Persistent Severe MCS and Downbursts in Southwestern South Dakota

 1. Convective Initiation & MCS Evolution (1900 UTC)

The early afternoon of 2 June 2026 was marked by the development of a persistent mesoscale convective system (MCS) over Fall River County, SD as shown in Figure 1 below.

Satellite Observations: The 1900 UTC composite satellite image shows the system advecting east-northeastward, exhibiting rapidly increasing ice-phase cloud tops and a significant rise in lightning flash rates.

Structural Signatures: At this stage, the MCS already exhibits a well-defined bow echo complex and a prominent rear-flank dry-air notch. These features indicate
that the system is efficiently processing dry mid-level air to generate strong surface outflows.

Figure 1: Composite SZA cloud phase distinction, MRMS reflectivity, and LightningCast probability product image at 1900 UTC 2 June 2026.

2. System Intensification and Dual Bow Echoes (2030 UTC)

By 2030 UTC, Figure 2 shows the convective complex underwent further intensification and expansion as it tracked across southwestern South Dakota.

Complex Organization: The system evolved into a more formidable MCS consisting of two distinct bow echo complexes.

Severe Potential: Each bow echo was accompanied by its own rear-flank dry-air notch. This dual-notch presentation signaled a marked increase in downburst potential, as the system became increasingly organized and capable of producing widespread damaging winds.

Figure 2: Composite SZA cloud phase distinction, MRMS reflectivity, and LightningCast probability product image at 2030 UTC 2 June 2026.

Figure 3. Comparison between the GOES-19 (G19) sounding retrieval 90 km SSE of Rapid City, SD (left) and the Rapid City (UNR) RAOB sounding at 1800 UTC 2 June 2026 (right).

3. Thermodynamic Environment: Rapid City (1800 UTC)

An analysis of the 1800 UTC environment in Figure 3 explains the high-end wind potential observed.

Sounding Profile: A comparison between the GOES-19 sounding retrieval and the Radiosonde observation (KUNR) at Rapid City, SD, reveals a textbook "hourglass-inverted-V" profile.

Instability & Wind Potential: The environment was characterized by large CAPE (1014 to 1584 J/kg). Correspondingly, the Wind Gust Potential (WGP) was calculated between 41 and 47 knots, providing strong evidence for the severe gusts that followed.

4. Regional Validation & Surface Verification

Regional sounding data further confirmed the widespread nature of this volatile environment.

NUCAPS Comparison: A NOAA-21 NUCAPS sounding retrieved at 1919 UTC approximately 150 km southeast of Rapid City showed excellent structural agreement with the UNR radiosonde (RAOB).

Key Ingredients: Both profiles highlighted favorable wet-bulb zero heights for evaporative cooling and robust downburst generation.

Ground Truth: This thermodynamic setup culminated in a significant surface event: a severe 55-knot downburst wind gust was recorded at Cactus Flats, SD, at 2043 UTC— aligning well with the high WGP and structural signatures identified earlier in the afternoon.

Figure 4. Comparison between the 1919 UTC NOAA-21 NUCAPS sounding retrieval 150 km SE of Rapid City, SD (left) and the Rapid City (UNR) RAOB sounding at 1800 UTC 2 June 2026 (right).

StormRangerWX

Moisture advancing east in pre-convective Wyoming environment

 Simulated GeoXO Imager (GXI) imagery revealed the westward extent of higher moisture in the pre-convective environment of eastern Wyoming this afternoon.

Figure 1 shows the water vapor transmittance (WVT, derived from the 0.91 µm channel) in the left panel and the 5.15 µm brightness temperature in the right panel over a five hour period from 16-20 UTC..  A dashed green line indicates the approximate westward extent of the deeper moisture as estimated from the WVT imagery. In this “inverted” color scheme, drier areas appear darker in WVT (as does higher terrain), and moister areas appear whiter; high-topped clouds generally appear dark.  In the last frame of the loop, convection initiates near Douglas along this moisture boundary on the southern end of this green line.

