Severe thunderstorms in Wyoming and South Dakota

June 29th, 2018 |

GOES-16

GOES-16 “Red” Visible (0.64 µm) images, with SPC storm reports plotted in red [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 large clusters of thunderstorms that moved from northeastern Wyoming into South Dakota during the afternoon and evening hours on 29 June 2018. These storms produced a variety of severe weather (SPC storm reports | NWS Rapid City), including tornadoes, hail of 4.50 inches in diameter and damaging wind gusts of 90 mph.

The corresponding GOES-16 “Clean” Infrared Window (10.3 µm) images (below) indicated that the coldest cloud-top infrared brightness temperatures associated with the strongest overshooting tops were generally around -70ºC (black enhancement).

GOES-16

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

GOES-16 Mid-level Water Vapor (6.9 µm) images (below) revealed a shortwave trough which was moving eastward across the northern Rocky Mountains — the approach of this mid-tropospheric trough was bringing enhanced forcing for ascent to aid in the development of thunderstorms.

GOES-16 Mid-level Water Vapor (6.9 µm) images [click to play MP4 animation]

GOES-16 Mid-level Water Vapor (6.9 µm) images [click to play MP4 animation]

===== 30 June Update =====

A comparison of before/after Terra MODIS True Color Red-Green-Blue (RGB) images viewed using RealEarth (below) revealed a pair of crop/vegetation damage swaths — the first (oriented northwest to southeast) caused by storms early on 27 June, and the second (oriented approximately west to east) caused by the 29 June storms shown on the GOES-16 imagery above. One SPC storm report listed hail of 2.00 inches in diameter with winds gusting to 69 mph near Mission Ridge SD — wind-driven hail of that size can easily inflict significant damage to structures and vegetation.

Terra MODIS True-Color images on 26 June, 27 June and 30 June [click to enlarge]

Terra MODIS True Color RGB images on 26 June, 27 June and 30 June [click to enlarge]

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

Aqua MODIS True Color RGB image [click to enlarge]

Aqua MODIS True Color RGB image [click to enlarge]

An Aqua MODIS True Color RGB image on 02 July (above) provided a cloud-free view of the segmented west-to-east 29 June hail/wind damage path across western/central South Dakota — NWS Aberdeen noted that the storm producing this damage traveled more than 420 miles. In addition, the hazy signature of smoke being transported northeastward (from wildfires in Colorado) was apparent at the bottom center of the image. These hail/wind damage swaths (as well as the wildfire smoke aloft) were also evident in GOES-16 Natural Color RGB imagery.

Looking at the corresponding Aqua MODIS Visible (0.65 µm) image, Normalized Difference Vegetation Index (NDVI) product and Land Surface Temperature (LST) product (below), the hail/wind damage swaths were characterized by NDVI values in the 0.2-0.4 range (compared to adjacent healthy vegetation values of 0.7-0.8) and LST values  warmer than 100-110ºF (adjacent healthy vegetation LST values were generally in the 80s F). The lowest NDVI values were observed in parts of Sully and Hughes Counties, within the northwest-to-southeast 27 June damage path — there were reports of extensive crop devastation and wildlife casualties in that area (media story).

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

Aqua MODIS Visible (0.65 µm) image, Normalized Difference Vegetation Index (NDVI) product and Land Surface Temperature (LST) product [click to enlarge]

Severe thunderstorms in the Southeast US

June 25th, 2018 |

GOES-16

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

GOES-16 (GOES-East) “Clean” Infrared Window (10.3 µm) images (above) showed the development of thunderstorms which produced small hail and widespread damaging winds (SPC storm reports) across the Southeast US on 25 June 2018.

A closer view of the storms was provided by GOES-16 “Red” Visible (0.64 µm) images (below).

GOES-16

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

A toggle between an 1854 UTC Aqua MODIS Infrared Window (11.0 µm) image and the corresponding Total Precipitable Water derived product (below) showed that abundant moisture was in place across the region — as pointed out by a SPC Mesoscale Discussion, TPW values in excess of 2.0 inches (50 mm, violet enhancement) suggested that wet microbursts were likely with any thunderstorms that developed.

Aqua MODIS Infrared Window (11.0 µm) image and Total Precipitable Water derived product, with plots of SPC storm reports [click to enlarge]

Aqua MODIS Infrared Window (11.0 µm) image and Total Precipitable Water derived product, with plots of SPC storm reports [click to enlarge]



Waves over the Upper Midwest / Great Lakes

June 23rd, 2018 |

GOES-16

GOES-16 “Red” Visible (0.64 µm) images, with hourly plots of surface reports [click to play animation]

GOES-16 (GOES-East) “Red” Visible (0.64 µm) images (above) revealed a curious pattern of waves moving east-northeastward across a patch of mid-level clouds over central Lake Michigan during the morning hours on 23 June 2018.

In an effort to determine the vertical extent of these waves, a look at GOES-16 Low-level Water Vapor (7.3 µm), Mid-level Water Vapor (6.9 µm) and Upper-level Water Vapor (6.2 µm) images from the UW-Madison AOS site (below) showed a signature of waves propagating northeastward across the region during the 0802-2102 UTC time period.

