Experimental Tornado Warning in Hastings, NE

One forecaster in the Hastings, NE WFO issued an experimental tornado warning based on his interrogation of base velocity data at 2137 UTC 01 May 2018.  The forecaster noted the ProbSevere All Hazards probability of tornado was low (9%) at the time he decided to issue the warning (2134 UTC), but then jumped to 40% in the following scan (see Figure 1).  The probability of tornado values continued to increase into the 60% range.  The forecaster commented, he realized the rotation increase he noted in base data took a few minutes to be captured in the MRMS AzShear fields and hence ProbSevere All Hazards.  In this case he said the probability of tornado confirmed his decision to warn and it gave him confidence in the probability of tornado, but to keep aware of the latency in base data into derived products.  This storm did produce a brief tornado shortly after the warning issuance.

Figure 1. KUEX 0.5 degree storm-relative velocity and ProbSevere All Hazards probability of tornado contours over Nebraska 2132-2142 UTC 01 May 2018.

-J. Sieglaff