GOES-16 (GOES-East) Mid-level Water Vapor (6.9 µm) images (above) showed the circulation associated with a midlatitude cyclone that moved southeastward from southern Canada across the Upper Midwest on 09 May 2020. This system brought a variety of precipitation to the region, including snow with several inches of accumulation in parts of North Dakota and Minnesota.

Anomalously strong winds were associated with this storm, which produced peak wind gusts of 60 mph or higher in North Dakota and South Dakota — hourly surface winds with gusts are plotted on GOES-16 Water Vapor images (below).

GOES-16 Day Cloud Phase Distinction RGB images (below) revealed the northwest-to-southeast oriented swath of fresh snowfall (brighter shades of green) from eastern Saskatchewan ad western Manitoba into north-central North Dakota. The edges of the snow swath began to rapidly melt during the day, due to the warming power of the early May sun.

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As the surface low’s occluded front moved across southern Wisconsin on the morning of 10 May, GOES-16 Day Cloud Phase Distinction RGB images (above) provided a nice depiction of of the brief period of dynamic cooling and transition from rain to snow as glaciated cloud tops (shades of green) blossomed over the Madison (KMSN) area.

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JMA Himawari-8 True Color Red-Green-Blue (RGB) images created using Geo2Grid (above) showed a cloud of dust moving southeastward off the coast of Victoria and New South Wales, Australia on 08 May 20120.

A more subtle signature of the airborne dust (shades of pink) was seen in a longer animation of Himawari-8 Dust RGB images (below), which included nighttime periods prior to and after the True Color image sequence.

The dust cloud was also apparent in a Suomi NPP VIIRS True Color RGB image as viewed using RealEarth (below).

Thick and large haze cloud coming of Australia , it could be dust (AEs are low) but cannot rule out resuspended ash from last summer’s fires. pic.twitter.com/Hcwz55oufi

— Santiago Gassó (@SanGasso) May 8, 2020

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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).

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.

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).

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 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.

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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)

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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.

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.

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?

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.

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.

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

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