While WVT is sensitive to the total column water vapor, the 5.15 µm channel is only sensitive to water vapor in lower levels, where lower brightness temperatures generally coincide with higher low-level moisture.  It is interesting to note that the WVT and 5.15 µm gradients do not always align with each other, possibly suggesting an evolving vertical distribution of water vapor.  Our future plans include developing methods to utilize these differences to derive information about depth of moisture in the column.

Figure 1: WVT (left panel; inverted color scale so whiter colors=more moist). The green dashed line indicates the approximate westward extent of deeper moisture as estimated from WVT. 

VortexTilting

CYS Lightning DSS

 For context, there ended up being no lightning within 15 miles of the DSS event. With storms developing on the Laramie Range and the event in Fort Laramie, this case was excellent given developing convection upstream. The LightningCastV1 and V2 looked different despite having no radar data from KCYS. Near the beginning, LightningCastV1 appears more bullish on the 10% and 30% contour nearly over the event range ring while the V2 is closer to the western edge of the 15 mile range ring.

Figure 1: LightningCast-ECONUS-compare panel.

LCv1 vs LCv2 probabilities for GOES-East and GOES-West were the most interesting results of this case. Objectively, the GOES-East V2 chances for lightning ended up performing the best with no strikes. The environment supported dominant left splits which ended up happening with 2 storms. The southwestern storm ultimately decayed but the lingering weak right mover was slightly problematic for chances of lightning near the end of the event with cloud flashes near Bordeaux, WY. The northwestern storm initiated near Laramie peak and ultimately threw a dominant left split away from the DSS event. The most interesting part was the chance of lightning from the 4 options ranged from nearly 20% to nearly 75% around 2120 UTC. What was notable at that time on the radar was the dying right split SW of Bordeaux, WY, and the dominant left split was moving away from the DSS radar just west of Sibley peak, WY which would make me think of lightning potential being very low. This is not to diminish the potential of the product but to raise awareness that different data sources resulted in a 65% difference in chances for lightning.

Figure 2: LCv1 vs LCv2 probabilities for GOES-East and West.

Dry Thunderstorms

Octane CONUS vs MESO

 I focused pretty closely on the comparison of the CONUS Octane Speed vs the Meso Octane Speed product.

Overall I found that the CONUS product was a bit too coarse to really pick up on the main features of interest.

CONUS 

MESO

The example above really highlights the yellow and dark blue hues making it easier to ID the rapid changing environment as opposed to the CONUS which you can kind of see with the green. But you completely miss the dark blue speed minima found in the MESO

Couple more examples below showing the stark difference between the two.

IsthataTOR

The Think Pony Club: Providing Decision Support Using New-Age Satellite Products

 Picture this: you’re out on the open prairie of Wyoming. The wind is whistling through the grass. The late-afternoon sun shines against the towering clouds that have made the Great Plains famous. Spread out in front of you along the hallowed and historic grounds of Fort Laramie, dozens of people wait in folding lawn chairs. There are picnics and music and the shouts of children playing in the warm June evening. Finally, as the sun starts to set, a shape appears along the horizon. Soon, everyone is pointing and squinting as the figure - a man on horseback - comes galloping onto the fort’s parade ground. Slung over his shoulder is a large bag full to the brim with letters.

It is 2026, and the Pony Express rides once again.

For this romantic and nostalgic scene to take place, the patrons of the event need to be kept safe from any sort of adverse weather. Fort Laramie is tremendously exposed to frequent summertime convection, and the National Park Service requested DSS for the great ride this evening. With good reason: by the time shift change occurred at noon MDT, storms were already beginning to develop along the Laramie Range 50 miles to the southwest.

This turned out to be a fascinating case throughout the afternoon - a real “will it or won’t it” as thunderstorms developed and pulsed multiple times over that 50 mile range. The forecasters at Simulated WFO Cheyenne noted increasing lightning potential as early as 1:30 MDT with a much stronger updraft moving off of the terrain. It was initially thought that by 2:30-3:30 MDT, the Fort Laramie area would likely see lightning. However, the storm weakened - a process captured much better by OCTANE Cloud Tops on the Meso band than the CONUS sector.

