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Two nights ago I camped out in Cwm Bychan (“Coom Bi-CAN”), planning to hike the ancient Roman Steps trail into the Rhinog Mountains. My streamside throwdown was gorgeous, a gnarled beech forest floored by golden leaves, with a clear cascade rushing nearby to lull me asleep with dreams of an early morning assault on the summit of Rhinog Fawr.
And the plan was looking good until just before dawn when a howling low pressure blew in off the Irish Sea, sounding like shotguns on the nylon. Within an hour my tent floor bulged like a waterbed. Then the gas canister I bought in Llanberis wouldn’t work, meaning (gasp!) no morning coffee. Still, I bucked up, packed up, and schlepped up the ancient track, armored head to toe in shell gear. That worked for about a mile.
With every foot I climbed, the rain got worse, the fog thickened, and the wind screamed louder until it seemed really stupid to be heading into a range I didn’t know, where no one knew I was hiking, with a marginal map, in the face of a building storm. So I tucked tail and pride between my legs, slopped back to trailhead and spent the rest of the afternoon shooting the ruins of Harlech Castle. Even the stone towers were getting blasted by horizontal rain, the ancient battlements moody as hell. Still, the weather was far more benign than in the highlands only miles distant and 500 feet higher – which brings us to today’s discussion of the relationship between elevation and weather.
There’s a reason mountains are colder, wetter and snowier than their surroundings: It’s called ‘atmospheric lifting.’ When moving air parcels are lifted to higher elevations, the gases expand and cool. Since colder air is less capable of holding moisture, the humidity in those parcels condenses. You can witness expanding gas cool any time you watch a blended fuel gas cartridge frost up as the stove runs. You can continue the experiment simply by popping the cap off a longneck bottle and watching the wisps of moisture that result from the expansion of moist air. So that’s the deal with cooling.
And then there’s lift. Atmospherically speaking (as opposed to plastic surgery-wise) there are three types of lift. They are: Thermal lifting, frontal lifting, and orographic (terrain) lifting.
–Thermal lifting happens when sun heats the ground, causing columns of air to rise and cool. This is the phenomenon that creates cumulonimbus thunderheads, and the cataclysmic storms that result when those columns of air reach super-cooled altitudes and drop like a stone, bringing their condensed moisture along for the ride, often in the frozen form of hail.
–Frontal lifting occurs when an incoming cold front, with its colder, denser air, wedges underneath an existing warm air mass, forcing it upwards. Usually the warm air is moister, so the lift – combined with the sudden cooling as air masses mix – creates powerful but often brief storms.
–Orographic lifting happens when an incoming air mass is forced upward by terrain. In mountain ranges with steep, tall windward slopes like Washington’s Cascades, Wyoming’s Tetons or Utah’s Wasatch, this creates extremely strong, fast lift and sudden, severe storms. sudden. Orographic lifting is the main reason why snow, and glaciers, and ski areas sit in high mountains.
The three types of lift often combine, which is why storms get big when they hit mountains. Add lots of moist incoming air and fast wind speeds, such as when mountains sit on coasts fronted by large seas (think the Rhinogs) and you get weather that can drown a duck. But fortunately, even ducks can smarten up and luck out, if they have the patience.
So yesterday I met up with my young friend Yael Kisel, a botany student working in London, and we hiked back into the boggy, foggy, but much drier Rhinogs, to find the ancient Bronze Age Celtic stone circle called Bryn Cader Faner (see above). Seriously big juju in the misty moorlands.
Now it’s off to the airport and back to burgerland. Yacchid Da! (good health). –Steve Howe