Minimum Flash Area: Capturing the "Pulse"

Taking a look at the Minimum Flash Area (MFA) product (part of the GLM suite) and comparing it to the Average Flash Area (AFA), my initial analysis leads me to think that there's more value in the MFA as opposed to the AFA. The MFA, when watching the evolution of a storm in the far northeastern part of SJT's CWA, shows the pulsiness rather well. The AFA, in comparison, had a washed-out look during the 19Z hour of analysis. I had a side-by-side of the meso-sector VIS satellite imagery with the MFA on top (1-min.) and the ProbSevere suite with radar products, including reflectivity (GIFs below). The MFA provided a few minute lead time over the ProbSevere and reflectivity products of the storm pulsing up. Thought: watching the trend of the MFA could provide some insight into the overall nature of the storm. In this particular case, the smaller flashes were consistent for several frames/minutes, and the ProbSevere/reflectivity core showed an uptick shortly thereafter. Because the smaller flashes remained confined to a smaller area/grid box (<72km^2), this indicated to me that this storm would remain pulsy and likely either sub-severe or low-end severe. Taking a look at what WFO SJT issued during this hour indicated to me that this thought process likely held true. From a mesoanalyst perspective, this could prove to be invaluable information to provide to a radar operator.

~Gritty

SJT Mesoscale Discussion

There is a warm front draped across the northern portion of the CWA with widespred cumulus developing along the front and broken skies in the warm sector. GOES-16 Day Cloud Convection RGB and Day Cloud Phase RGB show that a few of these storms have already glaciated indicating the convective initiation is underway. (Below)Laps All Sky retrievals show a relatively sharp instability gradient along warm front where our convection initiated. Storm motion is likely to be parallel to the front, so convection that does will likely be relatively long lived. (Below)Laps All Sky LI further indicates that the airmass is relatively unstable and there will be little convective inhibition at least in the midlevels. (Below)All Sky TPW indicates a relative moist airmass across the CWA with PWs above 1″ for most of the CWA. This matches the 12z sounding from MAF relatively well, and is well above the 90% threshold of the sounding climatology for that location and date. It’s interesting that the mid-level moisture (bottom left) is higher than the low level moisture (bottom right). Not quite sure what to make of that at this point. (Below)Finally, MRMS RALA indeed shows that showers and storms have developed along the front. When animated (not shown), you can see that the storms are tracking along the front, heightening my concern for flooding.  

Sandor Clegane

Weak Pulse Storm Analysis - GLM

In the below GIF from Top Left to Bottom Right you have:

• GLM Flash Extent Density from GOES-16 (East) and GOES-17 (West)
• GLM Average Flash Area from GOES-16 (East) and GOES-17 (West)
• GLM Total Optical Energy from GOES-16 (East) and GOES-17 (West)
• ENTLN Ground Based Lightning Detection and GOES-16 1 Minute Channel 2 Visible Satellite.

The animation shows the quick pulse life cycle of the storm - you can watch the updraft grow and then the anvil get sheared off of the storm in the visible satellite. The Flash Density and the Optical Energy show a quick uptick and GLM registers at the same moment the first ground indication shows up. The Optical Energy maxes out as the storm grows to its tallest before the top gets sheared off. The Flash Density seems to follow the progression of the updraft eastward as well. The smallest Average Flash Area also follow the 'newest' and/or 'growing' parts of the storm. While convection continues from the cell (it is sitting along a boundary across the SE Part of MAF's CWA), it does weaken (looks like lower tops in visible - could certainly check this in other ways) and you use lightning from all networks.

While there is nothing ground breaking here it does show how GLM handles pulse convection and the trends in the GLM data. The one downside that I would note here is the lack of some sort of downtrend before the storm weakens. It seems the data generally peaks then goes away rather than drops before the storm dies.

-Alexander T.

Week 1 Day 2 Operations

Today we will be operating across west and central Texas looking for developing storms along a slow moving front.

HWT Spring Experiment Begins

The 2019 combined satellite and radar Spring Experiment started today and will run for 6 of the next 7 weeks evaluating various satellite based products as well as some radar derived products. Today is generally a familiarization day as forecasters get set up to operate in forecast and warning mode over the next few days looking at some active weather hopefully. Look here for updates throughout the week on the satellite based products.

- Michael

NUCAPS in 4-Panel

When NUCAPS Sounding Availability is loaded in a 4-Panel and is 'Editable', you can sample the data by clicking on any of the other panels. This could be useful if there is an area of interest in one of your other datasets (i.e. vis/CAPE/PWAT) so that you don't have to find the nearest dot using the NUCAPS imagery; simply click the area of interest on the panel you're investigating. Works in panel combo rotate as well.

-- FLGatorDon

Precipitable Water Overview

Looking at the different precipitable water (PW) products available in the HWT and doing a quick overview the All-Sky products provides a great first guess to fill in the PW where it is cloudy. Both the Merged TPW and the All-Sky take the first step in filling in where there are clouds. The image below  shows the sheer volume of data that isn't available due to the pesky cloud cover. The 4-Panel to the left shows the All-Sky PW and CAPE on top vs. the raw derived PW and CAPE from GOES-16. On the right you can see the visible satellite and the All-Sky mask showing that most of the data, especially over Texas and Oklahoma is raw GFS (gray areas) at this point.



