PHS CAPE Gradient Use in Mesoanalysis

The PHS Sfc CAPE procedure was helpful in diagnosing the mesoscale environment. In particular, the depiction of CAPE gradients matched well with where the Day-Cloud-Phase Distinction showed where these boundaries lay as could be construed from the cumulus field.

The PHS Sfc CAPE depicted this surface boundary migrating southward through the central NE through the 21Z-00Z time frame. Observed cells moving left (east) off the boundary into a more stable environment as resolved by the PHS Sfc CAPE field all decreased in intensity and saw their convective updrafts weaken.

Seeing this after the first hour raised forecast confidence in the forecast thinking of today’s severe weather potential and was shared in a graphicast for this test case scenario.

PHS-CAPE-STP-PSv3 Procedure from 6/6 @ 20Z to 6/7 @ 01Z
Day-Cloud-Phase Distinction RGB at 20:06Z
– Trip

Analysis of a Line of Storms Moving Across Northeastern LA into Western MS

Today we focused on the slight risk across the southeast, specifically WFO Jackson, MS. During the afternoon hours, a small linear complex was coming across northern LA towards Jackson’s CWA. Right before the CWA line, there was a wind report of snapped tree limbs of 3” diameter from Monroe Airport. There was also a measured gust from the airport of 41 mph. The velocity on radar had ~60 knot outbound winds at around 14,000 – 15,000 feet, which easily could have produced a few severe gusts to the surface. The gifs below show the linear line of storms and the associated velocity as the system moved over Monroe Airport in northeast LA with the wind report at 1952z and then continued to enter western MS.

Image 1 shows a loop of radar reflectivity with prob severe overlaid and Image 2 shows the velocity associated with the radar loop.

In this situation, prob severe was not doing as good of a job on picking up on these “stronger” winds. Image 3 below shows the time of the wind damage report and 41 mph gust at the airport in northeast LA, but prob severe and prob wind are both only picking up about 20% probability of this potential. Almost two hours later, the line of storms are a bit weaker on reflectivity but just as strong or even stronger on velocity. Note, the storms were also closer to the radar at Image 4, so the stronger outbound velocities were closer to the surface. So this led to wondering is prob severe a good indicator for straight line winds?

Image 3 shows the prob severe time series at the time of the damaging wind report at Monroe Airport in northeast LA.
Image 4 again shows a prob severe time series for the same line of storms about two hours later and approaching the western MS border.

Prob severe utilizes azimuthal shear which as seen in the Images 3 and 4 below are not present with solely outbound velocities and little to no inbound present. This is common for straight line wind scenarios, but not super helpful in terms of how prob wind is calculated. Also, the prob severe is an object oriented product that utilizes reflectivity for these objects. In this scenario, the reflectivity definitely began to weaken but velocity did not. The toughest part was the prob severe began to decrease over the two hour time span shown above, but yet several damaging wind reports of roofs blown off and trees/power lines down led me to believe the probability of prob wind should have remained constant or increased over time.

While investigating the prob severe I also took a look into the lightning characteristics within the line as you can see in the GIF below (Image 5) that there is the formation of some trailing stratiform on reflectivity. A still image was taken (Image 6) to show how the lightning began to extend westward into the light stratiform. The flash area (top right of the four panel) shows the darker purple color extending westward, which indicates the storm mode is more of that light stratiform rain with longer flashes extending through it rather than the intense small flashes within the leading line. This can be helpful in time when you may have a DSS event and the main line has passed through, but lightning is still present in the trailing light rain. Pairing the ground networks with the GLM extent and area allows a forecaster to give DSS on the latest CG stroke within the large area.

Image 5 shows a four panel with reflectivity (top left), GLM flash area (top right), GLM flash extent (bottom left) and GLM optical energy (bottom right). The ground networks have been added to the flash area with CG strokes and then over the flash extent with polarity and cloud flashes.
Image 6 shows the same four panel layout as described in image 5, but as a still image. This shows a great use of GLM for examining storm mode and flash extent, along with DSS uses of CG strokes within the large westward expanding extent of flashes behind the main line of storms.

