Benchmark experiments with the explicit planetary isentropic coordinate (EPIC) model: Does it snow on Saturn? [abstract]

Abstract only availableThree experiments are conducted on the Saturnian atmosphere using the Explicit Planetary Isentropic Coordinate (EPIC) numerical model. The first is a control experiment, wherein no water (in any state) or ammonia is accounted for. The second is an experiment wherein water vapor is included and allowed to occupy the vapor, liquid, and solid states (including separate equations for rain and snow). The third experiment involved ammonia only. Beginning from a basic state, we examine the structure of the Saturnian atmosphere at 1 month into the simulation. Realistic-looking clouds did develop, with the banding expected in the atmosphere of this kind of gas giant. Ongoing analysis seeks to determine the vertical location of and chemical concentrations in these clouds in comparison to observed data returned from probes such as Cassini.CAFNR On Campus Research Internshi

The Application of a Simple Method for the Verification of Weather Forecasts and Seasonal Variations in Forecast Accuracy

The evaluation of weather forecast accuracy has always been a difficult subject to address for many reasons. In this study, a simple semiobjective method is used to examine the accuracy of zone forecasts issued by the Weldon Spring (Saint Louis) National Weather Service (NWS) Office for mid-Missouri over a period of 416 days with the goal of demonstrating the utility of this method. Zone forecasts were chosen because these forecasts are typically what the public will receive either directly or indirectly from various media outlets. Not surprising, the evaluation method used here demonstrates that forecasts issued by the NWS and the Nested Grid Model (NGM) model output statistics (MOS) represent a considerable improvement over persistence or climatological baseline forecasts. NWS forecasts were slightly better than NGM MOS forecasts, especially when considering temperature and precipitation only. All forecasts showed distinct seasonal variability. The NWS winter-season forecasts were superior to those issued in the summer season, and this superiority was found to be a function of the precipitation forecast parameter. This technique might represent an easily understandable and concise method for providing weather forecast performance information to the general public in such a way that it would instill or reinforce public confidence in the accuracy of weather forecasts

The Role of Sublimational Cooling in a Late-Season Midwestern Snow Event

Analysis is provided of a surprise late-season snow event over eastern Missouri and western Illinois. While snow totals failed to exceed 15 cm (6 in.) at any single location, the system was noteworthy because of the poor performance of public, private, and media forecasts in anticipating the event. Using observed data and a successful simulation with a mesoscale numerical model, the event is scrutinized to determine the forcing mechanisms for the precipitation over a small area. A region of enhanced frontogenesis is diagnosed over the region both in the observed data as well as the model output. That the precipitation fell as snow is shown to be the result of a dry layer of air between the surface and the cloud base that saturated and cooled due largely to snow sublimation–evaporation in just a few hours to permit the fall of snow uninhibited from the cloud base to the ground

A case study of colliding tornadic storms

Abstract only availableTornadoes occur frequently across the United States each year, causing millions of dollars in damage. Meteorologists are constantly searching for new and improved methods for predicting these weather phenomenons's in order to increase public awareness and warning times. In this case study, one event was found in which two storm cells collided and produced a tornado over the Kansas City, Missouri area, causing an extensive amount of damage. The goals of this study is to first determine what caused the collision between the two storm cells, secondly, whether the collision between the two storm cells increased the intensity of the tornado using NSSL/SPC (National Severe Storms Laboratory/ Storm Prediction Center) meteorologist Stephen F. Corfidi's “vector approach.” A method that involves the use of mathematics to find the mean of the wind directions throughout the cloud layers in the storms and also the location of the low-level jet. Radar imagery was also used in determining the location, time, intensity, and other details of the two storm cells. It is our hope, that the completion of this study will produce results that are conducive to the development of more innovative methods for forecasting this type of event.Louis Stokes Alliance for Minority Participatio

Assessing Upper Tropospheric Jet Streak Proximity Using the Rossby Radius of Deformation

The Rossby radius of deformation is a parameter that describes the relative role of buoyant and inertial forces for atmospheric phenomena in a flow regime. It will be demonstrated that it can also be used to determine whether or not forcing for vertical motions in the region between upper level tropospheric jet streaks overlaps or interacts. Using predefined points in the entrance and exit regions of neighboring upper level jet streaks, the distance between them is calculated for each event. If they are closer than twice the Rossby radius of deformation, the resulting region affected by both streaks is termed the Rossby Radius of Deformation Overlap Zone (RRDOZ). Plan-view and cross-sectional analysis shows that ageostrophic transverse circulations within the RRDOZ led to enhanced upward vertical velocities as predicted in prior research. Lastly, a short-term climatology for overlap events in North America is derived, and these are classified according to three proposed archetypes

