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Growing TCU was noted in the Octane Speed product around 2030Z (1530 CDT). While no lightning was detected by ENI, the Octane product indicated a growing trend in CI.
Octane Speed (Top Left), indicates a growing trend in cloud speed at the cloud top, indicating these cu are growing into a more strongly sheared environment.
– Rain-Free Bass Guitar
Octane indicates decent upper level divergence aloft in thunderstorm located east of Ft. Stockton 2240Z (1740 CDT). This prompted me to analyze the storm further with base radar data overlaid with ProbSvr v3.
Octane located in the upper left indicates strengthening values in the storm near Ft. Stockton. 
Further investigation analyzing base radar data with ProbSvr indicates the storm is still sub-severe.
– Rain-Free Bass Guitar
ProbSevereV3 showed an 83% probsevere contour and an 80% probhail countor. With the Octane Speed Sandwich showing great storm top divergence, and high probsevere values, went ahead and issued a severe thunderstorm warning for the locations just south of our railroad DSS event. 
-Dwight Schrute
We were watching a storm as it pushed from New Mexico into Texas. First looking at Octane speed we quickly identified a cell with good speed shear as it pushed from Curry County into Parmer County. This is one great application of Octane. The ability to identify the cell with the biggest potential to become severe in a cluster of storms.
Looking at ProbSev V3 you can see the values for hail compared to V2 are very similar at the end. However, the bigger thing we noticed is that V3 picked up on the hail much earlier in the event compared to V2. We also noticed the chance of tornadoes in V2 was nearly zero while V3 was almost 20%. Looking at velocity I would agree with V3 as we did see some good rotation in the low to mid levels. As of this writing the storm has produced at least 2 inch hail. 
-Thunderstruck
Growing TCU was noted in the Octane Speed product around 2030Z (1530 CDT). While no lightning was detected by ENI, the Octane product indicated a growing trend in CI.
Octane Speed (Top Left), indicates a growing trend in cloud speed at the cloud top, indicating these cu are growing into a more strongly sheared environment.
– Rain-Free Bass Guitar
Interesting case to the north of the CWA today showing different layers that were flowing near surface and aloft. Was able to use the estimated motions to get a quick idea of how quickly the airmass over the Atlantic was moving to the SE. Could use this to get a quick estimate for when this airmass may clash with the seabreeze front which could lead to additional convection that fires near my CWA (TBW).
Great example of a marginal case where I considered issuing a severe thunderstorm warning. Core had pulsed significantly, showing 50-60 dBZ at the -20C isothermal layer. MESH was showing upwards of 1” of hail, but my experience in the south tells me that MESH will overestimate hail size. VII had a decent burst at one point, but biggest question mark to everything was how long core could hold together to keep hail aloft, especially given lack of shear (generally <30 kts EBS, little to no storm relative helicity or chance for any updraft organization or rotation). My bigger concern for warning was derived from the potential wind threat of the core falling out quickly, with DCAPE values analyzed between 5-700 J/kg.
Probseverev3 topped out around 51%, which matches pretty well with my overall feeling of the situation, where I was already on the fence. Hail was the primary driver however, where I would have been a little bit more concerned with winds. That said, being right by the radar gave a good sample of winds as the storm fell, and they topped out at a whopping 32 kts. Hail was eventually reported at 0.5” near Riverview.
Otherwise, was using ProbSevere in combination with the OCTANE speed products for triage of storms, using the divergent signatures in OCTANE to pick out storms to quickly monitor and ProbSevere for continued development.
Due to a software error during an update, the GLM data dropped out for a few hours, which is an input into the ProbSevere model. It was good to see that ProbSevere seemed to remain well calibrated despite losing the data. I observed no large spikes or increase in the overall probabilities when the data was added back in – just a few small increases in some places. Data outages are not uncommon, so I think it is good that the model continues to perform well in the absence of a product.
The sequence of pictures above show the speed and height of clouds within the updraft core of a thunderstorm that was moving slowly along the sea breeze front at the surface but was encountering faster winds aloft, giving a bit of a picture of the hodograph.
Interesting case where this storm ended up having one of the highest ProbSevere thresholds on the day I saw (54%) despite having both wind and hail thresholds that remained well below 40%. It makes sense that these probabilities would “combine” in a sense in the overall probability, but this definitely was not the “storm of day” or anything, with a less powerful overall updraft and core when compared to several others.
This continued to have relatively higher probabilities as shown below, especially in the wind, despite once again looking less impressive than others. While these cores did produce some 30-35 kt winds per radar, they never really approached severe limits (IRIS obs showed peak winds of 30-33 mph at various stations around the area). Wondering if the unique set-up, which led to some pretty high EBShear values that may not be truly realized by the updrafts, was leading to some higher values in the model.
The overall theme of today is that convection in the south is hard.
– Carl Coriolis
Below is an image showing the default 4-panel procedure provided. The upper level is the Octane Speed product on top of the Red Visible Band (Channel 2), the upper right is the Octane Direction product on top of the Red Visible Band (Channel 2), the lower left is the Clean IR Band (Ch. 13), the lower right is the Day Cloud Phase Distinction RGB.
