A closer view of the tornadic supercell is shown below, with overlays of surface reports (metric units). The pulsing nature of the overshooting tops is evident in the fluctuation of the coldest cloud-top IR brightness temperatures (the coldest of which was -69º C, darker black color enhancement, on the 0300 UTC GOES-15 and 0315 UTC GOES-13 images). There are different apparent positions of the storms based on the satellite that views them because of parallax shifts. Such shifts are especially pronounced at higher latitudes with very tall storms.A 1-km resolution Terra MODIS 11.0 µm Infrared image at 0331 UTC is shown below; the minimum cloud-top IR brightness temperature was -73º C. Visible imagery from GOES-13 (above) and GOES-15 (below) showed the overshooting tops associated with the tornadic thunderstorm, as well as the rapidly expanding cirrus shield. A closer view of the tornadic supercell from GOES-15 vs GOES-13 is shown below, with overlays of surface reports (metric units). The overshooting tops are again apparent on the images, along with an above-anvil plume (which is easier seen on the GOES-13 images, due to a more favorable forward-scattering viewing geometry). The robust convective development was first seen on the 2030 UTC images, in the vicinity of the Saskatchewan/Manitoba/North Dakota border region. As an area of low pressure was deepening over eastern Montana, warm and humid air was surging northward into far southern Saskatchewan and Manitoba (surface analyses). GOES sounder derived product images (available from this site) of Convective Available Potential Energy (CAPE), Lifted Index, and Total Precipitable Water (below) showed that the environment across southern Manitoba was becoming increasingly unstable and moist leading up to the time of convective initiation.
GOES-13 sounder Convective Available Potential Energy (CAPE) derived product images (above; click to play animation) showed a large cluster of of severe thunderstorms that developed in eastern Kansas and moved southeastward across southern Missouri into northern Arkansas during the day on 14 July 2015. Due to strong surface heating and ample low-level moisture ahead of the storms, the atmosphere became quite unstable with GOES sounder CAPE values reaching the 5800-6000 J/kg range (lighter violet color enhancement) by 16 UTC. A long swath of damaging winds (SPC storm reports) was produced by these storms.
The visible and infrared images below show snapshots of this severe convective cluster at 3 different times, using high-resolution data from instruments on polar-orbiting satellites: Terra MODIS at 1657 UTC, Suomi NPP VIIRS at 1851 UTC, and POES AVHRR at 1916 UTC. The coldest cloud-top IR brightness temperatures were -83º C on the MODIS image, -86º C on the VIIRS image, and -87º C on the AVHRR image.
A strong mesoscale convective system (MCS) moving southeastward through the Upper Midwest from late 12 July 2015 into early morning 13 July caused numerous severe wind reports across Minnesota and Wisconsin. This MCS was forecast to drop southeastward and continue to produce severe weather during the day on 13 July 2015 (Storm Prediction Center outlook). The toggle above shows the 0420 UTC Terra MODIS 11.0 µm image and the 0400 UTC GOES-13 Sounder DPI Lifted Index product (which is available in realtime here). As the MCS moved over southern Wisconsin, the coldest cloud-top IR brightness temperature on the 0826 UTC MODIS 11.0 µm IR image was -85º C. The strong system continued to move southeastward as very unstable air as diagnosed by the Sounder fed into it (click here for 850-mb RAOB plots). The 0746 UTC Suomi NPP VIIRS 11.45 µm IR image, below, also toggled with a GOES-13 Sounder Lifted Index product, showed a similar story: very strong convection downwind of a source of strong instability. The GOES Sounder can also diagnose Convective Available Potential Energy (CAPE), with values from 5000-6000 J/kg seen over southern Minnesota and eastern Iowa.
The Suomi NPP VIIRS Day/Night Band, below, which is a source of visible imagery at night, depicted signatures of the active lightning that accompanied this system: numerous along-scan bright streaks over southern Wisconsin were caused by lightning illuminating the cloud as the VIIRS instruments scanned the cloud top. This toggle showed a comparison of Day/Night Band and 11.45 µm Infrared imagery.
A closer view comparing the 0746 UTC VIIRS IR and Day/Night Band images, below, includes overlays of METAR reports and both 15-minute and 1-hour cloud-to-ground lightning strikes. The coldest VIIRS cloud-top IR brightness temperature was -78º C.
At 0805 UTC, the coldest CLAVR-x POES AVHRR Cloud Top Temperature value was -81º C, with maximum Cloud Top Height values of 15 km along the southwestern portion of the MCS.
This image of Radar Composites of the main line of storms was produced by Greg Carbin of SPC and was posted on Facebook on 13 July 2015.
EUMETSAT Meteosat-10 SEVIRI High Resolution Visible (0.8 µm) images (above; click to play animation) showed the development of an isolated supercell thunderstorm that produced large hail and a violent tornado (1 fatality; estimated EF3 damage) near Venice, Italy (station identifier LIPZ) around 1530 UTC on 08 July 2015. Additional information and imagery is available from meteonetwork.
The corresponding Meteosat-10 Infrared (10.8 µm) images (below; click to play animation) revealed the development of a very cold overshooting top prior to the development of the tornado (1430-1500 UTC) — the minimum cloud-top IR brightness temperature was -70º C (darker black enhancement) on the 1445 UTC image. The overshooting top then rapidly collapsed, as seen by the warming cloud-top IR brightness temperatures on the 1515 and 1530 UTC images. Such an overshooting top collapse sometimes occurs prior to tornado formation in a supercell thunderstorm.
A close-up view of the 1500 UTC Metosat-10 Infrared (10.8 µm) image is shown below, as displayed using SSEC RealEarth.