Storms surging in northeast Texas

As we begin today's HWT shift, storms are already developing quickly. ProbSevere LightningCast was able to readily give objective probabilistic guidance on the next-hour probability of lightning for these storms, which developed under clear skies.

Figure 1: LightningCast probabilities (contours), GOES-16 ABI daytime cloud phase distinction RGB (background), and GOES-16 GLM flash-extent density (orange-foreground). 

The Dallas / Fort Worth metro is seeing severe hail from these rapidly developing storms. The GOES-R satellite growth rates are contributing to high probabilities of severe for both ProbSevere v2 and v3 (huge CAPE and effective shear doesn't hurt, either). 

Figure 2: ProbSevere v3 contours, MRMS MergedReflectivity, and NWS severe weather warnings for storms near the Dallas / Fort Worth metro.

Just a couple of central Texas hailers

Forecasters in moisture-poor Midland, TX yesterday were peeking into central Texas with envy, as surface dewpoint temperatures and resultant CAPE were much higher. One testbed forecaster noted that ProbSevere LightningCast was his first indication of strengthening convection to their east (Figure 1).

Figure 1: ProbSevere LightningCast contours, GOES-16 day-cloud phase distinction RGB, and GOES-16 GLM flash extent density for two storms in central Texas.

ProbSevere v3 later had a handle on these storms, which developed in an environment of strong CAPE (> 3000 J/kg) and modest effective shear (35-40 kt). Strengthening radar signatures, moderate satellite growth rates, and increasing total lightning flash rates helped to boost the PSv3 probabilities. PSv3 again ramped up probabilities before PSv2, whereas PSv2 probabilities were higher at peak maturity. Each storm produced severe hail (1.5" and 2" diameters, respectively). 

Figure 2: ProbSevere v3 contours, MRMS MergedReflectivity, and NWS severe weather warnings for two storms in central Texas. 

Convection in the heart of Texas

An amplified trough and associated lee cyclone developed in west-central Texas Sunday afternoon, with a dryline generating strong supercell thunderstorms. The Storm Prediction Center upgraded their outlook to a moderate risk at 16:30 UTC for mainly large hail and strong tornadoes.

The NOAA/CIMSS ProbSevere model was able to capture the strong initial convection along the dryline, with GOES East IR observations, as the satellite transitioning to rapid-scan operation.

In a very unstable and moderately sheared environment, a strong normalized vertical growth rate and less than 0.5" of MESH gave the first storm of the day a probability of severe of 34% at 17:32Z (see animation below). Ten minutes later, MESH was 0.65" and the probability accordingly rose to 58%. By 17:50Z, MESH was 0.85" and the probability was 81%. The first severe thunderstorm warning was issued at 17:52Z, 10 min after the first probability ≥ 50%.

Two counties to the south, strong vertical growth and moderate storm-top glaciation rate, along with 0.52" of MESH, combined for a 55% probability at 17:58Z. Four minutes later, the probability jumped to 72%, and 6 min after that (18:08Z) it increased to 80%, as MESH increased to 0.8". This storm was first severe-warned at 18:21Z. Softball hail was later reported from this storm, in Shackelford County.

Further south along the dryline, another storm had very strong satellite growth rates, and probability of severe of 83% by 18:26Z (MESH = 0.62"). This storm was warned at 15 min later at 18:41Z. This storm would go on to produce grapefruit-sized hail and large tornadoes SW of Forth Worth, TX.

ProbSevere was able to highlight the severe potential in these storms up to 20 min before the first warnings were issued. It should be noted that ProbSevere is meant to be a 'quick-look' additional guidance to forecasters, and not provide a warn/no-warn decision at some magical probability threshold. Future development of ProbSevere will incorporate other NWP, radar, and possibly satellite fields to hone in on a probability of tornado in the very short term.

John Cintineo

UW-CIMSS