Blowing dust in New Mexico, Texas, and Oklahoma

January 22nd, 2012 |
GOES-15 0.63 µm visible channel images (click image to play animation)

GOES-15 0.63 µm visible channel images (click image to play animation)

A large outbreak of blowing dust developed in the wake of a cold frontal passage across parts of New Mexico, Texas, and Oklahoma on 22 January 2012. At Lubbock, Texas winds gusted to 60 mph, and surface visibility was reduced to 0.5 mile. The strongest wind gust was 77 mph, farther to the north in the Texas panhandle region (NWS Lubbock summary). Early in the day, the consolidation of numerous smaller blowing dust plumes into a single large blowing dust “cloud” could be seen on 1-km resolution GOES-15 (GOES-West) 0.63 µm visible channel images (above; click image to play animation).

Later in the day, due to a more favorable forward scattering angle, the areal extent of the airborne blowing dust could be better seen on 1-km resolution 0.63 µm visible channel images from the GOES-13 (GOES-East) satellite (below; click image to play animation). The leading edge of the primary large dust plume began to move northeastward over Oklahoma, while a number of smaller dust plumes could be seen moving southeastward across the Oklahoma and Texas panhandle regions behind a secondary cold front. Note that the GOES-13 satellite had been placed into Rapid Scan Operations (RSO) mode, providing images as frequently as every 5-10 minutes.

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 250-meter resolution MODIS true color Red/Green/Blue (RGB) image from the SSEC MODIS Today site (below, viewed using Google Earth) displayed even greater detail in the structure of the blowig dust plume at 20:02 UTC.

Aqua MODIS true color Red/Green/Blue (RGB) image (displayed using Google Earth)

Aqua MODIS true color Red/Green/Blue (RGB) image (displayed using Google Earth)

There was also a bit of smoke mixed in with the blowing dust, due to a few small wildfires that were burning across the region. Three small wildfire “hot spots” (dark black to yellow pixels) could be seen on an AWIPS image of 1-km resolution MODIS 3.7 µm shortwave IR data at 20:00 UTC (below).

MODIS 3.7 µm shortwave IR image

MODIS 3.7 µm shortwave IR image

Over southern Oklahoma at 21:23 UTC a pilot reported that at an altitude of 9000 feet the flight level visibility was zero due to blowing dust (below).

GOES-13 0.63 µm visible channel image + Aircraft pilot report

GOES-13 0.63 µm visible channel image + Aircraft pilot report

A comparison of GOES, AVHRR, MODIS, and VIIRS IR images

January 19th, 2012 |
GOES-13 10.7 µm IR images + surface frontal analysis (click image to play animation)

GOES-13 10.7 µm IR images + surface frontal analysis (click image to play animation)

AWIPS images of 4-km resolution GOES-13 10.7 µm IR data (above; click image to play animation) showed a variety of cloud features across the central and southern US between 07:01 UTC and 09:30 UTC on 19 January 2012. In particular, note (1) the darker gray (warmer) low clouds streaming northward from the Gulf of Mexico into Texas, signalling a northward return flow of low-level moisture (Total Precipitable Water values of 15-25 mm); (2) a large lighter gray (colder) banner cloud extending downwind of the Rocky Mountains, due to northwesterly flow aloft interacting with the high terrain; and  (3) a long lighter gray (colder) cloud band exhibiting some transverse banding, associated with a strong 165-knot core jet stream flowing southeastward from Nebraska to Tennessee.

Below are corresponding examples of 1-km resolution IR images from polar-orbiting satellites from the 08:22 to 08:43 UTC time period. The oldest “legacy” instrument is the AVHRR, carried on the constellation of NOAA POES satellites. A newer instrument is the MODIS, carried on the NASA Aqua and Terra satellites. The most recently-launched satellite is the NASA NPP, which carries the VIIRS instrument.

