On Sunday it was forecast there would be rain, with snow possible down to 600m at first, easing to showers then gradually clearing. Southeasterlies would die out, and it would fall to 0C overnight.
Yesterday WeatherWatch reported heavy snow may affect motorists in surrounding areas.
Snow was in the forecast for Waiouru "day, after day, after day," for the first time this year - meaning the Desert Road could be closed due to snow and ice.
Snow might also fall on the other side of Mt Ruapehu, around National Park - which was an alternative route if the Desert Road is closed.
National Park has snow in the forecast for a week, off and on.
Snow is also expected on the Napier/Taupo highway on Friday or the weekend.
Police have advised motorists driving in winter conditions to allow extra time for their journey and to be aware of other road users who may not be easily seen, such as cyclists, motorcyclists and pedestrians.
Safe winter driving also includes keeping windscreens clean and fully defrosted, taking care in shady areas where there may be black ice on the road, using headlights in fog and increasing following distances.