Fog-related multiple-vehicle accident in eastern Texas

November 22nd, 2012 |
GOES-R IFR Probability product (click image to play animation)

GOES-R IFR Probability product (click image to play animation)

Dense fog was a factor in causing a multiple-vehicle accident (an estimated 140 vehicles involved; 2 fatalities; dozens of injuries requiring transport to hospitals) along Interstate 10 between Houston and Beaumont in eastern Texas on the morning of 22 November 2012. The GOES-R Instrument Flight Rules (IFR) Probability product (with the algorithm applied to GOES-13 data) showed that the likelihood of IFR conditions (visiblity less than 3 miles, and/or cloud bases less than 1000 feet) began to increase in coverage and magnitude over the area between Houston and Beaumont after around 08 UTC or 2 AM local time (above; click image to play animation), with the probability reaching the 80-90% range (darker red color enhancement) after 11 UTC or 5 AM local time.

According to media reports, the accident occurred around 14 UTC or 8 AM local time, near the “I-10” label on the eastbound portion of Interstate 10 that turned sharply northeastward toward Beaumont. There were no surface observations in the immediate vicinity of the accident, but the visibility had dropped as low as 1/4 mile at Houston (KHOU) and 4 miles an Beaumont (KBPT) during the pre-dawn hours.

The GOES-R Cloud Thickness product (again, with the algorithm applied to GOES-13 data) showed that the fog/low stratus feature near the accident site reached a maximum depth of around 1000 feet (cyan color enhancement) after 12 UTC or 6 AM local time (below; click image to play animation). For additional examples and information about these GOES-R Fog and Low Stratus (FLS) products, see the GOES-R Fog Product Examples blog or view the GOES-R FLS training material (VISITview | PowerPoint).

GOES-R Cloud Thickness product (click image to play animation)

GOES-R Cloud Thickness product (click image to play animation)

The traditional or “legacy” GOES-13 IR brightness temperature difference (BTD) “fog/stratus product” (below; click image to play animation) did exhibit a signal of fog and/or stratus (yellow to red color enhancement) increasing over that region, but part of that signal was being contaminiated by high cloud features (black enhancement) drifting overhead. In addition, the primary weakness of the legacy BTD fog/stratus product is that it does not provide the distinction between potentially hazardous fog on the ground and non-hazardous stratus clouds located above the surface.

GOES-13 IR brightness temperature difference "fog/stratus product" (click image to play animation)

GOES-13 IR brightness temperature difference “fog/stratus product” (click image to play animation)

Suomi NPP VIIRS IR BTD fog/stratus product images at 06:56 UTC or 12:56 AM local time and again at 08:35 UTC or 2:35 AM local time (below) also displayed a signal indicating that a well-defined fog/stratus feature was located over the area.

Suomi NPP VIIRS IR brightness temperature difference "Fog/stratus product"

Suomi NPP VIIRS IR brightness temperature difference “Fog/stratus product”

With higher spatial reolution (1 km) compared to GOES-13 (4 km), the Suomi NPP VIIRS IR BTD fog/stratus product image at 08:35 UTC (below) did a better job at showing the signal of fog/stratus in the area, even through the patches of high clouds (black enhancement) that were drifting overhead.

GOES-13 and Suomi NPP VIIRS IR brightness temperature difference "Fog/stratus product" images

GOES-13 and Suomi NPP VIIRS IR brightness temperature difference “Fog/stratus product” images

The fog began to burn off rather quickly after sunrise — however, the fog feature over the Interstate 10 accident area could still be seen on a POES AVHRR 0.63 µm visible channel image about 1 hour after the accident at 15:10 UTC or 9:10 AM local time (below). By this time, the surface visibility had improved to 3 miles at Houston (KHOU) and 10 miles at Beaumont (KBPT).

POES AVHRR 0.63 µm visible channel image

POES AVHRR 0.63 µm visible channel image

Using VIIRS imagery to help diagnose complex Gulf of Alaska circulations

November 21st, 2012 |
Suomi NPP VIIRS 11.45 µm IR image with surface analysis

Suomi NPP VIIRS 11.45 µm IR image with surface analysis

The National Weather Service forecast office at Juneau, Alaska mentioned their use of Suomi NPP VIIRS imagery:

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
553 AM AKST WED NOV 21 2012

.SHORT TERM…SOMEWHAT COMPLICATED PATTERN IN THE GULF AND NORTHEAST PACIFIC THIS MORNING. THERE ARE AROUND 4 SEPARATE
CIRCULATION CENTERS VISIBLE ON IR AND VIIRS NIGHTTIME VISIBLE IMAGES. THE STRONGEST IS WEST OF DIXON ENTRANCE CURRENTLY AND IS SLOWLY WEAKENING AS IT REMAINS NEARLY STATIONARY. A SECOND LOW IS JUST SE OF KODIAK ISLAND, A THIRD IS AROUND 50N 140W, AND THE FOURTH IS A VERY WEAK ONE OVER HAIDA GWAII.

AWIPS images of Suomi NPP VIIRS 11.45 µm IR channel (above) and 0.7 µm Day/Night Band data (below) at 12:14 UTC or 3:14 AM local time on 21 November 2012 showed the cloud features associated with the complex pattern over the Gulf of Alaska at that particular time (comparison of IR and Day/Night Band images).

