Although Sweden extends across nearly as much latitude as Norway, its north–south sweep is on the east side of Scandinavia's mountain corridor rather than the west side. That makes all the difference. With the mountains largely closing the door to Atlantic flow – though it's left ajar in places – Sweden runs distinctly colder and drier on average than its Nordic counterpart. The southwest corner of Sweden, especially Goteborg and other spots along the Kattegat coast, is really a climatic extension of The Netherlands and Denmark. It's damp and chilly in winter, with frequent light rain intermingled with snowfalls, and showery, but bright, and mild in summer. An east–west transition zone of sorts cuts across Sweden close to the latitude of Stockholm. North of this belt, Sweden has a much more continental climate, with summers just as mild as they are to the south, but far colder winters. The Gulf of Bothnia typically freezes over for months, which enables bitterly cold air to slide westward from Russia or south from the Arctic Ocean without passing over water. These frigid periods in mid-winter are marked by low clouds and light snow that can last for days. By contrast, as Atlantic winds cross the mountains they often become dry and relatively mild across central and northern Sweden, and temperatures can push a few degrees above freezing. A few low-pressure centres twirl across the Baltic Sea in most winters, bringing a heavier dose of snow to southern and central Sweden.
Spring is the driest, least cloudy period across most of Sweden. As the sun intensifies, spring fever takes over, although nights can still be quite cold and brief showers may scoot across the landscape. By early May, the snow has usually melted across all but the far north and the mountains, and temperatures then take a sharp turn upward. Sweden's mid-summer warmth fuels frequent showers and thunderstorms, some of them bearing decent downpours. These typically form along the mountains in the afternoon and move eastward by evening; thus, the Gulf of Bothnia coast often gets more afternoon sun than the mountains do. The lowlands near Stockholm and Uppsala tend to be Sweden's warmest region in mid-summer. As you head north from there, increasing clouds and a lower sun angle are partially offset by extra daylight, so temperatures cool down only slightly with latitude.
As far north as Lapland, the average highs in July exceed 16°C/60°F, and a thunderstorm may interrupt the 24-hour daylight. Nonetheless, mid-summer frost can occur above 1000m/3300ft, and the winter cold here is among the fiercest in Scandinavia. If you're hoping to catch Lapland at its mildest, plan on arriving during the relatively brief window between late June and early August. Because Sweden covers so much north–south distance, there's often unsettled weather somewhere along its length at any given time – when it's beautiful in the south, it may be wretched in the north, or vice versa.