Weather in Mount Isa in December

The month to avoid. December is the month most people should skip in Mount Isa. Daytime highs average 38.3 °C and the afternoon is not negotiable — outdoor plans move to early morning or evening.

December ranks 12 of 12 — near the bottom of Mount Isa's year. June is the month that works, and the swing between the two is 68 points, which is a different holiday rather than a slightly better one.

Rain on 10 days, 2 of them heavy. Enough to need a plan B, not enough to need a plan around it. Pack for heat management rather than style: shade, water, and a schedule that gives up on the middle of the day.

What the averages hide

Averages flatten a month, and this one hides a few things: 25 days of the month clear 35 °C — that is not a heatwave, it is the month. Across the twenty years measured, the hottest December day reached 45.7 °C and the coldest night fell to 15.9 °C, and the wettest single day dropped 43 mm — roughly 61% of the month's rain in one day.

December is moderately variable: 4 mm in the driest year against 168 mm in the wettest, around an average of 71 mm. Roughly two Decembers in three land near that average, and the third does something else entirely.

Wind is light at 11 km/h, so the temperature on the page is close to the temperature on your skin, and the air is dry at 40% humidity, which makes the heat far more bearable than the same figure somewhere humid — and dehydrates you faster than you expect.

How December sits in the year

Temperatures hold steady either side: 38 °C in November, 38.3 here, 35.8 in January. Nothing about the timing within the month matters much.

Daylight in December

December is at or near the longest days of Mount Isa's year: 13.4 hours of daylight, holding steady all month. Evenings are the real gain — dinner outdoors still happens in full light.

An inland climate

With no coast nearby, the year swings a fair way — 28 °C between the warmest afternoons and the coldest nights, wider than any coastal city at this latitude would manage.

How busy it gets

Off season. The genuine off season: cheapest by a distance, with the caveat that some tours and restaurants close entirely.

Crowd levels are estimated from climate desirability and school-holiday calendars, not from visitor numbers.

December in Mount Isa versus nearby

If Mount Isa is one option among several, the nearby comparison is worth making. Alice Springs is a better bet in December — within a degree on temperature, 2 days less rain. Cairns is a better bet in December — 5.7 °C cooler, 7 days more rain.

So: December is a compromise. June is 68 points better and is what Mount Isa is actually like at its best — worth moving the trip for if that is possible, and worth adjusting expectations for if it is not.

Every month in Mount Isa

See all twelve months in Mount Isa, or where else to go in December.