GOES-16 Low-level Water Vapor (7.3 µm) images [click to play MP4 animation]

GOES-16 Low-level Water Vapor (7.3 µm) images [click to play MP4 animation]

GOES-16 Mid-level Water Vapor (6.9 µm) images [click to play MP4 animation]

GOES-16 Mid-level Water Vapor (6.9 µm) images [click to play MP4 animation]

GOES-16 Upper-level Water Vapor (6.2 µm) images [click to play MP4 animation]

GOES-16 Upper-level Water Vapor (6.2 µm) images [click to play MP4 animation]

There also were scattered pilot reports of light to moderate turbulence across the region as these waves were moving through, including one report of continuous Clear Air Turbulence at 36,000 feet over eastern Wisconsin.  Due to the subtle nature of these waves, their signature was not as obvious in the 8-bit McIDAS-X Water Vapor images shown below as they were in 16-bit imagery displayed above (or what would be displayed using AWIPS II).

GOES-16 Low-level (7.3 µm) images, with hourly pilot reports of turbulence [click to play animation]

GOES-16 Low-level Water Vapor (7.3 µm) images, with hourly pilot reports of turbulence [click to play animation]

GOES-16 Mid-level (6.9 µm) images, with hourly pilot reports of turbulence [click to play animation]

GOES-16 Mid-level Water Vapor (6.9 µm) images, with hourly pilot reports of turbulence [click to play animation]

GOES-16 Upper-level (6.2 µm) images, with hourly pilot reports of turbulence [click to play animation]

GOES-16 Upper-level Water Vapor (6.2 µm) images, with hourly pilot reports of turbulence [click to play animation]

The waves were passing over eastern Wisconsin around the time of ascent of the 12 UTC sounding balloon launched from Green Bay (and continuous turbulence was reported at 38,000 feet) — a plot of weighting functions for the three GOES-16 Water Vapor bands (below) showed peak pressures in the 424-328 hPa (22,800-28,885 feet) range, although significant contributions of energy were still evident from the 300 hPa pressure level (31,000 feet) or higher.

GOES-16 Water Vapor weighting functions, calculated using 12 UTC rawinsonde data from Green Bay, Wisconsin [click to enlarge]

GOES-16 Water Vapor weighting functions, calculated using 12 UTC rawinsonde data from Green Bay, Wisconsin [click to enlarge]

About an hour prior to the start of the 2-km resolution (at nadir or sub-satellite point) GOES-16 Water Vapor animations, 1-km resolution Aqua MODIS Water Vapor (6.7 µm) imagery at 0801 UTC (below) showed a long narrow wave packet (oriented northwest to southeast) from far western Wisconsin to central Illinois — and these waves were also apparent along the tops of mid-level clouds along the Iowa/Illinois border. Was this the leading edge of the waves seen farther northeast over the Great Lakes during the subsequent morning and afternoon hours?

Aqua MODIS Water Vapor (6.7 µm) and Infrared Window (11.0 µm) images, with plots of pilot reports [click to enlarge]

Aqua MODIS Water Vapor (6.7 µm) and Infrared Window (11.0 µm) images, with plots of pilot reports [click to enlarge]

All things considered, the lack of a clear forcing mechanism for these waves qualifies this case to be placed into the “What the heck is this” blog category until a coherent explanation can be put forward…

Summer solstice TROWAL over the Upper Midwest

June 21st, 2018 |

Aqua MODIS Water Vapor (6.7 µm) image, with overlays of surface pressure/fronts (cyan), RUC model 310K equivalent potential temperature (red) and 24-hour precipitation (green) [click to enlarge]

Aqua MODIS Water Vapor (6.7 µm) image, with overlays of surface pressure/fronts (cyan), RUC model 310K equivalent potential temperature (red) and 24-hour precipitation (green) [click to enlarge]

A nighttime Aqua MODIS Water Vapor (6.7 µm) image (above) showed the well-defined circulation of a mid-latitude cyclone that was centered over northwest Iowa at 0814 UTC (3:14 am local time) on 21 June 2018. Contours of RUC model equivalent potential temperature along the 310 K isentropic surface indicated that a Trough of Warm Air Aloft (TROWAL) existed just to the north of the occluded surface frontal boundary, curving cyclonically from northeastern Iowa across southern Minnesota into southeastern South Dakota and then southward across eastern Nebraska. 24-hour precipitation totals in excess of 2-3 inches had already been observed at that time.

Suomi NPP VIIRS Infrared Window (11.45 µm) images (below) displayed minimum cloud-top brightness temperature values of -50 to -55ºC (yellow to orange enhancement) near the TROWAL axis.

Suomi NPP VIIRS Infrared Window (11.45 µm) images, with plots of surface reports [click to enlarge]

Suomi NPP VIIRS Infrared Window (11.45 µm) images, with plots of surface reports [click to enlarge]

An animation of GOES-16 (GOES-East) Mid-level Water Vapor (6.9 µm) images (below) revealed that the storm system moved very slowly during the 00-20 UTC time period, while moderate to occasionally heavy rainfall was observed beneath the TROWAL air stream. 24-hour precipitation amounts reached 4-6 inches by 12 UTC in parts of southwest Minnesota, northwest Iowa and southeast South Dakota (FSD PNS) — and a number of river gauges were reporting minor to major flooding by the afternoon hours.

GOES-16 Mid-level Water Vapor (6.9 µm) images, with hourly plots of surface weather type [click to play MP4 animation]

GOES-16 Mid-level Water Vapor (6.9 µm) images, with hourly plots of surface weather type [click to play MP4 animation]

It should be noted that TROWAL formation is rather unusual over this region during the summer months — but during the cold season a TROWAL can help to produce heavy snowfall (some examples are documented here, here and here).