EUMETSAT Meteosat-9 0.635 µm visible channel images (click image to play animation)

McIDAS images of EUMETSAT Metosat-9 0.635 µm visible channel images (above; click image to play animation) showed a very large outbreak of airborne Saharan dust streaming off the continent of Africa and moving west-southwestward out over the adjacent waters of the eastern Atlantic Ocean on 07 February 2012. In addition, a pair of long von Karman vortex streets can be seen moving southwestward from the Cape Verde islands.

While the viewing angle was more extreme, the Saharan dust could also be seen on GOES-13 0.63 µm visible channel images (below).

GOES-13 0.63 µm visible channel images + surface reports

The emergence of this Saharan dust over water can be seen to occur around 00:00 UTC on 06 February on the Meteosat-9 Saharan Air Layer tracking product (below).

EUMETSAT Meteosat-9 Saharan Air Layer tracking product

GOES-13 fog/stratus product (click image to play animation)

AWIPS images of the 4-km resolution GOES-13 10.7 µm – 3.9 µm “fog/stratus product” (above; click image to play animation) showed a large area of fog and/or stratus (yellow to orange color enhancement) that was increasing in areal coverage during the pre-dawn hours on 06 February 2012. Although the fog/stratus product is useful for locating the presence and temporal trends of such features, it does not offer any reliable indication of whether it is fog on the ground or stratus cloud aloft.

One product that attempts to give the forecaster some quantitative information is the GOES Low CLoud Base (LCB) prodcut (below; click image to play animation), which attempts to blend surface observations with satellite data to indicate whether the cloud base is above or below the threshold of 1000 feet.

GOES-13 Low Cloud Base product (click image o play animation)

With 1-km resolution data, the MODIS instrument aboard the polar-orbiting Terra and Aqua satellites offers a similar “fog/stratus product” (below) that provides better clarity, especially regarding the exact location of the edges of the fog and/or stratus.

MODIS fog/stratus product images

In this particular case, a number of locations beneath the western and southern edge of the fog/stratus feature were expereincing freezing fog (below) and visibilities of 1/4 mile or less, which was creating hazardous road conditions and prompting the issuance of Freezing Fog Advisories.

MODIS fog/stratus product with METAR surface reports

As part of CIMSS participation in GOES-R Proving Ground activities, products are being developed which can provide more quantitative information about such parameters as Fog Depth and the Probability of Marginal Visual Flight Rules (MVFR) or Instrument Flight Rules (IFR) conditions (below). In this case, across the southwestern part of Iowa (where widespread freezing fog was being reported), the fog depth was as high as 1400-1500 feet, with probabilities of MVFR and IFR conditions as high as 75-90% and 60-75%, respectively.

MODIS Fog Depth, MVFR Probability, and IFR Probability products

Shortly after sunrise, it is interesting to note that a comparison of 1-km resolution POES AVHRR 0.63 µm visible channel, 3.74 µm “shortwave IR” channel, and 10.8 µm channel “IR window” channel images (below) revealed that part of the swath of fresh snow cover (as deep as 4-6 inches) across western Iowa could be seen through the translucent western edge of the fog/stratus deck that was beginning to burn off during the morning hours. The fog/stratus deck appears warmer (darker gray enhancement) om the 3.74 µm image, due to the sensitivity of that channel to the reflection of solar radiation off the tops of supercooled water droplet clouds.

Farther to the south, note the presence of narrow fingers of valley fog in the Ozark Mountains and surrounding regions in Oklahoma, Arkansas, and Missouri.

POES AVHRR 0.63 µm visible, 3.74 µm "shortwave IR", and 10.8 µm "IR window" images

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

AWIPS images of 4-km resolution GOES-13 6.5 µm water vapor channel data (above; click image to play animation) showed the middle-tropospheric circulation and cloud features associated with the large storm system which brought heavy snow, heavy rainfall, and severe thunderstorms to much of the central US on 03 February – 04 February 2012. Snowfall amounts included 51.1 inches at Pinecliffe, Colorado, 26.0 inches at Laramie, Wyoming, 17.0 inches at Tyron, Nebraska, and 11.5 inches at Cumberland, Iowa.

Denver received 15.9 inches of snow during 02/03/04 February, setting a new 3-day record accumulation for the month of February. Boulder also set a new single-storm snowfall record, with 22.7 inches of snowfall (NWS Denver/Boulder CO storm summary).

POES AVHRR 0.63 µm visible channel + 3.74 µm shortwave IR channel images

As the storm departed, a comparison of AWIPS images of 1-km resolution POES AVHRR 0.63 µm visible channel and 3.74 µm shortwave IR data (above) at 15:06 UTC (8:06 am local time) on 04 February showed that some low clouds persisted across much of northeastern Colorado, backed up against the highest terrain of the Continental Divide in some places. The low clouds showed up as darker gray features on the shortwave IR image, due to the sensitivity of reflection of solar radiation off of cloud top supercooled water droplets at the 3.74 µm wavelength.

