CI/CI-Severe in West Texas Convection

I was able to watch the CI and CI-Severe products in some convection that developed over Glasscock county just west of the San Angelo CWA.

This image was taken at 2147Z on Wednesday, with CI in the upper left, CI-Severe upper right, Goes-16 Visible lower right, and SJT 0.5 degrees reflectivity lower left. While satellite has started to show buildups in the cumulus field in the county, no precipitation or lightning has developed. CI is in the 30-50% range over southeastern parts of the county, while CI-Severe was higher for the central area.

At 2157Z, precipitation developed over the northwestern part of the county, with low CI probability over the eastern part. The CI-Severe jumped up to 80%+ over the northeastern part of the county.

By 2212Z, 4 areas of precipitation had developed. Some lightning was occurring withe the easternmost and northwesternmost cells. Since convection was occurring, the CI and CI-Severe dropped almost completely.

The CI product was useful for anticipating where the showers and thunderstorms would develop, but did not provide a clue as to their intensity. All of the cells were producing lightning by around 2245Z.

Gary Cannalte

Convective Initiation over Arkansas

Looking at another example of the Convective Initiation Product over western Arkansas, from earlier this afternoon. The loop below shows the general CI product overlaid on the "sandwich" VIS/IR imagery, for the period approximately 18Z to 19Z. Looking at the cu or towering cu field over SW AR, the CI values vary considerably from one time to the next. Values are generally around 50 percent or less (green/blue), but sometimes jump up to 60-70 percent (yellow). Thunderstorms did develop over this area shortly after 21Z.  A. Cope

Overshooting top with Flash Extent Density

I found it interesting to watch the Flash Extent Density increase concurrently with the development of an overshooting top.The FED increased from a count of 2 at the onset of the overshooting top to a maximum of 11 at its peak.

Fig 1. Overshooting top detected by Day Cloud Phase Distinction RGB, overlayed with Flash Extent Density (5 minute with 1 minute update) from the GLM.

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Update to Earlier Blog Post on CAPE spread between AllSky/NUCAPS

In an earlier blog post today I showed that considerable spread existed between the AllSkyLAP CAPE and the NUCAPS Improved Latency CAPE values over northern SJT forecast area. While it was not available at the time of the previous blog post, the NUCAPS Modified sounding showed CAPE values that were in the ballpark of what AllSkyLAP was showing.

1941Z NUCAPS Modified sounding

Alex Brown

Other GLM Products

The 4-panel image below shows lightning over western AR. Upper-left is flash extent density (FED), which is scheduled to be the initial operational GLM product in AWIPS. Upper right is Event density which seems to show similar patterns to FED, but the values are 5 to 10 times higher. Not sure if this adds any significant value to FED.

The bottom two panels are Group Centroid Density and Flash Centroid Density. All the centroids are just single points, so each one highlights a single grid cell in the 2x2 km ABI grid, leading to a much finer "pixelated" appearance. At this point it's hard to see what operational use they might have.  A.Cope

Convection in SW Texas

An isolated thunderstorm developed over Pecos County in southwestern Texas. While the storm wasn't producing a lot of lightning, it was interesting to see how the increase in lightning activity corralated to brief increases in radar reflectivity, resulting in the production of some small hail. This thunderstorm pulsed up and down a few times in intensity and was proceeded by brief increases in the flash rate of lightning.

Also of interest was watching the anvil of the thunderstorm blow off to the east-southeast pretty rapidly, while a field of surface cumulus clouds steadily moved to the north-northwest in an area just to the east of the thunderstorm. It will be interesting to see if development takes place this evening in the zone of higher shear to the east of the afternoon thunderstorm.

Gary Cannalte

CI regular vs severe

I have noticed on severe occasions where the CI (for regular convective initiation) is much lower than the probability depicted by the Severe CI product.  Intuitively, one would think the probability for convective initiation should ALWAYS be higher than the probability for convective initiation to lead to severe weather.

Fig 1. "Regular" CI product at 2037 UTC. Note the green 50% CI probability toward central AR.

Fig 2. Severe CI product at 2037 UTC. There is a 90% probability for severe convection in the same location as the above image.

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Comparing 1-min, 2-min and 5-min running FED totals

For the GLM products such as Flash Extent Density (FED), we are looking at looking at running accumulations over different time periods of 1 minute, 2 minutes and 5 minutes (and maybe others?). The 5-min (1-min update) loops are smoother, but may miss or be slower to show sudden changes. The 1-min loops tend to be rather jumpy and may obscure trends. The 2-min (1-min update) loops might be a good compromise, but we are still comparing.

The 3-panel  below shows a 30-min loop comparing all three accumulation times for a storm over northwest MS. Comparing the frame-to-frame variability among the three options, the 5-min loop is certainly smoother, but has higher max values than the 2-min or 1-min loops, which may require a different color scale.

Also here is a plot from the Tracking Meteogram which compares the max values from all three accumulation types. Note the 5-min accumulation is in the middle. The 2-min running accumulation (bottom curve) might be the best combination of smoothness and sensitivity.  A.Cope

RGB of convective initiation

I found this capture of convective initiation to be interesting and cool to watch. As dry air on the south side of the MCV advected east into far western AR, storms would fire near the state line. The Day Cloud Phase Distinction shows this cycle very well and provides a nice optical depth to the satellite loop.

Fig 1. Mid-level water vapor loop showing dry air advecting into western Arkansas on the south side of the MCV.

Fig 2. Day Cloud Phase Distinction RGB depicting convective initiation on OK/AR state line on the leading edge of the dry punch.

I was looking for any obvious signal in the lightning data for that point but nothing significant seemed to stand out for this case. That said, it is producting consistently high Flash Event Density with relatively high Total Energy values and low to moderate Average Flash Area.

Fig 3. Clockwise beginning with upper-left image:  Flash Event Density 2 minute data (1 minute update), Average Flash Area 2 minute data (1 minute update), Total Power 2 minute data (1 minute update), ENTLN 5 minute data (1 minute update).

It was interesting, however, that the AllSkyLAP CAPE for this area was quite muted. Makes me wonder if this isn't a function of the model first guess. Since the sky was cloudy and the satellite data relied more heavily on the GFS (which was convectively contaminated), I didn't find this data particularly useful.

Fig 3. AllSkyLAP CAPE product showing CAPE values < 350 J/kg over eastern OK and western AR. This is using primarily the GFS background information.

Fig 4. GFS QPF for 18Z. The convective contamination likely resulted in erroneous CAPE values on the AllSkyLAP product.

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AllSkyLAP CAPE missing frames

The AllSkyLAP CAPE product was coming in at sporadic times. A good frame would arrive at a give time (example 1758 UTC) but then an empty frame would populate in AWIPS at 1800 UTC. This really limited the usefulness of looping the product.

Fig 1. AllSkyLAP CAPE loop with missing frames.

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