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)

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