At 17:47 UTC (10:47 am local time), a comparison of AWIPS images of 1-km resolution MODIS 0.65 µm visible channel data with the corresponding MODIS false-color Red/Green/Blue (RGB) image (created using MODIS channel 01/07/07 as the red/green/blue components of the image) indicated that most of the low clouds (which appeared as varying shades of white on the false-color image) had dissipated, revealing a good deal of the snow cover (which appeared as darker shades of red on the false-color image). A few streaks of high-level cirrus clouds could also be seen over the snow cover. Bare ground appeared cyan on the false-color image.

MODIS 0.65 µm visible channel + False-color Red/Green/Blue (RGB) images

About 2 hours later, a more detailed example of using false color images to discriminate between snow cover and supercooled water droplet clouds can be seen with a 375-meter resolution Suomi NPP VIIRS Red/Green/Blue (RGB) image (below), created using Band I1 (0.64 micrometer visible) as the red component and Band I3 (1.61 micrometer near-IR) as the green and blue components of the image.

Suomi NPP VIIRS false color RGB image

Farther to the east and south, heavy rainfall amounts included 9.30 inches at Romayer, Texas, 5.69 inches at Alexandria, Louisiana, and 4.34 inches at Medicine Lodge, Kansas. Wichita, Kansas received 2.86 inches of rain — the wettest February day on record at that location. Severe thunderstorms produced one tornado and hail up to 2.0 inches in diameter in Texas (SPC storm reports). A McIDAS image of 375-meter resolution Suomi NPP VIIRS 11.45 µm IR channel data (below) showed very intricate detail to the cloud top IR brightess temperature structure associated with strong thunderstorms producing heavy rainfall and flash flooding across the Interstate 35 corridor in the Austin/San Antonio, Texas region during the pre-dawn hours on 04 February. VIIRS IR brightness temperatures were as cold as -81º C with the far southwestern storm — and rare “warm trench” signatures (a ring of warmer cloud top temperatures surrounding a well-defined cold overshootng top) were seen associated with the 2 storms located near Austin-Bergstrom International airport (KAUS) and Houston County Airport (KDKR).

Suomi NPP VIIRS 11.45 µm IR image + Station locations and Interstate highways

===== 05 February Update =====

A large portion of the resulting swath of snow on the ground across parts of Wyoming, Colorado, Nebraska, and Kansas could be seen on a 250-meter resolution MODIS true color RGB image from the SSEC MODIS Today site (below, viewed using Google Earth) at 20:17 UTC on 05 February 2012.

MODIS true color image (viewed using Google Earth)

Suomi NPP VIIRS visible and IR images of the eye of Tropical Cyclone Funso

On 24 January 2012 NASA renamed the recently-launched NPP satellite (formerly known as the NPOES Preparatory Project)  the Suomi National Polar-orbiting Partnership (or Suomi NPP) in honor of Dr. Verner Suomi, recognized as “the father of satellite meteorology” (see: NASA News | University of Wisconsin News). A comparison of Suomi NPP 375-meter resolution VIIRS 0.640 µm visible channel and 11.450 µm IR channel images (above) showed the eye of Category 4 Tropical Cyclone Funso, which was located in the Mozambique Channel between Africa and Madagascar at 11:02 UTC on 24 January (track of Tropical Cyclone Funso).

On 25 January 2012, another Suomi NPP 375-meter resolution VIIRS 11.450 µm IR image (below) displayed very cold cloud top IR brightness temperatures (as low as -77º C) associated with a large thunderstom complex over Texas — this storm produced hail up to 1.25 inches in diameter (SPC storm reports) and heavy rainfall of up to 9.29 inches at Uhland (NWS Austin/San Antonio Texas Public Information Statement).

Suomi NPP VIIRS 11.450 µm IR image

The corresponding 4-km resolution GOES-13 (GOES-East) 10.7 µm IR image (below) showed much less structure to the cloud top temperature field, with the coldest IR brightness temperature being -70º C.

GOES-13 10.7 µm IR image

GOES-13 10.7 µm IR channel images + severe weather reports (click image to play animation)

A major outbreak of severe thunderstorms along a strong cold frontal boundary swept eastward across much of the southeastern US on 22 January – 23 January 2012, producing widespread damaging winds, large hail, and tornadoes (SPC storm reports). Two tornadoes produced EF-3 damage in Alabama. AWIPS images of 4-km resolution GOES-13 10.7 µm IR channel data with overlays of severe weather reports (above; click image to play animation) showed the cold cloud top IR brightness temperatures of -60 to -70 C (red to black color enhancement) associated with some of the strongest storms. For more information, see summaries from the National Weather Service forecast offices at Litttle Rock AR, Jackson MS, and Birmingham AL.

POES AVHRR 12.0 µm and MODIS 11.0 µm IR images

A sequence of 1-km resolution POES AVHRR 12.0 µm IR and MODIS 11.0 µm IR images (above) displayed greater detail in the storm top thermal structures, with a number of  -70 to -80 C (black to light gray color enhancement) IR brightness temperature values seen on the higher resolution imagery.

