No other region along the eclipse track has as capricious a climate as Oregon.
To its west lies the Pacific Ocean, which feeds the prevailing onshore winds with a limitless supply of moisture. On land, three mountain ranges that run the length of the state (Figure 1) insert a series of topographic barriers that induce cloud and precipitation on their upwind side and dry, sunny weather to their lee (Figure 2). Inland, toward the Idaho border, the landscape rises gradually onto the Columbia Plateau, nudging the westerly winds upward before dropping abruptly into the Snake River Plain at the state’s edge. The result is a pattern of alternating cloud and precipitation climatologies that challenge an eclipse seeker but also provide many promising areas from which to capture the solar spectacle.
The most westerly of the mountain ranges that block the Pacific winds is the diminutive 1000-m-high Coast Range, which rises steeply just inshore from the coast. As the first mountain barrier to the moisture-laden marine flow, the Coast Range elicits a strong response from the atmosphere as pristine ocean air is compelled to rise over its peaks, cooling and condensing along the west-facing slopes. Evidence of the mountain’s influence on precipitation is reflected in its vegetation—a dense forest canopy that provides a dark eastern backdrop to the communities that hug the ocean shore. The Pacific Ocean gives Oregon’s coast a distinct maritime climate, and the peaks of the Coast Range confine it to a narrow coastal strip.
These coast-hugging regions of Oregon are not especially favoured for eclipse watching. The state lies beneath the average position of the summer jet stream that carries weather systems onto the continent. More locally, the cold offshore water is a good manufacturer of fog and low clouds. Tendrils of mist are commonly found drifting across the beaches, especially on sunny days when the marine air is drawn inland by the diurnal warming of the land. In Figure 5, taken at eclipse time in 2013, a transparent haze can be seen in the background, partly a wind-blown spray and partly the remnants of an earlier fog. The dress of the beach-goers testifies to the unpleasant temperature and an onshore wind that drives stinging sand against unprotected ankles; the moist and salty air is not kind to camera optics and telescopes. Of course, an offshore wind will dissipate the fog and warm the air, so attention to the eclipse-day forecast will tell whether to stay or whether to move to an inland trans-mountain location.
Observations from airport weather stations (Table 1) show an average morning cloud amount of 64 percent at Newport, and a range from 52 to 78 percent at other sites along the coast; measurements from satellite images confirm the high frequency of cloud cover (Figure 3). Table1 shows that at Newport Airport, about 15 percent of August days have fog at eclipse time. Presumably the frequency is higher right on the beach, as the airport lies about 700 metres inland.
On an ordinary August day, afternoons are much less cloudy than the mornings, as fog and low cloud burns off under the influence of the warming sun. The eclipse comes at a difficult time, just before 10:16 a.m. PDT, when the morning clouds are just beginning to clear. It may not be enough magic for eclipse day and in any event, it is possible that any fog that dissipates before 9:20 a.m. will reform as the approaching shadow masks the Sun and cools the atmosphere. Though the prospects seem limited compared to other regions under the shadow path, undue pessimism is not warranted, as the eclipse comes ashore at one of the driest times of the year. If weather forecasts are favourable, Oregon’s coast will reward a considerable crowd on eclipse day.
Along the centre line, the Moon’s umbral shadow comes onshore just south of Fishing Rock State Park, a tiny promontory that juts out into the ocean on the south side of the community of Lincoln Beach. It’s a fitting place to start the eclipse, as Lincoln Beach and Fishing Rock were also under the shadow of the last mainland eclipse across the United States, on February 26, 1979. The park is approached from suburban streets by way of a short, twisty, forest trail with head-brushing branches and exposed tree roots designed to catch the unwary, but once on the point, a broad view across the Pacific opens up. The setting consists of a rough, grassy area (Figure 4) that is bordered by rounded boulders above a cliff face that drops sharply down to the ocean. It’s not a great venue for telescopes and heavy photographic gear but is a visual treat, especially when waiting for an eclipse shadow. There isn’t much parking at the entrance to Fishing Point, and not much room on the promontory itself, so viewing sites will likely fill quickly with those who want to be among the first to greet the 2017 lunar shadow.
