A striking display of the aurora borealis was seen on AWIPS images of Suomi NPP VIIRS 0.7 Âµm Day/Night Band data across Alaska (above) and across northern Canada (below) during the night-time (pre-dawn) hours on 17 December 2012. The corresponding VIIRS 11.45 Âµm IR channel images are also shown, to help distinguish cloud features (colder green to yellow to red color enhancedment) from the bright aurora signature on the Day/Night Band images.
An animation of 4-km resolution MTSAT-1R 10.8 Âµm IR images from the CIMSS Tropical Cyclones site (above) showed Category 4 Cyclone Evan passing just to the northwest of the Fiji island of Vanue Levu on 16 December 2012.
A closer view using a McIDAS image of 375-meter resolution Suomi NPP VIIRS 11.45 Âµm IR channel data at 13:12 UTC (below) revealed a number of concentric cloud-top gravity waves that were likely propagating outward away from the center of the tropical cyclone. The minimum IR brightness temperature in the core of the large yellow-enhanced area northwest of the eye was -98Âº C.
A subtle signature of these cloud-top gravity waves could also be seen on early-morning 1-km resolution MTSAT-1R 0.73 Âµm visible channel images (below).
===== 17 December Update =====
MTSAT-1R 10.8 Âµm IR images from 17 December (above) showed Cyclone Evan passing the western edge of the main isand of Fiji (Viti Levu), where it produced a wind gust to 90 knots (104 mph) at Nadi (station identifier NFFN).
AWIPS images of 4-km resolution GOES-13 10.7 Âµm IR channel images with overlays of surface reports and SPC storm reports (above; click image to play animation) showed the development of thunderstorms across the Panhandle region of Texas on 14 December 2012. As these storms intensified into an organized squall line, they produced small hail, widespread damaging winds, and 3 tornadoes. These tornadoes were the first tornadoes on record during the month of December in the Amarillo forecast area (NWS Amarillo news story).
A comparison of McIDAS images of GOES-15 (GOES-West) and GOES-13 (GOES-East) 0.63 Âµm visible channel images (below; click image to play animation) revealed an interesting cloud-top gravity wave structure with some of these thunderstorms.
1-km resolution POES AVHRR 0.86 Âµm visible channel images (above) and 12.0 Âµm IR channel images (below) showed the rapid development of a organized cluster of convection west of Amarillo (station identifier KAMA) between 20:24 UTC and 20:52 UTC (3:24 and 3:52 PM local time). Note how the surface winds were backing and becoming more southeasterly at Amarillo, likely helping to enhance surface convergence ahead of the approaching thunderstorms. To the south, winds were gusting in excess of 40 knots at Lubbock (station identifier KLBB), producing blowing dust reducing the surface visibility to 3 miles at times.
The Blended Total Precipitable Water (TPW) product (below; click image to play animation) showed the northward transport of moisture from the Gulf of Mexico during the day, with TPW values exceeding 20 mm or 0.79 inch (darker green color enhancement) across the eastern Texas Panhandle by the afternoon hours. These TPW values were in excess of 200 percent of normal for this region during this time of the year.
A few breaks in the widespread cloudiness across the region allowed a closer look at the moisture and instability ahead of the advancing cold front (HPC surface analysis), using 10-km resolution GOES-13 sounder Total Precipitable Water (above; click image to play animation) and GOES-13 sounder Lifted Index (below; click image to play animation) derived product imagery — TPW values were as high as 22 mm or 0.87 inch, and there were pockets of instabiity with LI values as low as -5.8Âº C in cloud-free areas where daytime heating was helping to destabilize the atmosphere.
A wide band of multi-layered clouds was oriented southwest-to-northeast along a cold frontal boundary moving through the Ohio River Valley region on 10 December 2012.Â On a 1-km resolution Suomi NPP VIIRS 11.45 Âµm IR image at 17:42 UTC (above), much of this cloud band was topped with cirrus clouds exhibiting IR brightness temperatures in the -50 to -60 C range (orange to red color enhancement), indicating a cloud top height in the 30,000-40,000 foot range (KILM rawinsonde data | KPIT rawinsonde data)– the general cruising altitudes of most aircraft.
It is interesting to note that the Suomi NPP VIIRS 3.74 Âµm shortwave IR image revealed a large number of contrails across that cloud band — the contrails appeared darker than the background cirrus clouds, due to reflection of solar radiation by smaller ice crystals or by supercooled water droplets. Either the contrails themselves were located above the cirrus cloud deck, or the aircraft were flying through the top portion of the cirrus clouds and altering the microphysics of the cloud ice crystals to make them smaller.
Similar contrails were seen about an hour later on a 1-km resolution MODIS 3.7 Âµm shortwave IR image (below).