CTC Signal Lead Time over First Operational Warning and Hail Report

Thick cirrus was preventing CTC from tackling any of the early convection over Oklahoma; however, where the cirrus shield has dissipated/cleared, we're getting some good CTC values.  An example of this is over extreme northwestern NM into the panhandle of OK.  The first CTC signal for the storm of interest was at 1825 UTC with a weak value of ~-8 to -10 K/15 min (Figure 1).

Figure 1.  UWCTC over extreme northeastern NM with a value of ~-8 to -10 K/15 min.

The very next scan at 1832 (Figure 2) exhibited a moderate CTC rate of -15K/15 min with the growing storm.

Figure 2.  UWCTC over extreme northeastern NM with a value of ~-15K/15 min.

The first severe warning for this storm was issued at 2003 UTC.  Lending a 38 minute lead time over the operational warning being issued.  Below is the radar imagery from KAMA valid at 2044 UTC.

Figure 3.  KAMA radar imagery valid at 2044 UTC when the second warning was issued.

The first hail report received at AMA was at 2037 UTC with 0.88 inch hail being reported by law enforcement (a little over an hour lead time for CTC).  The LSR text is shown below in Figure 4.

Figure 4.  LSR report from AMA WFO for hail in panhandle of OK.

PGLM Flash Extent Density Unusually Low for Severe Supercells

Below is a 4 panel image of Flash Extent Density, Composite Reflectivity, and MESH. With two supercells indicating large hail via MESH, one would expect larger values of FED, which have only maxed out around 5 flashes/min. However, this may have something to do with distance from the LMA centroids. We will continue to monitor. In any case, the PGLM products are very useful for aviation and public safety interests for points downstream.

**Update 2107 UTC**
Monitoring the storm following Flash Extent Density Trace Tool, it appears many of the storms have entered a period of decreasing lightning activity. This is also apparent in the plan view of FED. This would suggest a downward trend in storm severity, but will monitor to see if this comes to fruition.

Austin/Hampshire

Diagnosing Storm Growth Using Flash Extent Density

With convective initiation underway, we assess the intensification of thunderstorm updrafts using PGLM Flash Extent Density to determine electrical activity within the storm. The cell below has shown several weak lighting pulses over the last 15 minutes and is showing signs of becoming severe. Reflectivity is on the rise and the lightning activity appears to be foretelling of possible storm severity quite well.

Two panel of Flash Extent Density (left) and composite reflectivity (right)

Pseudo-GLM use from May 7th

Yesterday we had the opportunity to view the PGLM data southeast of Lubbock, Texas courtesy of the West Texas Lightning Mapping Array.  The results were interesting.  At past Experimental Warning Programs, we have seen flash extent densities of over 80 flashes for the Oklahoma LMA which updates every minute.  However, yesterday, the PGLM maxed out at 41 flashes for the storms that developed.  This was less than we had expected, based on previous years with one minute data.  The environment was interesting as these were elevated thunderstorms.

Although lower than viewed in the past, this maximum did precede the full development of the storms, although storm reports are hard to come by as this is a low population region.  Overall, this was a good dry run for today (May 8th) as we will be active in the western portions of the Oklahoma LMA today and will have the chance to fully try out the PGLM observations and the lightning tracking tool.

The PGLM observations at 2312 UTC showing a maximum flash extent density of 35 flashes (blue grid box).

The corresponding radar reflectivities from the Lubbock radar at 2321 UTC.  Note that the PGLM was greatest with the core of the main storm.

Daily debriefing: May 8th

Last night's focus area was in western KS, centering on the Dodge City and Goodland, KS CWAs with one team also monitoring activity in Lubbock, TX. Storms fired late in the afternoon and kept us fairly busy for the remainder of the night. Forecasters had a lot to say about the GOES-R products. Check out some of the feedback below:

Cloud Top Cooling:
- 'Cloud-top Cooling helped early before cirrus contamination.'
- 'Most storms that went on to product large hail had a strong CTC signal.'
- '[The CTC] provided good situational awareness, was a good quicklook and helped identify areas of interest.'
- 'It provided lead time of up to an hour for storms that produced large hail, especially wehre there was a persistent strong signal over through several satellite scans.'
- 'Seeing the consistently higher CTC signals in an operational environment would give me further confidence to warn on a particular cell.'
- 'A lot of time there were strong signals for the robust cores, though not always.'

GOES-R CI:
- 'The CI didn't help with individual elements; that is, it was noisy. There were a wide range of values in a small area. However, backing out and taking a broader view, it gave a general idea of where I could start to expect things to occur.'
- 'Even right before storms got going there weren't a lot of clustered 90% values, but there were a few here and there... so the trend was good.'
- 'The CI was noisy, especially within large cu fields. It may be helpful if it were thresholded a little bit, if only 50% or greater probability values were shown.'

Nearcasting:
- 'While waiting for stuff to get going, I really enjoyed the Precipitable Water difference. There was cu in an area of low-level moisture and as soon as they moved into an area of higher moisture, they fired.'
- 'It helped to know what was happening in the current atmosphere and what to expect later.'
- 'The development to the west was associated with marginal moisture, but just to the east there was a lot more, and as soon as those cu moved into that area it lit up like a Christmas tree.'

Simulated Imagery:
- 'The IR satellite forecast was a little early but really showed the individual storms from western KS south through Texas. It did also keep the are in KS a little longer, which did pan out.'

