Category: GLM

MAF Testbed Observations

Posted in GLM, LightningCast, NUCAPS, Optical Flow Winds, PHSnMWnABI, ProbSevere, SPG2022 on by Kevin Thiel.

ProbSevere v3

For the initiation of convective storms, I found that the ProbSevere performed the best over the other products available to me today. I have seen over the last couple of days that the best use of ProbSevere is the trend table. The steep increase in these total severe values support radar trends that suggest a warning is necessary. For the initial warning on severe storms, this was the best use.

The only negative to this product was the latency. While the latency was only on the order of 2-5 minutes, this was equivalent to appx. 2 radar scans that indicated to me ahead of time that this storm was strengthening. This can lead to some confusion especially if the storm is quickly pulsing and falling.

Additional upticks were noticed in subsequent SVR issuances throughout the afternoon that provided a nice heads-up in conjunction with the radar data. These were used in the context of the storm maintaining its strength after the storm was warned and again after the storm re-pulsed several minutes later.

It is also worth mentioning that the perceived threat of ProbSevere was also the shared opinion of the forecast (forecaster perceived threat for hail had the highest ProbS. probability). Once the storms reach the “cap” of their ProbSevere, it becomes of little use.

GLM

GLM was useful during convective initiation, but did best for storms that were already at the peak of the ProbSevere threshold. GLM showed additional pulses in a mature storm that had a 90% probability of being severe and added confidence to the warning forecaster that the storm had gained additional strength which manifested itself in larger hail for example.
It was however short-lived as the storm gained additional intensity but did not show the corresponding increase in GLM FED that one would expect. This was explained as a limitation due to the structure of a mature (and severe) thunderstorm.
Min Flash Area also reached its lower values on several storms which provided little to no additional data. Maybe this used in conjunction with total optical energy would be useful, but this yielded no significant results when investigating briefly.

PHS Model

The PHS model was very useful today ahead of convective initiation, but more so in an advective situation.
Instability parameters were observed as ongoing severe storms moved SW toward the established instability gradient. ProbSevere outlined areas are moving SW in the image below across an area of relatively high CAPE and low LIs. This provided useful information about the existence of a boundary and the motion of the storms along with the pre-conditioned environment.
The model did have limitations as the storms became ingested into the later runs of the model and the storms showed developed cold pools. The environment depicted in this situation had become dominated by nearby cold pools of incorrectly placed convection which limited the model’s usefulness.

LightningCast

Not much use of the lightning cast today due to the lack of CI within our CWA, but we did get a chance to look at the advection of lightning. In general, this proved to be a little too slow. It seemed the contours were tight to the storm and storm motion was rather slow, but the lead time on lightning detection was around 30-40 minutes. With an advecting storm, I would have expected this to be rather accurate to the 60 minute threshold that it attempts to achieve, but 30-40 minutes is still VERY useful for DSS and now-casting purposes.

NUCAPS

NUCAPS had some interesting results today, primarily in the way it reported green, yellow, and red data points. Some of the gridded data was unavailable for points with green-retrieval and this was puzzling because it would have indicated a dry slot over the DFW region that was evident in the water vapor and visible satellite. However, the data grid boxes were missing or contaminated with bad data over a mostly clear area. Areas with similar cloud coverage performed as expected. The pop-up skew-t continues to be the best tool in this suite of products, provided the data points are green-retrieval.

Optical Flow Winds

Not much use on the optical flow winds today due to the fact that ongoing convection muddied the data. Overshooting tops were visible for a brief moment, but quickly engulfed in strong storms and expanding anvils. The divergence field is really hard to gather meaningful intel from and the existing platform outside of AWIPS limits its overall usage. A suggestion in our group today was that divergence could be useful if the noise is limited. Perhaps remove values above and below a certain threshold. Instead of widespread values, draw attention to the important outliers.
– Overcast Ambience

Today’s details of products and warnings: Midland, TX

Posted in GLM, PHSnMWnABI, ProbSevere, SPG2022 on by Kevin Thiel.