Of particular interest was what appeared to be some sort of “cloud trench” oriented from north to south across Tennessee around 08:00 UTC, which exhibited significantly warmer MODIS 11.0 µm IR brightness temperatures and a warmer/drier signal on the corresponding MODIS 6.7 µm water vapor image (below). This feature was also apparent on a few of the 4-km resolution GOES-13 IR images around that time. The etiology of this satellite signature is unclear at this time.

MODIS 11.0 µm IR channel and 6.7 µm water vapor channel images

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)

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)

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

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 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

Aqua MODIS 11.0 µm IR image

NPP VIIRS M15 10.763 µm IR image

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%).

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)

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

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

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

Snowfall amounts as high as 10-15 inches fell across parts of west Texas and southeast New Mexico on 09 January 2012 as a strong upper level disturbance moved across that region (NWS Lubbock TX storm summary). On the following morning, a comparison of GOES-15 (GOES-West) and GOES-13 (GOES-East) 0.63 µm visible channel images (above; click image to play animation) showed the areal coverage of the snow cover that remained on the ground. Note how the patch of snow began to melt from the outer edges inward as the full day of sunshine warmed the ground surface. Also note the curious “donut hole” of bare ground on the northern end of the main snow cover — this feature rapidly disappeared, as the snow depth associated with this feature was not very high.

A comparison of 250-meter resolution MODIS true color and false color Red/Green/Blue (RGB) images from the SSEC MODIS Today site (below) showed greater detail in the snow cover (snow on the ground appears as darker shades of cyan on the false color image) at 18:02 UTC.

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

A comparison of AWIPS images of MODIS 0.65 µm visible channel data and the corresponding false color RGB image (below) offered another tool that can be used to discriminate between snow cover (which in this example appears as darker shades of red on the false color image) and supercooled water droplet clouds (which appeared as varying shades of white).

MODIS 0.65 µm visible image + MODIS false color RGB image

A comparison of the MODIS 0.65 µm visible image with the corresponding MODIS Land Surface Temperature (LST) product (below) revealed how the deep snow cover was helping to keep surface air temperatures significantly colder than adjacent regions with bare ground. MODIS LST values were in the low to middle 30s F across the deeper snow cover, in the upper 40s to low 50s F in the “donut hole” region where the snow had just melted, and in the 60s F to the north over bare ground. Also note how the urban areas of Midland and Odessa stand out in the LST image, with LST values in the low to middle 40s F.

MODIS 0.65 µm visible image + MODIS Land Surface Temperature product

The mechanism for the creation of the “donut hole” snow cover feature is unclear at this point. A comparison the MODIS Land Surface Temperature product with the regional topography (below) seems to suggest that this feature was not topographically-driven.

MODIS Land Surface Temperature product + Topography

The MODIS true color image viewed using Google Earth (below) showed that the community of Brownfield (which did received about an inch of snowfall the previous day) was aptly named, being located within the brown-colored snow-free region at 18:02 UTC.

MODIS true color image (viewed using Google Earth)

GOES-15 (GOES-West) and GOES-13 (GOES-East) 6.5 µm water vapor channel images (click image to play animation)

Strong winds aloft associated with a cyclonically-curved jet streak over the Northern Rocky Mountains were responsible for a number of mountain waves and lee “banner clouds” over parts of Wyoming and Montana on 25 December – 26 December 2011. A side-by-side comparison of GOES-15 (GOES-West) and GOES-13 (GOES-East) 6.5 µm water vapor channel images (above; click image to play animation) revealed some interesting differences in the appearance of these mountain waves. Note that the images are displayed in the native projection of their respective satellites.

A comparison of the GOES-15 and GOES-13 imager 6.5 µm water vapor channel weighting functions (below) showed that the satellite viewing angles (or satellite zenith angles) were very close — 56.41 degrees for GOES-15, and 59.95 degrees for GOES-13 — and the weighting function profiles were nearly identical. However, the fact that GOES-15 was viewing the region from the west allowed it to better resolve the warm/dry signatures (yellow color enhancement) of the most pronounced sinking regions associated with some of the stronger mountain waves. These warm/dry subsidence signatures were possibly masked by the high-altitude lee banner clouds when viewed from the east with GOES-13.

GOES-15 vs GOES-13 water vapor channel weighting function profiles

At 00:40 UTC there was one pilot report of brief moderate turbulence at an altitude of 37,000 feet near the Wind River Range in west-central Wyoming (below). Only a lee banner cloud was evident on the GOES water vapor imagery at that particular time, but a few hours later the warm/dry signature of strong mountain wave subsidence started to become more distinct over that location.

GOES-13 6.5 µm water vapor channel image + pilot report of turbulence

Had higher spatial resolution water vapor imagery been available closer to the 00:40 UTC time of the turbulence encounter, perhaps a more distinct mountain wave signature might have been apparent. For example, a comparison of 1-km resolution MODIS 6.7 µm and 4-km resolution GOES-13 6.5 µm water vapor images at 05:01 UTC (below) demonstrated the advantage of improved spatial resolution water vapor imagery for identifying subtle mountain wave signatures across the region.

MODIS 6.7 µm and GOES-13 6.5 µm water vapor channel images