Hail-producing supercell thunderstorm in Texas

May 7th, 2020 |

GOES-16

GOES-16 “Red” Visible (0.64 µm) images, with time-matched SPC Storm Reports plotted in red [click to play animation | MP4]

As a follow-on to this blog post, we will examine the period following convective initiation and take a closer look at the isolated supercell thunderstorm as it produced a long swath of large hail across far northern Texas on 07 May 2020. 1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) images with plots of time-matched SPC Storm Reports (above) revealed pulsing overshooting tops as the storm produced hail as large as 3.25 inches in diameter.

In the corresponding GOES-16 “Clean” Infrared Window (10.35 µm) images (below), the pulsing overshooting tops exhibited infrared brightness temperatures in the -70 to -80ºC range (black to white enhancement).

GOES-16 "Clean" Infrared Window (10.35 µm) images, with time-matched SPC Storm Reports plotted in cyan [click to play animation | MP4]

GOES-16 “Clean” Infrared Window (10.35 µm) images, with time-matched SPC Storm Reports plotted in cyan [click to play animation | MP4]

In a plot of 00 UTC rawinsonde data from Amarillo, Texas (below) the tropopause temperature was -61.7ºC at the 192 hPa (12.4 km) level — warming was seen directly above the tropopause, but then air temperatures cooled to the -60 to -70ºC range within the 122-100 hPa (15.2-16.3 km) layer. Judging from their infrared brightness temperatures, the overshooting tops likely penetrated into those higher levels.

Plot of 00 UTC rawinsonde data from Amarillo, Texas [click to enlarge]

Plot of 00 UTC rawinsonde data from Amarillo, Texas [click to enlarge]

Slightly longer animations of full-bit-depth GOES-16 Visible and Infrared images from AWIPS (below) showed the storm-top features in better detail. One low-level feature of interest was the brief formation of inflow feeder bands along the southwest flank of the storm during the 0015-0035 time period (rocking animation). The gradual north-northwestward flow of hazy, more humid boundary layer air was also apparent (which likely aided and helped to sustain convective development).

GOES-16 "Red" Visible (0.64 µm) and "Clean" Infrared Window (10.35 µm) images [click to play animation | MP4]

GOES-16 “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images [click to play animation | MP4]

A prominent and long-lived Above-Anvil Cirrus Plume (AACP) was seen with this severe thunderstorm — a toggle between GOES-16 Visible and Infrared images at 0105 UTC is shown below. The AACP appeared to exhibit colder infrared brightness temperatures, in agreement with the Amarillo rawinsonde profile at the highest altitudes.

GOES-16 "Red" Visible (0.64 µm) and "Clean" Infrared Window (10.35 µm) images at 0105 UTC [click to enlarge]

GOES-16 “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images at 0105 UTC [click to enlarge]

GOES-16 Visible images with and without an overlay of GLM Flash Extent Density (below) showed how electrically active the storm was. The lighting activity began at 2134 UTC, 1 minute after the cloud-top infrared brightness temperature first became -60ºC or colder.

GOES-16 "Red" Visible (0.64 µm) images, with and without an overlay of GLM Flash Extent Density [click to play animation | MP4]

GOES-16 “Red” Visible (0.64 µm) images, with and without an overlay of GLM Flash Extent Density [click to play animation | MP4]


GOES-17 also viewed the storm development, albeit at a 10-minute time increment because west Texas sits outside of GOES-17’s ‘CONUS’ domain. GOES-17’s more oblique view from the allows the satellite to see more structure on the western flank of the system, particularly beneath the cirrus shield! (Click here for a faster animation)

GOES-17 Band 2 (0.64 µm) Visible Imagery, 2000 UTC on 7 May 2020 through 0200 UTC on 8 May 2020 (Click to animate)

Where will convective initiation occur? NUCAPS can help.

May 7th, 2020 |

GOES-16 Band 2 (0.64 µm) visible imagery, 1900-2030 UTC rocking animation from 7 May 2020 (Click to animate)

Consider the rocking animation (if you click on it) of 1-minute visible imagery, above, showing the high plains of West Texas from 1900-2030 UTC on 7 May 2020. A dryline is present; can you predict from this imagery where convection will initiate? (Will it? Spoiler alert: Yes, and Yes!)

