Onnwal is located at about 27° and 28° north latitude and thus has a sub-tropical climate. Along with the rest of the Flanaess, Onnwal enjoys a particularly long summer and growing season. Typically Onnwal’s winters are dry and cool while the coming of summer brings rain. In general, the coastal areas of the peninsula receive more rain and remain cooler in summer than the inland areas. Conversely, during the winters the coast is warmer than the interior.

In the spring and summer, the prevailing winds come from the east and south-east, while in the autumn and winter they swing around to blow from the north and north-east. The spring wind is known as Atroa’s Laugh while the winter wind is known as Telchur’s Breath. With summer, warm southerly winds blowing up from the unknown seas beyond Hepmonaland sweep across Onnwal, dripping with moisture.

Spring heralds a shift in the winds from north to east and south-east. As the weather warms, the clash of Telchur and Atroa brings fierce tempests to the waves of the Gearnat. During this season the Storm Coast earns its name in earnest and travel by sea is foolhardy at best. In Summer, the weather is humid and hot with plentiful rain and sun in equal measure. As summer passes into autumn, tropical storms broil up from the warm Azure Sea, lashing the Azure Coast and passing across the Dragonshead in the Gearnat. Later as the weather cools and the winds again turn to east and north, the tempests subside and Telchur again rules.

In winter, Telchur’s Breath brings cool, dry air from the north. Despite this, it is never cold – and snow is rarely if ever seen except a rare dusting in the highest peaks of the Headlands. Occasionally dust and sand are carried from the Bright Desert across the Gearnat to fall on Onnwal. These glassy white deposits are commonly called “Telchur’s Gems” or “Onnwallish Snow”.