Though Fishing Rock lies on the centreline, there are many other fine observing spots along the coast if the weather cooperates. Prime among these are Lincoln City to the north (15 km) and Newport to the south (22 km). Both have spacious beaches and generous tourist facilities and all share pretty much the same kind of weather.
Highway 20 leads eastward from Newport across the Coast Mountains to the Willamette Valley. Eclipse-viewing options are limited on the highway, in part because of the tendency for cloud to build on the ocean-facing slopes and partly because visibility is restricted on the heavily treed and twisty route. Once over the Coast Range and into the Willamette Valley, however, the eclipse seeker’s chances improve modestly. The Coast Range is not very high and its ability to dry the air limited. Nevertheless, cloud measurements at Corvallis, Salem, and Aurora (Table 1) show a 15- to 20-percent reduction in average cloud cover compared to that at Newport.
A far better eclipse-watching location — perhaps the best anywhere in the United States — is on the east side of the second mountain chain — the Cascades, which, at 3,000 metres, are high enough to make a major dent in the cloud-cover statistics. After crossing this range, the eclipse track drops sharply into “The Basin,” a low valley centered on Madras that lies at the southernmost extension of the Columbia Basin. Airport observations at Redmond, at the south limit of the umbral shadow, show an average cloud cover of 27 percent at eclipse time. Over 50 percent of the reports at Redmond show “clear” skies and 75 percent have scattered cloud or less. According to satellite observations (Figure 3), Madras and its surroundings have the distinction of possessing the least August cloudiness anywhere along the central line of the eclipse track.
While the cloud-cover statistics are promising, eclipse seekers should always have a “Plan B” in case of bad weather. Even at the best sites, the frequency of broken to overcast skies is close to 25 percent and it may be necessary to move on the day before the eclipse to a more promising site. In the Willamette Valley, low clouds can circumvent the mountains by moving down the Columbia River valley to Portland and then spread southward to Salem and beyond. Numerical forecasts can often catch this type of invasion, providing a reliable 24-hour warning that conditions may deteriorate; satellite images will confirm the cloudy invasion in time to move to a more protected location south or east. Such clouds usually burn off during the day, but this eclipse comes too early in the morning to count on such dissipation. Of course, if large-scale weather systems with high-level clouds are moving across the west coast on eclipse day, the mountain terrain will have a more difficult time eroding the overcast. In such a case, sites close to the lee side of the Cascades have the best chances of finding a hole in the clouds, though there is not much road access to the mountain-hugging locations west of Madras.
Once past Madras, the lunar shadow moves onto the third of Oregon’s mountain ranges: the Ochoco Mountains, where the terrain becomes rougher and the average elevation begins to climb, eventually crossing the high terrain of the Columbia Plateau. From Mitchell eastward to the Plateau’s peak, average August cloudiness increases about 10 percent. It’s a pretty countryside after the flat landscape of the Columbia Basin, and offers a relatively small cloud penalty for the improved panorama. Though the region has a heavier precipitation than the Basin, the difference is small and not enough to support a dense forest cover on the slopes, leaving an open landscape with good viewing prospects. The community of Mitchell, with its very good weather prospects, will be a popular stopping spot, as will the region around the slightly cloudier Thomas Condon Paleontology Center, just south of the centre line (Figure 7).
Muc h of the cloudiness in eastern Oregon in August is convective — showers and thundershowers — and so is susceptible to dissipating as cooler temperatures arrive with the eclipse shadow, provided the buildups are not too large. Nevertheless, if the day is even half promising, these mountains are a good area for eclipse chasing, as Highway 26 follows the track of the umbral shadow all the way to Idaho and the very promising climate in the valley of the Snake River.
Against the Idaho border, the eclipse track descends into the northwest corner of the Snake River Plain, reaching Interstate 84 and the Idaho border at Ontario, OR. As the track descends to lower elevations, the average cloud cover also retreats to lower values, reaching a mean value of around 30 percent at the Idaho border. Airport observations at Ontario show an average cloudiness of only16 percent (with over 75% clear skies!), but the airport weather station has only provided a small number of observations over the past years and the values must be viewed with caution. The surface statistics cannot be discounted, however, as satellite observations are also kind to the region, showing average cloud amounts that nearly match the low values around Madras.
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Updated December 2016