Midwest mayhem

Warm muggy weather under northwest flow churned out a number of supercell thunderstorms last Saturday, June 11th, producing huge hail (up to 3.75" in diameter), damaging winds, and tornadoes. 

ProbSevere LightningCast gave a heads up on the quickly developing convection in Nebraska and Iowa (see Figure 1), with lead-times ranging from 10 to 40 minutes prior to the first flashes in several storms (measured from the 25% probability threshold). LightningCast is adept at predicting lightning in the next hour using GOES-R ABI images as predictors.

Figure 1: LightningCast contours, GOES-16 ABI day land cloud convection RGB, and GOES-16 GLM flash-extent density over the Missouri River valley.

ProbSevere v3, being evaluated at the HWT this month, quickly picked up on the developing convection, using the juicy environmental parameters, increases in total lightning flash rates, and strong satellite growth rates to predict increasing probabilities of severe weather. Numerous forecasters at the HWT have noted that increases in ProbSevere helps them identify potential threats more quickly.

Figure 2: ProbSevere v3 contours, MRMS MergedReflectivity, and NWS severe weather warnings.

Several supercells that spawned in Nebraska were soon tornado-warned and at least one produced multiple tornadoes, destroying trees, power lines, outbuildings, as well as industrial buildings in Maryville, KS. ProbTor v3, which is generally more conservative than version 2, had elevated probabilities of tornado before version 2 did. At 21:26 UTC, 6 minutes before the first tornado warning was issued, ProbTor v3 was 25%, whereas ProbTor v2 was only 1% (for the storm in Figure 3). In this case, the strong STP (2.6) and effective storm-relative helicity (SRH, 200 m2/s2), as well as the high MRMS MESH, were contributing to the enhanced probability of tornado for version 3, whereas the 0-1 km SRH in version 2 was relatively low (60 m2/s2). Forecasters should take note when ProbTor v3 is markedly higher than ProbTor v2.

Figure 3: ProbSevere contours (outer contours is colored by ProbTor v3 probability), MRMS MergedReflectivity, and NWS severe weather warnings for supercells in southeast Nebraska.