EWP Blog

For Day 2, we were the Wichita Office. They had mainly multi-cell convection, so we only issued 2 warnings, and these were for wind based on the 0.5 deg radar scan. In addition, our IDSS event was in lightning pretty much the entire time, so it was a fairly easy forecast to warn them, and then move on.

However, while evaluating the OCTANE, there was one event in WFO Pleasant Hill that showed persistent divergence aloft, and had this storm have been in our CWA, I would have issued a warning.

The animated gif above shows OCTANE speed (top left), Cloud top cooling (top right), Cloud Top Divergence (bottom left), and Cloud Top Divergence High Smooth (bottom right). In this case, notice the persistent high divergence values (red) in the lower two panels.

The image above shows a zoomed-in look at the storm of interest. I would have issued a severe TS warning had this been in our area.

With both discrete and cluster/multicell/linear storm modes, the cloud top cooling, speed, and divergence products proved fruitful in identifying convective intensity trends.

(Sorry, the gif got messed up a little bit)

Top right: OCTANE Speed

Others: OCTANE Cloud Top Cooling (stoplight) and OCTANE Divergence (blues/purples)

The speed product showed not only the motion of the storm tops and the acceleration tendencies of the storm top features, but also highlighted (through the texture and color curves) the presence of other storm scale features like the overshooting tops and above anvil cirrus plumes. The color curve had been modified for this product to be the “compressed” color curve, which made gradients stand out. Additionally, this provided information about the environment the storms were tapping into, in this case showing that storms had ample shear to tap into and use to persist.

The divergence and cloud top cooling products were beneficial at different stages of life. The cloud top cooling products were a bit more useful in the initiation stage of storms, showing strong intensification of new updrafts, but became less useful as the updrafts became better established because the cooling was not the same magnitude you would expect from the initiation stage and it stood out less.

The divergence product felt useful in both of these stages of life, but especially once the storm had matured, since the relative strength of signals were about the same during both (i.e. same pink/red hues). While the re-intensification of the updrafts that cycled was signaled by the re-appearance of the green colors, the persistent signals of strong divergence gave better insight into the intensity trends over the storm’s lifespan compared to the cooling product, which was more instantaneous in nature. Once storms reached the mature phase, the channel 13 IR imagery became a better way of assessing storm top temperatures (not shown).

On the DSS front, the Cloud Top Cooling was more beneficial when used in tandem with LightningCast (not shown) during the initiation stage to assess the storm/updraft motions and decide whether DSS calls needed to be made. The early indication of convective cloud top cooling was a signal to forecasters that the clouds would likely become strong enough in the near future and would begin posing a lightning threat to Rudy’s event.

– prob30

SYNOPSIS – Scattered to numerous thunderstorms developed along a frontal boundary as it moved south into KS/OK/TX. These thunderstorms developed in a strong instability (3000+ j/kg MLCAPE) and modest shear (20-30kt effective, ~100 m2/s2 0-1km SRH) environment.

OPERATIONAL NOTES AND FEEDBACK – Using OCTANE to nowcast convective intensity and improve mesoanalysis situational awareness

Today’s event seemed to highlight a significant advantage of using OCTANE products to keep situationally aware during scenarios where there is a lot of convection. Oftentimes, radar can get incredibly messy when numerous thunderstorms are present, making it challenging to know which thunderstorms to focus messaging and warnings on. OCTANE products made this less challenging, by highlighting the thunderstorms with the strongest updrafts and/or most persistent updrafts. This combined with GLM lightning density provided valuable information for warning forecasters to decide which thunderstorms were the best candidates for warnings, and which ones to hold off on. Situational awareness (SA) can be quickly lost in events like these, and it is crucial to have a way to keep good SA. OCTANE provided an important tool in this endeavor.

The image below is one such example, showing two separate areas of convection over the WFO Norman (OUN) CWA (outlined in orange). In west-central OK, the OCTANE Cloud top Cooling/Divergence product shows notable updrafts with a persistent signal for notable storm top divergence, suggesting an increased risk for severe thunderstorms. Meanwhile, the thunderstorm activity to the east, in central OK, seemed to have more of a transient signal for strong cloud top divergence, with a somewhat less persistent signal. This suggested that the central OK convection would favor more of a pulse-type of severe weather setup, which informed future warning decisions (in my experience, pulse environments are often handled differently than environments that support long-lived / long-swaths of severe weather).

Additionally, the cumulus fields with green shading in the image above gave forecasters a heads up for which areas were seeing the most vertical development (ie. towering cumulus), which also was a tip-off for which areas may see new convective initiation.

While not shown, there was also a notable updraft that developed on a severe-warned thunderstorm west of Norman, OK. The OCTANE products nicely depicted this updraft as being more prominent than surrounding updrafts, and this particular thunderstorm went on to produce a tornado a short time later. This thunderstorm was embedded within a larger line of thunderstorms, which sometimes makes it less prominent when compared to radar interpretation, alone.

Probably the biggest takeaway here is that this one image provides a very quick overview of where convection may initiate, where convection is the strongest, what mode the convection is taking on, and where the biggest target of opportunity is for warnings and IDSS.

It’s recommended that satellite interpretation continue to be an important part of the mesoanalysis role of NWS operations, and OCTANE products appear to more quickly mesh what forecasters often look for in visible and IR products separately. This more efficient overview could save the mesoanalyst valuable time in assessing thunderstorm trends, providing quicker insight to warning and DSS forecasters.

– NW Flow