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)

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-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-13 6.5 µm WV images (click image to play animation)

A potent winter storm moved into the southern Plains on 19 December 2011 as a cut-off circulation off the west coast of the US opened up and moved eastward. GOES water Vapor imagery (looped, above) shows a distinct dry slot. Stationary terrain features in the Cordillera of Northern Mexico are visible, suggesting that the surface radiation emitted at 6.5 micrometers is not absorbed by water vapor within the atmosphere (because of the extreme dryness). Cirrus that develops later in the loop along the southern border of the image does obscure some of the surface features. Note also how a strong moisture signal develops over New Mexico. Rising motion over that state moves water vapor to higher and higher levels in the atmosphere. At the start of the loop, most of the water vapor exists below the mid-tropospheric level where the Imager Sensor is detecting water vapor. Persistent rising motion allows the moist layer to deepen, and the imager starts detecting this higher, colder moisture. The loop in the computed weighting function for Albuquerque at 00 UTC and at 12 UTC on 19 December is here. Note that the amount of water vapor in the atmosphere increases between 00 UTC and 12 UTC as indicated on the linked-to charts. The weighting function describes the relative importance of emitted radiation from different levels in the atmosphere.

Lack of moisture in mid-levels (the peak response is around 500 hPa) at 00 UTC means the water vapor signal is being emitted from farther down in the troposphere, where it is warmer. As moisture deepens, the water vapor signal is emitted from colder regions. The water vapor detector on the imager shows the temperature at the top of the moist layer. It does not reveal the total moisture content in the column.

GOES-13/MODIS 6.5 µm WV images (click image to play animation)

MODIS and GOES-13 water vapor imagery (above) from between 1630 and 1700 UTC (that is, just after the loop at the top), show significant brightness temperature differences between sensed water vapor. Values from the MODIS instrument shows water vapor brightness temperatures that are uniformly colder than the GOES-13 values. Why? The Spectral Response Functions below (courtesy of Mat Gunshor, SSEC/CIMSS), for GOES-12 (the imager on GOES-12 is similar to that on GOES-13) and for the MODIS WV Channel suggest a possible reason. The Imager water vapor detection (in blue) spans a larger part of the electromagnetic spectrum, including regions at longer wavelengths. (The MODIS water vapor channel is a single sharply defined peak (shown in red)). As the wavelength increases, the level sensed decreases, so a broader spectrum that includes longer wavelengths will show warmer temperatures because it is detecting more energy from lower in the atmosphere where temperatures are warmer. At Nadir, GOES-13 will be about 1 K warmer than the MODIS Brightness temperature. (Use this website to show different weighting functions.

GOES-12/MODIS Spectral Response Functions for Water Vapor Channel

It is common to relate features in the water vapor imagery to structures in the atmosphere. The figure below shows a 325-K Jet maxima aligned, as expected, with the dry slot in the WV imagery. The dry slot is a region of sinking motion. Warm brightness temperatures develop in the dry slot because water vapor is confined to the lowest levels of the atmosphere, so the emitting surface is warm. A cross-section that is nearly orthogonal to the jet (here) shows an isentropic structure that is characteristic of an intrusion of stratospheric air into the mid-troposphere. It also shows extreme dryness in the middle of the tropopshere.

GOES-13 WV/GFS 325K Winds

This storm brought needed precipitation to parts of the southern Plains that have been plagued by drought all year.

MODIS true color RGB images (viewed using Google Earth)

Two days after the storm, the clouds had cleared to reveal the large swath of fresh snow cover on 21 December 2011, as seen on a composite of MODIS true color Red/Green/Blue (RGB) images from the SSEC MODIS Today site (above; viewed using Google Earth). Across the Southern Plains, the highest storm total snowfall amounts (in inches) in Texas, Oklahoma, Colorado, and Kansas are highlighted on the image.

A comparison of AWIPS images of the 1-km resolution MODIS 0.65 µm visible channel and the corresponding MODIS false color RGB image created using the visible and “snow/ice” channels 01/07/07 (below) revealed the swath of snow cover (red on the RGB image) on the 16:40 UTC overpass of the Terra satellite. Note the darker red appearance along the far southeastern edge of the snow cover on the false color image — this is a signature of areas where there was a significant accrual of ice due to freezing drizzle. Near Pratt, Kansas (station identifier KPTT) the thickness of the ice accrual was around 0.25 inch. Since ice is a stronger absorber of radiation than snow cover at the 2.1 µm wavelength, this leads to a darker appearance on a single-channel MODIS Band 7 imagery.