I found the PHS products useful for seeing the corridors of enhanced severe risk. They correctly showed that hail (or wind) was the highest risk compared to tornadoes.

ProbSevere was very useful with the trend lines. Again and again correctly identified risks as they occurred.

GLM showed strong ramp ups in activity prior to each severe issuance. No complaints here.

NUCAPS data was less useful, but with the skew-t pop up I was able to correctly see areas of mid level dry air. I did not use optical flow. Prob lightning was useful to see the first cells pop up but did not serve as much purpose after that with no known DSS opportunities.

Some Random Guy

ProbSevere on some early storms near ARX

Posted in GLM, ProbSevere on by Kevin Thiel.

We noticed a relatively high ProbSeverev3 (53%) on a rather innocuous looking storm (MESH around 0.5”) around 2030z. This was higher than the v2 value of 36%. The individual probs were relatively evenly weighted at lower values near 30%.

(clockwise from top left) MRMS 18dbz echo top, MESH, reflectivity and ProbSevere (storm in center), and low-level MRMS azimuthal shear.
(clockwise from top left) GLM FED, GLM MFA, reflectivity and ProbSevere (storm in center-right), and GLM TOE.

GLM FED was unimpressive, though it’s unclear how much of this is related to lower detection efficiencies in this area. ENI total lightning was halfway decent. High DCAPE values and other environmental parameters may have been sending the ProbSevere v3 higher.

Timeseries for the storm of interest.

Another storm further to the west over SE MN had slightly lower MESH (.39”) but in this case PSv2 was higher at 48% vs Psv3 at 23%.

– Barry Allen

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Progressive Disclosure & GLM Flash Points

Posted in GLM on by Kevin Thiel.

When loading GLM Flash Points, there is no preset density of the data.

This does affect how much flash point data is displayed depending on the zoom level of the map. In the 2 maps below, within the red square of the larger map, 13 flash points are indicated as opposed to 15 once you have zoomed in further:

Unless the forecaster knew to increase density to max, this could obscure some important clusters of lightning coincident with storm evolution.

– Guillermo

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GLM Flash Points

Posted in GLM on by Kevin Thiel.

Noted GLM flash points really help speed up the process of identifying where the cell of interest was located.  In the past, I would have to make a manual, on the fly “calculation” in my head where the actual cell was located.  If there was only one cell, that was easy by looking at radar.  When you get into the complex thunderstorm situations, that can be difficult and in the worse cases, it is too involved.  Seeing how the flash points seems to fix and/or surround the updraft, really helps speed this process up and give confidence to the forecaster which cell is the cell to be worried about.  This could also help with warning confidence.  The  image below shows an prominent example of this.

It is hard to see the flash points but there are 6 points surrounding the core of this small storm.  I chose this one to verify the positioning as it was on its own so it was easy to figure out which one it came from.  As such, seeing how close this is to the core, it makes it much easier to identify which FED “spike” is from which core.  

When looking at satellites with flash points, it also help confirm the location of the core as the ABI imagery is parallax corrected.

– Strato-Dragon

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GLM Lightning Preset 4-Panels

Posted in GLM on by Kevin Thiel.

GLM lightning data provides very useful information to the operational forecaster, especially when properly combined with radar/satellite imagery. Would it be possible to take best practices suggestions from frequent users to lead to the creation of some pre-set 4-panel procedures that could be found in the AWIPS GLM data section (similar to what is available with radar base date, etc.)?

Sample 4-panel image pulled from the GLM Quicklook Guide

– Guillermo

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ProbSevere and GLM with supercell moving offshore the South Carolina coast

Posted in GLM, ProbSevere on by Kevin Thiel.