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 Columbia, Missouri, Heat Island Experiment (COHIX) and the Influence of a Small City on the Local Climatology

The heat island effect is a well known feature in the microclimate of urban areas but only a few studies have addressed the effect for smaller urban areas. We examine here the impact of Columbia, Missouri and the University of Missouri campus on the microclimate (temperature and precipitation) of central Missouri. We purchased twenty Radio Shack® digital Max/Min thermometers and ten standard raised-edge rain gauges and these were given to students, staff, and faculty participants who were chosen for their reliability to provide daily data over the course of a year, site the instrument, and their location (in order to provide reasonable coverage locally). We also included information provided by automated and cooperative weather stations, and the weather station at the regional airport located 11 km (7 miles) southeast of Columbia. Our results indicate that the city has no discernable impact on the distribution of monthly precipitation totals. We found a distinct urban influence on the local surface temperatures, and the inner city region and the urbanized area of south Columbia were approximately 2 - 3 oF (1.0 - 1.5 oC) warmer in the mean than the surrounding environment. This difference grows to 3 - 6 oF (1.5 - 3.5 oC) when comparing the mean of the warmest station in the city to that of coolest station outside Columbia. We also observed a seasonal influence, as the heat island effect was more evident in the mean monthly maximum (minimum) temperatures during the warmest (coldest) months

Interannual Variability of Snowfall Events Southwest Missouri and Snowfall to- Liquid Water Equivalents at the Springfield WFO

In order to address the difficult issue of forecasting snowfall amounts for the general public, forecasters must be intimately familiar with the climatological behavior of snowfall events, and associated snowfall-to-liquid precipitation (SL) ratios that accompany events impacting the region. In Southwest Missouri, an average of 4 to 5 snowfall events of 3 inches or more occurred every year within the period of 1949 to 2002. These events were associated with an average SL ratio of about 12 inches of snow to one inch of rain (12:1). Past studies have also demonstrated relationships between the synoptic environment and SL ratios for a particular locale. Indeed, while many atmospheric and environmental factors contribute to the observed SL ratios in a particular event, quite often, recurring synoptic patterns are typically associated with similar SL ratios in Southwest Missouri. This study identified four synoptic patterns that bring heavy snowfalls to Southwest Missouri and these are associated predominantly with certain SL ratios. In Southwest Missouri, synoptic disturbances classified as southwest lows or deepening lows, processed large amounts of moisture and produced heavy snow. Sixty-seven percent of these events produced SL ratios of 12:1 or less, and 90% produced SL ratios of 14:1 or less. Snowfall events (progressive troughs and northwest lows) which brought less snowfall were typically associated with higher SL ratios. There was no significant El Nino-Southern Oscillation (ENSO) related difference in the number of snowfalls per winter season. When the study period was stratified to include interdecadal variability, changes in ENSO- related variability did emerge. Additionally, the SL ratios were smaller during El Niño years and there has been no trend in this tendency

An analysis of a long-lived MCV observed over the Southern Plains using Potential Vorticity diagnostics.

On the morning of 28 May 1998, a mesoscale convectively-generated vortex (MCV) was observed over the Southern Plains. This MCV was evident in the GOES-8 visual satellite imagery resulting in a spectacular picture. An analysis of this event is offered using many data sources, including products available now via the world-wide-web (WWW), the National Center for Environmental Prediction (NCEP) re-analyses, and Eta model initializations. This MCV developed out of a mesoscale convective system (MCS) that existed during 26 and 27 May over Texas. This MCV was associated with reports of severe weather and heavy precipitation over southern Arkansas. While the MCV is shown to have characteristics similar to other MCV events documented, this event is unique in that it maintained it's character, while propagating further east than other events. A dynamical analysis using potential vorticity diagnostics (PV) shows that the mid-latitude vorticity field strengthened at least partially as a result of diabatic heating. Also, the most severe weather was associated with high values of integrated 500 - 300 hPa PV values over the Southern Plains