The Bureau of Meteorology is updating equipment at sites near Adelaide, Melbourne, Brisbane and Sydney to improve forecasters' ability to differentiate types of precipitation and improve early-warning services.

Existing Doppler radar sites in those cities now only issue horizontal pulses that are reflected off rainfall droplets in clouds.

The upgrade will add a vertical detection capability, providing the bureau with a clearer view of the size and shape of the rain droplets - and whether it's falling as hail - or if the reflections are from smoke particles or even insects.

"This will give us the ability to distinguish heavy rain within a thunderstorm from a mix of rain and hail," Simon Louis, the bureau's acting weather services manager, said.

"It will help us confirm thunderstorms are occurring and help emergency management's response."

Sydney's multitudes of weather watchers will still get radar coverage from sites near Wollongong and Newcastle, while bureau forecasters will also be able to access radar information from Sydney Airport. "There shouldn't be any significant reduction" in coverage, Mr Louis said.

The Terrey Hills site will be down from Wednesday until the first week of October, with the timing deliberately avoiding "the middle of the peak storm season", he said.

The upgrades, costing about $4 million for the four locations, won't necessarily assist with the prediction of tornadoes. The use of similar equipment in the US, though, has helped identify when tornadoes have begun by detecting the debris thrown up by the twisters.

The bureau's investments in new equipment and computing power mean forecasts one week out are now as accurate as the next day's forecasts was 20 years ago, Mr Louis said.