Figure 1a: Cloud tops from OCTANE over the CONUS sector, showing deepening purples in far southwest Platte County associated with the storm moving toward Fort Laramie.

Figure 1b: Cloud tops from OCTANE over the Mesoscale sector, showing a decrease in the area of purples as the primary thunderstorm collapsed.

Eventually, convection did begin to approach the DSS location. Using a 15-mile range ring, it was unclear whether or not we would breach the event trigger. Two storms developed west of Fort Laramie by about 30 miles and were moving east. The southern storm would undoubtedly track through that 15-mile range ring, but it decayed before arriving. The storm’s final cloud flash occurred about 17 miles away from Fort Laramie proper.

The bigger question, of course, was the updraft on the northwestern flank. If it followed an easterly track, then lightning would assuredly get into the 15-mile range ring. However, a complicated storm splitting process occurred, and regional radar observations (primarily Rapid City radar, scanning at 20,000 feet - the Cheyenne radar is out of commission) suggested that the left split took most of the updraft mass due northward with it. This led to a fascinating case study for LightningCast, where the two MRMS-based V2 products predicted much lower lightning probabilities than the V1 purely satellite-based products, likely due to obfuscation of updraft movement under all of the anvils.

Figure 2: GOES-East (left) and GOES-West (right) LightningCast probabilities at Fort Laramie using the legacy (red) method and the MRMS-included (green) method.

Something to really keep an eye out for when using LightningCast in future IDSS deployments: depending on which product you hitched your wagon to, you could have predicted lightning probabilities of anywhere between 20 and 75% simultaneously. Be careful to use the best data available and blend when possible!

The storms did eventually decay and move off to the north, leaving our hypothetical crowd with a lovely afternoon to enjoy some classic prairie fare, and to prepare for the noble steeds of the Pony Express to ride again.

Sabrina Carpenter

Applications of OCTANE in Disorganized Convection

 
I had the privilege of serving as the initial warning operator for WFO Rapid City as we began operations during ongoing convection over the Black Hills. This activity remained very junky and disorganized throughout the morning, as evident on various satellite imagery and radar. I found OCTANE products to be very useful as a situational awareness tool throughout the day, and it also showed to be a great indicator of when the convection began to transition from junk to slightly more organized severe.

There were signals in the CONUS CTC product that more vigorous convection was beginning to develop underneath the broader anvil (not shown). Then the combined CONUS/mesoscale tracking, speed and direction products highlighted the transition to more intense convection starting roughly with the 1941Z image in the loop below. Increasing speeds at anvil top (yellow color) followed by the appearance of a strengthening color gradient from light blue to yellow denoted the transition in storm intensity. This prompted me to begin finer scale interrogation on radar for severe warnings. I issued the first severe thunderstorm warning at 2004Z for large hail and damaging wind potential, feeling pretty confident that these storms were tapping into a lot of available instability after observing the evolution of cloud top signatures.

Figure 1.  OCTANE Mesoscale Speed Product merged with CONUS Tracker Imagery 1857-2017Z.

As the event unfolded, I was pleasantly surprised at how helpful the CTC product was in highlighting additional intensifying storms underneath the ever-expanding anvil. The “stop light colors” of the CTC product contrasted nicely amongst the cooler Ch-13 colorscale as seen in the loop below, really catching the eye for which storms as viewed on radar should be further interrogated next. I can see this being a very valuable tool in warning operations, especially as mesoanalyst but warning meteorologist too.

