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!

Remnants of Hurricane Beryl off the East Coast of the US

July 13th, 2018 |

GOES-16

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

GOES-16 (GOES-East) “Red” Visible (0.64 µm) images (above) depicted the remnants of Hurricane Beryl, which was situated off the East Coast of the US on 13 July 2018. Note the presence of 2 apparent low-level circulation centers — the primary circulation became better exposed as areas of deep convection moved more quickly to the east.

Overlays of low-level (produced using Visible Band 2) and upper-level (produced using Water Vapor Band 8) Derived Motion Winds (below) highlighted the primary low-level circulation, as well as the trough aloft whose axis was located just to the west.

GOES-16

GOES-16 “Red” Visible (0.64 µm) images, with low-level (Visible Band 2) Derived Motion Winds plotted in yellow and upper-level (Water Vapor Band 8) Derived Motion Winds plotted in cyan [click to play animation]

Contours of Deep-Layer Wind Shear from the CIMSS Tropical Cyclones site (below) revealed that there was a large gradient in shear over the region at 19 UTC, with higher shear northwest of the system — this verified the subjective appearance of high shear in that particular area, where low-level and upper-level Derived Motion Winds were nearly orthogonal.

GOES-16 Visible (0.64 µm) image, with contours of Deep-Layer Wind Shear [click to enlarge]

GOES-16 Visible (0.64 µm) image, with contours of Deep-Layer Wind Shear [click to enlarge]

Super Typhoon Maria

July 5th, 2018 |

Himawari-8 Visible (0.64 µm, left) and Infrared Window (10.4 µm, right) images [click to play MP4 animation]

Himawari-8 “Red” Visible (0.64 µm, left) and “Clean” Infrared Window (10.4 µm, right) images [click to play MP4 animation]

Typhoon Maria underwent a period of rapid intensification (ADT | SATCON) while it was just northwest of Guam late in the day on 05 July 2018, becoming the first Category 5 Super Typhoon of the 2018 West Pacific season. Rapid-scan Himawari-8 “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.4 µm) images (above) showed Maria during this period of rapid intensification. Cloud-top infrared brightness temperatures reached -80ºC (violet enhancement) at times in the eyewall of the storm.

A GPM GMI Microwave (85 GHz) image from the CIMSS Tropical Cyclones site (below) showed the pinhole eye of Maria around the time it reached Category 5 intensity. The tropical cyclone was moving over water with high values of Ocean Heat Content — and was in an environment characterized by low values of Deep-layer Wind Shear.

GPM GMI Microwave (85 GHz) image [click to enlarge]

GPM GMI Microwave (85 GHz) image [click to enlarge]

Mesovortices could be seen within the eye on Himawari-8 Visible imagery (below). However, note how the eye became less distinct and increased in diameter toward the end of the animation.

Himawari-8

Himawari-8 “Red” Visible (0.64 µm) images [click to play MP4 animation]

Shortly after 00 UTC on 06 July, Maria began the process of an eyewall replacement cycle as shown in MIMIC TC morphed microwave imagery (below) — and during the following 6-12 hours a decreasing trend in storm intensity was seen (ADT | SATCON).

MIMIC TC morphed microwave image product [click to play animation]

MIMIC TC morphed microwave image product [click to play animation]

A toggle between Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images at 1603 UTC on 06 July (below; courtesy of William Straka, CIMSS) showed Category 4 Typhoon Maria after the eye had filled following the eyewall replacement cycle.

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images [click to enlarge]

===== 08 July Update =====

Himawari-8

Himawari-8 “Clean” Infrared Window (10.4 µm) images [click to play MP4 animation]

Super Typhoon Maria re-intensified to Category 5 intensity at 12 UTC on 08 July (SATCON) — Himawari-8 “Clean” Infrared Window (10.4 µm) images (above) displayed a large (30 nautical mile wide) eye. The subtle signature of mesovortices could be seen rotating within the eye.

During the preceding daylight hours, Himawari-8 “Red” Visible (0.64 µm) images (below) showed the eye mesovortices in better detail.

Himawari-8

Himawari-8 “Red” Visible (0.64 µm) images [click to play MP4 animation]

However, Maria was again downgraded to a Category 4 storm at 00 UTC on 09 July, as another eyewall replacement cycle took place (DMSP-17 microwave image) and the storm began to move over water having slightly cooler Sea Surface Temperature and Ocean Heat Content. The eye and its mesovortices continued to be prominent in Himawari-8 Visible and Infrared imagery (below).

Himawari-8

Himawari-8 “Red” Visible (0.64 µm, left) and “Clean” Infrared Window (10.4 µm, right) images [click to play MP4 animation]

Hurricane Aletta

June 7th, 2018 |

GOES-16

GOES-16 “Red” Visible (0.64 µm, left) and “Clean” Infrared Window (10.3 µm, right) images [click to play MP4 animation]

Tropical Storm Aletta was upgraded to Hurricane Aletta at 21 UTC on 07 June 2018. As was the case on 06 June, a GOES-16 Mesoscale Domain Sector centered over the tropical cyclone provided 1-minute data — and an eye eventually became apparent on  “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.3 µm) imagery (above).

DMSP-15, DMSP-17 and GPM GMI Microwave (85 GHz) imagery from the CIMSS Tropical Cyclones site (below) showed an increase in organization of the eye structure as the day progressed.

DMSP-15 SSMI Microwave image [click to enlarge]

DMSP-15 SSMI Microwave image [click to enlarge]

DMSP-17 SSMIS Microwave image [click to enlarge]

DMSP-17 SSMIS Microwave image [click to enlarge]

GPM GMI Microwave image [click to enlarge]

GPM GMI Microwave image [click to enlarge]

===== 08 June Update =====

GOES-16

GOES-16 “Clean” Infrared Window (10.3 µm) images [click to play MP4 animation]

Aletta went through a period of rapid intensification (ADT | SATCON), reaching Category 4 status by 15 UTC on 08 June. 1-minute GOES-16 Infrared (10.3 µm) images (above) showed the eye becoming more well-defined during the pre-dawn hours.

After sunrise, GOES-16 Visible images (below) initially hinted at the presence of mesovortices within the eye of Aletta.

GOES-16

GOES-16 “Red” Visible (0.64 µm, left) and “Clean” Infrared Window (10.3 µm, right) images [click to play MP4 animation]

Aletta had been moving over relatively warm water and within an environment characterized by low values of deep-layer wind shear (below) — both  of which were favorable factors for intensification. An animation of the deep-layer wind shear over the East Pacific Ocean during 06-07 June is available here.

Sea Surface Temperature and Deep-Layer Wind Shear products [click to enlarge]

Sea Surface Temperature and Deep-Layer Wind Shear products [click to enlarge]

Aletta peaked in intensity later in the day on 08 June (ADT | SATCON) — as pointed out by NHC “This is also consistent with GOES-16 measurements of increased inner-core lightning observed to be occurring to the east of the eastern eyewall, which some research suggests corresponds to a halting of the intensification process”. GOES-16 Infrared (10.3 µm) imagery with GLM Group Density counts are shown below.

GOES-16

GOES-16 “Clean” Infrared Window (10.3 µm) with GLM Group Density counts [click to play MP4 animation]