Mesoscale Convective System over the Southern Plains

October 6th, 2014
<strong>Suomi NPP VIIRS Day/Night Band (0.70 µm), Infrared Imagery (11.45 µm) and Day/Night Band imagery with lightning strikes at 0842 UTC on 6 October 2014</strong> (click to animate)

Suomi NPP VIIRS Day/Night Band (0.70 µm), Infrared Imagery (11.45 µm) and Day/Night Band imagery with lightning strikes at 0842 UTC on 6 October 2014 (click to animate)

The Suomi NPP VIIRS image toggle, above, from the pre-dawn hours (3:42 am local time) on 6 October 2014 shows a 0.7 µm Day/Night Band image and an 11.45 µm Infrared image, along with observations of postive and negative lightning strikes. With ample illumination by moonlight, the “visible image at night” Day/Night Band image highlighted areas of convective overshooting tops, but also included bright horizontal stripes that are associated with intense lightning activity; after scanning a particularly bright area of lightning in Arkansas, this image also showed a darker “post-saturation recovery” stripe downscan (to the southeast), which stretched from central Arkansas into Mississippi. This vigorous convective system dropped southeastward from Oklahoma towards the Gulf of Mexico, eventually becoming a Quasi-Linear Convective System (QLCS) which produced hail and wind damage (with one fatality) across parts of northeastern Texas and far northwestern Louisiana (SPC storm reports).

GOES Sounder DPI Lifted Index (click to animate)

GOES Sounder DPI Lifted Index (click to animate)

The southward-dropping Mesoscale Convective System followed a channel of unstable air as diagnosed by the GOES Sounder, above. Note that the Lifted Index values were smaller (less instability) along the path that the system had moved. Total Precipitable water was also enhanced in that corridor, suggesting a region where moisture return from the Gulf of Mexico was ongoing and concentrated.

GOES Infrared Imagery(10.7 µm) at 1600 UTC, and Pilot Reports of Turbulence (click to enlarge)

GOES Infrared Imagery (10.7 µm) at 1600 UTC, and Pilot Reports of Turbulence (click to enlarge)

Mesoscale Convective Systems can exhibit signatures that suggest the presence of turbulence in the atmosphere. In the GOES-13 IR image above, parallel filaments or “transverse bands” of cirrus  (extending approximately north-south) on the poleward side of the MCS suggest the presence of turbulence, and scattered pilot reports of Moderate Turbulence confirm that. Visible MODIS Imagery, below, also shows the transverse bands, as well as the outflow boundary arcing from Houston to the northwest and north.

Terra MODIS visible imagery (0.65 µm) at 1705 UTC  (click to enlarge)

Terra MODIS visible imagery (0.65 µm) at 1705 UTC (click to enlarge)

An animation of hourly GOES-13 Visible imagery, below, shows the motion of the western portion of the outflow boundary as the decaying QLCS moved into the Gulf of Mexico.

GOES-13 Visible (0.65µm) imagery (click to animate)

GOES-13 Visible (0.65µm) imagery (click to animate)

GOES-13 6.5 µm water vapor channel imagery, below, displayed a signature of subsidence immediately upstream of the dissipating MCS, in the form of an arc of warmer/drier (yellow to orange color enhancement) brightness temperatures that extended from the Texas coast into central Arkansas. One rapidly-developing convective cell which formed along the advancing outflow boundary was responsible for severe turbulence in eastern Texas; the subtle signal of the westward-propagating outflow boundary could also be followed on the water vapor imagery.

<strong>GOES-13 6.5 µm water vapor channel images, with pilot reports of turbulence</strong> (click to play animation)

GOES-13 6.5 µm water vapor channel images, with pilot reports of turbulence (click to play animation)

Re-suspended volcanic ash from the Novarupta volcano in Alaska

September 29th, 2014
GOES-15 0.63 µm visible channel images (click to play animation)

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

McIDAS images of GOES-15 0.63 µm visible channel data (above; click image to play animation) showed the hazy signature of a plume of re-suspended volcanic ash originating from the region of the Novarupta volcano in Alaska, moving southeastward over the Shelikof Strait toward Kodiak Island on 29 September 2014. The 1912 eruption of Novarupta left a very deep deposit of volcanic ash, which often gets lofted by strong winds in the early Autumn months before snowfall covers the ash (another example occurred on 22 September 2013). Surface winds gusted as high as 30 knots at regional reporting stations, with numerical models estimating terrain-enhanced winds as high as 40-50 knots over the Novarupta ash field.

An AWIPS II image of POES AVHRR 0.86 µm visible channel data (below) showed the ash plume at 22:46 UTC; a pilot report at 22:45 UTC indicated that the top of the ash plume was between 4000 and 6000 feet above ground level.

POES AVHRR 0.86 µm visible channel image, with METAR surface reports and Pilot reports (PIREPs)

POES AVHRR 0.86 µm visible channel image, with METAR surface reports and Pilot reports (PIREPs)

A sequence of 3 Suomi NPP VIIRS true-color Red/Green/Blue (RGB) images from the SSEC RealEarth web map server (below) indicated that the re-suspended ash plume had been increasing in areal extent during that period.

