Tornadoes in Wyoming

July 28th, 2018 |

GOES-16

GOES-16 “Red” Visible (0.64 µm) images, with hourly plots of surface observations (cyan/yellow) along with SPC storm reports and Interstate Highways (red) and State Highways (cyan) [click to play MP4 animation]

1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) images (above) showed the development of a supercell thunderstorm that produced tornadoes, large hail and damaging winds (SPC storm reports) across parts of eastern Wyoming on 28 July 2018. A distinct above-anvil cirrus plume could be seen with this storm.

The corresponding GOES-16 “Clean” Infrared Window (10.3 µm) images (below) revealed that the dominant northern storm began to exhibit a well-defined “enhanced-V” signature (2051 UTC image) about an hour before it began to produce tornadoes. Minimum cloud-top infrared brightness temperatures were in the -60 to -65ºC range (darker shades of red) with the stronger pulses of overshooting tops.

GOES-16 "Clean" Infrared Window (10.3 µm) images, with hourly plots of surface observations (yellow) along with SPC storm reports (cyan) Interstate Highways (violet) and State Highways (cyan) [click to play MP4 animation]

GOES-16 “Clean” Infrared Window (10.3 µm) images, with hourly plots of surface observations (yellow) along with SPC storm reports (cyan) Interstate Highways (violet) and State Highways (cyan) [click to play MP4 animation]

A sequence of Infrared Window images from Suomi VIIRS (11.45 µm) and Aqua MODIS (11.0 µm) (below) showed minimum cloud-top infrared brightness temperatures rapidly cooling from the -40s to -72ºC as the dominant storm crossed Interstate 25.

Suomi NPP VIIRS and Aqua MODIS Infrared Window images [click to enlarge]

Infrared Window images from Suomi NPP VIIRS (11.45 µm) and Aqua MODIS (11.0 µm) [click to enlarge]

A comparison of the Terra and Aqua MODIS Total Precipitable Water product (below) indicated that TPW values increased from the 10-20 mm range to the 20-30 mm range in less than 2 hours.

Terra and Aqua MODIS Total Precipitable Water product [click to enlarge]

Terra and Aqua MODIS Total Precipitable Water product [click to enlarge]

Large hail and high winds in South Dakota and Nebraska

July 27th, 2018 |

GOES-16

GOES-16 “Red” Visible (0.64 µm) images, with SPC storm reports plotted in red [click to play MP4 animation]

A supercell thunderstorm which developed in southeastern Montana during the afternoon hours on 27 July 2018 produced damaging wind-driven hail as it moved southeastward across western South Dakota into far northern Nebraska (SPC storm reports | NWS Rapid City summary). 1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) images (above) showed the evolution of this storm.

The corresponding GOES-16 “Clean” Infrared Window (10.3 µm) images (below) revealed minimum cloud-top infrared brightness temperatures in the -60 to -70ºC range (darker red to black enhancement) with the strongest pulses of overshooting tops. The storm began to exhibit a well-defined “enhanced-V” signature once it crossed the South Dakota / Nebraska border after about 0200 UTC.

GOES-16

GOES-16 “Clean” Infrared Window (10.3 µm) images, with SPC storm reports plotted in purple [click to play MP4 animation]

 


===== 30 July Update =====

Terra MODIS True Color and False Color RGB images [click to enlarge]

Terra MODIS True Color and False Color RGB images, with hail damage swath highlighted by red arrows [click to enlarge]

A comparison of 250-meter resolution Terra MODIS True Color and False Color Red-Green-Blue (RGB) images from the MODIS Today site (above) showed the northwest-to-southeast hail damage swath across southwestern South Dakota on 30 July.

Before/after (16/30 July) comparisons of MODIS True Color RGB images viewed using RealEarth and MODIS Today (below) further illustrate the appearance of the hail damage swath.

MODIS True Color RGB images from 16 July and 30 July [click to enlarge]

Terra MODIS True Color RGB images from 16 July and 30 July [click to enlarge]

Terra MODIS True Color RGB images from 16 and 30 July [click to enlarge]

Terra MODIS True Color RGB images from 16 July and 30 July [click to enlarge]

In a comparison between the 30 July Terra MODIS Visible (0.65 µm) image and the corresponding Land Surface Temperature (LST) and Normalized Difference Vegetation Index (NDVI) products (below), within the core of the hail damage swath (near Oglala) LST values warmed into the 90s F and NDVI values were reduced to the 0.2 to 0.3 range (compared to cooler LST values in the 80s F and higher NDVI values of 0.3 to 0.6 over healthy vegetation areas immediately adjacent to the damage swath).

Terra MODIS Visible (0.65 µm) image and Land Surface Temperature and Normalized Difference Vegetation Index products [click to enlarge]

Terra MODIS Visible (0.65 µm) image and Land Surface Temperature and Normalized Difference Vegetation Index products [click to enlarge]

===== 31 July Update =====

MODIS True Color RGB images from Terra (14 July) and Aqua (31 July) [click to enlarge]

MODIS True Color RGB images from Terra (14 July) and Aqua (31 July) [click to enlarge]

In a better, more cloud-free before/after comparison of MODIS True Color images from 14 and 31 July (above), it can be seen that the NW-SE oriented hail damage swath extended into Nebraska (where hail as large as 3.0 inches was reported).