Lastly, there was a NUCAPS CONUS NOAA-20 satellite pass at around 19z, which was well before the line of storms made it to the western Jackson CWA line. No special radiosonde launches were made by local offices, so the next best observational guess of the atmospheric profile would be from satellite. Model soundings were also available to compare at the time. A RAP sounding at 19z was taken just east of the western MS border (see Image 7 below for location of this sounding) and a very nearby NUCAPS sounding was also retrieved for comparison (see Image 8 below for location of this sounding).

Image 7 (left) shows the location of the retrieved 19z RAP sounding (circled in white) and Image 8 (right) shows the location of the retrieved 19z NUCAPS sounding (circled in white).

The soundings (Image 9 and 10 below) looked fairly similar between the model and satellite profiles; however, there were several major differences that played a key role in changing the instability parameters. The NUCAPS sounding was still slightly too low of a surface temperature with 86 deg F versus the RAP’s 89 deg F. Surface observations from 19z at that location showed a temperature of  around 91 deg F. Also, the surface dewpoint was far too low on the NUCAPS profile at the surface as it was 5 degrees below the current observation at 19z. Meanwhile, the RAP was only one degree lower than the current surface dewpoint. These subtle differences caused significant variations in the CAPE values.

Image 9 shows the 19z RAP sounding through sharppy.
Image 10 shows the 19z NUCAPS sounding from sharppy.

After realizing the NUCAPS profile was not accurately depicting the surface temperature/dewpoint, I decided to see what the modified sounding might look like through NSHARP. Image 11 below shows the modified NUCAPS sounding through NSHARP with a much cooler surface temperature of near 80 deg F. This was almost 10 deg below the actual surface temperatures and 6 deg below the original NUCAPS profile. The boundary layer was not representative due to this drastic difference and therefore the modified sounding had to be thrown out of the comparison.

Image 11 shows the modified 19z NUCAPS sounding shown through NSHARP.

Lastly, with knowing the line of storms were headed into the area of interest I decided to see how the forecast products were looking. Unfortunately, I did not get to save the images off in time as the forecast images disappear from AWIPS when the next pass occurs. So I was left with the web-browser version which is only in a gridded format. Unfortunately it is very difficult to depict changes in this format, whereas in AWIPS you can interpolate the image and smooth the results for a more concise display of values. Image 13 shows the comparison of the web-browser gridded format versus the AWIPS smoothed version for the West Coast pass of the NOAA-20 satellite.

Image 13 shows the gridded NUCAPS CAPE forecast for 6 hours in the future from the web-browser (left) and the same exact data and image displayed in AWIPS smoothed (right).

– Harry Potter

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Optical Flow Winds on Tuesday- 2105-2202Z

Today operations were centered over Bismarck, ND, where a large storm complex was in progress much of the day.  The storms developed near a warm front, and benefitted from an approaching short wave trough as well as orographic lift and differential heating.  You can see the extent of the anvils from storms centered over southern ND and northern SD.  This complex dominated the local environment and seemed to take advantage of most of the local instability.

The new optical flow winds tool uses 1-minute imagery from GOES-16/17 ABI imagery to provide high resolution wind estimates at 2-km resolution using an optical flow technique.  You can plot the winds in different layers, from 1000-800mb up to 100-50mb.  As you can see, it is mainly the higher level winds that were plotted above the anvil plumes, and show the divergence at the higher levels of the storm.  

Optical flow winds over storms in southern ND on the afternoon of June 8, 2021.

Taking a look at the SPC mesoanalysis at 300mb for this time, you can see the speeds and directions roughly match the 400-200mb winds plotted on the optical flow plots.

SPC 300mb analysis including heights, divergence, and winds at 2100Z.

Winds closer to the surface did not plot as much, mainly owing to the dense cloud cover the satellite was seeing.  After some discussion, surface plots were added to the 1000-800mb layer, which helped to orient forecasters.  Forecasters still need to mentally adjust the satellite imagery which was overlaid for parallax.