Suomi NPP VIIRS true-color images from 27, 28, and 29 September

Suomi NPP VIIRS true-color images from 27, 28, and 29 September

A sequence of 4-panel products from the NOAA/CIMSS Volcanic Cloud Monitoring site (below) shows False-color images, Ash/dust cloud height, Ash/dust particle effective radius, and Ash/dust loading (derived from either Terra/Aqua MODIS or Suomi NPP VIIRS data).

4-panel MODIS/VIIRS products: False color image; Ash/dust cloud height; Ash/dust particle effective radius; Ash/dust loading

4-panel MODIS/VIIRS products: False color image; Ash/dust cloud height; Ash/dust particle effective radius; Ash/dust loading

Hat tip to Mark Ruminski (NOAA/NESDIS) for alerting us to this event.

Tropical Invest 97L in the western Atlantic Ocean

September 29th, 2014
GOES-13 0.63 µm visible channel images with METAR surface reports (click to play animation)

GOES-13 0.63 µm visible channel images with METAR surface reports (click to play animation)

Tropical Invest 97L formed near Bermuda during the pre-dawn hours on 29 September 2014. After sunrise, AWIPS II images of GOES-13 0.63 µm visible channel data (above; click image to play animation) revealed a well-defined low-level circulation spinning just to the west of Bermuda. It is interesting to note that at 12:55 UTC a waterspout was reported 4 km to the east of the Bermuda International Airport (station identifier TXKF), associated with a band of deep convection that was moving northward (below).

GOES-13 0.63 µm visible channel image with Bermuda METAR observation

GOES-13 0.63 µm visible channel image with Bermuda METAR observation

An overpass of a Metop satellite at 14:38 UTC provided a good view of the surface wind field with data from the ASCAT scatterometer instrument (below). There was one wind vector with a speed around 30 knots (green) just to the east of the center of circulation.

GOES-13 0.63 µm visible channel image with Metop ASCAT scatterometer surface winds

GOES-13 0.63 µm visible channel image with Metop ASCAT scatterometer surface winds

A comparison of Terra MODIS 0.65 µm visible channel and 11.0 µm IR channel images at 15:25 UTC (below) showed that the coldest cloud-top IR brightness temperatures of -55º C (orange color enhancement) were located to the north of the circulation center.

Terra MODIS 0.65 µm visible channel and 11.0 µm IR channel images

Terra MODIS 0.65 µm visible channel and 11.0 µm IR channel images

Strong early-season storm in the North Pacific

September 23rd, 2014
GOES-15 6.5 µm IR channel images (click to play animation)

GOES-15 6.5 µm IR channel images (click to play animation)

The GOES-15 6.5 µm water vapor channel imagery above showed the development and evolution of a strong mid-latitude cyclone in the eastern North Pacific Basin during the 21-23 September 2014 time period; of particular interest was the development of strong subsidence behind the storm (depicted by brighter shades of yellow), and also a second jet starting to approach the storm from the west (as evidenced by increasing cold cloud tops in the base of the trough at the end of the animation). A closer view of the storm using AWIPS II imagery is available here. The strong storm had access to abundant sub-tropical moisture, as depicted in the MIMIC Total Precipitable Water animation below.

MIMIC Total Precipitable Water (click to enlarge)

MIMIC Total Precipitable Water (click to enlarge)

The ASCAT Scatterometer that flies on METOP gives routine observations of surface winds over the ocean. A large area of storm-force winds (in red) was depicted in the image below (from 0630 UTC on 23 September), overlain on the GOES-15 Water Vapor imagery.

 GOES-15 6.5 µm water vapor channel image and ASCAT winds, 0630 UTC on 23 September (click to enlarge)

GOES-15 6.5 µm water vapor channel image and ASCAT winds, 0630 UTC on 23 September (click to enlarge)

A comparison of 4-km resolution GOES-15 6.5 µm and 1-km resolution Aqua MODIS 6.7 µm water vapor channel images at 11:30 UTC, below, demonstrated the benefit of higher spatial resolution for providing a more accurate display of the water vapor gradients and various small-scale features (such as transverse banding associated with cold clouds to the north of the storm), along with the polar-orbiter image elimination of geostationary parallax error for more more precise feature location.

GOES-15 6.5 µm and Aqua MODIS 6.7 µm water vapor channel images

GOES-15 6.5 µm and Aqua MODIS 6.7 µm water vapor channel images

The GOES sounder Total Column Ozone product, below, showed an increase in ozone values (350-380 Dobson Units, darker green to lighter green color enhancement) as the tropopause was lowered in the vicinity of the deepening mid-latitude cyclone.

GOES sounder Total Column Ozone product (click to play animation)

GOES sounder Total Column Ozone product (click to play animation)

A Suomi NPP VIIRS true-color image from the SSEC RealEarth web map server, below, provided a good view of the lower-level clouds associated with the storm.

Suomi NPP VIIRS true-color image

Suomi NPP VIIRS true-color image

For a more detailed analysis of this event from the Ocean Prediction Center perspective, see the Satellite Liaison Blog.