WRAL WeatherCenter Blog

Our Snow from Space!

Posted January 23, 2009

Terra/MODIS image of snow on the ground across NC on Wednesday 21 Jan 09.

One of the fun things about a snowfall around here these days is the ability to have those of you with digital cameras almost immediately send in all kinds of nice photos showing the snow (and snowmen) up close and personal.

It's also nice to step back and get a "big picture" of how the snow was distributed, but the day of the storm there are usually too many clouds around for a good look at the aftermath from above. However, it isn't unusual for dry air and mostly clear skies to build in for a day or two after the storm, and when that happens we can get a good look from "on orbit," thanks to weather and other special-purpose satellites. Here, I've assembled three satellite images (remember you can click on the thumbnail at right to get an enlarged view). The first two are from a satellite called Terra, and its "Moderate Resolution Imaging Spectroradiometer," or MODIS. The images were posted on the MODIS Rapid Response System web site at http://rapidfire.sci.gsfc.nasa.gov/. Both show central and eastern NC, and were taken on Wednesday and Thursday, and you can clearly see how much snow can vary from place to place as a system moves through, and also see how much snow has melted away and become less reflective of sunlight from one day to the next, as temperatures remained in the 30s on Wednesday but climbed to near 50 Thursday afternoon. Note that you can orient yourself location-wise by finding the Virginia and South Carolina borders (kind of thin) and also Jordan and Falls lakes, which stand out nicely.

This satellite follows an almost polar orbit at an altitude of a little over 430 miles above the ground, so only crosses most locations on earth about once a day or so, and most of its applications are not related to real-time weather analysis and forecasting. However, the low altitude allows for a lot of detail as you see in the attached images.

The third image, in black and white, does come from one of our more typical weather satellites, one that sits in a geostationary orbit above the equator at about 22,300 miles up. At that distance, the detail and resolution is not as good, but a new image is available about every 15 minutes from the same location relative to earth's surface, which is great for time lapse movies and following rapidly changing weather systems. Comparing such animations from a shot like this can also aid in distinguishing snow from bright white clouds in more detailed still images like those from the Terra/MODIS system. This image was obtained from NOAA's Aviation Digital Data Service at http://adds.aviationweather.gov/satellite/, and was taken on Wednesday, pretty close to the time of the first MODIS image in the series. So there you have it - an image gallery on our main weather page of the snow as it appeared from right here in it, and a few shots of the same stuff from hundreds (and thousands) of miles away!



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  • Mike Moss Jan 27, 2009

    Thanks for posting that address, PackManSJP - as you noted, an especially sharp boundary between plenty of snow and almost none in that event!

  • PackManSJP Jan 23, 2009

    Those are some very impressive images. Perhaps the most impressive satelite image of snow I have ever seen was from the snow storm that affected eastern NC the day after Christmas. The line between areas with snow and areas without was very sharp. Here is a link to the image: "http://www4.ncsu.edu/~nwsfo/storage/cases/20041226/snow.cover.sat.500m.jpg". I was at home for Christmas break in Nash County, and we got 7 inches of snow that stuck around for about a week. I talked to a friend in Raleigh, and she said all there was was a dusting that was gone the next afternoon.