Storm-Scale Environmental Analysis of Early Convective Development

This case at WFO OUN brought forth a challenging situation monitoring developing severe weather with no available radar data, and only relying on satellite products for storm interrogation and convective warning decisions. This analysis will primarily focus on the evolution of early convective development and how satellite products/PSH data helped gain a better understanding of the environment.

My role in the team monitoring/analyzing the environment was focused on issuing warnings and having the Mesoanalyst(s) relay satellite, PSH and GREMLIN information to support warning decisions. To prepare and gather a greater situational awareness of the environment and what satellite was observing, I loaded in RAP13 Right/Left Bunkers vectors which would aid me in effective polygon design. Given the orientation of the hodograph per observed soundings earlier, storms would support the potential for left/right splitters meaning proper storm motion/polygon flare is very important.

Convective initiation began around 21-22Z with noticeable towering Cu across Cotton County, OK, prompting the first issuance of a SVR at 21:56Z given cooling cloud tops/increasing storm top divergence.

Towards the end of the loop above, observation was made that the overshooting tops were turning more ENE biasing closer to the bunkers right, implying the likelihood of the storm developing a mesocyclone. Not shown here, but a useful trick of enhancing the contrast of the Day Cloud Phase RGB became extremely useful in tracking overshooting top motion and intensity, along with other satellite products diagnosing an intense updraft in progress.

The pre-storm environment was analyzed using PHS data, highlight ample MUCAPE on the order of 3500-4500J/kg around the area of CI,  and large-scale 0-3km SRH ranging around 250-350m2/s2, bringing support for stronger/severe storms to attain rotation in a volatile, highly unstable/moderately sheared environment.

WIth the storm obtaining a developing/intensifying left splitting  updraft (later in the first loop), confidence of a strengthening mid-level mesocyclone increased leading to a transition to a base TOR warning, with polygon design mainly following the bunkers right motion vector to imply near-term motion to continue ENE.

Modifying the OCTANE speed product by decreasing the max observed values downward and min values upwards helped diagnose a more eye turning signature to storm top divergence. Additionally, modifying the direction scale, albeit took some work, came out with a product that illustrates (in red) backed sfc winds <`180 degrees which existed well ahead of it, inferring the likelihood of larger curved hodographs and greater attendant estimated low-level SRH.

However, one item that was not noticed until after the TOR warning was the winds being ingested into the storm (shown in green) averaged around 210-230. This appeared very accurate looking at feeder cumulus ingesting into the inflow region of the cell just to the SSW. Less backing of the surface winds yields much less available streamwise vorticity (in fact is mainly crosswise) leading to the likely reason the storms rotation did not strengthen, and ultimately collapsed 30 minutes after the image above and the left-turning supercell became the dominant storm.

Overall, OCTANE exhibited great, practical uses to understanding not just the storm intensity/trends but the environment explaining why the storm was behaving the way it did.

– RED11248

OCTANE in a Pulse Environment

The environment across the ILN CWA this afternoon was one which favored pulse convection as deep layer shear was fairly weak. At around 4:45, we began watching a storm in the northern portion of the CWA that seemed to be strengthening quickly. Unfortunately, the OCTANE data was coming in around 30 minutes late at this point, so we had to rely on traditional methods to assess storm strength. We decided to put out a Severe Thunderstorm Warning on the storm as radar indicated that it was capable of producing 1” hail. Luckily, the OCTANE data caught up not long after and I was able to analyze it as well.

This first image is from around the time that the warning was issued. Looking at the speed and direction products, we see that the gradients are rather diffuse. This is indicative of the weak deep layer shear. However, looking at the cloud top cooling, we see cooling of around 3°C which implies that the updraft was strengthening at the time the warning was issued.

This next image is from 4 minutes later. The speed and direction products still show a diffuse gradient, but the cloud top divergence product really stands out. This lines up with when the storm appeared strongest on radar.

This final image is from around the time that the warning expired. The cloud top divergence is considerably weaker than it had been and radar also indicated that the storm was weaker. We were comfortable with letting the warning expire.

This storm made me think about the utility of OCTANE products in a pulse severe environment. It seems that the cloud top cooling and cloud top divergence products would be significantly more useful than the speed and direction products as you can use them to quickly infer changes in the severity of the storm based on updraft strength.


San Antonio Waiting Game

San Antonio: broad cu field is still fighting substantial dry aloft despite extreme instability in the Great Bend region. No notable cooling or anything of note in the OCTANE data. Residual outflow boundary from earlier MCS is acting as a mechanism for a lone strong-severe thunderstorm just north of our CWA. Strong OCTANE divergence and cooling seen along the nose of PHS instability gradient with 3500+ CAPE; shear is essentially zero across this region. PHS composite reflectivity clearly did not forecast this outflow and thus the convection.

2100z: Strong-severe lone thunderstorm with very clear and strong divergence signal in both divergence field and speed fields. Rainbow signal seen in the direction field due to the very limited shear.

