On the Potential for using Unmanned Aircraft Systems for Mesoscale Analysis and Short-range Numerical Weather Prediction of Severe Convection

The potential for using Unmanned Aircraft Systems (UAS, a.k.a. “drones”) for monitoring the severe convection environment is explored relative to more customary observing systems. Weather radar has proven invaluable for the detection of severe storms, and is also the primary observing system utilized in numerical weather prediction models dedicated to their short-term prediction. Yet, radar cannot measure the near-storm moisture and temperature fields, nor can it adequately detect low-level convergence areas that are important for triggering new storms – namely, determining whether air parcels reside long enough within such areas to be able to reach their Level of Free Convection. The evolution of convection once initiated is largely governed by the environmental instability and vertical wind shear, neither of which is again measurable by weather radar. Ground-based remote sensing systems have been advocated as a viable solution to this need, but their cost makes deployment of large networks of such instruments impractical currently. Geostationary satellite sensor systems lack the needed vertical resolution in the Planetary Boundary Layer (PBL) to be able to determine this information with sufficient fidelity and are further limited by cloud cover.

Low-altitude, short-endurance type UAS may help to fill this void of critically-needed information. An experiment was conducted in Oklahoma in Spring 2017 to test the capabilities of both fixed-wing UAS to measure the spatial heterogeneity of the atmosphere between Oklahoma Mesonet sites, and rotary-wing UAS to obtain 15–30 minute sampled profiles of winds, temperature, and humidity within the PBL with very high (~10m) resolution. The accuracy of the UAS measurements were validated against independent observing systems. Also, an assessment of their utility in real-time operations was conducted in a coordinated activity involving the NWS-Norman Forecast Office. Challenges in obtaining waivers for Certificates of Authorization to fly beyond the nominal 400-ft AGL limit, in conditions Beyond Visual Line-Of-Sight, and even to fly multiple UAS simultaneously, will be addressed. The future vision is one of targeted, adaptive sampling within preapproved COA regions that would be executed in a semi-autonomous manner by the National Weather Service as needed when severe weather threatens.