Suomi NPP VIIRS images showing Arctic Ocean ice movement

April 28th, 2012
Suomi NPP VIIRS 0.64 µm visible channel images

Suomi NPP VIIRS 0.64 µm visible channel images

AWIPS images of Suomi NPP VIIRS 0.64 µm visible channel data (above) and 11.45 µm IR channel data (below) showed cloud and ice features over the Arctic Ocean on 28 April 2012. For geographic reference, station identifier CWMD is Mould Bay, located on Prince Patrick Island in the far northwestern portion of the Canadian Arctic Archipelago.

The meteorological cloud features at this time were fairly benign, with some low stratus seen over the northern portion of the satellite scene, and multi-level clouds associated with a cyclone developing to the south. Of particular interest was the amount of sea ice motion during this relatively short 8-hour period — several ice leads opened up and became very prominent features on both the visible and the IR imagery.

Suomi NPP VIIRS 11.45 µm IR channel images

Suomi NPP VIIRS 11.45 µm IR channel images

Suomi NPP VIIRS 1.61 µm near-IR images (below) revealed a number of narrow “streaks” of supercooled water droplet clouds (which appear as brighter white features) moving away from the islands, suggesting that there were strong winds across the region helping to move the sea ice. Water (and cloud shadows) appear black on the near-IR images, while ice and snow cover appear as darker shades of gray.

Suomi NPP VIIRS 1.61 µm near-IR images

Suomi NPP VIIRS 1.61 µm near-IR images

Surface analyses at 12 UTC and 18 UTC (below) indicated that there was a strong pressure gradient over the region, between the High over the Arctic Ocean and a deepening Low over far northern Canada. The effect of this tightening pressure gradient was strong offshore (easterly) winds — the closest available observation site was Sachs Harbour on Banks Island, where they had easterly winds of 25 knots with gusts to 30 knots, and zero visibility with heavy snow and heavy blowing snow at 22 UTC.

12 UTC and 18 UTC surface analyses (NOAA/NCEP/OPC)

12 UTC and 18 UTC surface analyses (NOAA/NCEP/OPC)

 

Severe thunderstorms across Missouri, Illinois, and Indiana

April 28th, 2012
GOES-13 sounder Total Precipitable Water derived product imagery

GOES-13 sounder Total Precipitable Water derived product imagery

AWIPS images of 10-km resolution GOES-13 sounder Total Precipitable Water (TPW) derived product imagery (above) and the corresponding GOES-13 sounder Convective Available Potential Energy (CAPE) derived product imagery (below) showed that moisture (TPW values as high as 45 mm or 1.78 inches near Saint Louis, Missouri at 16 UTC) and instability (CAPE values as high as 4300 J /kg acorss southern Illinois at 20 UTC) was in place along and to the south of a quasi-stationary warm frontal boundary that was located from eastern Missouri across southern Illinois and southern Indiana during the late morning and early afternoon hours on 28 April 2012.

GOES-13 sounder CAPE derived product imagery

GOES-13 sounder CAPE derived product imagery

4-km resolution GOES-13 10.7 µm IR channel images (below; click image to play animation) indicated that thunderstorms developed in Missouri and southern Illinois, and then tracked east-southeastward along the warm frontal boundary. These storms produced a long swath of large hail and severe wind gusts, as can be seen by the SPC storm reports overlaid on the IR imagery. Later in the afternoon, some of the organized convection began to exhibit well-defined “enhanced-V” storm top signatures, which often denotes thunderstorms that are likely producing (or will soon produce) either large hail, damaging wind gusts, or tornadoes.

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)

Greater details can be seen in a 1-km resolution POES AVHRR 10.8 µm IR image with overlays of METAR surface reports and cumulative SPC storm reports of large hail and damaging wind gusts (below). A long swath of hail and damaging winds can be seen, including one incident where a wind gust of 50 mph blew over an outdoor beer garden tent around 20:50 UTC (resulting in a number of injuries and one fatality).

POES AVHRR 10.8 µm IR image + cumulative SPC storm reports of hail and  wind gusts

POES AVHRR 10.8 µm IR image + cumulative SPC storm reports of hail and wind gusts

A compariosn of the 1-km resolution POES AVHRR 0.63 µm visible channel image with the corresponding 10.8 µm IR channel image (below) again showed great detail in the overshooting top and cloud top thermal couplet structure.

POES AVHRR 0.63 µm visible channel image + 10.8 µm IR channel image

POES AVHRR 0.63 µm visible channel image + 10.8 µm IR channel image

A comparison of the 1-km resolution POES AVHRR 10.8 µm IR channel image with the corresponding 4-km resolution GOES-13 10.7 µm IR image (below) demonstrates the value of higher spatial resolution for detecting important cloud top temperature patterns. In this case, the coldest cloud top IR brightness temperature on the POES AVHRR image was -78º C, compared to -69º C on the GOES-13 IR image. Also note the slight northward parallax shift in the GOES-13 IR image.

GOES-13 10.7 µm IR channel image + POES AVHRR 10.8 µm IR channel image

GOES-13 10.7 µm IR channel image + POES AVHRR 10.8 µm IR channel image

Using VIIRS imagery for snow/ice vs cloud discrimination over Alaska, the Arctic Ocean, and the Bering Sea

April 26th, 2012
Suomi NPP VIIRS 0.64 µm visible channel + 1.61 µm near-IR channel images

Suomi NPP VIIRS 0.64 µm visible channel + 1.61 µm near-IR channel images

AWIPS images of 1-km resolution Suomi NPP VIIRS 0.64 µm visible channel and 1.61 µm near-IR channel images (above) demonstrated the value of using the near-IR imagery to help discriminate between snow/ice (which appears darker on the near-IR image) and supercooled water droplet cloud features (which appear as brighter shades of white on the near-IR image) over northern Alaska and the Arctic Ocean on 23 April 2012. Numerous large leads (or cracks) in the Arctic Ocean sea ice are apparent on the visible channel image.

