Forecasting the Air Race Classic: Lessons in Interdisciplinary Aviation Weather Support and Decision-Making

The Air Race Classic (ARC) is an all-female Visual Flight Rules air race held each June. Embry-Riddle Aeronautical University Daytona Beach (ERAU-DB) has had primarily student race teams participate and frequently place strongly in the ARC since 1996. The ERAU-DB Meteorology Program has provided successful weather support to ERAU-DB race team(s) for the past decade, including as the terminus host institution in 2016. In 2014, the weather support was formalized as a three-credit interdisciplinary summer course, incorporating a mix of aeronautical science (pilot), dispatch, and meteorology students. Using concepts of service and experiential learning, the ARC course has successfully integrated students from varying educational backgrounds into cohesive weather support teams that serve the ERAU-DB air racers. As such, students from primarily aviation backgrounds have had to learn about aviation weather support tools and techniques they were not previously aware of, while students from primarily meteorological backgrounds had to integrate aviation concepts such as fuel burn and service ceiling into their forecasts. The ARC weather support experience has helped to expose students to real-world situations and decision-making, given them an increased sense of purpose and service to the ERAU-DB community, and improved their ability to combine aviation and meteorological thinking for the purpose of real-time aviation weather forecasting

New Metric for Defining the Time of Extratropical Transition of Tropical Cyclones

Almost half of all tropical cyclones (TCs) in the Atlantic basin undergo extratropical transition (ET). During an ET event, wind fields often expand dramatically, resulting in more widely-felt impacts. Moreover, the heaviest precipitation typically shifts to the left-of-center (LOC), which can result in inland flash flooding hundreds of kilometers from the cyclone center. While several objective metrics to track and predict ET have been developed, they rely at least partially on internal tropical cyclone structure, for which numerical models show less skill. Further, these metrics fail to account for static stability, which plays a vital role in determining precipitation amounts. In this study, a coupled dynamic and thermodynamic metric using the eady moist baroclinic growth rate (EMBGR) is proposed to define the time of ET. The EMBGR parameter relies on well forecasted environmental flow characteristics and static stability. The time of ET deduced from the EMBGR is then compared using different methods i.e. HURDAT, storm precipitation distribution (left or right of center), interaction between the mid-latitude trough and tropical system from a vorticity perspective, and the Cyclone Phase Space

Synoptic-Scale Precursors, Characteristics and Typing of Nocturnal Mesoscale Convective Complexes in the Great Plains

Mesoscale convective complexes (MCCs) occur frequently during the warm season in the central U.S. and can produce flooding rains, hail and tornadoes. Previous work has found that the synoptic-scale environment can greatly affect, and be affected by, the development and maintenance of MCCs. Ninetytwo MCC cases from 2006–2011 are manually identified using infrared satellite imagery and partitioned into three types (upstream trough, zonal and ridge) using a unique manual synoptic typing based on 500- hPa height patterns. Upstream trough cases feature an amplified longwave 500-hPa trough upstream of the MCC genesis region (GR), while the 500-hPa flow is relatively flat in zonal cases, and a strong 500-hPa ridge is present over the Rockies in ridge cases. Individual case and storm-relative composite analyses of a subset of 28 cases show that of the three types, upstream trough cases feature both the strongest quasigeostrophic forcing for ascent and lower-tropospheric frontogenesis, the latter of which enhances ascent and is associated with a strong southerly low-level jet (LLJ). Zonal and ridge cases feature smaller magnitudes (in descending order) of all ascent-forcing parameters. Ridge cases, in particular, are characterized by weak Q-vector convergence, but easterly upslope flow likely acts as a compensating ascent mechanism. A thermodynamic analysis shows that high-θe air is advected into the GR in all three MCC types, and serves as fuel for development and maintenance. However, while the southerly LLJ advects high-θe air from the Gulf of Mexico in the upstream trough and zonal cases, such air is already pooled in the High Plains in the ridge cases and advected into the GR by easterly flow. In accordance with the synoptic-dynamic analysis, upstream trough cases have the longest duration and largest impact on the synoptic-scale environment, while ridge cases are the shortest-lived. The various underlying precipitation structures of each group are also explored; zonal cases, for example, appear to preferentially be associated with bow echoes