MODIS 0.65 µm visible channel + MODIS false color RGB image

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

A 250-meter resolution MODIS true color Red/Green/Blue (RGB) image from the SSEC MODIS Today site (above) showed the areal coverage of lake-effect snow cover downwind of Lake Erie on 11 December 2011. Snow depths across this particular region were generally small, in the 1 to 4 inch range.

MODIS true color Red/Green/Blue (RGB) image

A significant rain and snow event occurred across parts of southeastern Wyoming and western Nebraska on 08 October 2011 (see NWS Cheyenne story) — snowfall amounts as high as 12.0 inches were reported near Cheyenne , Wyoming with 2.73 inches of rain reported farther to the northeast near Crawford in western Nebraska. Two days later (on 10 October 2011), a large patch of low-elevation snow cover could still be seen in far southeastern Wyoming  on a 250-meter resolution MODIS true color Red/Green/Blue (RGB) image  from the SSEC MODIS Today site (above, viewed using Google Earth).

MODIS 0.65 µm visible channel image + MODIS 2.1 µm "snow/ice channel" image

On a comparison of AWIPS images of 1-km resolution MODIS 0.65 µm visible channel and MODIS 2.1 µm “snow/ice channel” data (above), snow cover (along with clouds) appears bright on the visible image, but snow appears very dark on the snow/ice image (since snow is a very strong absorber at that particular wavelength).

Another method to discriminate between clouds and snow cover is to use different MODIS images to create a 3-channel RGB false color image — snow cover appears darker red on such a false color image (below), which used MODIS channels 01/07/07 as the Red/Green/Blue components.

MODIS 0.65 µm visible image + MODIS false color Red/Green/Blue (RGB) image

In far southeastern Wyoming, the areas that still had significant snow cover exhibited much colder MODIS Land Surface Temperature (LST) values (below), with LSTs ranging from the middle 30s F (darker green color enhancement) over deeper snow cover to the upper 60s to low 70s (darker orange color enhancement) over adjacent areas of bare ground.

MODIS Land Surface Temperature product

With the high October sun angle helping to produce warm temperatures (the daytime high at Cheyenne, Wyoming that day reached 59ºF or 15ºC) the patch of lower-elevation snow cover just to the north of Cheyenne began to melt during the day, as can be seen on an animation of GOES-15 0.63 µm visible channel images (below; click image to play animation).

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

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MODIS 11.0 µm IR image + topography

Another feature of interest on the satellite images was the formation of a  “cloud banner” or “cloud crest” just downwind of the ridge of higher terrain that ran northwest to southeast across the Wyoming/Colorado border region — this cold cloud feature could be seen on the 1-km resolution MODIS 11.0 µm IR image (above). The 4-km resolution MODIS Cloud Phase product (below) showed this to be an ice phase cloud feature (salmon color enhancement), with the 4-km resolution MODIS Cloud Top Temperature (CTT) product indicating CTT values as cold as -45ºC (darker blue color enhancement).

MODIS Cloud phase product + MODIS Cloud Top Tempeature product

The 1-km resolution MODIS 6.7 µm water vapor channel image (below) revealed a signature of mountain waves farther downwind of the cloud banner feature. A few hours later (at 23:58 UTC), there was a pilot report of light turbulence in that region at an altitude of 37,000 feet.

MODIS 6.7 µm water vapor channel image

CIMSS participation in GOES-R Proving Ground activities includes making a variety of MODIS images and products available for National Weather Service offices to add to their local AWIPS workstations. Currently there are 49 NWS offices receiving MODIS imagery and products from CIMSS.

MODIS true color and false color images

A previous blog post discussed the sediment features seen in southern Lake Michigan in early October of 2011. However, looking a bit farther to the east over Lake Erie several days later, a 09 October 2011 comparison of 250-meter resolution MODIS true color and false color Red/Green/Blue (RGB) images from the SSEC MODIS Today site (above) showed a notable contrast between the two lakes: large green colored features covered much of western Lake Erie, compared to the cyan colored sediment that was seen in southern Lake Michigan (as well as southern Lake Huron).

