Deep Learning for Spatially Explicit Prediction of Synoptic-Scale Fronts

• Published in: Weather and forecasting Vol. 34; no. 4; pp. 1137 - 1160
• Main Authors: Lagerquist, Ryan, McGovern, Amy, Gagne II, David John
• Format: Journal Article
• Language: English
• Published: Boston American Meteorological Society 01.08.2019
• Subjects: Body height; Cold; Cold front; Cold fronts; Deep learning; Dynamic height; Extreme weather; False alarms; Fronts; Geopotential; Geopotential height; Machine learning; Meteorologists; Neural networks; Numerical weather forecasting; Potential temperature; Predictions; Probability theory; Specific humidity; Variables; Weather; Weather forecasting; Wind speed; Wind velocities
• ISSN: 0882-8156; 1520-0434
• DOI: 10.1175/WAF-D-18-0183.1

Abstract This paper describes the use of convolutional neural nets (CNN), a type of deep learning, to identify fronts in gridded data, followed by a novel postprocessing method that converts probability grids to objects. Synoptic-scale fronts are often associated with extreme weather in the midlatitudes. Predictors are 1000-mb (1 mb = 1 hPa) grids of wind velocity, temperature, specific humidity, wet-bulb potential temperature, and/or geopotential height from the North American Regional Reanalysis. Labels are human-drawn fronts from Weather Prediction Center bulletins. We present two experiments to optimize parameters of the CNN and object conversion. To evaluate our system, we compare the objects (predicted warm and cold fronts) with human-analyzed warm and cold fronts, matching fronts of the same type within a 100- or 250-km neighborhood distance. At 250 km our system obtains a probability of detection of 0.73, success ratio of 0.65 (or false-alarm rate of 0.35), and critical success index of 0.52. These values drastically outperform the baseline, which is a traditional method from numerical frontal analysis. Our system is not intended to replace human meteorologists, but to provide an objective method that can be applied consistently and easily to a large number of cases. Our system could be used, for example, to create climatologies and quantify the spread in forecast frontal properties across members of a numerical weather prediction ensemble.