Optical winds with station plots added.

I think the optical wind flow could be useful to investigate storm strength and maintenance.  It could be helpful in both warning operations and for IDSS purposes.  The storm complex in question lasted for at least 12 hours, and produced wind damage, large hail, and torrential rains leading to flash flooding. 

– Dana Scully

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Using GLM

Using the minimum flash area to show where the smaller lightning strikes occur but is associated with stronger updraft with cells building faster (Yellow) to generate lightning. Larger lightning strikes occur in the stratiform area of the precipitation field where charge building is slower (Purple). This is also a good way to indicate convective mode as the system translates from individual (SuperCell) to a linear mode.

(Upper Left – ProgSvr/Ref), (Upper Right – Flash Extent Density), (Lower Left – Optical Energy), (Lower Right – Minimum Flash Area) Note the area of enhancement behind the main convective line. This is stratiform lightning strikes where the charges are slower to build vs. the convective linear line, and individual cells out in front of the storm.
Note the differences from the previous image as the Optical/FED and Minimum Flash Area has less flashes. This is due to the building of the charges.
A four panel of GR2 where reflectivity (Upper Left), and ZDR (Lower Right) depict linear striations (above melting level – 30 dBz) to show the build-up of charges in the stratiform area of the storm. A good way to use it is for IDSS and the likeability of lightning strikes developing.

Using NUCAPS (Modified vs. Unmodified). Why the CAP at mid-levels noted in Arkansas? Is this reasonable or an artifact of the program that isn’t real.


– wxboy65

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Utilizing NUCAPS Profiles to Analyze the Pre-Convective Environment Across West Texas

WFO Amarillo launched a 19z special sounding today in support of potential severe storms later in the evening. Meanwhile, NOAA-20 passed over WFO Amarillo at 1935z, merely 30 minutes after the observed sounding release but likely about an hour before the full observed profile was complete.

An SPC marginal risk was over west Texas (see below) for the 20z issuance with the main threats being large hail and damaging wind gusts. The 12z observed sounding from Amarillo shows a pronounced low level capping inversion with a convective temperature of around 86 degrees F. Overall, the wind profile is weak with little to no shear but just enough to support a few strong to severe storms. Mixed layer CAPE is around 1000 J/kg, but the downdraft CAPE is closer to 1200 and supports the potential for some strong to damaging wind gusts with collapsing storms and/or areas conducive to strong downward motion.

Image A: 12z Observed Sounding from AMA on June 7, 2021.

Sharppy was then utilized to compare the observed 19z sounding from Amarillo to the closest NUCAPS sounding to the office’s location. Image B contains the values for the observed sounding with the purple representing the sharppy NUCAPS sounding. Image C contains the values for the sharppy NUCAPS with the observed sounding in purple. One of the biggest differences between the soundings that plays a key role in the instability parameters is the surface temperatures. The observed sounding recorded a surface temperature of 83 degrees F, which the sharppy NUCAPS sounding recorded a surface temperature of 89 degrees F. That difference of 6 degrees fully breaks the capping inversion on the sharppy NUCAPS sounding, but the observed sounding still appears to be a few degrees shy of breaking the 750mb cap. The values such as MLCAPE are drastically different with the observed sounding showing around 1500 J/kg, while the sharppy NUCAPS sounding shows ~2500 J/kg. The observed sounding does show an increase since the 12z launch of DCAPE now around 1600 J/kg, but the sharppy NUCAPS does not relay this same increase and instead remains near 1200 J/kg.

Image B: 19z observed sounding (colored) compared to the 1935z sharppy NUCAPS sounding (purple). The values represent the observed sounding.
Image C: 1935z sharppy NUCAPS sounding (colored) compared to the 19z observed sounding (purple). The values represent the sharppy NUCAPS sounding.

