Dry lightning, 37 degrees, and why Sydney is under a total fire ban today

Greater Sydney is under a total fire ban today. The Bureau of Meteorology is forecasting temperatures up to 37°C in the city's west, and the Rural Fire Service has named the specific hazard that makes today different from an ordinary hot day: dry lightning — thunderstorms that produce little or no rain.

That detail is the whole story, and it's worth being precise about why it matters. Lightning starts fires. Rain usually limits how far they spread, because a storm that drops water on the ground also dampens whatever the lightning ignites. Dry lightning removes that limit. The electrical strike arrives without the rainfall that would normally follow it, so any fire that starts has nothing working against it from the moment it begins.

Combine that with the heat and the existing dryness — the ground and vegetation are already primed to burn before any strike happens — and you get a day where the ignition source and the fuel are both present, with none of the usual moderating factor in between. That is the specific chain the Rural Fire Service is pointing at when it calls today's risk severe, and it's a different claim from the general 'fire danger is high' that gets said on a lot of summer days.

A total fire ban is not a suggestion. It is a legal restriction: no open flame, no machinery work that throws sparks, no hot works, anywhere in the declared area, for the duration of the ban. Breaching it carries penalties. The ban is the Rural Fire Service's way of marking that today's conditions have moved past what people can be trusted to manage on their own judgment.

That's the claim, and it stands on named authorities — the Bureau of Meteorology for the forecast, the Rural Fire Service for the ban and the risk assessment — a defined area, and a same-day window. Nothing more is needed to make it worth knowing, and nothing less would tell you why today is the day it applies.