MODIS visible, cirrus, 3.7 µm IR, and water vapor images

Strong winds were producing plumes of blowing dust across parts of southeastern New Mexico and the  Texas panhandle region on 14 December 2008 — this blowing dust was reducing surface visibility to 1 mile at Lubbock, Texas (station identifier KLBB). AWIPS images of the MODIS visible, “cirrus detection”, 3.7 µm shortwave IR, and 6.7 µm water vapor channels (above) showed the plumes around 19:51 UTC. The plumes of airborne aerosols exhibited a lighter gray “hazy” appearance on the visible image (and to a lesser extent on the “cirrus detection” image, due to that channel’s sensitivity to particles that scatter light).

In addition, there was a small cluster of hot MODIS 3.7 µm IR pixels with a maximum temperature of 46º C located just northwest of Hobbs, New Mexico (station identifier KHOB), due to a grass fire that was burning in that area (MODIS 3.7 µm image) — and 250-meter resolution MODIS true color imagery (below) confirmed the presence of a lighter-colored smoke plume embedded within the longer orange-colored blowing dust plume. The burn scar from this fire was clearly evident on MODIS true color imagery (viewed using Google Earth) on the following day (located between Lovington and Maljamar, New Mexico).

MODIS true color image

The strong winds (which gusted as high as 71 mph at Tatum, New Mexico) were producing mountain waves immediately downwind of the higher terrain in the “Big Bend region” of Texas — a comparison of 1-km resolution MODIS 6.7 µm and 4-km resolution GOES-12 6.5 µm water vapor images (below) demonstrated the value of better spatial resolution for detecting such mesoscale phenomena.

MODIS 6.7 µm and GOES-12 6.5 µm water vapor images

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MODIS visible and "snow/ice channel" images

A major ice storm impacted much of the Northeast US on 11 December – 12 December 2008 — many locations across that region experienced several hours of freezing rain, leading to widespread ice accumulations of 0.5 to 1.0 inch which brought down tree limbs and power lines (causing power outages for an estimated 1 million customers). After the storm, AWIPS images of the MODIS visible and near-IR “snow/ice” channel from the morning of 13 December 2008 (above) offered some clues as to the areal coverage of the more significant ice accrual. Since snow and ice are strong absorbers of radiation at the near-IR 2.1 µm wavelength,  the darkest areas on the snow/ice image are areas where the thickest accrual of ice occurred (although lakes and other bodies of water also appear as dark black features). Note that some of the darker ice-covered areas on the snow/ice image do not look as “bright” on the visible image as adjacent areas with deeper snow cover, since the ice (without a layer of snow on top) is generally more “translucent” or light gray in appearance than the brighter white snow cover.

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GOES-12 6.5 µm water vapor images

An unusually-early snowfall event occurred in parts of Louisiana and Mississippi on 11 December 2008. AWIPS images of GOES-12 6.5 µm water vapor images (above) revealed a well-defined axis of a deformation zone pivoting over the region that received the heaviest snowfall. The GOES sounder Total Column Ozone product (below) showed values in the 350-400 Dobson Unit range (bright green to red colors), indicative of the lowering dynamic tropopause associated with the intensifying disturbance.

GOES sounder Total Column Ozone product

MODIS visible, 11.0 µm IR, and 6.7 µm water vapor images at 19:19 UTC (below) showed a narrow banding structure in place over the area where moderate to heavy snowfall was falling at the time.

MODIS visible, 11.0 µm IR, and 6.7 µm water vapor images

SSEC MODIS Today true color imagery from the following day (below, displayed using Google Earth) displayed a large area where snow remained on the ground. The highest snowfall accumulations included 9 inches at New Hebron in Mississippi and 8 inches at Amite in Louisiana. For locations such as Beaumont/Port Arthur in Texas and Lake Charles, Baton Rouge and New Orleans in Louisiana, this was the earliest snowfall on record.

MODIS true color image on 12 December (displayed using Google Earth)

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GOES-13 6.5 µm water vapor images

A minor “high wind event” was noted in Boulder, Colorado on 01 December – 02 December 2008, when  winds gusted as high as 48 mph during the night-time hours. GOES-13 6.5 µm water vapor channel images (above) showed the formation of mountain waves clouds over the Foothills region of Colorado, as the westerly winds began to increase at Boulder (located in the center of the images). Curiously, Boulder was the only location what experienced the strong winds — and their winds were light southerly until around 18:00 UTC on 01 December (below).

Boulder, Colorado meteorogram

A comparison of GOES-12 and GOES-13 6.5 micrometer water vapor images (below) showed that a distinct warm/dry “hydraulic jump” signature formed immediately downwind of the highest terrain. Even though both GOES-12 and GOES-13 have a 4-km resolution water vapor channel, the better viewing angle afforded by the position of GOES-13 at 105º West longitude allowed a clearer depiction of the hydraulic jump (there was an outage of GOES-12 images during the 17:00-21:30 UTC period, due to a GOES-12 North-South station-keeping maneuver).

GOES-12 and GOES-13 6.5 µm water vapor images

AWIPS images of the 1-km resolution MODIS and the 4-km resolution GOES-12 water vapor images (below) showed that the hydraulic jump was well-defined at that time, with one pilot report of moderate to severe turbulence at a flight level of 18,000 feet seen over the area of the warm/dry hydraulic jump signature on water vapor imagery.

MODIS 6.7 µm and GOES-12 6.5 µm water vapor images

Note that the position of the warm/dry hydraulic jump signature was slightly farther to the west on the MODIS water vapor image — this placed the hydraulic jump closer to the spine of the highest terrain as seen on an AWIPS-2 image of the topography (below). The large viewing angle of the GOES satellite does not allow as accurate of a placement of such mesoscale features (compared to the more direct viewing angle of an overpassing polar orbiter satellite).

AWIPS-2 topography image

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