Orphaning anvils in the cooling OCTANE fields to the west of the primary convection suggest the PSH fields for instability are just displaced to the east at 2100z.

Nice depiction of the PHS being wrong but right at the same time. Clearly slightly displaced with instability gradient to the east, but accurately showed the single cell or two behavior that we have seen.

Impressive single cell continues as of 2130z, and some notable cloud top cooling and divergence is now seen in the cell to the southeast. Instability axis is clearly ~50 miles to the north of the PHS.


Lightningcast is bullish on both the southeast and south newly developing convection. Very broad contours however, possibly too much false alarm area here (?).

Broad persistent divergence in OCTANE fields in the southern cell. DHX radar shows 50 dbZ core over 30k feet within an extreme instability zone of 4000+ j/kg. Issued a severe

Large jump in cooling seen above the divergence field in OCTANE, expecting further intensification shortly in the next.

DHX Radar Divergence maxing out around ~90-100 knots as of 2150z. OCTANE cloud top divergence is generally sitting between 25-40 knots.

Double Rainbow!

Deep persistent OCTANE divergence in speed and direction, core weakening slightly based on DHX radar but still likely warranted a second warning. No signs of real weakening in any of the satellite products, but radar not quite as tall with 50 dbZ core.


Application of Octane, LightningCast and GREMLIN across western Maine

Maine has an overall weaker radar coverage compared to many other CWA’s across the CONUS. This made it a great place to test out some satellite convective products such as Octane, LightningCast, and GREMLIN. The first image shows the confidence of LightningCast in the development of thunderstorms across parts of north central Maine. Shading shows >75% confidence of seeing 1 or more lightning strikes within the next hour. This was supported by Octane, which showed increased cloud cooling occurring over this area along with large areas of cloud top divergence. What happened nearly an hour later was for the most part on point. GREMLIN and reflectivity showed patchy storms developing across the region; this was also shown on ENTLN lightning plots. GREMLIN did a great job of highlighting the stronger storms with higher reflectivity although those were lower than the actual reflectivity. The lightning plots showed large clusters of lightning, which was nearly identical to where LightningCast had drawn contours nearly an hour before. Overall, the use of all these products together in my opinion would greatly improve convective forecasting as I feel they work great together. This was once again shown today across Maine by highlighting areas with potential convective development and eventual patches of high density lightning strikes.

-Sven The Puffin


 Thunderstorms formed over portions of New England (Maine and New Hampshire) along the periphery of an exiting upper level low. This convection was primarily diurnally driven with a lack of forcing.

With marginal storms that developed I wanted to take the approach that I was without certain data, like some radar tools and probsevere.  There were two storms that were showing a little promise of getting near Severe limits. One storm developed south of Portland in which we warned on which was very close to the radar cone of silence.  A second cell developed further to the west with some dialesing and some poorer radar quality.  When going through the various experimental data since the storms were marginal I attempted to see if I could qualify relative storm intensity with the use of OCTANE.

Below you can make out the first cell which weakened towards Portland, however a second cell has ticked up showing 60 dbz reflectivity for this scan at 21:18z.

I began examining this second cell a few minutes earlier with satellite products.  I noticed earlier with visible satellite data and along with the CTC (Cloud Top Cooling OCTANE product) that there was convective initiation.  But then use of the CTD (Cloud Top Divergence -see purple shading in OCTANE bottom left of 4 panel below) also indicated divergence aloft, and in subsequent scans speed divergence was increasing (upper left panel).  You can make out on the upper left panel the Octane Speed which shows a second area of speed divergence with activity off to the west. I played with the color table to draw out this feature a touch just as the cloud top divergence indication began to increase in order to attempt to see a visual trend.

This was a storm that ticked up briefly.  I pretended that I did not have probsevere, along with radar reflectivity and velocity.  As it turns out ProbSevere did tick up to 20 percent around 21:18z

The decision was made not to warn on this cell.  It turned out to be a good thing as afterwards I inspected various radar features and MESH did not indicate a severe hail threat as it only ticked up to under a half inch.  And radar reflectivity briefly ticked up to 60 dbz but with no velocity core and thus no severe hazard threat.

What OCTANE provided here was a guide as to where to look next.  OCTANE can be helpful, at least it was in this case in terms of where to look next, especially when you get the speed divergence and cloud top divergence (CTD) signatures.  IF speed divergence signatures values decreased (lower down the color curve) on the upshear side of the cell, then perhaps that may have been a signal to warn, but they did not increase and this was the proper decision as available radar tools suggested not to warn on this cell.

– 5454wx

Monitoring Convective Trends across WFO MPX

This scenario began at WFO MPX with a broken line of strong thunderstorms approaching from the west. Many small-scale features were identified using OCTANE and radar trends, with focus on a DSS event ongoing “Fishing Derby” in Wright County, MS.

Doppler radar and Day Cloud Phase Distinction both illustrate new development ahead of the main activity to the west, ahead of an eastward surging outflow boundary. This led to the first DSS notification giving the event a heads up for >30mph winds and lightning in the next 1 to 2 hours. LightningCast was helpful showing probabilities increasing from the west.