PGLM:
- 'It was a precursor to what happened... flash density increased to 30 flashes/min with one cell and five minutes late it produced large hail, the only hail report near Lubbock.'


Again, keep an eye on the blog. Today looks to be a busy day with the focus on Texas and Oklahoma. More details on this later in the afternoon...

Hail Lead Time from Cloud Top Cooling Products

As several storms developed in the DDC forecast area, and very slowly reached maturity (and severe intensity), the Cloud Top Cooling (CTC) product provided a significant amount of lead time.

CTC at 2202Z, showing strong indications in Lane, Clark, and Haskell Counties.

At 2202Z, three areas showed strong (20+) indications on the CTC product. The two areas in Lane and Clark Counties went on to produce severe thunderstorms. However, the smaller area in Haskell County did not end up with severe hail reports. All three of these CTC areas continued for several consecutive time steps.

CTC at 2232Z. A new area has developed in Ness County.

An hour and a half later, a new area of strong CTC developed in Ness County. This area also persisted for several time steps, and preceded severe thunderstorm development as the storm moved into Trego and Ellis Counties. The area near Haskell County was associated with the one storm that did not become severe, while the Clark County CTC area was associated with the severe storm moving out of Ford County.

With the exception of the sub-severe Haskell County storm, the other three CTC indications were associated with future severe hail reports.

Hatzos

EWP2013 7 May 2330 UTC Mesoscale Discussion

We continue to monitor isolated to widely scattered supercells extending from NW KS through SW KS/NW OK, with more isolated activity near LUB.

Recent sfc obs show area of backed winds over NW KS on northeast fringe of a broad lee trough drifting eastward from CO. Here, pooling moisture has contributed to modest instability per recent mesoanalysis with impressive wind fields, albeit somewhat weak in the upper levels. Some meager low level rotation has resulted from this area of backed surface flow, with a few reports of weakly rotating wall clouds. As LCLs decrease this evening, a very narrow window for tornadic development will exist, but low level shear will continue to limit this threat.

Further south, large hail and damaging winds have been the main threats with a few reports of up to golf ball sized hail. Deeply mixed boundary layer has resulted in high based storms within impressive steep mid level lapse rates favorable for hail production. Also, with inverted V nature of area soundings, would not be surprised if very strong winds are occurring with the most severe storms.

Even further south, areas in and around Lubbock have seen very isolated storm development this evening. One single slow moving supercell has been located near the border of Garza and Crosby counties. This storm also developed in a very localized area of backed surface winds, with enhanced surface convergence. Also, surface heating likely played a role in convective initiation, with temperatures climbing into the mid to upper 80s. This development was preceded by multiple CI and CTC signals, though they tended to be sporadic and indicated there may be many more storms than actually developed.

Heading into the evening, expect severe storms will generally persist through around 02z to 03z. Most activity appears to be diurnally driven. On exception to this will be parts of NW/N Cntrl KS, where an eastward propagating cluster may develop later this evening. Taking a look at Nearcast products, we observe that instability has taken a bit of a hit over the entirety of the area with ongoing convection, as has moisture depth. It still appears the most favored areas for persistent severe convection and supercellular activity will be over NW KS in Goodland’s CWA, eventually migrating into Hasting Nebraska’s area of responsibility.

Lubbock’s convection has diminished in the last hour, and will discontinue operations there. Will keep operations at DDC and GLD active through end of day as activity is expected to continue.

Austin

Possible Impacts to CTC from Cloud Ice in Anvil Cirrus Shield

The use of CTC was restricted quickly across the GLD CWA this evening as the cirrus shield from the first updraft quickly contaminated the region due to cloud ice. From this point on, the MRMS products became the primary aids in deducing severe hail development.

VIS imagery, CTC, IR, and MRMS QC composite reflectivity

Note the lack of CTC within the GLD CWA, while new updrafts continue to be detected by the CTC across the northern portion of the DDC CWA.

Kurtz/Guseman

EWP2013 7 May 2013 2215 UTC Mesoscale Discussion

With multiple scans of CI/CTC showing iminent or ongoing convective initiation over Lubbock’s area, will localized one desk at the LUB wfo. This will give the testbed an opportunity to evaluate some of the PGLM products available in the LUB LMA. The image below from 2145 UTC shows where storms are developing in extreme south central parts of the CWA.

Radar trends show activity is also on the uptick at DDC, with ongoing supercells over GLD’s area. Will keep two teams stationed at these locations to optimize this marginal severe weather setup. The image below is a four panel of MESH products and composite reflectivity over the DDC and GLD CWAs.

Will continue to monitor trends, but all areas appear to be covered at this time.

Austin

Cloud Top Cooling rate Combined with MESH for Enhanced Lead Times

We continued to monitor Cloud Top Cooling (CTC) rates in combination with MESH from the MRMS to investigate a elevated storm in Sheridan County Kansas. CTC was able to provide 15 to 20 minutes of lead time before the MESH indicated .71 inch hail. Below is a four panel at 2115z of the CTC, instantaneous MESH, base reflectivity at KGLD, and 120 min MESH.

Four Panel: CTC, MESH, 0.5 refl. KGLD, 120min MESH

Continuing to monitor the storm, the HSDA has continued to indicate large (LH) to giant (GH) hail. With modest mid-level lapse rates (7.0-8.5 C/km) and decent mid-level shear, these storms continue to indicated mid and upper level rotation, indicative of large hail growth.

Guseman/Kurtz