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)

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GOES-15 full disk 6.5 µm water vapor channel images (click image to play animation)

An animation of McIDAS images of GOES-15 (GOES-West) 6.5 µm water vapor channel data from 27 January to 31 January 2012 (above; click image to play animation) revealed the presence of an unusually large and persistent warm/dry region over the central Pacific Ocean (centered southwest of Hawaii). Water vapor brightness temperatures as warm as +3.5 C (darker orange color enhancement) were seen — such warm values are rarely seen on water vapor imagery.

AWIPS images of the MIMIC Total Precipitable Water (TPW) product (below; click image to play animation) showed a number of areas exhibiting TPW values as low as 15 mm (0.6 inch) within the large dry feature seen on GOES-15 water vapor images. At 00 UTC on 30 January, the Hilo, Hawaii rawinsonde data indicated a TPW value of 0.93 inch, with very dry air above the 800 hPa pressure level. The strong subsidence aloft was acting to prevent significant rainfall over the Hawaiian Islands, prompting a Red Flag Warning to be issued for elevated fire danger during the 29-30 January period. It was also very warm in Hawaii — the highest temperature recorded in the 50 United States was 84 F at Kahului on 28 January, and 85 F at Kalaeloa on 30 January.

MIMIC Total Precipitable Water product (click image to play animation)

A comparison of an AWIPS water vapor image composite with the corresponding MIMIC TPW product (below) offers a good example of the fact that not all features of high TPW are evident on water vapor imagery. In particular, note the plume of higher TPW being drawn northeastward along a frontal boundary west and northwest of Hawaii — this plume crossed through the western portion of the dry feature on water vapor imagery.

Water vapor image + MIMIC TPW product + surface analysis

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POES AVHRR 3.74 µm shortwave IR image

Thick smoke from a 62-acre brush fire that was burning in the Paynes Prairie Preserve State Park just southwest of Gainesville, Florida (station identifier KGNV) was blamed for causing a deadly multiple-vehicle crash along Interstate 75 at around 07:45 UTC (3:45 am local time) on 29 January 2012. Detection of the fire “hot spot” on shortwave IR satellite imagery was difficult due to the relatively small size of the fire, and the fact that some thin cirrus clouds were drifting over the region. However, evidence of what could be the fire hot spot was seen on a 06:58 UTC  AWIPS image of 1-km resolution POES AVHRR 3.74 µm data (above), with an IR brightness temperature (BT) of +9 C at the darker black pixel that is circled.

The fire “hot spot” was a bit easier to see on a 06:53 UTC  McIDAS image of 375-meter resolution Suomi NPP VIIRS 3.74 µm data (below). The darker black pixel that is circled exhibited an IR brightness temperature of +24.7 C.

Suomi NPP VIIRS 3.74 µm shortwave IR image

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POES AVHRR 12.0 µm and MODIS 11.0 µm IR images (with METAR surface reports)

Record cold continued across the interior of Alaska, with Fairbanks reaching a minimum temperature of -50º F on 28 January 2012 and -51º F on 29 January 2012. These were the first -50º F temperatures at Fairbanks since 2006 (NWS Fairbanks public information statements). The coldest temperature reported was -65º F at Galena and by a coopertive observer at Fort Yukon (Fairbanks region temperature and precipitation data).

A sequence of AWIPS images of 1-km resolution POES AVHRR 12.0 µm IR and MODIS 11.0 µm IR data (above) revealed the expansion of surface IR brightness temperatures of -50º C or colder (violet to white color enhancement) during the early morning hours on 28 and 29 January. The coldest surface air temperatures at the times of the IR images included -50º F at Fairbanks (station identifier PAFA) and -60º F at Fort Yukon (station identifier PFYU) and Tanana (station identifier PATA). The signature of cold air drainage into lower elevation terrain (such as the relatively narrow river valleys along the south side of the Brooks Range, and also the broad Yukon Flats) could be seen on the 1-km resolution IR images.

Suomi NPP VIIRS 11.450 µm (Band I5) IR image

The pattern of cold air drainage into lower elevations could be seen in even greater detail using McIDAS images of 375-meter resolution Suomi NPP VIIRS 10.450 µm IR data at 12:06 UTC on 28 January, over northwestern Alaska and the Yukon Territory of Canada (above), and also just to the southwest over the eastern interior of Alaska (below). These 2 VIIRS images use a different color enhancement, where the coldest surface IR brightness temperatures are darker blue.

Unfortunately, there was no surface air temperature report for Arctic Village (station identifier PARC) at this time, but the coldest surface IR brightness temperatures within some of the deeper valleys near that site was -58.4º C (-73.1º F).

To the south, a broad area of very cold (dark blue) surface IR brightness temperatures was seen across the Yukon Flats, with a minimum value of -58.3º C (-72.9º F). The hourly surface air temperature at the Fort Yukon (PFYU) reporting station close to the time of the satellite image was -56º F, while the surface IR brightness temperature at that location was -54º F. Although there is not always a direct 1:1 correspondence between satellite-sensed IR surface temperature values and the actual air temperature measured within an instrument shelter at a height of 5 feet above ground level, the IR satellite imagery can be used to located areas that might have the coldest surface air temperatures.

Suomi NPP VIIRS 11.450 µm (Band I5) IR image

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