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Seasons and Weather

  

Let's start off with the most asked questions: When will the rain stop? When will the fog lift?

  Tell Me When....

If it's raining on the mountain, you can be 90 percent sure it's raining throughout the surrounding area. In summer, look for a Washington or Richmond paper at one of the lodges, and check the weather forecast. Or try to get a local station on your car radio at news time. The weather forecast is usually posted on a bulletin board at the front door of the Byrd Visitor Center at Big Meadows.

The fog is different; its coming and going can't be predicted. On the average, you can expect fog on the mountaintop two or three times a month in winter, and once or twice a week in midsummer. To a large extent, the mountain causes fog. Moving air masses must rise to get over the mountain. As the air rises, it expands and cools; if the air is moist, cooling may cause moisture to precipitate as tiny droplets, and produce the clouds that we call fog. As the air descends the eastern slopes it warms, and the fog dissipates. How long will this go on? A morning fog will often lift before noon, as the air grows warmer. But "often" it is difficult to tell.

But, don't despair. There may be no views from the overlooks, or from the mountain peaks. But the streams and waterfalls still work. Wildflowers still bloom, and the flowers and leaves are more attractive with water droplets on them. (Some wildflower photographers carry atomizers to spray their subjects.) The rocks are still there, and their subdued colors seem brighter on a gray day. Wildlife are less timid in fog, so you're more likely to see a fox or a deer on a foggy day. And finally, if it's a really damp July or August, mushrooms are popping up all over.


A 'Fog Ocean' (Low Lying Clouds And Fog)
Photo taken by Larry W. Brown

You say you can't take pictures in the fog? Sure you can. This is the time for close-ups. Wildflower pictures are better with a soft and subtle background than with spotty sun and shadows. And pictures of trees in foggy woods have a certain fascination. A couple of hints: look for moderately open woods. Compose your pictures with one or two trees in the foreground, fairly well defined, and others at various distances, fading by steps into invisibility. To record the scene as you see it, if you have a digital camera try several settings. With standard film, trust your exposure meter. You might want to experiment with a one- or two-stop underexposure, for a "spooky" effect.

Half a dozen times a year, an atmospheric inversion may produce a strange effect: fog lies like a soft white blanket on the valley and the Piedmont, while the mountaintop is clear. Then you can look down on a "fog ocean," with the lower peaks rising above it like islands. Several times, from the Big Meadows Campground, Heatwole watched a thrilling sight, a fog ocean rising on the Piedmont side of the mountain, then flowing through Fishers Gap and spilling down the western slope like a giant Niagara half a mile high.

 

  Climate

Because of its elevation, the mountaintop has from fifteen to twenty percent more precipitation than surrounding lowlands. The average temperature is about ten degrees cooler at Big Meadows than in the valley, and fifteen degrees cooler than downtown Washington or Richmond. The following table gives the average temperature (in degrees F), and precipitation (in inches), at Big Meadows (elevation 3535 feet) for a recent twelve-year period.

Month High Low Rain Snow
Jan. 35.9 18.6 3.1 12.7
Feb. 35.2 18.3 3.3 10.4
Mar. 45.0 26.1 3.7 6.8
Apr. 55.0 34.9 3.1 2.6
May 63.6 44.5 5.0 0.
June 72.0 53.8 4.8 0.
July 74.8 57.9 4.4 0.
Aug. 73.6 56.7 4.4 0.
Sept. 67.9 50.4 5.3 0.
Oct. 57.7 39.2 6.2 0.2
Nov. 47.1 30.3 4.1 7.2
Dec. 39.1 23.2 3.6 8.2
TOTALS 51.0 48.1

There you have the averages. But few days, and fewer years, are average. The weather seems to go in cycles, so that several dry years are followed by several wet ones, and several cool years by warmer ones. At Big Meadows, the highest temperature during the twelve-year period was 89 degrees, and the lowest 20 below zero. Most winters are "open," which means that snow falls only occasionally and soon melts, so that the ground is bare during most of the season. But every five or ten years a snowy winter raises the average.