According to the NASA Earth Observatory site, this is one of the worst algae blooms in Lake Erie in decades, brought about in part due to large amounts of runoff into the lake following a period of above-normal precipitation. The thickest portions of the algae bloom appear brighter green in the false color images, similar to the way that dense vegetation does.

A comparison of the consecutive Terra (16:52 UTC) and Aqua (18:33 UTC) MODIS true color images (below, viewed using Google Earth) seemed to suggest a slight northward movement of the algae features during the 91 minutes between the two images.

Terra (16:52 UTC) and Aqua (18:33 UTC) MODIS true color images

An animation of GOES-15 0.63 µm visible channel images (below) confirmed the gradual northward movement to the algae bloom features over western Lake Erie during the day. Surface winds were generally light out of the south across the region, so most of this motion was likely driven by lake currents.

GOES-15 0.63 µm visible channel images

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

A McIDAS image comparison of GOES-11 (GOES-West) 0.65 µm visible channel, GOES-15 0.63 µm visible channel, and GOES-13 (GOES-East) 0.63 µm visible channel data (above) showed the dark smoke plume from a fire burning at a chemical plant in Waxahachie, Texas (about 30 miles south of Dallas) on 03 October 2011. (Note: GOES-15 is scheduled to replace GOES-11 as the operational GOES-West satellite in December 2011).

A similar comparison of the GOES-11, GOES-15, and GOES-13 3.9 µm shortwave IR channels (below) indicated that no obvious fire “hot spot” was evident before the appearance of the dark smoke plume — the brighter yellow colors highlight pixels which have an IR brightness temperature hotter than 45º C. This 45º C threshold was exceeded at 16:30 UTC on the GOES-15 and GOES-13 images, and at 16:45 on the GOES-11 images; on the visible channel imagery, the dark smoke plume was seen 30 minutes earlier at 16:00 UTC on all 3 satellites.

GOES-11, GOES-15, and GOES-13 shortwave IR images

A 17:32 UTC Terra MODIS Red/Green/Blue (RGB) true color image from the SSEC MODIS Today site (below, viewed using Google Earth) confirmed the very dark nature of the smoke plume from this particular fire, which was causing some evacuations (news media story).

MODIS true color RGB image (viewed using Google Earth)

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

McIDAS images of GOES-13 0.63 µm visible channel data (above; click image to play animation) revealed numerous pyrocumulus clouds and large areas of very dense smoke associated with the “Honey Prairie Fire” in the Okefenokee Swamp area of southeastern Georgia on 20 June 2011. The shadows cast by the pyrocumulus towers almost resembled those cast by overshooting tops which are often seen on the anvil tops of severe thunderstorms.

A sequence of 3 AWIPS images of POES AVHRR 0.63 µm visible channel data (below) offered a larger-scale view of the smoke as it drifted eastward across the adjacent offshore waters of the Atlantic Ocean. The shadow cast by a pyrocumulus tower could be seen on the final 21:22 UTC image. As expected, this dense smoke plume exhibited very high Aerosol Optical Depth (AOD) values (see the US Air Quality “Smog Blog” and the NOAA IDEA sites for AOD imagery).

POES AVHRR 0.63 µm visible channel images

The 21:22 UTC POES AVHRR 10.8 µm IR image (below) showed that the coldest cloud top IR brightness temperatures at that time were -18º C, which corresponded to an altitude of nearly 24,000 feet using the interactive Skew-T diagram with data from the rawinsonde report from Charleston, South Carolina.

POES AVHRR 10.8 µm IR image + interactive Skew-T for Charleston SC rawinsonde

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On the following day (21 June 2011) the winds were much lighter across the region, so the smoke was not being transported as far eastward over the Atlantic Ocean. In fact, GOES-13 0.63 µm visible channel images (below; click image to play animation) showed that significant amounts of the smoke remained just offshore — so when a sea breeze front began to move inland during the afternoon hours, much of this smoke was brought back inland. For example, at St. Augustine, Florida (surface identifier KSGJ), the surface visibility dropped from 10 miles to 0.75 mile after the surface winds shifted to easterly behind the sea breeze front.

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

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A sequence of 250-meter resolution MODIS true color Red/Green/Blue (RGB) images from the SSEC MODIS Today site (below; displayed using Google Earth) showed varying regimes of transport of the thick smoke on 19 June, 20 June, 21 June, and 22 June 2011.

MODIS true color RGB images (displayed using Google Earth)