The Frostmoore Fog
One would think the sea route from Brackenfels to Bogholm is comparatively safe. Just a short trip along a well-protected coast. But trust me, it is not.
You have to keep a constant balance: Head out too far on the sea, and the maelstrom pirates will get you. Keep too close to the shore and the fog will get you—and some say its the more vicious of the two. I know no one who travels this route and didn't have to shout "hard to starboard" when suddenly a lighthouse appeared in front of the ship instead of its port side. For some of them, that has been their last realization.
Manifestation
The weather in the Frostmoore is dominated by two different kinds of fog:
White Fog
This type of fog manifests itself as a thick white layer of fog very close to the ground.
Usually, normal visibility is restored at 10-30 cm above ground level, but on extreme days it can climb up to 1m.
It can be observed in the coastal regions at all times of the year but is more common in spring and autumn.
It causes a major issue for all travellers:
With no means to see the ground, many lose their way in the moore and sink in.
Additionally, ships sailing along the coastline are unable to see where the line between land and sea is.
Lighthouses are built along the shore, but they are far apart and unexperienced navigators are still in danger of running aground.
Yellow Mist
This type of mist is much rarer than white fog and a very local phenomenon.
It only occurs on (comparatively) warm summer days and further away from the shore.
It appears as a faint yellowish mist that stinks of sulfur.
It is highly noxious.
Anyone experiencing yellow mist should leave the area.
Cause
White Fog
White Fog is caused by the combination of two effects.
The Frostriver picks up pieces of ice from glaciers in the heights of Heleg'Orodim and carries them all the way to the shore.
Thus, its water is close to 0°C at most times of the year.
At its mouth, the river forms a very shallow delta.
Much of the water seeps away to groundwater which then forms the Frostmoore.
This cold underground flow keeps the surface cold all year.
However, near the shore, warmer air with a higher humidity flows above it. As it is cooled down by the ground, it forms the typical white fog. The fog is thicker if the temperature difference is higher. This is typically the case in spring and autumn where the sun starts to warm up the lower regions but in the mountains, the weather is still cold as winter.
However, near the shore, warmer air with a higher humidity flows above it. As it is cooled down by the ground, it forms the typical white fog. The fog is thicker if the temperature difference is higher. This is typically the case in spring and autumn where the sun starts to warm up the lower regions but in the mountains, the weather is still cold as winter.
Yellow Mist
For a long time, this process causing the yellow mist was not well understood until Dwarven pioneers tried to found a new underground colony in the Frozen Forest.
While digging they discovered vast underground caves filled with sulfuric gas.
Its origins are unknown.
The more superstitious people say it is the miasma of the Frostdrake Melas who died here centuries ago.
As for the White Fog, the Frostriver also plays a major role in the formation of yellow fog—or rather in its prevention. Under normal conditions its cold water keeps the lower ground levels frozen at all times. This ice seals those caves and prevents any gas from getting to the surface. But on warmer summer days the frost layer may partially melt and allow the gas to pass through the cracks and reach the surface. Together with tiny water droplets formed by the wetland, it surfaces as a yellow noxious mist.
As for the White Fog, the Frostriver also plays a major role in the formation of yellow fog—or rather in its prevention. Under normal conditions its cold water keeps the lower ground levels frozen at all times. This ice seals those caves and prevents any gas from getting to the surface. But on warmer summer days the frost layer may partially melt and allow the gas to pass through the cracks and reach the surface. Together with tiny water droplets formed by the wetland, it surfaces as a yellow noxious mist.
Both weather phenomena are also affected by the wind:
Even a light breeze disperses the fog and allows normal sight.
In case of the yellow mist, this reduces the concentration enough the remove its toxicity, but in exchange, the stench is spread over a larger area.
Type
Natural
Northern Cape of Arendir
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Do many people have to face the yellow mist when it happens? Did someone already died of it? P.S.: your map is cute
Thanks! The Frostmoore isn't very densely populated and the regions where the yellow mist occurs are even less. Though, there are of course a few small hamlets and people passing through the area. Those would have to face the mist itself, most others will only observe the stench. Most people in the area are aware of the danger, so they look for the signs and get to safety early. But foreigners, travellers or careless people are in danger and over the years a few of them will definitely have died. However, there were no particularly notable or well-known incidents.