POES AVHRR 12.0 µm IR image

POES AVHRR 12.0 µm IR image

Aqua MODIS 11.0 µm IR image

Aqua MODIS 11.0 µm IR image

NPP VIIRS M15 10.763 µm IR image

NPP VIIRS M15 10.763 µm IR image

NPP VIIRS 10.763 µm IR image (viewed using Google Earth)

NPP VIIRS 10.763 µm IR image (viewed using Google Earth)

Images such as these from polar-orbiting satellites are available less frequently that those from GOES, but they offer a more detailed view of cloud features due to improved spatial resolution. The more modern instruments such as MODIS and VIIRS also contain many more channels (or spectral bands) than are available from the current generation of GOES satellites. These additional bands allow the creation of a variety of quantitative satellite products.

For example, if we focus our attention on the low cloud features in Texas, using MODIS data we can be more descriptive in terms of the Cloud Type (water), Fog Depth (as deep as 1300 feet), and Probability of Marginal Visual Flight Rules MVFR (as high as 70-80%) or Probability of Instrument Flight Rules IFR (as high as 50-60%).

Strong cold front and a lee-side frontal gravity wave

January 17th, 2012 |
GOES-13 10.7 µm IR channel images (click image to play animation)

GOES-13 10.7 µm IR channel images (click image to play animation)

A strong cold front moved southward across the south-central US on 17 January 2012, dropping temperatures as much as 20 degrees F in 1-2 hours with wind gusts of 30-40 knots. The cold air behind the front (lighter gray enhancement) was clearly evident on AWIPS images of 4-km resolution GOES-13 10.7 µm IR channel data (above; click image to play animation).

GOES-13 6.5 µm water vapor channel images (click image to play animation)

GOES-13 6.5 µm water vapor channel images (click image to play animation)

As the cold front moved southward, a lee-side cold frontal gravity wave was seen along its leading edge on 4-km resolution GOES-13 6.5 µm water vapor channel images (above; click image to play animation). Note the very complex wave structure that was displayed on a 1-km resolution MODIS 6.7 µm water vapor channel image at 08:34 UTC (below). In addition, the MODIS water vapor image showed great detail in the mountain waves across parts of New Mexico and far southwestern Texas, as strong westerly flow was interacting with the terrain in that region.

MODIS 6.7 µm water vapor channel image + Surface frontal analysis

MODIS 6.7 µm water vapor channel image + Surface frontal analysis

 

Jayton, Texas NOAA Wind Profiler time series

Jayton, Texas NOAA Wind Profiler time series

As the cold front passed the Jayton, Texas NOAA wind profiler site (station identifier JTNT2) after about 12 UTC, the transition to a northeasterly flow of cold air was evident (above). Even though the depth of the cold air was not more than about 1.5 km, the lee-side cold frontal gravity wave was able to be seen on the water vapor imagery due to the fact that the cold, dry air mass shifted the peak of the GOES-13 water vapor weighting function down to within the 700-500 hPa pressure level — much lower than the height of the water vapor weighting function of the US Standard Atmosphere air mass (below).

Amarillo, Texas water vapor weighting function vs US Standard Atmosphere water vapor weighting function

Amarillo, Texas water vapor weighting function vs US Standard Atmosphere water vapor weighting function

 

Cold air and snowfall invade the Pacific Northwest

January 15th, 2012 |
POES AVHRR 0.86 µm visible channel + POES AVHRR 12.0 µm IR channel images

POES AVHRR 0.86 µm visible channel + POES AVHRR 12.0 µm IR channel images

A surge of cold air brought the first measurable snowfall to parts of the Pacific Northwest states on 14 January15 January 2012. The Seatle-Tacoma aiport received 2.4 inches of snow on 15 January. A comparison of 1-km resolution POES AVHRR 0.86 µm visible channel and 12.0 µm IR channel data (above) displayed a classic example of “open cell convection” — this type of open-cell mesoscale convective cloud pattern is a signature of strong instability (via boundary layer cold air advection over relatively warmer waters) in an environment of cyclonic flow.

A sequence of 1-km resolution POES AVHRR 12.0 µm IR channel images (below) showed the inland progression of the open cell convection, eventually producing snowfall at Seattle, Washington (station identifier KSEA) and Portland, Oregon (station identifier KPDX).

POES AVHRR 12.0 µm IR channel images

POES AVHRR 12.0 µm IR channel images