Zombie Weather Map

Rain and storms

Precipitation radar (animated)

Two hours of past radar from RainViewer, stitched into a loop. This is a global composite, so it works outside the United States, and it is the layer to use for the simple question of where the rain is and which way it is going. The animation is the point: a single frame tells you where rain is, and a loop tells you whether it is coming for you.

NEXRAD base reflectivity (US)

The raw return from the National Weather Service’s network of Doppler radars, at the lowest scan angle. Reflectivity is measured in dBZ, and the colour scale is a measure of how much is up there bouncing the beam back — not directly how hard it is raining. Around 20 dBZ is drizzle; 40 is a decent downpour; above 50 usually means hail is involved, because ice reflects far more strongly than water does. That is why the deepest reds so often sit over the part of a storm that is doing damage rather than the part that is merely wet.

Storm structure, hybrid-scan (MRMS)

MRMS combines every radar in the network with satellite and rain-gauge data instead of showing one radar at a time. It fills the gaps radar coverage leaves — a single radar beam climbs as it travels, so at long range it is sampling the middle of a storm and missing the rain underneath entirely.

Rainfall, past 24h · Rain accumulation

How much has already fallen rather than what is falling. This is the pair to check for flooding: flash floods are driven by what the ground has already absorbed, and ground that is saturated from yesterday will flood on a rainfall that would have drained away last week.

Tropical systems

Hurricane cone & track (NHC official)

The National Hurricane Center’s forecast cone, straight from the source. The cone shows where the centre of the storm may go, and historically contains it about two thirds of the time. It says nothing at all about how large the storm is: damaging wind, rain and surge routinely reach well outside it. Being outside the cone is not the same as being safe, and a great many people have learned that the expensive way.

Spaghetti model guidance

Individual computer models, each drawing its own line. This is not a forecast and is labelled as such on the map. It is useful for one thing only: seeing whether the models agree. A tight bundle means confidence; lines fanning across a thousand miles of ocean mean nobody knows yet, whatever the headline on a weather app says.

What the watches and warnings actually mean, and whether any are in force where you are: Hurricane Watch vs Warning.

Satellite and the rest

Satellite (true colour)

NASA GIBS imagery, showing the planet roughly as an eye would see it from orbit. It is deliberately dated to yesterday, because the current day’s mosaic is assembled as the satellites pass and is full of holes until it is finished. Yesterday exists in full; today does not yet.

Wind speed, temperature, clouds, pressure

Model overlay tiles. These are smooth, continuous fields rather than measurements at any particular point — useful for the shape of a system and misleading if you read a specific number off them for your street. For that, use the forecast for your location, which uses observations.

Reading a radar image without fooling yourself

Radar sees what is in the air, not what reaches the ground. In dry air the rain can evaporate before it lands — forecasters call it virga — so the map shows a storm and your window shows nothing.

The beam climbs with distance. Radar energy travels in a straight line while the Earth curves away beneath it. Two hundred miles from the transmitter the beam is a mile or more up, sampling the top of a storm and missing everything below. Coverage looks complete on a map and is not.

Not all returns are weather. Flocks of birds leaving a roost at dawn, insect swarms on a summer evening, wind turbines and smoke plumes from large fires all show up. If a bloom expands in a perfect circle from one point at sunrise, that is birds, not rain.

The bright band lies. Where snow melts into rain there is a layer of wet, ice-cored particles that reflect enormously and read as far heavier precipitation than is actually falling. In winter this puts a false ring of intense rain around the radar site.