The GWCC home page contains a four-panel graphic containing satellite and radar observations and a severe weather outlook (all from NOAA). The following is a brief overview of these graphics (organized by column from left to right):
- GOES Enhanced Infrared satellite image (upper left) – This image, obtained by a GOES (Geostationary Operational Environmental Satellite) measures the “heat” given off by clouds, large water bodies, land surfaces, and clouds. Using a special “enhancement” scale (see color bar at the bottom of the image, just below the NOAA logo), warmer colors appear as blues and greens and colder temperatures appear as yellows and reds. Note, that GOES satellite images on different web pages (or in different GWCC posts) may use different enhancement or “false color” image temperature scales. Colorized images, such as these, should always have their own color key.
- GOES Water Vapor satellite image (lower left) – This geostationary satellite image also measures “heat,” but the satellite sensors used are more sensitive to the amount and distribution of atmospheric water vapor. When the atmosphere at the middle and high altitudes is dry, infrared energy from lower altitudes (where temperatures are normally warmer) is able to escape to space and be detected by the GOES (Geostationary Operational Environmental Satellite) sensors. This image has been false-colored using a special “enhancement” scale: dry (black and orange), mid- and high-level moisture (white), and cloud-laden at mid- and high-levels (blue and green through red and purple).
- Storm Prediction Center (SPC) convective outlook (upper right) – SPC issues a wide array of severe weather and other thunderstorm-related guidance and outlook products. They also issue tornado and severe thunderstorm watches and fire weather outlooks. This image, which is often updated several times a day, shows expected thunderstorm and severe thunderstorm activity for “Day 1.” “Day 1” extends from the forecast time until the next 1200 GMT (Greenwich Mean Time or 8:00 a.m. E.D.T / 7:00 a.m. E.S.T. Favored areas for thunderstorm / severe thunderstorm activity are depicted as, “to the right of a line,” as shown by an arrow at the end of any line.
- National radar composite image (lower right) – This image brings together radar reflectivity data from some 100 plus radar sites throughout the contiguous 48 states. Radars measure how much energy atmospheric solids and liquids (hydrometeors such as snow, hail, and rain, as well as particles such as dense smoke and volcanic ash) reflect back to a radar site. The greater the reflectivity value (shown in dBz units), the greater the concentration of so-called “hydrometeors,” solids and other objects (e.g., birds, bats), the radar beam may intercept. The color scale ranges from blues and greens (the lowest reflectivities) to reds and purples (the highest reflectivities).
© 2017 H. Michael Mogil
Originally posted 4/7/17
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