WoFSCast: A machine learning model for predicting thunderstorms at
watch-to-warning scales
Abstract
Developing AI models that match or exceed the forecast skill of
numerical weather prediction (NWP) systems but run much more quickly is
a burgeoning area of research. Most AI-NWP models, however, have been
trained on global ERA5 data, which does not resolve storm-scale
evolution. We have therefore adapted Google’s GraphCast framework for
limited-area, storm-scale domains, then trained on archived forecasts
from the Warn-on-Forecast System (WoFS), a convection-allowing ensemble
with 5-min forecast output. We evaluate the WoFSCast predictions using
object-based verification, grid-based verification, spatial storm
structure assessments, and spectra analysis. The WoFSCast closely
emulates the WoFS environment fields, matches 70–80% of WoFS storms
out to 2-h forecast times, and suffers only modest blurring. When
verified against observed storms, WoFSCast produces a similar CSI as
WoFS but with a lower frequency bias due to fewer false-alarm storms.
WoFSCast demonstrates that AI-NWP can be extended to rapidly evolving,
small-scale, chaotic phenomena like thunderstorms.