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

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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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