 

  Spring

Hepatica
Photo taken by Charlie Johnson

Spring comes late on the mountain. If you visit the park at the end of March, you'll drive through springtime in the lowlands and ascend into winter on the mountain. The trees and grass are brown. Only if you look closely, and in the right places, will you see signs of hope: willow catkins opening, coltsfoot and hepatica blooming tentatively. Not until April, when you see flowers of bloodroot and marsh marigold, will you know that springtime is irreversibly here.

In May, the green line glides up the mountain. From high points you can look down the slope and see that trees below a certain level are a pale new green, while those higher up are still brown. Some people say that the green line comes up the mountain at a hundred feet a day. By which they mean, of course, that it gains a hundred feet of altitude a day. (Heatwole observed that a hundred is a nice, round number. He never heard anyone say that the green line comes up the mountain at 30.48 meters a day.)

 

  Summer

View From Hightop Summit, August 1966
Photo taken by Henry Heatwole

Summer is the time for camping, for conducted walks, and campfire programs. An unending succession of wildflowers bloom--those with leading roles stay all summer, while bit players come and go. Days are warm, but nights can be nippy. You'll need a sweater or jacket at the evening campfire program, and a warm blanket if you're camping out. The air, which was fairly clear in springtime, is now hazy, and visibility is often limited. At times, Heatwole's sketches of views from the overlooks might not be of much value, they show what you might have seen on a clearer day.

The haze has two causes. One is dust in the air combined with water vapor and organic compounds given off by the trees. That's the haze that makes the Blue Ridge blue, and it's been here for a long time. The earliest descriptions of views from the mountains begin, "On a clear day...."

But now the Blue Ridge haze has a second ingredient: smog from industry and automobile exhaust. Summer smog used to be a dirty purplish blanket that lay on the lowlands, so that we could look down on the top of it. Just as the green line creeps up the mountain day by day, the summer smog line crept up year by year, and in 1976 it reached the top. Hopefully as various anti-pollution programs take full effect, the smog line will recede downward. Then once again we can say, even in midsummer, "On a clear day..."

 

  Fall

Autumn Foliage At Whiteoak Canyon
Photo taken by Dean Souleles

 

In September, the wildflowers still in bloom are goldenrod, asters, white snakeroot, and gentians. Fall colors begin to appear: first the Virginia Creeper, and toward the end of the month the black gum - both a rich, deep red. In an "average" year the peak of fall colors comes, so they say, between the tenth and twenty-fifth of October. By then the leaves of the maples are yellow, gold, and red, and maybe a little beyond their best color. But along the Drive you see an occasional maple, for this is primarily an oak-hickory forest. Red maples are, however, starting to fill voids left by gypsy moth kill. The oaks and hickories turn dark brick-red, or a modest dull yellow-orange, soon fading into brown. The cove hardwoods, at lower elevations, produce a more colorful display.

 

  Winter in Shenandoah

Rime Ice on Hawksbill Mountain, March 1972
Photo taken by Henry Heatwole

Winter is special. The air is cold, and sometimes so clear that only the curvature of the earth limits your visibility. The wildflowers are dead, but real aficionados can identify their dry remains. Leaves are down, so that all the trails offer views through bare brown branches that you could never see in summer. Fair-weather visitors are gone; if solitude is what you came for, you needn't look very far.

You have to be lucky to arrive just after a fresh snowfall, but you can depend on ice. There are rock faces along the Drive that develop spectacular masses of icicles - for example at Mile 39.5 in the Central District, and mile 10.8 in the North. A trip to a waterfall is a different experience now; you may find it frozen solid. Columns of hoarfrost here and there lift the surface of the trail, and crunch underfoot as you walk.