Composite Analysis of Cool-Season Florida Tornado Outbreaks

The study of tornado outbreaks has been well documented, however, there has only been a few on Florida tornado outbreaks. This study details the composite dynamic and thermodynamic conditions associated with these events. Consistent with past research, a tornado outbreak was defined as 4 or more tornadoes occurring within a 24-h period during the winter and early spring months (Dec–May) from 1979–2016. December–May was chosen to eliminate tornado outbreaks that were associated with tropical cyclones. In total, 35 outbreaks were identified using archived severe weather reports. Composites were produced using the North American Regional Reanalysis (NARR).Initial results show Florida tornado outbreaks are associated with a negatively tilted mid-tropospheric trough (dynamics), moderate CAPE and low LCLs (thermodynamics), strong lower-tropospheric wind shear, and the upper-level divergent exit region of the Polar Front Jet (PFJ)

A Diagnostic Metric for Predicting Tropical Cyclone and Mid-Latitude Floods

This study details a dynamic and thermodynamic metric (i.e., Extreme Flood Index [EFI]) designed to diagnose the frequency and intensity of extreme precipitation events associated with stagnant mid-latitude flow patterns (i.e., Rex blocks). As the global climate warms, rapid Arctic warming may be helping to slow the mid-latitude westerly jet stream, resulting in increased mid-latitude flow stagnation. The combination of long-duration ascent associated with easterly winds and warm moist air increases the severity of extreme precipitation events; as such, the EFI is specifically designed to detect this potent combination of ingredients. In 2013, a Rex block stalled a low-pressure system over Alberta which caused the worst Canadian flood disaster ever seen. To that end, the recent billion-dollar flood catastrophe produced by Tropical Cyclone (TC) Harvey was also associated with a Rex Block (dynamics) in the presence of warm, moist air (thermodynamics). Despite dynamic differences between TC-related and mid-latitude floods, the EFI is successfully able to detect both. The dynamics component of the EFI is derived from two atmospheric blocking criteria, used operationally by the European Centre for Medium-Range Weather Forecasts (ECMWF) and National Oceanic and Atmospheric Administration (NOAA), respectively, and adapted here for the shorter duration of extreme precipitation events. The EFI’s thermodynamic component utilizes standardized anomalies of equivalent potential temperature. Finally, the ability of the EFI to diagnose and predict high-impact flood events using reanalysis data and operational numerical weather prediction models is explored

An Analysis of the First Ever DOW-Observed Mesolow

Embry-Riddle Aeronautical University Convective-Boundary Research Engaging Educational Student Experiences 2.0 (ERAU CBREESE 2.0) was a 15-day Doppler-on-Wheels (DOW) and Mobile Mesonet educational deployment from the Center for Severe Weather Research (CSWR). Building off the success of ERAU CBREESE in May 2015, the educational deployment was designed to observe and measure sea-breeze processes and convection, with a specific focus on Central Florida sub-regions that contain multiple mesoscale breezes and boundary collisions. On 6 July 2018, the first-ever DOW-observed mesolow was recorded along the Space Coast near Titusville, Florida. The purpose of this study was to examine the ability of the High-Resolution Rapid Refresh (HRRR) model to accurately diagnose and forecast this feature. After calculating the height of the DOW beam at each elevation scan, it was noted that the mesolow was predominantly observed in the 900–600-hPa layer. The 20 UTC HRRR analysis shows that the mesolow circulation was resolved by the model as it occurred. Since the HRRR explicitly diagnoses and forecasts many variables that other models, such as the Global Forecast System (GFS), are only able to parameterize, this also yielded the opportunity to explore what mechanisms may have contributed to the initial formation of the mesolow

A Thermodynamic Analysis of an Intense North American Arctic Air Mass

Northwestern Canada is a genesis region of arctic air masses often considered to be formed primarily through radiative processes. However, the details of their life cycle are poorly understood. This paper examines the formation, maintenance, and dissipation of an intense and long-lived arctic air mass, using a thermodynamic budget analysis. The airmass formation is characterized by a deep-layer, multistage process that begins with snow falling into a nascent air mass. Radiative cooling from cloud tops begins the process. After the snow abates and clear skies are observed, the surface temperature drops rapidly, aided by the high emissivity of fresh snow cover, falling 178C in two days, creating an intense but shallow temperature inversion. Once the surface temperature falls below the frost point, ice crystals form. Afterward, although the surface temperature remains constant, the height of the inversion rises, as radiative cooling at the top of the ice fog layer decreases temperatures. During the maintenance phase, a cold-air damming structure is present with an anticyclone in the lee of the Canadian Rockies, low pressure in the Gulf of Alaska, and an intense baroclinic zone parallel to the mountains, separating warmer maritime air from colder continental air. The air mass persists for 12 days, undergoing several cycles of deep-layer weakening and intensification

