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

Hat tip to Chad Gravelle (CIMSS), who asked about the curious pattern of trailing edge cloud clearing across South Carolina on the morning of 28 November 2012. Given that the etiology of these elongated cloud clearing line features is unknown at this point, this case is a perfect candidate for the “What the heck is this?” blog category. An animation of GOES-13 0.63 µm visible channel images (above; click image to play animation) shows the unusual cloud edge clearing pattern moving southwestward across South Carolina.

These cloud features were also seen on an AWIPS image of POES AVHRR 0.63 µm visible channel data at 13:53 UTC (below). Surface observations showed that air with drier dew point values was being advected southwestward into the trailing cloud edge, but the wind speeds were generally light at most reporting sites — so the cause of the elongated “clear slot” features is unclear.

POES AVHRR 0.63 µm visible channel image

The three POES AVHRR products shown below indicated that these trailing edge cloud features were liquid water clouds, which exhibited cloud top temperature values of +1 to +3º C, with a cloud top height value of 2 km.

POES AVHRR Cloud Type product

POES AVHRR Cloud Top Temperature product

POES AVHRR Cloud Top Height product

On the GOES-13 and POES AVHRR images, you can see some evidence of similar cloud edge clearing lines over the Alabama/Georgia border region. During the previous overnight hours, this cloud signature was very well-defined over Georgia, as seen on a Suomi NPP VIIRS 0.7 µm Day/Night Band “night-time visible image” at 06:43 UTC or 1:43 AM local time (below).

Suomi NPP VIIRS 0.7 µm Day/Night Band image

View only this post Read Less

GOES-13 3.9 µm shortwave IR images (click image to play animation)

4-km resolution GOES-13 3.9 µm shortwave IR channel images (above; click image to play animation) detected a number of “hot spots” (black to yellow to red colored pixels) due to widespread small agricultural fires that were burning across parts of the southeastern US on 26 November 2012. This type of burning is a common practice to clear debris from fields and prepare them for future planting of crops.

Suomi NPP VIIRS 3.74 µm shortwave IR image

A 1-km resolution Suomi NPP VIIRS 3.74 µm shortwave IR image at 18:45 UTC (above) showed many more very small hot spots across the region. A comparison of this VIIRS image with the corresponding GOES-13 image (below) showed some interesting differences. First of all, the higher spatial resolution of the VIIRS data (375 meters, re-mapped onto a 1-km AWIPS grid) detected a greater number of the smaller fires, compared to the more coarse (4 km resolution) GOES data. Secondly, even though the image times were close (GOES-13 was scanning the region at 18:49 UTC, while the Suomi NPP satellite was passing over at 18:47 UTC), a couple  of the fires in Georgia exhibited hotter IR brightness temperatures on the GOES image. As can be inferred from the GOES animation, many of these fires were fairly short-lived, so GOES may have been scanning the area when those particular fires were flaring up to their largest size.

GOES-13 3.9 µm and Suomi NPP VIIRS 3.74 µm shortwave IR channel images

If you look at the adjacent offshore waters in the VIIRS and GOES shortwave IR images above, you can see the warmer signature (darker gray enhancement) of the Gulf Stream. A comparison of 1-km resolution MODIS Sea Surface Temperature (SST) product images at 15:22 UTC and 18:40 UTC (below) revealed some very intricate structure to the axis of the Gulf Stream, with a number of cold and warm eddy features. Note the very sharp SST gradient along the north wall of the Gulf Stream, off the coast of North Carolina: the SST values change from 60s F (green colors) to 70s F (orange colors) over a very short distance.

MODIS Sea Surface Temperature product images

A comparison of the MODIS SST product with the Real-time, global, sea surface temperature (RTG_SST_HR) analysis (below) showed that the model was unable to resolve many of the smaller eddy features — so the model SST values were as much as 5-10 degrees F different in some of those locations.

MODIS Sea Surface Temperature + RTG_SST_HR model analysis

View only this post Read Less

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)

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)

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”

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

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

View only this post Read Less

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

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

View only this post Read Less