The Split Window Difference field shows the difference in brightness temperatures sensed at 10.3 µm and 12.3 µm. In clear skies, a distinct signal can be apparent along a dryline because of more water vapor absorption at 12.3 µm than at 10.3 µm. (A classic example is shown here, and discussed in this journal article) On 7 May 2020, however, abundant thin cirrus (which cirrus also has a very strong signal in the split window difference) masked much of the surface-based dryline signal.

GOES-16 Split Window Difference (10.3 µm – 12.3 µm) field, 1801-2056 Rocking animation, 7 May 2020 (click to animate)

On 7 May 2020, NOAA-20 overflew the high plains shortly at around 2000 UTC (map, from this site). Data from individual NUCAPS profiles (shown as green, yellow or red dots on the image below) can be interpolated to horizontal grids that allow for an easy presentation of thermodynamic features. Total precipitable water, below, derived from those individual vertical profiles, shows a gradient over west Texas, as expected when a dryline is present.  Any kind of impulse moving eastward from New Mexico will encounter an increasingly moist airmass as it traverses the Texas panhandle.

Gridded NUCAPS estimate of Total Precipitable Water, ca. 2000 UTC on 7 May 2020 (Click to enlarge)

How does NUCAPS gauge the instability of this airmass? Convective Available Potential Energy (CAPE) from the NUCAPS profiles is shown below.  A maximum in CAPE occurs just southwest of Childress, TX.  Perhaps this region of maximum instability is where the strong convection will initiate?

NUCAPS-derived Convective Available Potential Energy, ca. 2000 UTC on 7 May 2020 (Click to enlarge)

Note the NUCAPS sounding profile point that sits within the maximum in CAPE in the image above.  It is green — a color that denotes an infrared retrieval that converged to a solution.  That CAPE-filled vertical profile is show below.

NUCAPS Profile, ca. 2000 UTC on 7 May 2020 at 34.1 N, 100.4 W (Click to enlarge)

Animated visible imagery, below (at a 5-minute time step) — click here to see the animation at every minute) — shows initiation just after 2130 UTC near where the western gradient of the CAPE maximum sits at 2000 UTC.

GOES-16 Band 2 (0.64 µm) visible imagery, 1800-2156 UTC on 7 May 2020 (Click to animate)

The 2356 UTC 7 May 2020 Clean Window image, below, (toggled with the 2056 UTC image) shows the result of rapid development!

GOES-16 Band 13 (10.3 µm) infrared imagery, 2056 and 2356 on 7 May 2020 (Click to enlarge)

Tropical Moisture moving into Florida

May 7th, 2020 |

GOES-16 ABI Band 13 (10.3 µm) Infrared Imagery, 1800 UTC on 7 May 2020 (Click to enlarge)

GOES-16 Clean Window imagery from 1800 UTC on 7 May 2020, above, suggests a frontal zone from the central Atlantic southwestward through the Florida Straits.  What products can be used to diagnose the moisture differences between the dry airmass over the southeast United States/Florida and the far moister airmass over the central and western Caribbean Sea?

Total Precipitable Water is a Baseline Level-2 GOES-16 Product that is produced in clear air, and the toggle of it, with the Clean Window Imagery (and also overlain on top of the Clean Window Imagery), below, shows abundant moisture to the south and east of Florida.  The cloud-free demand of this Level 2 product makes it difficult to determine exactly where the moisture gradient sits.

GOES-16 ABI Band 13 (10.3 µm) Infrared Imagery and Level-2 Total Precipitable Water Product, 1800 UTC on 7 May 2020 (Click to enlarge)

NOAA-20 overflew the east coast of the United States shortly after 1800 UTC on 7 May 2020 (map, from this site).  The gridded field of Total Precipitable Water that was derived from the different vertical profiles (shown below in a toggle with the TPW and the points) shows a tight gradient over central Cuba.

NOAA-20 NUCAPS Profiles and Derived Total Precipitable Water field, ca. 1800 UTC on 7 May 2020 (Click to enlarge)

A strength of the NUCAPS-derived TPW is that it is produced in regions of clear and cloudy skies because it can rely on microwave sounder data in regions where clouds prevent the infrared sounder from giving a complete solution. The toggle below compares the GOES-16 Total Precipitable Water (a global product that gives cloud-free values every hour) with the NUCAPS product that gives an image along the swath).  Both products give similar values of TPW.

GOES-16 Level 2 Total Precipitable Water and NUCAPS Total Precipitable Water, ca. 1800 UTC on 7 May 2020 (Click to enlarge)