and evolution of each extreme rain event. Sixty-five percent of the total number of events are associated with mesoscale convective systems (MCSs). While a wide variety of organizational structures (as indicated by radar reflectivity data) are seen among the MCS cases, two patterns of organization are observed most frequently. The first type has a line, often oriented east–west, with “training” convective elements. It also has a region of adjoining stratiform rain that is displaced to the north of the line. The second type has a back-building or quasi-stationary area of convection that produces a region of stratiform rain downstream. Surface observations and composite analysis of Rapid Update Cycle Version 2 (RUC-2) model data reveal that training line/adjoining stratiform (TL/AS) systems typically form in a very moist, unstable environment on the cool side of a preexisting slow-moving surface boundary. On the other hand, back-building/quasistationary (BB) MCSs are more dependent on mesoscale and storm-scale processes, particularly lifting provided by storm-generated cold pools, than on preexisting synoptic boundaries.

North American extreme temperature events and related large scale meteorological patterns: a review of statistical methods, dynamics, modeling, and trends

Abstract: This paper surveys the current state of knowledge regarding large-scale meteorological patterns (LSMPs) associated with short-duration (less than 1 week) extreme precipitation events over North America. In contrast to teleconnections, which are typically defined based on the characteristic spatial variations of a meteorological field or on the remote circulation response to a known forcing, LSMPs are defined relative to the occurrence of a specific phenomenon—here, extreme precipitation—and with an emphasis on the synoptic scales that have a primary influence in individual events, have medium-range weather predictability, and are well-resolved in both weather and climate models. For the LSMP relationship with extreme precipitation, we consider the previous literature with respect to definitions and data, dynamical mechanisms, model representation, and climate change trends. There is considerable uncertainty in identifying extremes based on existing observational precipitation data and some limitations in analyzing the associated LSMPs in reanalysis data. Many different definitions of “extreme” are in use, making it difficult to directly compare different studies. Dynamically, several types of meteorological systems—extratropical cyclones, tropical cyclones, mesoscale convective systems, and mesohighs—and several mechanisms—fronts, atmospheric rivers, and orographic ascent—have been shown to be important aspects of extreme precipitation LSMPs. The extreme precipitation is often realized through mesoscale processes organized, enhanced, or triggered by the LSMP. Understanding of model representation, trends, and projections for LSMPs is at an early stage, although some promising analysis techniques have been identified and the LSMP perspective is useful for evaluating the model dynamics associated with extremes.