Storm tracking for offshore wind: radar now, future radar ahead

The radar, at the present moment

In the United States the present moment is NEXRAD radar, the National Weather Service's network of Doppler radars, served through Iowa State University's mesonet. Beyond its reach the view uses Environment and Climate Change Canada's radar composite and a global radar mosaic, so a storm is drawn wherever the map is.

The next hours: radar handed over to the model

For the first half hour the observed radar is carried forward along the storm's motion. From there it is blended, step by step, into the HRRR — NOAA's High-Resolution Rapid Refresh model, run every hour — which carries the forecast by two hours, because a model can grow, decay and turn a storm where moving a picture cannot. Play eight hours in 15-minute steps, or finer.

Motion that follows the storm

The storm's speed and direction are read by matching the rain pattern from one 15-minute frame to the next, the way radar nowcasting works, instead of following the centre of all the rain in view — which orbits a turning system and used to point the wrong way. When the field is turning, the turn is measured and the radar is turned with it. When the rain has no clear motion, the view says so and holds the radar where it was observed while the model takes over.

What the colours mean

Rain, thunderstorm, hail risk, snow and blizzard. A thunderstorm is rain with convective energy (CAPE) of 1,000 J/kg or more, hail risk 2,500 J/kg or more, and a blizzard is snow with wind of 35 mph or more: operational rules of thumb, stated so they can be judged.