So the biggest fault in the NUCAPS values being off was likely the surface temperatures being too warm. In order to validate this reasoning, the modified NUCAPS sounding for this time and location was utilized. However, since the modified soundings are calculated with NSHARP and not sharppy, the original NUCAPS from both algorithms were compared. Image D shows the NSHARP NUCAPS sounding pulled from the CAVE in awips. This can be compared to Image C, which was the NUCAPS sounding plotted with a different program called sharppy.

Looking at the profile itself, the biggest difference that stands out would be near the surface. As stated before the surface temperature on the sharppy NUCAPS sounding was 89 deg F, while the NSHARP sounding reveals a surface temperature of around 80 deg F. The NSHARP sounding temperature is lower than the observed sounding at 19z, but yet was able to mix out the capping inversion. Knowing that NUCAPS in general is not overly impressive with the boundary layer, there is a chance had there been a 12z pass, that the NUCAPS sounding wouldn’t have had such a strong inversion as the observational sounding at 12z showed. Therefore the surface temperature wouldn’t have needed to be as warm. The remainder of the parameters seem to compare pretty well between the two versions of the NUCAPS profile.

Image D: 1935z NSHARP NUCAPS sounding from CAVE.

Now, what happens if the surface temperature from observations are used to modify the NSHARP NUCAPS profile for better representation of that boundary layer. Image E represents this modified sounding where the surface temperature is now closer to 83 deg F, which is what the 19z observed sounding from the same location measured. Comparing this modified sounding to the observed, there is still the issue of the NUCAPS wiping out the inversion layer at around 750 mb. Warming the temperature was not going to bring the inversion back, so this is something that is more a failure starting with the non-modified NSHAPR NUCAPS profile. MLCAPE is still significantly different, but ignoring the inversion in the observed sounding and looking at a surface based parcel, the two soundings are pretty comparable with around 3500 J/kg of SBCAPE. Downdraft CAPE values did not change with the modified NSHARP NUCAPS sounding and this could allude to the fact that again the NUCAPS profiles lack good boundary layer details and a much smoother profile.

Overall, had Amarillo not done a 12z launch, the NUCAPS profiles were pretty comparable to the observed sounding. The biggest concern would be if the purpose was to find if there still remains a capping inversion in place that may hinder storm development. Spoiler alert, storms did develop as temperatures warmed a bit more through the afternoon and were also just a bit warmer further west along the New Mexico/Texas border. A few severe wind reports occurred with the cluster of storms, along with some small hail and maybe even a few larger hail stones of around a quarter that weren’t reported.

– Harry Potter

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Hail or No Hail- Assessing ProbSevere v2 and v3 – Monday case – 2026Z

Today was the first day of Week 2 for the Satellite HWT Experiment.  One of the main applications we are looking at this week is the new ProbSevere Model version 3.  We are able to compare this version to the one currently in use (version 2).  This is the version most operational forecasters are familiar with, and that is available in AWIPS2 and GR2 Analyst.  

The target today was convection occurring in the Shreveport, LA CWA this afternoon.  A QLCS was moving across the region from west to east, as shown below.  The reflectivity was not especially impressive, but velocity scans occasionally showed some stronger winds.

Above: A line of storms moving through Louisiana on June 7, 2021.

The image shows MRMS Vertically Integrated Ice (VII) on the left, a parameter many forecasters are familiar with and may use as perhaps a “sanity check” to see if a cell may be trending towards strong or severe.  On the right is a screenshot of the Shreveport radar (KSHV) at the 0.3 degree reflectivity slice.  Overlaid is the ProbSevere Model with ProbSevere2 and ProbSevere3 parameters both listed for comparison.  

As you can see there are a few areas of concern.  A quick glance at VII indicates there may be some strong updrafts capable of hail over the area of convection over southeastern Caddo County in northwestern Louisiana.  Looking at the output for ProbSevere2 in this same area, there is a 43% chance for hail in this area, and a 14% chance for hail according to ProbSevere3.  The new and not yet operationally available ProbSevere3 uses a newer, more highly-skilled algorithm that should theoretically better match with ground truth.  

