Blowing dust event in Texas and New Mexico

October 18th, 2011 |
GOES-11, GOES-15, and GOES-13 visible channel images (click image to play animation)

GOES-11, GOES-15, and GOES-13 visible channel images (click image to play animation)

A major blowing dust event occurred in the wake of a strong cold frontal boundary that moved rapidly southward across western Texas and eastern New Mexico late in the day on 17 October 2011 — the blowing dust reduced surface visibilities to near zero in some locations as winds gusted as high as 75 mph (see NWS Lubbock story). McIDAS images of GOES-11 (GOES-West), GOES-15, and GOES-13 (GOES-East) visible channel data during the daylight hours and shortwave IR data after sunset (above; click image to play animation) showed the southward propagation of the well-defined arc of blowing dust (or “haboob”), along with the surge of cooler air behind the cold front. A few wildfire “hot spots” (darker black pixels) were also evident on the GOES shortwave IR images, a result of fires started by downed power lines.

Much of that region had been experiencing long-term extreme to exceptional drought conditions — and an AWIPS image of the MODIS Normalized Difference Vegetation Index (below) showed very low NDVI values across much of western Texas the day before the dust storm.

MODIS Normalized Difference Vegetation Index

MODIS Normalized Difference Vegetation Index

 

The first 0ºF (-18ºC) temperature of the season in Alaska

October 12th, 2011 |
GOES-11 10.7 µm IR images

GOES-11 10.7 µm IR images

The first “official” 0ºF (-18ºC) temperature of the 2011/2012 winter season in Alaska was recorded at Anaktuvuk Pass on 12 October 2011. AWIPS images of “4-km resolution” GOES-11 10.7 µm IR data (above) indicated that portions of the Brooks Range in northern Alaska were beginning to exhibit IR brightness temperatures of -20ºC and colder (cyan to blue color enhancement), with Anuktuvuk Pass (station identifier PAKP) situated between a quasi-stationary deck of colder (darker blue) clouds to the east and another area of multi-layered clouds approaching from the west. Due to the very large viewing angle from the geostationary GOES-11 satellite positioned over the equator, the effective resolution of the IR pixels over northern Alaska was actually on the order of 10-15 km.

A more detailed view was available using a 1-km resolution POES AVHRR 12.0 µm IR image at 05:40 UTC (below), which did a better job of portraying the arc of colder (-20ºC to -28ºC, cyan to darker blue) high-elevation portions of the Brooks Range, as well as the boundaries of the cloud deck that was covering parts of northeastern Alaska. With calm winds and no clouds at Anaktuvuk Pass, strong radiational cooling allowed the temperature to get much colder than adjacent areas with a blanket of cloud cover.

POES AVHRR 12.0 µm IR image

POES AVHRR 12.0 µm IR image

The corresponding 05:40 UTC POES AVHRR Cloud Top Height product (below) showed that the northeastern Alaska cloud deck extended to heights of 3-4 km (darker violet color enhancement).

POES AVHRR Cloud Height product

POES AVHRR Cloud Height product

A MODIS Cloud Type product at 07:03 UTC (below) indicated that the cloud deck covering northeastern Alaska was primarily a “mixed phase” (supercooled water and ice, darker green color enhancement) feature.

MODIS Cloud Type product

MODIS Cloud Type product

Tropical Storm Jova: very cold cloud top IR temperatures

October 7th, 2011 |
GOES-15 10.7 µm IR images (click image to play animation)

GOES-15 10.7 µm IR images (click image to play animation)

GOES-15 10.7 µm IR images (above; click image to play animation) showed a large area of very cold cloud top IR brightness temperatures associated with Tropical Storm Jova over the East Pacific Ocean on 07 October 2011. Embedded within the large region of cloud top IR temperatures colder than -80º C (light purple color enhancement) were smaller areas that exhibited cloud top IR temperatures of -90º C or colder (dark purple color enhancement) — and the coldest cloud top IR brightness temperature seen was -94.65º C at 09:30 UTC. It is unusual to see cloud top IR brightness temperatures of -90º C or colder on 4-km resolution GOES IR imagery.

===== 10 October Update =====

A comparison of GOES-11 (GOES-West), GOES-15, and GOES-13 (GOES-East) visible channel images (below) showed the eye of Category 3 Hurricane Jova on 10 October 2011. Note how the difference in satellite viewing angle produces very different eyewall illumination characteristics.

GOES-11, GOES-15, and GOES-13 visible channel images

GOES-11, GOES-15, and GOES-13 visible channel images

GOES-15 is scheduled to replace GOES-11 as the operational GOES-West satellite in December 2011.

Okreek Fire in south-central South Dakota

October 5th, 2011 |
GOES-11 + GOES-15 + GOES-13 visible channel images

GOES-11 + GOES-15 + GOES-13 visible channel images

Strong southerly winds (gusting as high as 50 mph) helped a large grassland fire (named the Okreek fire) spread rapidly northward across south-central South Dakota during the afternoon hours on 05 October 2011. The light gray smoke plume and the dark burn scar grew very quickly, which could be seen on GOES-11 (GOES-West),  GOES-15, and GOES-13 (GOES-East) visible channel images (above). Each of the 3 sets of images is displayed in the native projection of the respective satellite.

The corresponding 3.9 µm shortwave IR images from each satellite (below) showed the large and intense “hot spot” (dark black to yellow pixels) associated with the Okreek fire. Note there were also a few other smaller fires burning in other parts of central South Dakota during that time period, which also exhibited very intense hot spot signatures.

GOES-11 + GOES-15 + GOES-13 shortwave IR images

GOES-11 + GOES-15 + GOES-13 shortwave IR images

A comparison of 250-meter resolution false-color Red/Green/Blue (RGB) images from the SSEC MODIS Today site from before (04 October), during (05 October), and after (07 October) the Okreek fire revealed the development and growth of the 26 mile long burn scar (which appears as the light brown line). The bright pink feature on the 05 October image was the heat signature of the active front line of the fire, which was rapidly advancing northward on that day.

MODIS false-color RGB images from 04 October, 05 October, and 07 October 2011

MODIS false-color RGB images from 04 October, 05 October, and 07 October 2011