Many of the cloud features over the Arctic Ocean were thin and at a low altitude, so there was not a great deal of thermal contrast seen on the corresponding 11.45 µm IR image (below).

Suomi NPP VIIRS 1.61 µm near-IR channel + 11.45 µm IR channel images

Suomi NPP VIIRS 1.61 µm near-IR channel + 11.45 µm IR channel images

Three days later (on 26 April 2012), a similar comparison of a Suomi NPP VIIRS 0.64 µm visible channel image with the corresponding 1.61 µm near-IR image (below) showed that much of the ice in the Bering Sea was beginning to break up (although a significant amount of land-fast ice remained along the western coastline of Alaska). The near-IR image also helped to highlight other interesting features along the far left edge of the satellite scene: aircraft contrails over Nunivak Island, and a thin trail of wave clouds extending downwind of St. Matthew Island.

Suomi NPP VIIRS 0.64 µm visible channel + 1.61 µm near-IR channel images

Suomi NPP VIIRS 0.64 µm visible channel + 1.61 µm near-IR channel images

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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)

An animation of 1-km resolution GOES-15 0.63 µm visible channel images (above; click image to play animation) showed the motion of the southern extent of the ice in the Bering Sea on 26 April. On the previous day, the sea ice had retreated northward from Saint George Island (station identifier PAPB), after a record-setting 79 consecutive days with sea ice. Farther to the north, the sea ice would remain at Saint Paul Island (station identifier PASN) into early May, also setting a new record for sea ice duration at that island.

A significant amount of sea ice motion could be seen on the GOES-15 visible images, due to strong surface winds over the southern Bering Sea on that day. In addition, the visible images revealed some interesting wave clouds immediately downwind of the higher terrain of some of the Aleutian Islands.

A better view of the southern extent of ice in the Bering Sea was available using a 1-km resolution NOAA-19 AVHRR false-color Red/Green/Blue (RGB) image (below). As with the GOES-15 images above, Saint Paul Island and Saint George Island are located near the center of the image.

NOAA-19 AVHRR false-color Red/Green/Blue (RGB) image

NOAA-19 AVHRR false-color Red/Green/Blue (RGB) image

Historic Late April Nor’easter Storm

April 23rd, 2012
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)

A historic late-April “nor’easter” storm affected much of the northeastern US during the 22 April23 April 2012 period. This storm produced heavy snowfall (as much as 23.3 inches at Laurel Summit, Pennsylvania), heavy rainfall (as much as 5.74 inches at New Boston, New Hampshire), and wind gusts as high as 94 mph at Mount Washington, New Hampshire. AWIPS images of 4-km resolution GOES-13 6.5 µm water vapor channel images (above; click image to play animation) showed the development of various features of the storm on 23 April, including a large and well-defined comma head, dry slot, and deformation zone.

By tracking the movement of various water vapor image features between consecutive images, atmospheric motion vectors can be calculated which give an indication of the wind direction and wind speed within the middle to upper troposphere. GOES-13 6.5 µm water vapor images with overlays of MADIS 1-hour interval water vapor winds are shown below  (click image to play animation).

GOES-13 6.5 µm water vapor images + MADIS 1-hour water vapor winds (click image to play animation)

GOES-13 6.5 µm water vapor images + MADIS 1-hour water vapor winds (click image to play animation)

Satellite-derived water vapor winds can also be used to calculate an upper-tropospheric (150-300 mb) divergence product (below), which in this case showed persistent divergence aloft over much of the northeastern US on 23 April. This upper-level divergence created an environment that favored upward vertical motion within the atmospheric column, helping to enhance and prolong the ongoing precipitation over those areas.

GOES-13 water vapor images + Upper-level divergence derived from water vapor winds

GOES-13 water vapor images + Upper-level divergence derived from water vapor winds

A series of 1-km resolution MODIS 11.0 µm IR and POES AVHRR 12.0 µm IR images (below; click image to play animation) indicated that enhanced areas of colder clouds (some exhibiting a banding structure) developed over the region of persistent upper level divergence.

MODIS 11.0 µm IR + POES AVHRR 12.0 µm IR images

MODIS 11.0 µm IR + POES AVHRR 12.0 µm IR images

The 10-km resolution GOES-13 sounder Total Column Ozone (TCO) product (below; click image to play animation) revealed an anomalously large area of elevated TCO covering much of the eastern US, indicative of a lowered tropopause associated with the large upper-level trough of low pressure.

GOES-13 sounder Total Column Ozone + RUC 500 hPa geopotential heights

GOES-13 sounder Total Column Ozone + RUC 500 hPa geopotential heights

===== 24 April Update =====

MODIS 6.5 µm visible channel image + MODIS false-color RGB image

MODIS 6.5 µm visible channel image + MODIS false-color RGB image

A comparison of the 1-km resolution MODIS 0.65 µm visible channel image at 16:09 UTC (12:09 pm local time) with a corresponding false-color Red/Green/Blue (RGB) image created using the MODIS 2.1 µm “snow/ice detection” channel (above) helped to identify high-elevation areas with significant snow cover remaining after the passage of the storm — snow appears brighter white on the visible image, and darker red on the false-color image. Note that cirrus clouds appear as a lighter shade of red in the RGB image.

A 250-meter resolution MODIS true color image from the SSEC MODIS Today site (below; viewed using Google Earth) showed even better detail of the snow-covered high terrain.

MODIS true-color RGB image (viewed using Google Earth)

MODIS true-color RGB image (viewed using Google Earth)