Scotland has had two summers.

There's been the long, depressingly dark and damp one endured by millions in the south and east, and the cheerfully sunny and dry one enjoyed by thousands in the northwest highlands and the Western Isles. So while there have been floods in Lothian and the Borders, there have been droughts in Stornoway and Skye and Lochalsh. While city-dwellers have piled up the sandbags, islanders have splashed on the sun cream – and been urged to use less water flushing their toilets.

Figures released by the Met Office make the point in dramatic fashion. Across the UK, June was the wettest it's been since records began in 1910 with 145.3mm rain, as was April with 126.5mm.

The south of Scotland was well and truly drenched in June, with Dumfriesshire receiving 221.4mm of rain, 2.67 times the average for the month. But Sutherland, and Ross and Cromarty, in the north had only 55.6mm and 56.5mm, just 60% of their monthly averages (see map).

The main reason for the unusual weather patterns is that the jet stream has got stuck to the south of the UK. This is a band of fast-moving winds moving from west to east across the Atlantic high up in the atmosphere.

According to the Met Office, the jet stream guides rain-bearing low-pressure systems that regularly move across the Atlantic. Normally in the summer it would be to the north of the UK, and would drag bad weather away from our shores.

But this year it has remained to the south of the UK, giving us weather systems we are more accustomed to seeing in the winter. "The jet stream, like our weather, is subject to natural variability," says a Met Office spokesman.

"We expect it to move around and it has moved to the south of the UK in summertime many times before in the past. It has, however, been particularly persistent in holding that position this year – hence the prolonged unsettled weather."

But it's not just the UK's weather that's been affected. The track taken by the jet stream has also caused floods near the Black Sea in Russia, and an unprecedented heat wave in large parts of the US.

The US has just experienced the warmest first six months of the year since records started, with blisteringly hot record-breaking temperatures in many places. Last week 1,000 drought-stricken counties across 26 states were officially declared disaster areas.

According to the US authorities, 56% of the country is now experiencing drought conditions. There has also been a rash of fierce wildfires in Utah, Idaho, Colorado, Arizona and New Mexico.

"The recent heat and dryness is catching up with us on a national scale," said Michael Hayes, director of the US national drought-mitigation centre.