Precipitation Modulation by the Saint Lawrence River Valley in Association with Transitioning Tropical Cyclones

The St. Lawrence River valley (SLRV) is an important orographic feature in eastern Canada that can affect surface wind patterns and contribute to locally higher amounts of precipitation. The impact of the SLRV on precipitation distributions associated with transitioning, or transitioned, tropical cyclones that approached the region is assessed. Such cases can result in heavy precipitation during the warm season, as during the transition of Hurricane Ike (2008). Thirty-eight tropical cyclones tracked within 500 km of the SLRV from 1979 to 2011. Utilizing the National Centers for Environmental Prediction (NCEP) North American Regional Reanalysis (NARR), 19 of the 38 cases (group A) had large values of ageostrophic frontogenesis within and parallel to the SLRV, in a region of northeasterly surface winds associated with pressure-driven wind channeling. Using composite and case analyses, results show that the heaviest precipitation is often located within the SLRV, regardless of the location of large-scale forcing for ascent, and is concomitant with ageostrophic frontogenesis. The suggested physical pathway for precipitation modulation in the SLRV is as follows. Valley-induced near-surface ageostrophic frontogenesis is due to pressure-driven wind channeling as a result of the along-valley pressure gradient [typically exceeding 0.4 hPa (100 km)−1] established by the approaching cyclone. Near-surface cold-air advection as a result of the northeasterly pressure-driven channeling results in a temperature inversion, similar to what is observed in cool-season wind-channeling cases. The ageostrophic frontogenesis, acting as a mesoscale ascent-focusing mechanism, helps air parcels to rise above the temperature inversion into a conditionally unstable atmosphere, which results in enhanced precipitation focused along the SLRV

Synoptic-Scale Characteristics and Precursors of Cool-Season Precipitation Events at St. John\u27s, Newfoundland, 1979-2005

The issue of quantitative precipitation forecasting continues to be a significant challenge in operational forecasting, particularly in regions susceptible to frequent and extreme precipitation events. St. John’s, Newfoundland, Canada, is one location affected frequently by such events, particularly in the cool season (October–April). These events can include flooding rains, paralyzing snowfall, and damaging winds. A precipitation climatology is developed at St. John’s for 1979–2005, based on discrete precipitation events occurring over a time period of up to 48 h. Threshold amounts for three categories of precipitation events (extreme, moderate, and light) are statistically derived and utilized to categorize such events. Anomaly plots of sea level pressure (SLP), 500-hPa height, and precipitable water are produced for up to 3 days prior to the event. Results show that extreme events originate along the Gulf Coast of the United States, with the location of anomaly origin being farther to the north and west for consecutively weaker events, culminating in light events that originate from the upper Midwest of the United States and south-central Canada. In addition, upper-level precursor features are identified up to 3 days prior to the events and are mainly located over the west coast of North America. Finally, results of a wind climatology produced for St. John’s depict a gradual shift in the predominant wind direction (from easterly to southwesterly) of both the 925-hPa geostrophic wind and 10-m observed wind from extreme to light events, inclusively. In addition, extreme events are characterized by almost exclusively easterly winds

Dynamical and Precipitation Structures of Poleward-Moving Tropical Cyclones in Eastern Canada, 1979-2005

Tropical cyclones in the western North Atlantic basin are a persistent threat to human interests along the east coast of North America. Occurring mainly during the late summer and early autumn, these storms often cause strong winds and extreme rainfall and can have a large impact on the weather of eastern Canada. From 1979 to 2005, 40 named (by the National Hurricane Center) tropical cyclones tracked over eastern Canada. Based on the time tendency of the low-level (850–700 hPa) vorticity, the storms are partitioned into two groups: ‘‘intensifying’’ and ‘‘decaying.’’ The 16 intensifying and 12 decaying cases are then analyzed using data from both the National Centers for Environmental Prediction (NCEP) North American Regional Reanalysis (NARR) and the NCEP global reanalysis. Composite dynamical structures are presented for both partitioned groups, utilizing both quasigeostrophic (QG) and potential vorticity (PV) perspectives. It is found that the proximity to the tropical cyclone and subsequent negative tilt (or lack thereof) of a precursor trough over the Great Lakes region is crucial to whether a storm ‘‘intensifies’’ or ‘‘decays.’’ Heavy precipitation is often the main concern when tropical cyclones move northward into the midlatitudes. Therefore, analyses of storm-relative precipitation distributions show that storms intensifying (decaying) as they move into the midlatitudes often exhibit a counterclockwise (clockwise) rotation of precipitation around the storm center