Items of interest to note on the VIIRS IR image: (1) wave clouds well downwind (to the south of) the Aleutian Islands, where northerly winds were as strong as gale force, and (2) large patches of fog and stratus clouds (VIIRS IR brightness temperature difference “Fog/stratus product”) across parts of the Yukon, east-central Alaska, and the North Slope region of Alaska.

Interesting features to point out on the Day/Night Band image include: (1) the bright city lights of populated areas such as Anchorage and Fairbanks, (2) bright northwest-to-southeast oriented swaths of the Aurora Borealis across parts of Alaska and the Yukon, as well as just off the Arctic Ocean coastline, and (3) the cluster of bright lights associated with drilling activity in the Prudhoe Bay oil field area along the northern coast of Alaska.

Suomi NPP VIIRS 0.7 µm Day/Night Band image with surface analysis

Suomi NPP VIIRS 0.7 µm Day/Night Band image with surface analysis

A comparison of GOES-15 10.7 µm IR and Suomi NPP VIIRS 11.45 µm IR images (below) shows that in far northern latitudes the superior spatial resolution of imagery from polar-orbiter satellites provides much clearer view of many of the the various cloud features.

Suomi NPP VIIRS 11.45 µm IR and GOES-15 10.7 µm IR images

Suomi NPP VIIRS 11.45 µm IR and GOES-15 10.7 µm IR images

Total solar eclipse shadow crossing northeastern Australia and the South Pacific Ocean

November 13th, 2012 |
MTSAT-1R 0.7 µm visible channel images

MTSAT-1R 0.7 µm visible channel images

The shadow from a total solar eclipse could be seen moving east-southeastward across northeastern Australia and the adjacent waters of the South Pacific Ocean on Japanese MTSAT-1R 0.7 µm visible channel images (above).

The solar eclipse shadow was also evident on a visible image from the Korean COMS-1 satellite (below).

COMS-1 visible channel image

COMS-1 visible channel image

As the eclipse shadow continued to move eastward, it was seen on a US NOAA GOES-15 0.63 µm visible channel image (below).

GOES-15 0.63 µm visible channel image

GOES-15 0.63 µm visible channel image

Mesoscale lake-effect snow bands: the Great Salt Lake, and the Missouri River

November 11th, 2012 |
GOES-15 (left) and GOES-13 (right) 0.63 µm visible images (click image to play animation

GOES-15 (left) and GOES-13 (right) 0.63 µm visible images (click image to play animation

Cold air flowing southeastward across the Great Salt Lake in Utah had enough of a fetch over the warm waters to help set up a well-defined lake-effect snow (LES) band that produced several inches of snowfall downwind of the lake at Salt Lake City on 11 November 2012. The LES band could be seen in McIDAS images of GOES-15 (GOES-West) and GOES-13 (GOES-East) 0.63 µm visible channel data (above; click image to play animation).

AWIPS images of POES AVHRR 0.63 µm visible channel and 10.8 µm IR channel data (below) showed that IR cloud top brightness temperatures within the LES band were as cold as -27º C (darker blue color enhancement).

POES AVHRR 0.63 µm visible channel and 10.8 µm IR channel images

POES AVHRR 0.63 µm visible channel and 10.8 µm IR channel images

On the previous day, the MODIS Sea Surface Temperature (SST) product (below) indicated that mid-lake SST values were as warm as 51.5º F (light green color enhancement) — so the cold air flowing over the warm waters created a very unstable lower-tropospheric thermal profile that aided the development of the lake-effect snow band. For more discussion on this particular case, see a write-up on The Weather Channel site.

MODIS Sea Surface Temperature product

MODIS Sea Surface Temperature product

Meanwhile, farther to the east in South Dakota, cold arctic air was flowing southeastward across the still-unfrozen waters of the Missouri River (whose flow is controlled by several dams that create large reservoirs such as Lake Oahe and Lake Sharpe). Even though the fetch of the cold air across the water was relatively small, there were still a number of “lake-effect” or “river-effect” cloud bands seen on GOES-13 0.63 µm visible channel images (below; click image to play animation) — in particular, a long and well-defined cloud band extending downwind of the large horseshoe-shaped oxbow bend in Lake Sharpe. Such lake-effect clouds were also described in 2009 and 2008 on this blog.

GOES-13 0.63 µm visible channel images (click image to play animation)

GOES-13 0.63 µm visible channel images (click image to play animation)

A comparison of AWIPS images of MODIS 0.65 µm visible channel and a false-color Red/Green/Blue (RGB) composite (below) demonstrated the value of using RGB imagery to help discriminate between snow cover (enhanced in darker shades of red) and supercooled water droplet clouds (which appear as varying shades of white).

MODIS 0.64 µm visible channel and false-color Red/Green/Blue (RGB) images

MODIS 0.64 µm visible channel and false-color Red/Green/Blue (RGB) images

A closer view using 250-meter resolution MODIS true-color and false-color RGB images from the SSEC MODIS Today site (below) showed even greater detail in the structure of these cloud bands downwind of the Missouri River in South Dakota. In this RGB image, snow cover appeared as shades of cyan.

MODIS true-color and false-color Red/Green/Blue (RGB) images

MODIS true-color and false-color Red/Green/Blue (RGB) images