Temperatures climbed as high as 13 degrees above average across much of the Riverina on Sunday, with some towns sweating through their warmest October day on record.

In Wagga, the mercury hit 34.7 degrees on Sunday afternoon; 13.1 degrees above the city's average October maximum.

The warmth meant hydration was key at many Labour Day holiday weekend events, including for the thousands of cyclists who took part in the Gears and Beers Festival.

While the blast of heat didn't break any Wagga weather records, the Bureau of Meteorology said the history books were rewritten elsewhere.

Temora Airport's maximum of 37.1 degrees on Sunday delivered the north-eastern Riverina town its hottest October day on record, beating the previous high of 36.3 set in 2014.

In the South West Slopes, the temperature at Young Airport climbed to 35.0 degrees, surpassing its existing October heat record of 34.4.

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Elsewhere in the Riverina, the mercury climbed to 37.1 degrees at West Wyalong, 36.6 in Griffith, 36.1 at Narrandera and 33.7 in Hay.

Temperatures are expected to remain warm to round out the Labour Day holiday weekend on Monday, with forecast tops of 24 degrees in Wagga, 25 at Hay and 26 in Griffith and Narrandera.

However, the weekend's warmth and sunshine is expected to make way for cooler conditions and some much-welcome rain come Tuesday.

The bureau said a low pressure trough is moving northeastward across the state and will bring a cooler change to southern parts of NSW.

There's a high chance of showers, and the chance of a thunderstorm, in Wagga on Tuesday, with a maximum of just 16 degrees.

Between one and six millimetres of rain could fall across the city, according to the bureau, with a similar amount possible in Junee.

Rainfall is less likely in western parts of the Riverina; up to 4mm is possible in Narrandera and 0-2mm is forecast for Hay.