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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Prob Severe V 3

Posted in ProbSevere on by Kevin Thiel.

See a significant improvement in the Prob Severe with V3.  Looking at a particular storm in the panhandle of FL shows a significant difference between the two versions.  The image below is the cell to the right of the screen and the new prob severe v3 time series along with a cross section from GRAnlysist.

What can’t be seen is the sample over the prob severe v3 outline which shows both the v2 and v3 output.  In this case, the v2 showed a 65% chance for severe hail but the v3 only showed 7% for severe hail.  Severe wind was 52% and 58% respectively.  Looking at the cross section and knowing the PW values are in the 1.7-1.8 range shows the main threat would be more of a wind/rain rather than hail.  This is a big improvement.  To be honest, the issue with over forecasting hail on the v2 is a big reason why I usually don’t use prob severe.  Seeing this change with V3, I am much more likely to be looking at it as it seems to be more refined and takes the climate, area and conditions into account before producing significant hail or wind values.  While I don’t think it was looking at the cross section to help make its decision, this cross section is a very good example of a wind risk over hail.

-Strato-Dragon

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ProbSevere Time Series & Cell Merger

Posted in ProbSevere on by Kevin Thiel.

Two separate thunderstorms gradually merged to the WSW of New Bern between 1845-1900 UTC. As ProbSev polygons merged into 1, some of the probabilities took a small dip. Eventually the eastern storm cell intensified slightly, bringing ProbSev values back up.

– Guillermo

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ProbSevere Data Readout/Sampling

Posted in ProbSevere on by Kevin Thiel.

The ProbSevere readout is useful with all the details shown, but when in 4-panel mode, it takes up a lot of space, sometimes with some data being omitted by the frame. Would it be possible to have the option of a simplified readout displaying only the top 2 line probabilities and then have the option of displaying the additional data? (Perhaps akin to the double left click on a ProbSev polygon for the time series chart)

– Guillermo

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Optical Wind Inferences

Posted in Optical Flow Winds on by Kevin Thiel.

The “All” winds display setting was useful in combining the multiple layers of wind data, however, without a proper understanding that the winds displayed (and subsequently shaded), a user may incorrectly infer regions of convergence/divergence. I found it useful to ‘build’ the wind layers from the top of the atmosphere (100-50mb) down, to see in which layer the winds displayed where located.

Circled in red are areas that one might incorrectly infer the presence of strong speed divergence, when, while divergence may be present, the winds displayed are at different levels of the atmosphere based on the level of the optical wind sensing. Perhaps there is a way to color-code the wind barbs to correlate height / pressure level (Red for surface with a gradient toward blue for 100mb, or so)?

– Guillermo

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NUCAPS Sounding comparison to Observed Sounding

Posted in NUCAPS on by Kevin Thiel.

Noticed an across the board temperature discrepancy between the Observed Sounding at KJAX and two of the NUCAPS soundings from the afternoon pass of NOAA-20.  Looked at two different NUCAPS soundings which straddled KJAX.  The morning sounding at KJAX (12Z) showed a typical morning, warm tropical but capped sounding.  The two NUCAPS soundings were from six hours later showed a surface change that would be expected but then showed decent cooling from the morning through the entire column.  The image below shows the two NUCAPS soundings, one is in focus (red/green), the second NUCAPS soundings is the drab color and the observed sounding is in blue.  This shows the two NUCAPS soundings to be very similar and follow each other well but are also a few to several degrees cooler than the observed sounding. 

While I would expect some areas of the column to cool with a sea breeze front coming through, but not the entire column.  When I see this type of discrepancy, it makes me not want to trust the NUCAPS sounding in this case as it does not seem to make much sense with the ground truth of the actual measured RAOB.  Of note, when the NUCAPS sounding was taken, the line of sight was free of clouds and the “dots” were green; however, there were thunderstorms to the north and west of KJAX and they had an outflow boundary approaching the area rapidly.  Could this have made a difference?  I don’t know but it is worth noting this did occur.  Also, we also noted the NUCAPS soundings for this area were all cold in comparison to the morning RAOB.  Looking further west to KTLH, the NUCAPS soundings and the observed soundings looked much closer and made a lot more sense.  So, could this be a marine layer influence?  Could this be just a bad batch?  Could this be a bad thermometer and wet bulb sensor on the actual RAOB?  All valid questions that I can’t answer but put here as possibilities that can’t be verified.  

Of note, we also looked at the differences between the KSC 15Z sounding and the afternoon and the afternoon pass of the NOAA-20 NUCAPS soundings.  These two were much closer and seemed to be much closer together.  Also note, the time difference between the two soundings is only 3 hours in comparison to six.  The image below is the KSC sounding comparison.  The sounding in focus is the actual KSC RAOB and the NUCAPS sounding is in the background.

-Strato-Dragon

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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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GLM Lightning Data & Convective Insight

Posted in GLM on by Kevin Thiel.

Assessing the various GLM lightning products, I found the MFA and FED particularly useful in correlating the more active thunderstorm core / updraft areas. TOE was useful, but maybe a slight change in color scale may help to better identify those very active convective areas. (perhaps the sharper color gradient change could start at a slightly higher value than currently)

Upper Left: FED img + Flash Point + ENTLN; Upper Right: TOE img + Flash Point + ENTLN Lower Left: Radar img + ProbSev + Flash Point + ENTLN Lower Right: MFA img + Flash Point + ENTLN

The GLM flash point data didn’t show as much ‘clustering’ as I had expected to see, as compared to other surface-based data sources (ENTLN). Is this related to a data display density or a more sensitive surface-based lightning detection? However, due to the parallax correction, the flash point data did line up with fairly well with active convection, although there were a few flash point detections well displaced from any radar reflectivities (see bottom left)–perhaps related to stratiform lightning?

– Guillermo

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GLM in Northern Florida

Posted in GLM on by Kevin Thiel.

Comparing the Flash Extent Density to base reflectivity in northern Florida, we noticed an area of exceptionally high flash density just north of the best convection. Adding flash points (parallax corrected) to the radar image and they were more where one would expect in the storm. This indicates a parallax issue with the Flash Extent Density. This is a good example of where the flash points can be a good sanity check when interrogating a storm.

Base reflectivity and flash points (left) and five minute Flash Extent Density (right).

– Earl Grey Tea and Fear the Shear

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Florida lightning

Posted in GLM on by Kevin Thiel.

Using GLM for an IDSS event  allows for great flexibility and confidence in providing warnings for decision makers.  In the image below, this shows a complex organization of thunderstorms. In this case, a lightning alert or warning for them.  In this case, since the thunderstorm structure is much more complicated, it is unlikely an all clear would be provided for some time.  It is likely this would be persistent through the afternoon as the surface front is pushing the sea breeze front back toward the coast and keeping the activity nearly parallel with the coast.   In this example, the FED product does provide the forecaster a good idea of the forward extent of the which is to the south and east, despite the fact the upper level winds are pushing the avils to the north.  The lightning points are also helpful to get an idea of where the potential return strokes are actually reaching the ground enveing though the GLM “can’t” actually 100% determine this but just based on the probability.  

Point flashes also provide the user with an idea of the size and potentially the ability to identify which core the lightning originated from.  Not sure how well this will work or if it will work but just a thought.  Think more work and or research will be required before we can say one way or the other if this will actually work.

– Strato-Dragon

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