During this time there were no hail reports in SPC’s database, severe or otherwise.  There were some areas of surface based CIN noted, and this may have suppressed stronger updrafts and thus large hail. So in this case, it appears that the newer version of ProbSevere was correct about hail not being severe.  

-Dana Scully

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Northern VA/Maryland Convective Episode on 6/3/2021

Image 1: 1943 UTC GOES East Mesosector Day Cloud Phase Distinction

The modified NUCAPS sounding from 1730 UTC revealed in excess of 2,000 J/kg of CAPE (image 2) and by 1900 UTC thunderstorms had developed in an area less shaded by high level cloud cover. Comparing this to RAP mesoanalysis data, it initially seemed too high as RAP mesoanalysis suggested closer to 1000-1500 J/kg (not shown)  and based on initial lightning activity. SBCAPE from NUCAPS was extremely high and close to 4,000 J/kg which seems very high (image 3). We did note that for some reason the NUCAPS forecast image showed CAPE being “missing” over central MD/northern VA while the CIN fill was more complete. When sampled over the “missing” data in AWIPS in the Cloud,  the readout showed actual values.

Image 2: NUCAPS Sounding near Washington D.C.
Image 3: NUCAPS CAPE and CIN forecast at 2100 UTC
Image 3: 2000 UTC 4 Panel of Day Land Cloud Phase

Initially, storms appeared to struggle with flash counts on the order of 10 to 20 flashes. Over the course of 30 to 45 minutes, lightning flash counts increased by an order of magnitude (closer to 100-150 flashes)

Closer to 2020-2030 UTC the rigor of convective elements increased and we started seeing transient echo overhang/along with some weak echo regions in tandem with an increase in both lightning activity as well as ProbSevere trends (especially ProbSevere3) as seen in Image 4. This increased our confidence in issuing our own warnings with LWX having a couple of warnings already issued.

Image 4: ProSevere Time Series just after 2000 UTC.
Image 5: LWX 0.9 Reflectivity Image near 2000 UTC
Image 6 and 7:(LEFT) ProbSevere Time Series around 20:30 UTC.  (RIGHT) 4 Panel (from top left to bottom right) of Day Land Cloud Phase Distinction, Radar+GLM FED, Day Land Cloud Convection + TOE, ProbSevere3 + GLM MFA

Closer to 21:50 UTC things became a bit more interesting from both a radar and lightning standpoint. Imagery from the KDOX radar (Central Delaware) suggested increasing mesocyclogenesis across Baltimore County (image 8) due north of Baltimore.

Image 8: 20:48Z 0.5 degree cut from KDOX indicating low level mesoscyclone.
Image 9: 4 Panel of ProbSevere, GLM FED, GLM MFA, GLM TOE at 20:45 UTC
Image10: 4 Panel of ProbSevere, GLM FED, GLM MFA, GLM TOE at 20:51 UTC

From a comparison of these images, there was certainly an indication that the updraft was increasing  as FED magnitude increased from 51 flashes/5 min to 99 flashes/5 min. MFA also became more concentrated NW of the City of Baltimore and Baltimore County as seen in images 9 and 10. WFO LWX issued a Tornado Warning around 20:51 UTC.

An animation of the TDWR at Baltimore Washington Airport (image 11) had signs of a possible low-level RFD surge (not shown) in the 0.5 degree rapid scan tilt and increasing low level rotation consistent with either a stronger surge of straight line winds or a QLCS mesovortex/tornado. Aloft, (not shown) there did appear to be healthy reflectivity aloft and the concentrated MFA may suggest that a strengthening updraft.  

Image 11: TBWI 0.5 Reflectivity and Velocity image at 20:50 UTC looking at tornado warned storm.

Image 11 from KDOX shows a loose mid-level mesocyclone with a gradual increase in ProbSevere3 with the time series. In this image, the storm was currently tornado warned by WFO LWX. At time we’d likely opt for a tornado possible warning and monitor very, very closely.

