The storms over southwestern Oklahoma have recently increased in intensity and have warranted NWS and EWP severe thunderstorm warnings, with multiple reports of quarter to golf ball sized hail.  The ProbSevere values for these storms with golf ball sized hail are well in excess of 90%–even some at 100% for times.  The evolution of these storms and the generation of severe thunderstorm warnings is demonstrated in Figure 1.

A question was posed to the forecasters on the KOUN desk within EWP today, “There have been a number of storms with ProbSevere values in excess of 50% today, some of which seem to be false alarms, is this hampering the use of the product?” The forecasters replied,

“No I like that the storms with the highest ProbSevere probabilities are in excess of 90% and these are the ones producing golf ball sized hail–these are not marginal hail stones. The ProbSevere is drawing me to which storms are likely to need severe warnings in the near future. The false alarm storms, while they have high probabilities today, are in the 70-85% range–which makes them different than these with 90+% probabilities. I’ve easily been able to adjust to the probabilities and use them appropriately. Also I know the ProbSevere model has not been validated as a tool to reissue severe warnings, but I like how the probabilities diminish a bit when the radar intensity decreases and then come back up if the storm re-intensifies. If you look at this display (Figure 2) it has high probabilities on the right storms, but the ones further west are only (correctly )10-20%”

-Sieglaff, Week 1 ProbWarn PI

First isolated cell builds with a CI of 40-50%.

Initial cell continues to grow with a CI of 80-90%.

Initial cell reaches a CI of >90% with a new cell developing to the southwest showing a CI 80-90%.

Initial cell eventially goes “poof”, with secondary cell continuing to grow and show a CI of >90%.

Second cell continues to grow with CI still >90% on the southwest flank.

Second cell continues to grow. A warning was eventially issued for this storm.

Scott Rudge.

Convection in CO, NE, WY has exhibited persistent (30 min) OTs as of the 22:15 vis sat pic.

These have been over persistent strong…and at times severe…storms.  OTs have not always meant the storms were severe…and have seen SVR and even TOR under cells that have not had OTs detected.

db

As seen in the first image, CI is picking up on come cloud cover out ahead of the main convection. Probabilities were 50% and higher in this area at the time. Shortly after, thunderstorms began to develop just to the south of the main line that had already been warned on. These new storms later merged with the northern cell to produce more of a cluster. This example shows how the CI tool has some skill at time that cirrus isn’t inhibiting detection and can also raise awareness on development in a messy area.

This cell in Laramie Co, WY had a storm report of 1.75″ hail, measured, at 3:51 MDT.

2150Z ProbSevere: 54%, MESH 1.05″

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2156Z was 18%, .70″

A pronounced cluster of higher CI values evolves into a cluster of convection.

Time stamp 2007Z.

Time stamp 2045Z.

Scott Rudge.

Nearcast forecast instability still at its highest across parts of CO, WY, and NE over the next few hours.  Some data gaps here, but the surrounding trend in the data around the gaps lead me to believe there’s still a good road for these storms to travel and hold strength, if not intensify in some areas where daytime heating continues…

The storm that developed earlier this afternoon cycled a few times through its development. At times is showed decent rotation, which was warned on by the Denver WFO. The storm continued to show signs of some possible hail and weak rotation as it crossed the border into Wyoming. The lightning density tool did a good job in picking up on the storm, as show above. Lightning density seems to be a neat tool for awareness, not only for lightning being produced, but also what storms may be the strongest.