Prediction of Convective Storm Hazards for Aviation

Background

The Next Generation Air Transportation System (NextGen) is a national priority designed to meet the air transportation needs of the United States in the 21st century—in particular, a significant growth in demand for air traffic services, possibly on the order of two to three times today's demand levels. Meanwhile, the number of commercial applications of Unpiloted Aerial Systems (UAS) has been growing rapidly with primary operating space being the lowest 400 feet of the atmosphere. The expected increase in congestion of the NAS requires improved detection and prediction of weather hazards and their translation into air traffic flow impacts in order to maintain aviation safety and improve the efficiency of Air Traffic Flow Management.

For the past several years, the Aviation Applications Program within NCAR’s Research Applications Laboratory (RAL) has been engaged in multiple FAA-funded R&D efforts aimed at improving convective weather prediction, including in areas such as lightning impacts on airport operations and the subsequent ripple-effects throughout the National Airspace System (NAS), developing state-of-the-art CONUS-scale short term predictions of convective storms for tactical-to-strategic time scale planning of the NAS, and optimization of global-scale probabilistic predictions of convective storms in support of the ICAO-led harmonization of global weather hazard products.

FY2019 Accomplishments

Convective Weather Forecast System Bridging Tactical-to-Strategic Planning Time Horizons.

Figure 1. Image examples from NWP demonstrating the performance of the (left) 2 hour forecast of precipitation when compared with (right) corresponding observed precipitation intensity valid as obtained from the new NWP display.
Figure 1. Image examples from NWP demonstrating the performance of the (left) 2 hour forecast of precipitation when compared with (right) corresponding observed precipitation intensity valid as obtained from the new NWP display.

CoSPA is a forecast system that produces 0-8 hour forecasts of convective storm intensity and convective cloud top heights by blending extrapolation and model based forecasts using image processing techniques and forecast heuristics.  CoSPA, under FAA sponsorship, was developed collaboratively by MIT Lincoln Laboratory, NOAA Earth System Research Laboratory, and NCAR RAL to improve convective weather forecasts spanning the tactical to strategic time frames. The inputs to NCAR-developed blending include MIT-LL multi-scale advected VIL and Echo Tops and longer range model forecasts from the High Resolution Rapid Refresh (HRRR) Model. Currently the blending algorithms developed in RAL are undergoing final enhancements as part of the technology transfer to enable faster throughput while maintaining forecast performance and to meet specific FAA requirements for reliable forecast generation. The system latency continues to be improved compared to the legacy version of CoSPA (See Table 1), and features such as a “hot start” capability have been added to support an extremely rapid 15 minute failover capability without a fully redundant host. Additional features to support FAA integration and testing activities have also been added that allow for historical data processing.  Finally, portions of the technology were streamlined to meet modern computing system architecture.  

Table 1. Blending algorithm capabilities and characteristics. The NWP-Latest version is currently undergoing technology transfer to the FAA.
Table 1. Blending algorithm capabilities and characteristics. The NWP-Latest version is currently undergoing technology transfer to the FAA.

The latest version of the blending system (V5.5.2.x) was delivered to the FAA in August 2019 and is being implemented as part of the NextGen Weather Processor (NWP). An example of the latest version’s performance is shown in Figure 1. We continue to support a legacy version of the blending (V4.0) used in CoSPA which will continue to be made available year-round to aviation planners (i.e., ARTCCs, the FAA Command Center, the Aviation Weather Center and airline industry partners) until NWP forecasts become available.

Lightning Impact on Airport Terminal Operations and Safety.

Lightning poses a safety risk to personnel working outdoors at airports.  At larger United States (US) airports major airline and airport stakeholders have established safety guidance rules and procedures to mitigate such risks.  These, however, result in outdoor work being halted which causes interruptions in servicing of the arriving and departing aircraft at airport gates.

In a collaborative effort with AvMet Applications, Inc. (hereafter simply AvMet), this project aimed to quantify air traffic impacts due to lightning-caused ramp closures in terms of delay cost and safety risk cost with the goal of identifying an optimal range of safety guidance rules. To investigate the tradeoff cost associated with both safety risks and traffic delays, NCAR and AvMet established a framework to compare safety & efficiency costs based on model simulations of air traffic flow. Traffic simulations used were from AvMet’s weather-aware superfast-time NAS / Air Traffic Management (ATM) simulation model called the “Dynamic Airspace Routing Tool (DART)” as it allowed us to directly identify delays associated with lightning induced ramp closures. Utilizing the developed framework, the goal was to conduct a wide range of traffic simulations that capture different types of convective scenarios, different traffic demands and different types of ramp closures based on different safety rules as well as lightning data to comprehensively quantify impacts in terms of delay cost and safety risk cost. This was done based on air traffic flow simulations for various realization scenarios for three months of the 2014 convective season 2014 for two of the core 30 airports, Atlanta (ATL) and Orlando (MCO).