Image 12: 21:02 UTC Showing ProbSevere Time Series with KDOX 0.5 data (left panels) and GOES/GLM data (right panels) + ProbSevere

By 21:13Z The storm of interest is looking LESS favorable for tornado although prob severe tor increased significantly to closer to 20% perhaps due to an elongated zone of low level shear.

Image 13: 21:13Z KDOX Radar Imagery

Prob Severe Table Ideas:  If the tables could open in a floating tab in Awips that would be very helpful. This way you can manually dock and move the tab around in awips. This way you can quickly view the tab and keep it open until you want to just close it.  You can also rename the tab to whatever will help you keep track of the storm that it belongs to. This would get around needing to color code multiple tables etc.

A separate tab will also allow room to show additional information (beyond just prob severe).

Prob Severe jumped to nearly 80% with a fast moving bowing segment through Montgomery County.

Storm in question is the southeastern storm here.

– By Miles and Dwight Schrute

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Observations over the Sterling CWA

Looked at the modified NUCAPS sounding for and the low levels, below 700mb, were un representative (had an inversion when SPC mesoanalysis had no CINH), however the sky had roughly 80% cloud cover.

NUCAPS Base Sounding
NUCAPS Modified Sounding, Same Location as Above

Looking at the NUCAPS forecast, the holes in the output field due to the cloud cover.  The lack of data was in a bad location, preventing us from seeing the instability potential for a line of storms coming in from the west.  The gridded format was actually better to use in this case as it helped fill in the gap.

Interpolated CAPE NUCAPS Imagery

The interpolated data is easier to visualize gradients in the variables, but our experience was that some important data was filtered out by having this turned on.

The time in the lower left is 19.99z.  A key for the “all” field would be helpful to understand what I am looking at.

Having the CWA borders is handy, however having it as it’s own layer would be more helpful, and separating out the CWA borders from the state borders.

Can storm names be used to correlate the time series (F6, D3) and also have the names plotted in AWIPS for the storms I am looking at a time series of; would be more beneficial than having the lat/lon

-for example, click for a time series of one storm triggers a storm ID to show up in the time series and in AWIPS

-I click another storm and another time series shows up with the storm ID in the time series and in AWIPS allowing me to see which time series goes to which storm

If prob severe and its time series could be put into GR that would greatly improve DSS services when outside the office.  The AWIPS thin client is sloooow, so being able to have the same ability, or similar ability to interrogate storms as in the office would greatly help improve the quality of DSS when deployed.

Prob severe version three continues to look more reasonable for severe wind than version two

Noticed an increasing 5 minute trend in the minimum flash area that was reflected in the FED about 5 minutes later.  Seeing the sustained increase in one minute minimum flash area caused me to pay more attention to that storm than I did earlier due to the sustained growth

While monitoring a storm with FED and minimum flash area, the FED suddenly went down.  The same trend was not seen in the minimum flash area as easily.  Maybe the minimum flash area is more useful tool for monitoring the growth of storm while the FED is better suited for monitoring the overall trend in storm strength and sudden weakening.

Downward trends in FED for one of the storms matched what was being seen on satellite of the storm updraft becoming more ragged as it weakened due to entraining dry air.

-would be great to have lightning data such as FED plotted in a time series as well so trends are more easily seen

The stronger storm we were monitoring (same as in the screenshot below), prob severe version 3 was higher than version 2 for 15 minutes atleast.  Looking closer this was due to the hail category being higher than version two; version three was also higher than version two in the wind category, but not nearly as much.  Toward the end of our time version two was higher due to higher probabilities in the wind category.  Interesting.

We monitored this particular cell on and off throughout the afternoon and tried to gain a better understanding of the minimum flash area. We noticed a close cluster of negative strikes, which really helped as a visual aide for what the GLM was seeing. The GLM MFA was able to isolate the core of the storm really well. We combined this with ProbSevere, and watched the probabilities on this storm increase which was a further confidence booster that the storm was intensifying in addition to what was seen by GLM and ENTLN.  

– Accas and Groot

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