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)

NASA Global Hawk flight to study Tropical Storm Dolly

September 2nd, 2014
NASA Global Hawk flight path, with Cloud Height, Tropical Overshooting Tops, and Lightning data (click to play animation)

NASA Global Hawk flight path, with Cloud Height, Tropical Overshooting Tops, and Lightning data (click to play animation)

The NASA Global Hawk aircraft are once again being used to study tropical cyclones during the 2014 season. As part of CIMSS participation in GOES-R Proving Ground activities, a Global Hawk flight path tool was developed to display important parameters such as ACHA Cloud Top Height, Tropical Overshooting Tops, and lightning (above; click image to play animation). Global Hawk pilots use this product to navigate the aircraft around locations of potential turbulence.

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

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

To support the Global Hawk investigation of Tropical Storm Dolly on 02 September 2014, the GOES-13 satellite was placed into Rapid Scan Operations (RSO) mode to provide images at 5-7 minute intervals. GOES-13 0.63 µm visible channel images (above; click to play animation) and 10.7 µm IR channel images (below; click to play animation) are shown which cover the 3-hour period of the Global Hawk flight segment shown above. There is evidence of overshooting tops seen in the visible imagery, with cloud-top IR brightness temperatures of -80º C and colder (purple color enhancement).

GOES-13 10.7 µm IR channel images (click to play animation)

GOES-13 10.7 µm IR channel images (click to play animation)

Tropical Storm Arthur forms east of Florida

July 1st, 2014
GOES-13 0.63 µm visible channel images (click to play animation)

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

The first tropical depression (update: Arthur was named as a tropical storm at 1500 UTC 1 July) of the season in the tropical Atlantic has formed just to the east of Florida. The visible imagery animation, above, shows persistent strong thunderstorms with overshooting tops in the area of disturbed weather over the Gulf Stream and the Bahamas. Refer to the National Hurricane Center and the CIMSS Tropical Cyclones sites for particulars on the future track of this system. Note that current forecasts have the system strengthening to a hurricane in the next few days, and close to the North Carolina coast on July 4th.

Metop ASCAT surface scatterometer winds at 1541 UTC, below, indicated that the strongest winds (green barbs, 30-39 knots) were found within the northeastern quadrant of the tropical storm.

GOES-13 visible images with Metop ASCAT surface scatterometer winds (click to play animation)

GOES-13 visible images with Metop ASCAT surface scatterometer winds (click to play animation)

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GOES-13 10.7 µm infrared channel images (click to play animation)

GOES-13 10.7 µm infrared channel images (click to play animation)

The tropical Atlantic has lately been besieged by Saharan Air Layer (SAL) dust (see, for example, this post from last week, or this image from today); that dry air suppresses tropical cyclone formation. The animation of GOES-13 10.7 µm imagery, above, shows that this Tropical Depression formed out of an impulse that sank southward from the Carolinas over the past 6 days, so its gradual development has not been impeded by the SAL.

The VIIRS instrument on board the Suomi NPP satellite provided high-resolution imagery over this tropical system shortly after midnight on the 1st (see below). A large cirrus shield with brightness temperatures cooler than -70º C (Green in the enhancement) with a few overshooting tops that are colder than -85º C are present. An analysis of some NUCAPS Soundings from this overpass is here.

Suomi NPP VIIRS 11.35 µm infrared imagery, Day/Night Band imagery (0.70 µm) and lightning data at ~0715 UTC on 1 July 2014 (click to toggle through images)

Suomi NPP VIIRS 11.35 µm infrared imagery, Day/Night Band imagery (0.70 µm) and lightning data at ~0715 UTC on 1 July 2014 (click to toggle through images)

Arthur’s projected track moves the storm up the East Coast over very warm waters associated with the Gulf Stream. Both MODIS and VIIRS analyses of SSTs show widespread temperatures in excess of 80º F.

A comparison of Suomi NPP VIIRS 11.45 µm IR channel images at 0717 UTC and 1840 UTC, below, showed that the areal coverage of cold cloud tops was increasing during the day on 01 July, but the deep convection remained well to the southeast of Arthur’s low-level center of circulation.

