Recalibrator and FrontalAnalysis use Nx for tensor math, but Nx is
declared `only: [:dev, :test]` in mix.exs because neither module has a
prod entry point — Recalibrator is invoked by hand from IEx and
FrontalAnalysis is research scaffolding. The prod compile would emit
"Nx.to_number/1 is undefined" warnings on every Nx call. Add a
`@compile {:no_warn_undefined, Nx}` directive to both modules so the
prod build is clean without dragging Nx/Axon/EXLA (~hundreds of MB) into
the runtime image.
FrontalAnalysis module (Weather.FrontalAnalysis):
- detect_fronts/3 computes the Thermal Front Parameter (TFP) from
2D grids of surface temperature and pressure using Nx vectorized
ops. TFP = -nabla|nabla(theta)| . nabla(theta)/|nabla(theta)|.
Most negative values mark cold fronts.
- central_gradient/1 for 2D finite differences with edge handling
- nearest_front/3 finds closest front point with distance and bearing
- path_front_angle/2 computes angle between a QSO path and the
front (0 = parallel = good, 90 = crosses = dead)
Backtest feature stubs for distance_to_front and parallel_to_front
(return nil until the pipeline caches per-cell frontal features from
the hourly HRRR grid run). The FrontalAnalysis module itself is
tested and ready for integration.
NEXRAD spike docs also included in this commit.