One specific updraft noticed around 20:00Z, with the decision for a warning to follow along with 40dbz around 40,000ft ARL. OCTANE products were specifically helpful, especially by modifying the colorbar settings for OCTANE Speed. Decreasing the MAX from 200 to 100 and increasing the MIN from 0 to 15 gave a greater contrast and “bullseye” to help diagnose strengthening divergence.

Several additional DSS notifications were sent to the site to alert them of not only the approaching activity, but how long the activity might last over the next following hour.

A TSTM Wind Dmg LSR followed with this storm that led to an injury.

LSR:  *** 1 INJ *** Corrects previous tstm wnd dmg report from 7 N Hutchinson. Relayed report from sheriffs office of a shed with roof blown off and sides collapsed

Again, OCTANE gave great situational awareness to support alongside with radar to lead to proactive warning decision.

– RED11248

Tracking convection across DLH CWA with Octane, LightningCast, and GREMLIN

Forecasting in DLH today was challenging due to the radar being made unavailable. However, some of the satellite convective products were able to create accurate forecasts regarding the location of storms and lightning. Firstly, looking at Lightningcast there were gradients of ~25% appearing 1 hour out around the DSS point indicating the possibility of lightning developing within the next hour. This was also supported by Octane, which was showing storms initiating to the south with early signals of cloud top cooling and divergence occurring. Around 1 hour later this seemed to mostly come to fruition, which can be seen on the 4 panel image with GRMLN data on it. Lightning seemed to be mainly concentrated east of the DSS point which was shown in lightningcast. Also these storms originated from the south which Octane began to hint on early out. Overall, it looks as if all three of these satellite convective products did a good job in forecasting possible convection without the use of a radar.

-Sven The Puffin


Without the use of radar out of Duluth more reliance was given to Satellite derived observations and satellite derived output.

Below is the OCTANE cloud top cooling and cloud top divergence product.  You may notice in an area of moderate but increasing instability there is convective initiation ahead of the main line of convection.  However, you can notice early in the loop that there is convective cooling indicated in the south-central portion of the CWA and the far SE portion of the CWA.  Notice how in the far SE portion of the CWA there is the purple shading indicating cloud top divergence.  And in south central portions there are “hotter” yellow and tiny red(s) (may be hard to notice due to scale) pixels indicating cooling cloud tops, but with no purple shading and thus no meaningful divergence at the cloud top.  This is indicative of orphan anvils. The moral of the story here is that without radar the OCTANE product heightens your attention to the cells in the far SE portion of the CWA, and this would be where to consider SVR or SPS product release, with the activity across South Central portions of the CWA failing to produce significant convection at this point in time despite moderate to strong instability.

Further southeast however notice that there is stronger instability over SE portions of the CWA, thus the OCTANE product is giving you a result which coincides with where there is higher instability (higher MLCAPE – see SPC mesoanalysis).

Lightning Cast continued to show high confidence of lightning over the next 60 min with the linear MCS moving into western portions of the CWA.  This lead to high confidence in forecasting lightning for a DSS location (Solana State Forest) during this event.

Steady behavior with the greater than or equal to 10 flashes in the next hour.

High probability of 1 flash of lightning in the next hour, increasing then holding steady

Here (below) is the Lightning Cast and GLM dashboard output comparing the forecast to the GLM flash count.  Note: the dashboard was down initially but came back online

Thus we were able to give a high confidence lightning forecast for DSS.

Here is the GLM Flash Extent Density at the time of the Lightning Cast 1 hour forecast.

– 5454wx

OCTANE Speed Product Shows Weakening Trend in Storm Well

A strong storm with a well defined mid-level mesocyclone entered the western portion of the MKX CWA at around 4:00 PM CDT. At the time, the OCTANE speed product showed a well defined gradient and the divergence product showed fairly high values, indicating that the updraft was quite strong. We decided to issue a severe thunderstorm warning with a tornado possible tag on this cell as a result.

Not long after the warning was issued, we noticed a significant weakening trend in the reflectivity signatures. This weakening trend was supported by the OCTANE products as well, with a much more diffuse gradient in the speed product and lower values in the cloud top divergence. An interesting thing to note, though, is that the Day Cloud Phase imagery looks nearly identical to when we issued the warning, so it did not capture the weakening trend.

Another interesting thing to note is that the IR imagery did not seem to indicate that there was as much weakening either. One image from around the time of warning issuance and one from around the time when the warning expired are shown below.

In all, the OCTANE products seem to be very useful in assessing the strength of a storm’s updraft. Looking forward to gaining more experience with it and the other products throughout the rest of the week.

– EI2018

Severe thunderstorm warning issued for South Central Wisconsin

Solid signature from both nearby radars but the beam height was at least 8k feet. PHS environmental fields were supportive of a primary wind hazard. OCTANE divergence fields distinctly noted this cell with persistent strong divergence as it moved into the CWA. Low level wind fields were not as impressive with widespread STP of less than 0.2, despite strong instability in the PHS fields.