Fog/stratus along the New England coast

July 24th, 2018 |

GOES-16 Total Precipitable Water product [click to play animation | MP4]

GOES-16 Total Precipitable Water product [click to play animation | MP4]

The GOES-16 (GOES-East) Total Precipitable Water product (above) showed a northerly/northwesterly flow of tropical moisture toward New England during the day on 24 July 2018, with TPW values in the 1.0 to 1.6 inch range moving toward the region. As this moist air moved over relatively cool water — as indicated by Aqua MODIS Sea Surface Temperature values generally in the 60s F on the previous day (below) — areas of marine boundary layer fog/stratus developed.

Aqua MODIS Sea Surface Temperature product from 23 July [click to enlarge]

Aqua MODIS Sea Surface Temperature product from 23 July [click to enlarge]

1-minue Mesoscale Domain Sector GOES-16 “Red” Visible (0.64 µm) images (below) revealed interesting patterns in the resulting marine layer fog/stratus — for example, bow shock waves along the eastern edges of Nantucket Island and Cape Cod, and narrow clear swaths to the lee of some of the smaller islands off the coast of Maine.

GOES-16

GOES-16 “Red” Visible (0.64 µm) images [click to play MP4 animation]

Cloud-top “warm trench” infrared signature over Colorado

July 22nd, 2018 |

GOES-16

GOES-16 “Clean” Infrared Window (10.3 µm) images, with plots of surface reports [click to play animation | MP4]

GOES-16 “Clean” Infrared Window (10.3 µm) images (above) revealed a well-defined “warm trench” signature (ring of brighter red enhancement) surrounding the cold overshooting top (cluster of pixels enhanced as black to lighter shades of gray) of a thunderstorm in far eastern Colorado during the nighttime hours on 22 July 2018. This warm trench appears to be a ring of compensating subsidence immediately surrounding the vigorous overshooting top; the cold/warm (overshooting_top/warm_trench) “delta-T” on the 0412 UTC image was 16.4ºC (-85.5ºC / -67.1ºC). Just to the south, at 0453 UTC there was a northerly peak wind gust to 45 knots or 52 mph at KITR (Burlington Colorado: plot | text) as the updraft supporting the overshooting top collapsed — but no other SPC storm reports were seen in that area.

A 250-meter resolution Terra MODIS Infrared Window (11.0 µm) imageat 0402 UTC (below) with a slightly different color enhancement showed similar delta-T values (-81ºC/-67ºC) with the overshooting top / warm trench. The diameter of the warm trench was approximately 30-40 miles.

Terra MODIS Infrared Window (11.0 µm) image, with plots of surface reports [click to enlarge]

Terra MODIS Infrared Window (11.0 µm) image, with plots of surface reports [click to enlarge]

A plot of 00 UTC rawinsonde data from North Platte, Nebraska (below) showed a tropopause temperature of -73ºC at an altitude of 15.7 km or 51,500 feet — so the much colder infrared brightness temperatures seen on GOES and MODIS imagery were indicative of a very robust overshooting top that penetrated the tropopause a significant distance.

Plot of 00 UTC rawinsonde data from North Platte, Nebraska [click to enlarge]

Plot of 00 UTC rawinsonde data from North Platte, Nebraska [click to enlarge]

The GOES-16 Cloud Top Height product at 0412 UTC (below) indicated values of 54,000 ft / 49,000 ft for the cold overshooting top / warm trench features — however, note that the resolution of this infrared-derived product is 10 km (and the accuracy is within 1500 feet).

GOES-16 Cloud Top Height derived product at 0412 UTC [click to enlarge]

GOES-16 Cloud Top Height derived product at 0412 UTC [click to enlarge]

Another interesting (and yet-to-be-explained) feature was an arc of warming cloud-top infrared brightness temperatures that was seen propagating southwestward toward the overshooting top / warm trench signature. A larger-scale view (below) showed this wave feature moving from southwestern Nebraska at around 02 UTC to southern Colorado/Kansas by 10 UTC.

GOES-16

GOES-16 “Clean” Infrared Window (10.3 µm) images, with 11.2 µm infrared Derived Motion Winds [click to play animation | MP4]

This cloud-top wave feature was also apparent on GOES-16 Upper-level Water Vapor (6.2 µm) images (below) — at times the wave was tracked by Derived Motion Winds at speeds of 20-30 knots (0252 UTC | 0337 UTC | 0922 UTC). According to rawinsonde data from Dodge City, Kansas (plot | data) as well as North Platte, winds with a northerly to easterly component were only found at altitudes of 20 km or higher!

GOES-16 Upper-level Water Vapor (6.2 µm) images, with 6.2 µm water vapor Derived Motion Winds [click to play animation | MP4]

GOES-16 Upper-level Water Vapor (6.2 µm) images, with 6.2 µm water vapor Derived Motion Winds [click to play animation | MP4]

Special thanks to NWS Grand Rapids forecasters Brett Borchardt and TJ Turnage for bringing this case to our attention!