Figure 2.  OCTANE Cloud Top Cooling (CTC) Speed Product merged with CONUS Tracker Imagery 2026-2146Z

Astrophage

Severe Thunderstorm Divergence

 Multiple severe warned supercells were visible today over southwest South Dakota. These were producing impressive updrafts as indicated by the green cooling cloud tops in the overshooting tops of the anvils. The direction of the cloud top flow in the anvils is clearly split along the line of development with both the speed, cooling cloud tops, and divergence providing a defined location for the center of each supercell. This location is particularly evident in the cooling cloud tops which provided a lead time of 5 to 15 minutes ahead of the divergence and potentially a couple of minutes before the strengthening of the radar reflectivity signal. I was also surprised by how much of a difference the parallax makes in this region. Overlaying these satellite images with radar, there was a noticeable difference in location of the supercells. This was visible in both the GOES-18 and GOES-19 images, with an offset of roughly 10 miles to the northeast and northwest respectively. With such a large gap, I am curious if this was accounted for when issuing severe thunderstorm and especially tornado warnings for the Cheyenne region that had little radar to go off of.

Figure 1: GOES-18 WMESO Octane speed, direction, cloud top divergence, and cloud top cooling.

Cloudius

Overview: Week 3, Day 2

10 AM

Tuesday began with our morning discussion from Monday's operation/orientation day. Forecasters had plenty of storms to observe yesterday, which allowed everyone to get acquainted with OCTANE. Forecasters talked about the applications of OCTANE data, and one said it can be a 'super tool' for mesoanalysis but also needs 'super users'. For the Synthetic GXI WVT product, forecasters also showed early support for the 'flipped' color table but wanted to see it in action more this week before deciding. First impressions of the Lightning Stoplight and SZA Imagery were also positive, with forecasters finding the Stoplight tool easy to understand and message to partners.

I showed an example of some SZA imagery on CIRA-SLIDER from this morning of river valley fog in the Northeast US. When comparing with traditional imagery and the Nighttime Microphysics RGB, forecasters reacted positively to the 'brighter' SZA imagery and expressed the difficulties of transitioning from day to night when observing fog from their respective home CWAs.

SZA Day Cloud Phase Distinction RGB

Regular Day Cloud Phase Distinction RGB

Nighttime Microphysics RGB

After talking about the GeoXO GXI in our focus group, our forecast discussion for the day sent us back to the Cheyenne, WY (CYS) and Rapid City, SD (UNR) NWS offices to monitor developing storms along a cold front. Forecasters were also assigned mock-IDSS events in Fort Laramie, WY and Sturgis, SD.

1 PM

Similar to Monday, shortly after operations began SPC issued an MD for our area followed by a Severe Thunderstorm Watch.

In the CYS office (still without a radar), discussion focused on their mock-IDSS event and the timing of lightning activity within the event's range ring. With thunderstorms developing upstream of the site, timing dominated the conversation and the forecasters talked about how the LightningCast dashboard helped identify trends, especially if the partner needed more time to execute their safety plans.

The forecasters also looked at OCTANE, and noted that the the MESO Cloud-Top Cooling products showed a decreasing intensity trend while the CONUS CTC product appeared relatively steady.

3PM

The UNR office frequently viewed OCTANE products today, with several severe thunderstorm warnings issued today. Their mock-IDSS site appeared to 'miss' the storms today, but we'll see what they say tomorrow!

I plan to show this to the forecasters tomorrow to get their thoughts. Sorry for spamming the blog with SZA imagery.

-Kevin

Orographic Thunderstorms and Downbursts over Southeastern Wyoming

 Convective Initiation (1900 UTC)

The afternoon of 1 June 2026 has been convectively productive over and east of the Rocky Mountain Front Range of Wyoming and Colorado. The 1900 UTC composite satellite image in Figure 1 below captures the early afternoon development of a complex of strong, orographically-forced and high-based thunderstorms. These cells initially fired over the Rocky Mountain Front Range of southeastern Wyoming. As the system advected east-northeastward, satellite and MRMS data indicated rapid storm intensification, characterized by sharply cooling, ice-phase cloud tops and a significant surge in lightning flash rates. 

Figure 1: Composite SZA cloud phase distinction, MRMS reflectivity, and LightningCast probability product image at 1900 UTC 1 June 2026.

