Severe thunderstorms in Kansas and Oklahoma

June 23rd, 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 a number of Mesoscale Convective System (MCS) features across the southern Plains (with a focus on Kansas and Oklahoma) after sunset on 23 June 2018. A Mesoscale Domain Sector was positioned over that region, providing images at 1-minute intervals; SPC storm reports are plotted in cyan.

A toggle between Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images at 0748 UTC or 2:48 am CDT (below) showed two MCS features — one with its core in north-central Oklahoma and another over eastern Oklahoma. Features exhibited by the northern storm included numerous bright lightning streaks on the Day/Night Band image, with one cluster located over an area of damaging wind reports. The minimum cloud-top infrared brightness temperature associated with this storm was -86ºC (violet enhancement). Over Kansas, packets of gravity waves could be seen on both images, propagating radially outward from the storm core along the cloud top. The combination of lightning and damaging winds (which downed power poles) led to power outages that lasted into the next evening (map | provider listing) across parts of Oklahoma.

With the MCS over eastern Oklahoma, a large cluster of bright lightning streaks was co-located with the overshooting top (which had a minimum cloud-top infrared brightness temperature of -80ºC) — and a distinct above-anvil plume could be seen flowing east-southeastward from the overshooting top.

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images, with SPC storm reports of damaging winds plotted in cyan [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images, with SPC storm reports of damaging winds plotted in cyan [click to enlarge]

About 48 minutes later, a 0836 UTC overpass of the NOAA-20 satellite provided similar VIIRS Day/Night Band and Infrared Window images (below). However, in that relatively short amount of time the Moon had moved to a position low on the western horizon, providing much less illumination of the cloud tops for the Day/Night Band image. Another striking difference was the presence of long black or dark gray “post-saturation recovery streaks” downstream of bright clusters of lightning in north-central Oklahoma — as the VIIRS instrument scanned across-track (from northwest to southeast), the Day/Night Band optical detectors became saturated by the brightness of the intense lightning activity. The minimum cloud-top infrared brightness temperature in eastern Oklahoma was -86ºC.

NOAA-20 VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images [click to enlarge]

NOAA-20 VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images [click to enlarge]

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).

Mesoscale Convective System in the Plains

June 11th, 2018 |

GOES-16

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

A Mesoscale Convective System (MCS) developed over eastern Nebraska early in the evening on 11 June 2018, then propagated southward across the Plains during the subsequent overnight hours. GOES-16 (GOES-East) “Clean” Infrared Window (10.3 µm) images with plots of SPC storm reports are shown above; a Mesoscale Sector was positioned over the region, providing images at 1-minute intervals.

A closer look over Kansas using Infrared imagery from polar-orbiting satellites (below) revealed some very cold cloud-top infrared brightness temperatures, which included -87ºC on MODIS, -90ºC on VIIRS and -92ºC on AVHRR.

POES AVHRR, Terra/Aqua MODIS and Suomi NPP VIIRS Infrared images, with plots of SPC storm reports [click to enlarge]

Metop-B AVHRR, Terra/Aqua MODIS and Suomi NPP VIIRS Infrared images, with plots of SPC storm reports [click to enlarge]

The coldest air temperature on 00 UTC rawinsonde data from Dodge City and Topeka, Kansas (below) was -69.5ºC (at altitudes of 14.6 km/49,900 feet at Dodge City, and 17.6 km/57,700 feet at Topeka) — so in theory air parcels and cloud material within a vigorous overshooting top could have ascended a few km (or thousands of feet) beyond those altitudes to exhibit an infrared brightness temperature of -92ºC.

Plots of rawinsonde data from Dodge City and Topeka, Kansas [click to enlarge]

Plots of rawinsonde data from Dodge City and Topeka, Kansas [click to enlarge]

A toggle between re-mapped versions of the GOES-16 ABI and Metop-B AVHRR Infrared imagery over Kansas at the time of the very cold cloud-top infrared brightness temperature (below) revealed 2 important points: (1) with improved spatial resolution (1 km for AVHRR, vs 2 km *at satellite sub-point* for ABI) the instrument detectors sensed much colder temperatures (-92.6ºC with AVHRR vs -81.2ºC with ABI), and (2) due to parallax. the GOES-16 image features are displaced to the northwest. In addition to the isolated cold overshooting top in south-central Kansas, note the pronounced “Enhanced-V” storm top signature in far northeastern Kansas.

Comparison of GOES-16 ABI and Metop-B AVHRR Infrared images [click to enlarge]

Comparison of GOES-16 ABI and Metop-B AVHRR Infrared images [click to enlarge]

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Cape Newenham, Alaska bow shock waves

June 10th, 2018 |

GOES-15 Visible (0.63 µm) images, with hourly plots of wind barbs [click to play animation]

GOES-15 Visible (0.63 µm) images, with hourly plots of wind barbs [click to play animation]

GOES-15 (GOES-West) Visible (0.63 µm) images (above) showed patches of fog and low stratus moving southwestward off Southwest Alaska and across the adjacent offshore waters of the Bering Sea on 10 June 2018.

A closer look using 250-meter resolution Terra/Aqua MODIS and 375-meter resolution Suomi NPP VIIRS true-color Red-Green-Blue (RGB) images from RealEarth (below) revealed a packet of “bow shock waves” created as the shallow fog/stratus interacted with the relatively rugged terrain of the narrow Cape Newenham land feature (Google Maps). Other examples of similar bow shock wave cloud features have been documented here, here and here.

Terra MODIS, Aqua MODIS and Suomi NPP VIIRS true-color RGB images [click to enlarge]

Terra MODIS, Aqua MODIS and Suomi NPP VIIRS true-color RGB images [click to enlarge]

A 30-meter resolution Landsat-8 false-color RGB image (below) provided a more detailed view of the bow shock wave structure. Snow cover (cyan) could be seen on some of the higher-elevation land features.

Landsat-8 false-color RGB image [click to enlarge]

Landsat-8 false-color RGB image [click to enlarge]

A time series plot of Cape Newenham surface observations (below) showed the fluctuations in visibility as northerly winds brought patches of fog over the site.

Time series plot of Cape Newenham surface observations [click to enlarge]

Time series plot of Cape Newenham surface observations [click to enlarge]