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    Jim Andrews

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    Snow Versus Rain Is Often About Elevation, Elevation, Elevation

    March 27, 2013; 8:39 AM ET

    In the post of Tuesday, March 26, I included a video to help illustrate not only the severity of the March 22-23, 2013, snowstorm impact in parts of the U.K., but also the striking contrast fostered by small variation in elevation.

    Here, I would like to use online mappers to shed further light upon the amazing contrast in snow cover over short distances.

    The video description names not only the town (Holywood, Northern Ireland), but also the road (Church Road), along which the video was taken.

    The online mapper, google.maps.com, has "Street View" for Church Road. Street View is a feature that gives the perspective of "being there," as the imagery is captured by vehicle-based cameras.

    Using Street View, I was able to match video landmarks with those on the mapper, including their relative locations with respect to elevation.

    The opening video images are taken near the foot of the hill surmounted by Church Road. Here, only patches of slush are seen, little evidence of any major snowfall.

    Site of the "Road Closed" sign. (Google Maps Street View)

    Next stop on the way up the hill is a brick house below the 100-meter elevation contour (about 300 feet). In this scene, snow is all about, including on the road. A temporary closure sign hints at worst conditions ahead.

    Well up the hill, this homestead was in deep-drifted snow. (Street View)

    Nearing the crest of the hill, at an estimated elevation of 160 meters (525 feet), the road and surroundings, among them a large homestead, are literally snowbound, the road blocked by deep drifts.

    Wide open over the crest of the hill, deep drifts buried the roadway at this landmark. (Street View)

    The top of the hill, roughly at 190 meters (625 feet), the view is wide open, as is the exposure to wind. Here, impassible drifts still cover the road, confirming in fact the road closure. It is in this area that the photographer captured scenes of drifts to at least 3 meters (about 10 feet), by my conservative estimation.

    How much snow fell here, near the 600-foot elevation, is not fully clear. However, a snow depth of 40 cm (16 inches) was observed on Monday at Ballypatrick Forest, located at about the same elevation northwest of Belfast. The heavy fall of snow ended on Saturday, even though drifting likely lingered.

    This is the likely direction marker in the snowbound last frame of the video, only 3 km from town. (Street View)

    Temperature difference over the roughly 150 meters (500 feet) between town and the crest of the hill was likely 1.0-1.5 degrees C (2-3 degrees F), based upon the atmospheric "lapse rate." Since the atmosphere was well stirred by strong winds, the difference in pressure between hill and dale would be maximized. Assuming no fog, the upper end of the range would hold true. A moist lapse rate, altered by condensing of water to fog, would be lower.

    At Belfast/Aldergrove (81 meters, or 265 feet), temperature range during the storm was 0.5-2.0 degrees C, or 33-36 F. At this elevation, slushy snow struggled to lay, greatly limiting snow depth. Given the storm's heavy dose of water-equivalent precipitation, only a 0.5-1.0 degree C (1-2 degree F) lowering of temperature would make the difference between several centimetres of heavy, melting slush and the deep drifted snow (30 cm or more), lying above 150 meters, as shown in the video.

    I would like to thank the YouTube videographer for the use of this video in illustrating the nature of the Blizzard of March 2013.

    The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or AccuWeather.com


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