Linear Organization & Downburst Signatures (2006 UTC)

By 2006 UTC, the convection underwent a clear structural evolution into a downburst-producing thunderstorm system. The previously disorganized multicell clusters organized into a short-segment linear complex. Key Feature: The satellite presentation highlights a prominent rear-flank dry-air notch, which is a classic morphological signature of severe downburst potential as mid-level dry air is entrained into the storm's downdraft. Surface Observation: Validating this remote sensing presentation, a severe 52-knot downburst wind gust was recorded at the surface in Bordeaux, WY, at 1958 UTC, just minutes before this satellite scan.

Figure 2. Composite SZA cloud phase distinction, MRMS reflectivity, and LightningCast probability product image at 2006 UTC 1 June 2026.

Figure 3. Comparison between the GOES-19 (G19) sounding retrieval and the Rapid Refresh (RAP) model sounding at 1800 UTC 1 June 2026.

Thermodynamic Environment: Cheyenne Soundings (1800 UTC)

To understand the atmospheric mechanics driving these downbursts, we can analyze the 1800 UTC thermodynamic environment over Cheyenne, WY in Figures 3 and 4. A comparison between the GOES-19 (G19) sounding retrieval and the Rapid Refresh (RAP) model sounding reveals a prominent "hourglass-inverted-V" profile in the lower and mid-troposphere—a textbook thermodynamic setup for evaporatively cooled, severe convective wind gusts.

The associated Wind Gust Potential (WGP) derived from these profiles showed values ranging from 39.2 knots (G19) to 44.5 knots (RAP), which closely aligns with the observed severe gusts in the region.

Regional Corroboration: Denver ACARS Profile (1647 UTC)

Further corroborating the regional environmental setup is an ACARS vertical sounding profile retrieved at 1647 UTC from Denver, CO  (Denver International Airport). When compared to the Cheyenne RAP model sounding, the Denver ACARS data demonstrates excellent structural agreement across the Front Range boundary layer. Specifically, the profile highlights highly favorable wet-bulb zero heights and substantial Downdraft CAPE (DCAPE), confirming a widespread optimal thermodynamic environment for the robust downburst generation observed throughout the afternoon.

Figure 4. Comparison between the Denver, CO ACARS sounding profile at 1647 UTC and the Cheyenne, WY Rapid Refresh (RAP) model sounding at 1800 UTC 1 June 2026.

StormRangerWX

Dry Signals in Synthetic GeoXO

Today’s setup featured a typical high plains return flow pattern with low-level moisture upslope evident on surface observations and both the synthetic WVT & 5.15um channel imagery. One feature that caught my attention initially in the synthetic imagery was a dry pool over the Cheyenne Ridge, spanning from Weld County, CO up into Kimball County, NE (highlighted with yellow circle in the image below).  Observed surface dew points in this area were in the mid to upper 40s in southeasterly flow, likely on the leading edge of the plume of higher moisture in KS and CO. I did not see this level of detail on any other satellite imagery.

With this feature, I was curious on two fronts: the placement of this feature compared to reality, but also how would this dry pool affect convection later in the day. Compared with surface obs, the dry pool seemed to be slightly displaced to the east from reality, but not by far.  My gut was telling me that convective initiation on the Cheyenne Ridge itself would be nil due to the dry pool (perhaps with a hint of subsidence?), and that any established convection moving through the drier air would not exhibit explosive growth and would overall be weaker, and/or perhaps we’d see an enhanced downdraft wind threat. 

See below the loop of synthetic imagery highlighting the 5.15um imagery that covered the majority of our test period. Reality played out pretty close to the evolution of convection as seen in the loop. A left split fired off the mountains near Fort Collins and persisted northeast up into Wyoming. This storm produced severe hail slightly larger than quarter size in Cheyenne, but then appeared to weaken on visible satellite as it progressed further east-northeast along the Cheyenne Ridge where the drier air was forecast to reside.

This case shows the utility of highlighting moisture content, or lack thereof, that you cannot necessarily see on traditional satellite imagery.

Astrophage