A thunderstorm located east of Charleston appeared to have some supercell characteristics as it moved south-southeastward towards the coast, with a kidney bean shape in reflectivity and a weak mid-level mesocyclone, as well as some deviant motion from the northwesterly flow. As it was over land it appeared to be strong but sub-severe, and maintained generally consistent 20 to 35 percent ProbSevere in v3. ProbSevere v3 seemed more consistent overall, with v2 jumping up and down more often, dropping down into the single digits at times. ProbSevere v3 did jump down below 20 percent briefly when GLM FED really dropped down. But the consistent lower-end probabilities at least indicated that this was a storm to be watched relative to the lower v2, and this may have at least allowed lead time on a low-end special marine warning before it moved offshore and strengthened.

The timeseries is somewhat useful if you just have one storm to look at, but with multiple storms I would probably just look at the loop in the ProbSevere plan view instead.

After it moved offshore, GLM FED increased, slightly in advance of a jump in MESH and associated jump in ProbSevere v3. ProbSevere v2 jumped ahead of v3 in probabilities as often occurs, though at that time MESH around 0.9 inches may have warranted the more conservative ~50-60% v3 approach. Later MESH jumped up to around 1.3 inches, and ProbSevere v3 jumped above 70 percent at this time as well.

Clockwise from top left: MRMS 18dbz echo top, MESH, reflectivity/ProbSevere/low-level azimuthal shear at 2130z.
Clockwise from top left: GLM FED, minimum flash area, reflectivity/ProbSevere, total optical energy at 2130z.

– Barry Allen

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ProbSevere in Jacksonville

Posted in GLM, ProbSevere on by Kevin Thiel.

The 0.5 degree SRM from JAX shows a concentrated area of wind within the cluster of storms in St. John County, FL with radar estimates of the wind near 50kts. Given the lightning jump illustrated by FED values quickly rising to ~170 flashes per 5 min, the storm is intensifying.

However, ProbSevere values are rather low with version 3 showing only 22% and version 2 showing 33%. ProbWind surprisingly was even lower with only 19%. This is a reflection of the lack of base radar data involved in the ProbSevere and ProbWind algorithms. Especially for ProbWind, base radar velocity data needs to be included in ProbWind for this product to be useful in identifying wind producing severe thunderstorms.

It would be useful to integrate base radar data from multiple single radars and combine these values into one algorithm. It may be useful to identify notable/sharp changes within velocity data between pixels which could help in picking out downdrafts.

– Fear the Shear

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Storms in northern and central Florida

Posted in GLM, NUCAPS, ProbSevere on by Kevin Thiel.

GLM:

On the afternoon of June 15, 2 different convective regimes were noted across Florida, with different GLM lightning characteristics. A cold front was sinking southward towards the Florida panhandle, with convection developing along the Gulf sea breeze along the FL panhandle. Convection of more uncertain forcing developed in Central Florida.

Convection along the FL panhandle had higher MLCAPE and DCAPE due to mid-level drier air and steeper lapse rates, with somewhat lower PWATs. SBCAPE in excess of 5000 J/kg and MLCAPE in excess of 3000 J/kg was unusually high for this region. Convection in central FL was in a more tropical air mass, with PWATs at or above 2 inches and more saturated profiles. Convection in the FL panhandle developed in an area with very high microburst composite parameter values, indicating conditions very favorable for microbursts and localized damaging wind gusts.

12z TAE sounding:

15z XMR sounding:

MLCAPE 19z:

19z DCAPE:

19z PWATs:

Microburst composite parameter 19z:

The FL panhandle convection was more intense on radar and also had higher flash extent densities. It also tended to have lower minimum flash areas, centered on locally strong updrafts. Notable hail cores were observed aloft, and melting of these hailstones caused strong downdrafts and damaging wind reports, and in a few instances quarter size hail made it to the ground, with one instance of golf ball size hail..

1920z:

The central FL convection was weaker and had also been going on for longer, so there was some convective debris stratiform precipitation with larger minimum flash areas. Flash extent densities were lower than in the FL panhandle. There were still areas of lower minimum flash area centered on the updrafts.