Figure 2. Total traffic delay cost and total lightning safety cost based on different safety rules and lightning data from three different lightning sources  (colored icons).
Figure 2. Total traffic delay cost and total lightning safety cost based on different safety rules and lightning data from three different lightning sources  (colored icons).

Results of this study show that the cost of ground traffic delays caused by lightning related ramp closures are substantial. This also applies to costs associated with lightning risk if not mitigated. Results also show significant dependencies of risk and delay costs to air traffic demand at the time of impact and ramp closure durations. Typical lightning safety procedures that are employed at US airports often range from lightning safety procedures employing a critical radius of 3 miles and a 6 minute wait period after the last lightning strike to a 5 mile radius with a 15 minute wait period. In our study we found that a 3mile/6min safety rule more frequently has periods of unmitigated risk, at times these can be substantial. Conversely, a  5 mile/15 minute safety rule can be associated with substantial traffic delay costs. A 5 mile /10 minute rule represents a compromise – it decreases the delay cost in most cases at the expense of slight increases in the risk cost (Fig. 2). Our study also found that human factors resulting in delayed ramp closures or reopenings can cause significant safety and delay costs.

This project also focused on investigations concerned with the accuracy and potential usability of short-term lightning hazard predictions (instead of traditional lightning detection systems) based on a limited amount of existing methods. Investigating various lightning hazard predictions can identify opportunities for improved guidance and together with the efficiency/safety analysis can identify opportunities in minimizing avoidable impacts.

Results show that radar, satellite and ground based electric field mill based lightning predictors have some skill in identifying a lightning hazard. Their accuracy in predicting the onset and cessation of lightning varies. We found it most reliable for nowcasts based on radar data. Satellite and electric field data from surface electric field mills were not found to be as reliable in providing accurate lightning warnings when used on their own. Finally, a high temporal and spatial resolution is needed for lightning hazard predictions at airports to minimize unnecessary ramp closures due to latency.

Ensemble Prediction of Oceanic Convective Hazards (EPOCH).

Figure 3.  Example quality assessment selector panel (top left) and accompanying high-glance value plots, ROC curve (bottom left) and Reliability Diagram (bottom right).
Figure 3.  Example quality assessment selector panel (top left) and accompanying high-glance value plots, ROC curve (bottom left) and Reliability Diagram (bottom right).

Work on improving techniques to generate aviation weather hazard probabilistic forecasts continued this past year, with the overarching goal of achieving a practical, transparent approach that can be easily implemented for operational use.  We examined in more detail forecast quality and performance metrics, implementing an online routinely-updated evaluation capability.  Figure 3 shows an example ROC (Receiver Operating Characteristic) plot and reliability diagram along with the web-based selection user-interface.  Updated with each forecast run (as observations become available), these show high value at-a-glance quality metrics applicable to the previous 30 days.  Notable additions to the system this year include adjustments to handle ½ degree horizontal resolution data with a 3-hourly lead-time resolution.  Figure 4 provides an example of the forecast with increased resolution in comparison to a satellite-derived verification field called, Convective Diagnostic Oceanic (CDO).    

Figure 4. Comparison of 1 degree 6 hourly (left column) and ½ degree 3 hourly (middle column) EPOCH 24-hour forecasts with CDO (right column), for two regions. Upper row (highlighted in gold) for a central/western portion of Africa and lower for a region (highlighted in red) in the US central plains.
Figure 4. Comparison of 1 degree 6 hourly (left column) and ½ degree 3 hourly (middle column) EPOCH 24-hour forecasts with CDO (right column), for two regions. Upper row (highlighted in gold) for a central/western portion of Africa and lower for a region (highlighted in red) in the US central plains.

Finally, work began on transitioning the EPOCH system to NOAA (World Area Forecast Center [WAFC] - Washington), the anticipated host entity for operations.  Operational products from the WAFC will support the World Area Forecast System (WAFS) requirement for high-resolution probabilistic gridded forecasts of aviation weather hazards.  As part of this in an effort to help understand how future model upgrades could impact EPOCH, we also examined the differences between GFS v15, a precursor to the anticipated next version of the GFS ensemble, and the previous version (v14).  V14 is based on the underlying model core that is used in the current ensemble system that is utilized by EPOCH.  Our goal is use these results to achieve an EPOCH design that minimizes changes required due to model upgrades, in an effort to lower the overall cost of software maintenance.

FY2020 PLANS

RAL will continue to support the technology transfer of the latest version of the blending to the FAA for inclusion in the NextGEN Weather Processor (NWP) and work will continue on the EPOCH system development and technology transfer.  Enhancements for EPOCH will include updates to the calibration algorithm to support higher (northern) latitude coverage.  Other updates will seek to optimize probabilistic forecast skill and measures of economic value through examination of case studies selected from industry examples. These products are aimed at aiding aviation weather forecasters in their development of guidance products as well as aid airline dispatchers in their strategic planning for transoceanic flights.