Suomi NPP VIIRS 11.45 µm IR channel images

Suomi NPP VIIRS 11.45 µm IR channel images

At 1840 UTC, a comparison of the Suomi NPP VIIRS 11.45 µm IR channel image with the corresponding 0.64 µm visible channel image with an overlay lightning data, below, revealed a large number of cloud-to-ground strikes within the 1-hour period ending at 1900 UTC.

Suomi NPP VIIRS 11.45 µm IR channel image and 0.64 µm visible channel image (with lightning data)

Suomi NPP VIIRS 11.45 µm IR channel image and 0.64 µm visible channel image (with lightning data)

===== 02 July Update =====

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

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

Arthur continued to slowly intensify on 02 July, and began to show hints of an organized eye structure on GOES-13 0.63 µm visible channel images (above; also available as an MP4 movie file).

A comparison of AWIPS-2 images of Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images (below) showed that the coldest cloud tops were north of the center of Arthur at 1822 UTC. A buoy just southwest of the center reported winds gusting to 52 knots (60 mph).

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images

Even though an eye was not evident on GOES-13 10.7 µm IR channel imagery around 2045 UTC, a DMSP SSMIS 85 GHz microwave image at 2049 UTC did display a well-organized eye signature (below).

GOES-13 0.63 µm visible channel image and DMSP SSMIS 85 GHz microwave image

GOES-13 0.63 µm visible channel image and DMSP SSMIS 85 GHz microwave image

Mesoscale Convective Systems over the Upper Midwest, and a Mesoscale Convective Vortex over Wisconsin

June 18th, 2014
Suomi NPP VIIRS 11.45 µm IR channel and 0.7 µm Day/Night Band images, with cloud-to-ground lightning strikes

Suomi NPP VIIRS 11.45 µm IR channel and 0.7 µm Day/Night Band images, with cloud-to-ground lightning strikes

A comparison of AWIPS images of Suomi NPP VIIRS 11.45 µm IR channel and 0.7 µm Day/Night Band data (above) showed very large areas of cold cloud-top IR brightness temperatures associated with Mesoscale Convective Systems (MCSs) over the Upper Midwest region of the US at 08:00 UTC (3:00 AM Central time) on 18 June 2014. The coldest IR brightness temperature was -88º C over far southern  Minnesota.  Numerous bright white “streaks” were seen on the Day/Night Band (DNB) image, which indicated portions of the cloud that were illuminated by intense lightning activity. Cloud-to-ground lightning strikes are also plotted on the DNB image, showing how electrically-active these storms were at the time. The western MCS initially formed over eastern South Dakota during the previous evening, producing a few tornadoes there (SPC storm reports). The eastern MCS began to form later along the Wisconsin/Illinois border region — one aircraft flying near the northern edge of a rapidly-developing thunderstorm encountered severe turbulence.

Shortly after the time of the Suomi NPP satellite overpass, a 08:21 UTC overpass of the NOAA-19 POES satellite provided AVHRR-derived CLAVR-x Cloud Top Temperature (CTT), Cloud Top Height (CTH), and Cloud Type products (below). The minimum CTT value was -84º C, and the maximum CTH value was 14 km; much of the MCS cloud shield was classified as the Overshooting Top type (magenta color).

POES AVHRR Cloud Top Temperature, Cloud Top Height, and Cloud Type products

POES AVHRR Cloud Top Temperature, Cloud Top Height, and Cloud Type products

After sunrise, McIDAS  images of GOES-13 0.63 µm visible channel data (below; click image to play animation; also available as an MP4 movie file) showed that the eroding MCS cirrus shield aloft exposed a middle-tropospheric Mesoscale Convective Vortex (MCV) which continued moving eastward across Wisconsin during the day.

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

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

Consecutive overpasses of the Terra and Aqua satellites provided MODIS 0.65 µm visible channel images of the region (below). The convective outflow boundary from the earlier MCS activity had acted to push the warm frontal boundary (which had been acting as a focus for convective development) south of the Wisconsin/Illinois border, leaving a relatively stable boundary layer with a weak capping inversion aloft over Wisconsin — as a result, the MCV circulation did not play a role in initiating any new convective development.

MODIS 0.65 µm visible channel images, with surface reports and surface fronts

MODIS 0.65 µm visible channel images, with surface reports and surface fronts