Orange is expecting up to 80mm of rain on Friday afternoon and evening.

Forecasts initially had Orange expecting a maximum of 40mm in Orange but that outlook was upped on Thursday night as a possible thunderstorm will loom over the region.

Forty millimetres is now the minimum expected over the next 30 hours from 12 noon on Friday.

The city has recorded 21 millimetres in the first three days of the month at the observation station at the airport, and just 23 millimetres - half of the minimum expected rainfall - would exceed Orange's average rainfall for April.

A full 80mm would also be the wettest 24 hours in the city in April since 1997, with the highest 24-hour April total set at 68 on April 22 in 1998.

However, Friday's storm is the only rain expected to both the rain gauges, with less than 1mm expected on each day for the rest of the week - although Friday's storms may extend into Saturday morning.

The cold will arrive in the middle of the week too, with a minimum of two degrees overnight on Tuesday and four degrees on Wednesday.