The GLM flash points were very useful and lined up with the NLDN and ENTLN strikes and flashes. The parallax correction was especially useful for DSS purposes as partners often request notification on lightning strikes within a particular radius on the order of 8 to 20 miles, so an accurate location is important. At first glance there were much less flash points but this appeared to be due to the data only being 1 minute data without having the 5 minute accumulation that the NLDN and ENTLN offers. Having this similar 5 minute accumulation would be imperative for using the GLM flash points in operations. The sampled metadata for the flash points appeared less useful operationally. The flash area would be more of interest than the duration, but with a large number of flash points some sort of graphical depiction would be needed, and flash extent density seems to serve this purpose.

ProbSevere:

One interesting thing that was noted was v3 had much lower ProbHail than v2, while still having decent ProbSevere (mainly wind-driven values). We speculated that this was due to some of the machine learning based on environment and climatology, since severe hail would be less likely this time of the year with higher freezing levels/hot surface temperatures causing melting. However, in this case a golf ball size hail LSR was issued at 19:59z (report time appeared to be incorrect) for 2 ENE Saunders in Bay County, FL. This was comparable to MRMS MESH which maxed out at 1.89”.

On the technical side, I did want to note that typically I have sampling turned off in AWIPS, but then double-click on something that I want to sample. Since the ProbSevere timeseries plugin is also opened by double-clicking on the object, sometimes when I meant to double-click to sample the ProbSevere values I accidentally ended up opening a time series. And then I would double-click outside the ProbSevere area to sample something else or turn off sampling and I would get a black banner. Perhaps the timeseries doubleclick function could be turned on and off by making the ProbSevere product editable or not editable in the legend.

NUCAPS:

Gridded NUCAPS and individual NUCAPS soundings at 1840z showed steeper 700-500mb lapse rates than what was shown on the SPC mesoanalysis and some of the morning soundings, in areas away from convection. It’s hard to say which one was right, but the hail cores observed do seem more consistent with 700-500 mb lapse rates of near 7 C/km or greater. (Note that it would be useful to have contours to go with the images on the gridded NUCAPS plots.)

NOAA-20 sounding availability and example sounding (1823z)

1840z gridded NUCAPS 700-500mb lapse rate:

18z SPC mesoanalysis 700-500mb lapse rate:

NUCAPS also indicated the more saturated profiles/weaker lapse rates in the central FL convective regime.

NUCAPS did indicate some of the higher CAPE values, but with missing data in much of the area of interest as convection had already initiated when the pass occurred.

– Barry Allen

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Optical Wind, GLM, and ProbSevere Use in Convective Environments in North Carolina and South Carolina

Posted in GLM, Optical Flow Winds, ProbSevere on by Kevin Thiel.

Looking at multiple levels of optical winds can be useful in analyzing the amount of wind shear over an area in near-real time. In this case, the tool shows limited wind shear, so one would expect storms to be a bit more short lived. Would it be possible to add wind shear fields directly into this tool for quicker analysis?

Optical winds for the ILM CWA on 6/15 at 18Z showing little difference in the winds between the 800-600mb and 600-400 mb levels.
4 panel of the GLM data at ILM around 19 UTC illustrates Flash Extent Density (top right), Minimum Flash Area (bottom left) and Total Optical Energy (bottom right). We adjusted the colormap of the minimum flash area so that we could identify the updrafts more easily since the minimum flash areas were under 100km^2 and the default map was set to cover images up to 2000km^2. This allowed us to identify which storms featured the strongest updrafts which when combined with data from the Flash Extent Density, we could watch for storms that were strengthening and thus posed a greater need for a warning.

Three Body Scattered Spike & ProbHail

Three body scattered spike is visible in the storm in the top right panel.
ProbHail shows values of ~65% when the three body scattered spike appears with MESH values over 2” supporting the likelihood of at least severe size hail in the discrete cell.

Watching the meteogram on this storm, we can see the probhail values jumped up to 65% over the last 15 minutes. It’s probably best to have ProbHail values of 60% or more last for a few volume scans because that suggests the residence time in the hail growth zone is long enough for hail to grow and become 1” in diameter or larger.

–Earl Grey Tea and Fear the Shear

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