Personally, have at times struggled with what exactly the speed and direction products are showing…but especially the direction. Decided to plot the GOES East Derived Winds onto the imagery, as I am used to looking at wind direction with vectors/arrows/etc. Below is the same Octane image with the 250-350mb wind barbs. When comparing the sampling/data readout of the Octane direction and the derived winds, they were within a few degrees.
Perhaps an option going forward would be to have a single panel Octane procedure with the speed shown as the color, continue to have the direction in the background that shows up when sampling the data (image below), but then at least have the option to load the the direction data as an arrow/barb/etc. Having the barbs show up as the default in a dense enough of a manner that it’s useful may use up too much AWIPS power and drag it down.
– Bubbles
PHS Model Analysis
PHS model struggled to properly capture convective initiation within the Texas Panhandle on the day. While it did see a few cells possibly starting, overall coverage was significantly underdone with many of these storms reaching severe thresholds including numerous reports of hail over 1″. The overall output shared many of the same struggles as the HRRR model on the day. Unclear what the exact problem was, but dry line convergence may have been better than in models on this day.
Above: 15Z PHS model output forecast for 17Z to 22Z from 5/22 with MRMS Reflectivity overlaid.
Below: 15Z PHS model output for 17Z to 22Z from 5/22.
NUCAPS Forecast
As I was beginning to test out these products, this caught my eye as a forecaster on the east coast that regularly deals with Cold Air Damming along the Appalachians. Models regularly struggle with multiple aspects of the dam, including extent, depth, and actual temperature and strength. Additionally, one of the most common pathways for large winter storms in the southeast is when low pressure passes across the Gulf Coast and into the Atlantic while an Arctic high in the northeast helps drive cold air damming into the area. Models again struggle with the dam, but also with strength of the warm nose aloft. I would love to see how this system performs in these scenarios – I know it isn’t “convective”, but it still is an incredibly impactful event, where the strength of the warm nose can be the difference between a few inches of snow or half an inch or more of ice. We regularly attempt to send up special soundings to get the best sample we can, but since GSP does not do a sounding, we rarely get a meaningful sample of the cold air damming in the SE states.
Above: NUCAPS Forecast from morning pass over east coast showing CAD feature over the east coast.
Octane Speed and Direction
Above: Octane image around 22Z for storm just south of AMA.
The Octane product was extremely useful in seeing when updrafts were really “taking off” and hitting the tropopause, immediately highlighting storms which require quick attention. Another extremely useful feature is sampling the actual speed, which gave a potential proxy for storm top divergence. Noticed that the Octane product gave a value around half of what the radar was measuring on this storm – ~50 kts on the Octane product vs ~100-110 kts on the radar. I’m assuming the resolution combined with some of the smoothing within the algorithm may be playing a role here, but it would be interesting to see if there is a consistent way to match the two up, even if there is just a “rule of thumb” or something. This would be huge in areas of sparse radar coverage (portions of the west or the ocean, for example).
Below: Radar image of storm top divergence near 22Z from KAMA.
ProbSevere v3
Noticed an interesting time period where two close updrafts – one fading, one picking up, resulted in some jumping of the ProbSevere product as it would sometimes combine the objects and then sometimes track them separately. I think this shows the importance of pairing the algorithm with analysis – just looking at the time series of the product could lead to misinterpretation of what was happening.
-Carl Coriolis
This video shows a storm’s evolution as it moves into far SW Lamb County just before 21Z. The upper left hand shows the Octane Speed product…the upper right shows the Octane Direction product…the lower left is the GOES-16 Ch. 13 Clean Window IR Band…the lower right is the Day Cloud Phase Distinction RGB product.
Looking at the Octane Speed product, as this storm is initially growing, the cloud top features moderate cloud top divergence with the variation in Octane Speed (as the greens and yellows nearby). The storm evolution then plateaus and eventually diminishes in intensity, shown as the cloud top speed becomes more consistent (with the loss of the yellow colors). The Octane Direction product shows a southerly component to the direction across the north of the storm with a westerly component along the southern side of the cloud top. At the end of the loop you can see the yellow (the southerly component) begin to disappear as the loss of cloud top divergence causes the direction to change from the motion of the divergence to the environmental westerly component. 
Below is an image showing the storm’s trends via the ProbSevere Time Series (storm location now just NNW of Anton). Though the ProbSevere values will lag behind the satellite imagery, one can note the storm’s gradual increase in ProbSevere values with the “warming” colors of the Octane Speed product. The values then also level off, before dropping off as the cloud tops become more consistent. 
Joaq & Bubbles
The octane speed sandwich detected a developing severe thunderstorm near the gulf coast, to the south southwest of Tallahassee. Values increased to above 30 m/s (~60 kts) in this cell, compared to around 20 m/s (~40 kts) in cells to the north and east. Shortly thereafter, a severe thunderstorm warning was issued.
Rain-Free Bass Guitar
