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The Great Lakes: a diversity of lake-effect snow mechanisms

GOES-12 visible channel imagery (above) displayed several different lake-effect snow (LES) producing mechanisms across the Great Lakes on 20 February 2008: multiple LES bands over Lake Superior, meso-vorticies over both Lake Michigan and Lake Huron, and a single LES band over Lake Ontario. Even though the Great Lakes water temperatures were getting... Read More

GOES-12 visible images (Animated GIF)

GOES-12 visible channel imagery (above) displayed several different lake-effect snow (LES) producing mechanisms across the Great Lakes on 20 February 2008: multiple LES bands over Lake Superior, meso-vorticies over both Lake Michigan and Lake Huron, and a single LES band over Lake Ontario. Even though the Great Lakes water temperatures were getting quite cold (generally around 32-40ºF), a very cold arctic air mass (overnight minimum temperatures on 20 February were as cold as -33ºF at Grand Forks, North Dakota and Embarrass, Minnesota; -30ºF at Upson, Wisconsin; -28ºF at Stammbaugh, Michigan) was spreading across the region (GOES-12 IR image + surface reports) creating a large water-air temperature difference.

So what about Lake Erie? Since Lake Erie is the most shallow of the five Great Lakes, it often freezes the earliest; due to a large concentration of ice over that particular lake (as seen on SSEC MODIS Today true color imagery from 4 days earlier, viewed using Google Earth, below), Lake Erie was not able to contribute the necessary heat and moisture flux needed to produce LES mechanisms on the scale that the other lakes were producing on this day.

MODIS true color image (Google Earth)

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Using MODIS imagery to detect thin stratus/fog over snow cover

AWIPS images of the MODIS visible channel, the 1.6µm near-IR “snow/ice channel”, and the 11.0µm “IR window” channel (above) revealed a large patch of supercooled water droplet stratus cloud (and/or fog) over northeastern Utah on 19 February 2008. This stratus/fog cloud feature was confined to the lower elevations (AWIPS topography image | Johns Hopkins topography image) where... Read More

MODIS visible + snow/ice + IR images (Animated GIF)

AWIPS images of the MODIS visible channel, the 1.6µm near-IR “snow/ice channel”, and the 11.0µm “IR window” channel (above) revealed a large patch of supercooled water droplet stratus cloud (and/or fog) over northeastern Utah on 19 February 2008. This stratus/fog cloud feature was confined to the lower elevations (AWIPS topography image | Johns Hopkins topography image) where several river valleys converge just south of Vernal, Utah (station identifier KVEL); at the time of the images, the surface visibility at Vernal was restricted to 1 mile with fog. The areal extent of this cloud feature was difficult to judge using either the 1-km resolution MODIS visible image (due to the bright white appearance of both the stratus/fog and the surrounding non-cloudy snow cover) or the 1-km resolution MODIS IR window image (due to the light gray enhancement of both the cloud feature and the cold air that had collected within the remainder of the lower elevations) — but on the snow/ice image, the contrast of the brighter gray-to-white enhancement of the supercooled water droplet stratus/fog feature really stood out against the dark appearance of the surrounding snow-covered terrain.

The corresponding 250-meter resolution MODIS true color image from the SSEC MODIS Today site (below, viewed using Google Earth) showed the “translucent” nature of the patch of stratus/fog — note that you can actually see the outlines of some of the converging rivers (the Green River, White River, and Duchesne River) through the optically-thin cloud feature.

MODIS true color image (Google Earth)

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Streaks of snow cover in the Northern Plains

A comparison of MODIS true color and false color RGB images (above) reveals multiple narrow streaks of snow cover across parts of the Northern Plains on 18 February 2008. The white snow streaks show up well against the surrounding brown bare ground regions in central South Dakota and Nebraska on the true... Read More

MODIS true color + false color images (Animated GIF)

A comparison of MODIS true color and false color RGB images (above) reveals multiple narrow streaks of snow cover across parts of the Northern Plains on 18 February 2008. The white snow streaks show up well against the surrounding brown bare ground regions in central South Dakota and Nebraska on the true color image (created using MODIS channels 01/04/03 as red/green/blue); in the corresponding false color image (created using MODIS channels 02/07/07 as red/green/blue), the snow cover exhibits a red enhancement, while supercooled water droplet cloud features appear as varying shades of white.

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Snow cover in southern Califorinia and Baja California

MODIS true color imagery from the SSEC MODIS Today site (above, viewed using Google Earth) shows extensive snow cover over the higher elevations of southern California (and Baja California in Mexico) on 15 February 2008. According to media reports, this snow closed sections of Interstate 8 (between Alpine and Ocotillo) for more than 12 hours on the... Read More

MODIS true color image (Google Earth)

MODIS true color imagery from the SSEC MODIS Today site (above, viewed using Google Earth) shows extensive snow cover over the higher elevations of southern California (and Baja California in Mexico) on 15 February 2008. According to media reports, this snow closed sections of Interstate 8 (between Alpine and Ocotillo) for more than 12 hours on the previous day; as much as 8.5 inches of snow was reported at Cuyamaca Peak (elevation 4820 feet) in San Diego county.

An AWIPS image of the MODIS Land Surface Temperature (LST) product (below) indicated that LST values were in the 30º-40º F range (green enhancement) in the region of the snow cover, compared to the much warmer bare ground areas to the west and to the east where LST values were generally between 60º and 70º F (orange enhancement).

MODIS Land Surface Temperature product

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