ProbSevere in Lubbock Warning Decision

The first warning decision in the Lubbock CWA was based in large part on the  increase of ProbSevere to above 50% in combination with a three-body scatter spike. The storm decreased in intensity thereafter, and no severe reports were received during that warning period.

- Bucky

first impressions of GLM prods

The color scale for the Flash Area product should emphasize the smaller flash sizes. It rather has the gradient at the high end (~8000 km2) where diagnosis of severe updrafts would be done in the continuous blue color. The total energy product shows very large values (in excess of 1000) with very low flash rates (1-2 flashes/min) which sounds counter intuitive.

Convective Initiation in Lubbock

Given the cirrus cloud cover today, the CI algorithm was unable to provide information in the Lubbock area today where convection developed. Referring to IR data, the cirrus cover was confirmed thick enough to block the signal below. However, convective initiation could be seen in the raw visible imagery.

Figure 1: CI and VIS

- Bucky

Nice Example of ProbSevere Lead Time

Instability had increased in Hall county over the last hour with CAPE near 2500J/Kg, LI -6 to -7 and mid level lapse rate -7.5 to 8.  Ended up with a report of hail to 1.5" (unofficial) at 2314Z.

ProbHail jumped from 29% to over 70% in one update at 2242Z, and remained above 70% for the over thirty minutes leading up to the report.

-Forrest

Lubbock, Texas Severe Hail with ProbSevere

The weather this afternoon was quiet for much of the operations period, but in the afternoon thunderstorms developed along the dryline in the Lubbock, Texas WFO.  Initially storms pulsed (strengthened but then subsequently weakened) with ProbHail values in the 50-60% range.  Figure 1 below shows progression of a weak thunderstorm that slowly strengthened between 2226 and 2238 UTC (ProbSevere values ~20-35%) and then rapidly strengthened from 2240 - 2256 UTC (ProbHail and ProbWind values both first exceeded 80% at 2256 UTC).

Figure 1.  MRMS Composite Reflectivity and ProbSevere (All Hazards) 2226-2312 UTC 30 April 2018.  

The storm continued to strengthen with ProbSevere values in excess of 90%.  At 2313 UTC (1 minute after the final frame of the animation) 1.5" hail was reported by a trained spotter.  This example shows how ProbSevere can provide lead-time ahead of severe hazards (ProbSevere exceeded 80% 19 minutes before the first severe hail report)--which can increase forecaster confidence and lead-time in issuing severe thunderstorm warnings.

-J. Sieglaff

NE CO supercell - ProbSvr

ProbSvr performed reasonably well on this isolated storm despite somewhat unfavorable environment with 73T/37Td ahead of storm as it moved across far NE CO.  The 75% prob hail contour appeared about a scan ahead (2242 UTC) of when I would have seriously considered a warning, it peaked at 93% when the storm was at its most intense. - S. Coulomb.

NUCAPS Sounding in Lubbock

A (green) NUCAPS sounding was analyzed ahead of the dry line in the east-central portion of the CWA (Fig 1).

FIgure 1: NUCAPS sounding availability. Hand represents NUCAPS point discussed in this blog post.

The NUCAPS sounding selected indicates CAPE well above what was analyzed from other data sources. SBCAPE is over 4000 j/kg, MLCAPE around 5400, and MUCAPE around 6900.  All three CAPES are around or below 3000 j/kg based on SPC mesoanalysis and hi res model data. Some reasons for the too high of CAPE in the NUCAPS profile, based on comparison with SPC mesoanlysis and other nWP data: 1) the well-mixed layer was unrealistic, moistening too fast vertically and lowering the LCL, 2) the profile was too cold in areas, including around 700 mb. Adjusting for these reasons made for more realistic NUCAPS values. Figure 2 shows the unmodified "modified sounding", while figure 3 shows the modified "modified sounding". The modified "modified sounding" shows thermodynamic fields closer in line with what was likely reality, though probably still slightly high.

Figure 2: Modified NUCAPS (not modified by user)

Figure 3: Modified NUCAPS (Further modified by user)

- Bucky

NE Colorado Supercell

After moving almost due east along the CO/WY border the storm turned right and intensified. It was likely producing large hail based on radar data by 2245UTC. GLM during the time of intensification showed lower flash sizes with increased flash rates. The color curve for the flash area was consistently blue which made it more difficult to see the trend in decreasing flash size. Other GLM products such as GED and Total Energy had more continuously "bright" colors but didn't show much difference in trends from non-severe to severe. FED remained in single digits throughout which was surprising as I was expecting much higher values (probably based on experience w/ ENI data).  - S. Coulomb.

Lubbock, TX Mesoanalysis

Operating in the Lubbock, TX CWA to start today. At 2100 UTC, GOES-16 upper-level water vapor imagery (Fig 1) indicates a weak shortwave lifting to the northeast across SE Colorado/N Texas this afternoon, rounding the base of a broader upper trough over the western US. For viewing synoptic scale trends in water vapor imagery, I prefer to load the full disk imagery with CONUS imagery as an overlay. Time match to the full disk imagery allows for 15-min imagery which, for me, is ideal for longer term water vapor analysis. Meanwhile, loading the CONUS imagery allows for the full resolution (2km) to be displayed over the CONUS (full disk imagery has reduced resolution).

Figure 1

A GOES-16 1-min mesoscale sector was available over the forecast area today. In 0.64 um visible imagery (Fig 2), high to mid cirrus clouds mask much of the scene. A cu field has established itself across much of the southeast half of the state, on the eastern half of a dry line.

Figure 2

With the cloud cover in place, the LAP thermodynamic fields were missing significant data. The all sky products are useful in  filling in the cloud-induced gaps in data. The cloud type all sky product tells us whether a given pixel is derived from the GFS, cloudy sky retrieval algorithm, or clear-sky retrieval algorithm, allowing for comparison between the different algorithms and GFS first guess. Comparing adjacent pixels of different types for CAPE, the cloudy and clear sky pixels have lower values (~1800 j/kg) than the GFS first guess (~2400 j/kg). Comparing both with HRRR model runs and the SPC mesoanlysis, the lower values in the satellite retrievals seem to be more on par than does the GFS first guess. This leads one to believe the satellite is providing a correct adjustment to the model first guess. The LAP data indicates a max in instability through the center of the CWA along the dry line, decreasing east. LI values were also slightly lower in the retrievals compared to the GFS first guess, while TPW values were similar.

Figure 3: cw from top left: CAPE, LI, Retrieval Type, TPW. Sampling for clear sky pixel

 

Figure 4: cw from top left: CAPE, LI, Retrieval Type, TPW. Sampling for cloudy sky pixel

 
As for trends, the half-hourly all-sky LAP data indicates CAPE increasing steadily from around 1000 j/kg at 1728 UTC to around 1800 j/kg at 2028 UTC. A half-hour temporal resolution is adequate for analyzing trends in thermodynamic fields.

- Bucky

First Hit on ProbSevere for Lubbock Convection, note on CI

Two firsts for me:  1) First cell I've seen so far to register a SevereProb today, and 2) First cell I've ever seen with SevereProb!

As of 2156Z, 24 minutes later, flash rates just jumped over the previous update, and probs made a modest jump to 12/3/0.

One thing that I did notice was that these cells didn't seem to be picked up by the Convective Initiation algorithm prior to development.