A winter phenomenon that only the luckiest visitors will see depends on a combination of special conditions. First there must be a thick fog, moving in a slow breeze at below-freezing temperature. The fog freezes on everything it touches, building up a thin, white, icy feather on the upwind side of every twig and blade of grass. Then, if the fog lifts and the sun comes out while the temperature stays below freezing, you'll see a mountain range covered not with snow, not with ice - but with Rime Ice, which resembles a brilliant white frosting of sugar.

Equally spectacular, and equally rare, is a major ice storm. Aggie Crandall, in her campfire program "White on Blue," provides a beautiful description. Here's Aggie:

Rain, too, can be different in winter. The gentle rain that precedes a warm front sometimes falls into below-freezing air at the earth's surface. So, instead of soaking in or running off, it freezes as clear ice. If it rains long enough under such circumstances, thick deposits of heavy glaze ice are built up on trees and shrubs and anything else the rain touches. For a long time the forest is a fairyland of crystal branches that tinkle against one another in the gentle wind. But slowly, despite the fairy charm of the landscape, a sense of impending danger begins to seep into your awareness. As the gentle rain falls and falls and freezes and freezes a limit is reached. Either the load of ice gets too great or the faint wind gets a little stronger, and branch after branch breaks off and falls with a crash like a huge crystal chandelier dropping onto a pile of glasses.

Long after the forest has struggled against a severe ice storm the scars of the conflict remain. Gnarled and twisted trees, like the Imagination Tree on the AT at Big Meadows, are the result of freezing rain. They are usually oak trees - strong, but brittle. The gray birch, on the other hand, survives undamaged because of its flexibility. As the burden of ice increases it bends lower and lower until it lets the ground help support the weight. Then, when the ice melts, it stands up straight again.




Ice Cascades, March 1967
Photo taken by Henry Heatwole

If you really want to know yourself and test your capabilities, winter is the time for it. In January and February you'll find no food, lodging, or gasoline the whole 105 miles of Skyline Drive. Even water is hard to get. There are frost free faucets in some, but not all, of the picnic grounds. Rangers will still help you when you need help, provided they know about it. But the temporary summer rangers are gone; the park is down to its permanent staff, which is small. Self-reliance is expected of you in winter. Come with a full tank of gas. Use snow tires or carry chains. Bring food, water, and proper clothing.

There's always a chance, however small, that your car will break down, get stuck in snow, or that its gas line will freeze. Be prepared to survive a breakdown without help. The temperature can get down to 20 below zero. With a strong wind that could have a chilling effect equal to still air at 60 or 70 below. If you have a breakdown it's safer to stay with the car, which will protect you from the wind. Don't depend on the car heater, because the danger of carbon monoxide poisoning is too great.

For a safe visit to the mountaintop in the coldest part of winter, wear very warm clothing such as fleece pants and parka, and insulated boots. For camping out you should also have a mountain tent and a fleece or down-filled sleeping bag. Many areas have stores with appropriate equipment rated by temperature. Here's Aggie Crandall again:

"Because the wintertime staff of the park is limited, the winter visitor must be ready to depend on his own resources. The ice and cold have created a uniquely beautiful world that often seems like fairyland. But it's not fairyland, because the ice and cold are real - and real ice is slippery and hard, and real cold freezes.

"But, for anyone who makes the extra effort and takes the extra precautions, the rewards of a winter visit to Shenandoah can be very, very special."


Icicles, Dark Hollow Falls Trail, Feb. 1966
Photo taken by Henry Heatwole
 
Snow on Skyline Drive, Feb. 1966
Photo taken by Henry Heatwole



    National Park Service Articles Related To Winter Weather At Shenandoah



Plowing Skyline Drive
Photo by National Park Service

The Winter of 2010 brought unprecedented snowfall to Shenandoah National Park.

SNP Records Three Significant Winter Rescues In Two Months - a daily report published by the National Park Service which featured SNP in February 2010.



Trees Damaged By Ice
Photo by National Park Service

Shenandoah National Park experienced extensive damage caused by a freakish ice storm which occurred in November 2006. Click here for more details and photos.

Click here to read the local newspaper story about this event.

 

   
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