Looking at the Blended TWP vs. the All-Sky there are significant differences over north Texas and Oklahoma for this time frame. The BTWP product "is not forecast model dependent. ATPW uses  GFS model winds to advect the microwave retrievals and the GOES-16 component uses GFS in its TPW solution." You can see where the blended product (big window below) only shows about 0.75 in PW, while the All-Sky is showing 1.25 in. across the Norman WFO. This can make a big difference when looking at rainfall forecasting and trying to assess just how much moisture in the atmosphere is over an area. In this case would certainly lean towards the All-Sky and then compare the information to other model soundings (from the HRRR, NAM, ECMWF, etc.) and to actual Upper Air soundings to see how the areas populated by the raw GFS are doing.



-Alexander T.

ProbSevere: Color Table Modification

While I've been a big fan of the ProbSevere Model for some time now, the default color curve has always been a little challenging for me to differentiate between the different percentages. Trying to find the right balance between the radar color tables and ProbSevere I know can be tough, but here's my first go at attempting to better differentiate when the percentages move into the next 10% range. Unfortunately, I'm unable to really test this modified color table out since we're currently not getting radar data in from the Davenport area, so will reassess this once I'm able to overlay the model output with radar imagery. But, just having the colors pop a little more is already helpful to me! Oh, and I'm very appreciative that ProbSevere v.2 now includes the separated values (i.e. ProbWind, ProbHail, ProbTor). Looking forward to testing this out once there's a case to evaluate with it.

*Note: As of this posting, WFO DVN issued a Severe Thunderstorm Warning.

~Gritty

Comparing RAOB to NUCAPS and AllSky Layer Precipitable Water

Davenport launched an 18Z balloon, which gave me the opportunity to compare the RAOB with a NUCAPS sounding (first and second images below, respectively). Initially, I attempted to modify the sounding in NUCAPS to try to bring it closer to the observed values, but after several minutes and attempts at doing that, I realized that I'd have to do multiple levels of modifications before it came anywhere close to the observed sounding. As great as it is to have the ability to modify the NUCAPS sounding, my initial thoughts are that I'm not sure how feasible it would be to do this in a much quicker-paced operational setting. If I'm sitting in the mesoanalyst seat during a severe weather event, I'd need to be able to analyze the available data much faster than doing a more detailed modification would allow.

I was also able to do a PWAT comparison between these two soundings and the AllSky Layered Precip product. The NUCAPS and RAOB are very close together in values, whereas since the AllSky product (last image below) is currently utilizing the GFS to fill in the data in the DVN area, it's noticeably higher (RAOB: 1.0"; NUCAPS: 1.1"; AllSky: 1.3"). I am very happy to be able to underlay the data type for the LAP products, since this is crucial for me to be able to see where the data is coming from and how to correctly assess and apply the right bias adjustments, as necessary.
As for the AllSky Layered Precip product, in general, this is very helpful to be able to identify potential atmospheric rivers and quickly diagnose PWAT trends with a decent degree of confidence, when again combined with the knowledge of what data is being used to compute the output.

~Gritty

Deadly tornadoes in Dixie

Alabama and Georgia were hit particularly hard by a series of tornadoes on March 3rd. A subtle yet energetic shortwave trough with a strong 850mb jet zoomed through the deep south spawning the tornadic storms from the early afternoon through the evening hours. NOAA's Storm Prediction Center (SPC) issued a 10% hatched convective outlook for strong tornadoes (this is 10% probability of a tornado within 25 miles). SPC later issued a mesoscale discussion (MD) for one supercell that formed in central Alabama around 1pm CST (19 UTC). The MD cited pressure falls ahead of the surface low, very strong 0-1km helicity (~500 J/kg), and ample buoyancy and environmental shear for the textual warning of "tornadogensis will likely occur within the next 30-60 minutes with the possibility of a strong tornado occurring."

According to preliminary reports, that was an excellent prediction, as this storm first produced a tornado at about 2pm (at 20:03 UTC). ProbTor, a product of NOAA's ProbSevere*, had increasing probabilities for this storm from 18:36 to 18:50 UTC, jumping from 20% to over 70% in those fourteen minutes (Fig. 1 and Fig. 2), largely due to increasing MRMS azimuthal shear. Strong total lightning density later played a role in increasing the probability of tornado to over 90%. Unfortunately for Lee county, AL, a second tornadic storm followed close behind. The NWS issued a rare tornado emergency at about 20:20 UTC for Lee County, AL and Harris and Muscogee Counties, GA (for the first supercell). These two storms combined for at least 23 deaths in communities between Beauregard and Smith's Station, AL. Many other tornadic storms were reported elsewhere in Alabama, Georgia, and Florida.

Fig. 1: The probability of any severe (contours), with NWS severe weather warnings and MRMS MergedReflectivity composite. The thicker tornado warning polygons (red) denote tornado emergencies.

In AWIPS2, when the probability of any severe product is loaded, a second contour will appear around the radar-identified object when ProbTor exceeds a given value. In Figure 1, we set that threshold to 20%. Users can change this threshold through their ProbSevere USER bundle files. We created this feature so that forecasters can visually see changes in the probability of tornado as well as the probability of any severe. Setting a higher threshold (~10-25%) may be prudent in a strong kinematic environment, whereas a lower threshold (3-5%) may help users visually pick out potential tornadic threats in more mundane environment.

Fig. 2: ProbHail, ProbWind, and ProbTor (red) for the life cycle of this storm. Durations of NWS warnings and times of preliminary LSRs are plotted on the bottom axes.

* The NOAA/CIMSS ProbSevere model (v2.0) will be an operational subsystem within MRMS as early as August 2019.