Struggling High-based Convection in SE CO using CI/CTC

A few high based storms have been struggling to develop across southeast Colorado due to abundant dry air and SBCAPE 500-1000 J/kg.

The first image was at 2045 UTC on May 16 where the GOESR UAH CI suggested some potential for convection with a few locations 61-78%, and the CIMSS CTC depicted a maximum of -18C/15 min. This appeared promising for deep convection.

The next image was at 2115 UTC and continued to depict a few areas 20-62% for CI as well as -16C/15 min along with a few weak cells. At this point, there still remained hope for some deep convection.

The last image was at 2145 UTC respectively with lower CI and CTC values as well as a few non-severe/rather weak cells. So far, these cells have failed to intensify or become severe. Weak forcing aloft in conjunction with the lack of low level moisture may be the main culprits for the poor development of storms.

Close... but No Cigar... Held Off SVR Based on GOES-R CI/MRMS

051613 2138 UTC MRMS fields

Held off issuing a severe thunderstorm warning for a developing storm over northern Nebraska due to MESH staying around 0.75 inch and maximum reflectivity of only 55 dBZ at the -20C level.

051613 2045 UTC GOES-R CI

In addition, the GOESR UAH Convection Initiation Products depicted a few pixels of 10-40% in the hour prior to this storm developing, perhaps suggesting that the environment may not be conductive for explosive storm development.

Flash Extent Density and Updraft Strength

Playing a bit with the SPoRT flash initiation density product and the evolution of an updraft. Although it’s not a serious storm, it represents the ongoing pulsating activity very well which could eventually gain strength when entering a more unstable air mass to the east. Below you can find the ‘Flash initiation density product’ at 2035Z and 2040Z, showing a marginal increase in lightning activity. Reflectivity at the same time showed a core with 35-40 dBz and only a few isolated lightning strikes occurred.

051613 2035 UTC PGLM Flash Extent Density

051613 2040 UTC PGLM Flash Extent Density

051613 2055 UTC Reflectivty

At 2055Z, the storm finally strengthened in reflectivity fields (the core peaked at near 60 dBz) . Although that was just a temporal strengthening trend of that storm it is great to see the lead time you get with that lightning product before the updraft eventually strengthens. 

Helge

MESH and CTC in the GLD CWA

Setting up in the Goodland KS CWA today. A small cluster of storms is ongoing and certainly producing a lot of rainfall and lightning…note the 0.5 reflectivity on the upper left. To the upper right is CTC on top of the visible. No detections here…likely due to anvil cirrus hinderance. On the lower left, we have MESH from MRMS. Nothing at one inch or above here either. Reports from the area have consisted of small hail lately…0.75″ and less. This seems to reinforce the marginal nature of the storms depicted by MESH and other experimental products.

051613 2018 UTC Reflectivity (top left), CTC (top right), and MESH (bottom left)

CL

RGB Airmass Use Over NE and KS

051613 1901 UTC RGB Airmass

The GOES Sounder Air Mass image is very useful in highlighting the different features of interest for today. First of all the compact disturbance which is about to leave NE Colorado to the east/northeast is well visualized by mid-level drying in the image. Weak forcing ahead of that feature already caused some initiation over N/NE Nebraska with another round of storms evolving over extreme NE Colorado. Of interest is a southward extending and weakening vorticity lobe which is about to enter Kansas from the west right now. Also, the dryline is well recognized by that product, showing warm/moist air ahead of the dryline advecting to the north (green-ish colour). This correlates well with mid-level moisture, seen in latest RAP output. A gradual transition from ‘green to blue’ occurs when moving westward (e.g. towards the TX Panhandle). This corresponds well with some residual low-level moisture f.ex. in the lowest 850 hPa, which gradually mixes out. We will monitor both the dryline and the eastward moving but weakening PVA lobe for some kind of interaction during the following hours and eventually for sporadic CI. 

 Helge

Daily Debrief: 5/15/13

Yesterday turned out to be the best day of the experiment thus far! Later in the evening we saw rapid convective initiation in Southern OK and Northern TX. Supercells formed just west of the Dallas-Fort Worth metroplex and produced very large hail as well as a series of strong tornadoes in the area. Check out the image below of the pair of supercells just west of DFW. Tornados from these cells caused a lot of damage in Cleburne and Granbury.

051513 0036 UTC Reflectivity (top left), Velocity (top right), CC (bottom left), and TDS (bottom right)

A lot of blog posts and feedback were collected from this event on the various experimental products. Here are some of the comments noted in this morning's debriefing:

PGLM
- 'I noticed a correlation between the MESH and the lightning data. Several minutes after there was a big jump in flashes, there was also a big jump in MESH values.'
- 'The OUN network kept losing sensors so it was hard to know what was a jump and what was data loss. It would be helpful to have the status information so we know that we've actually lost sensors and and when we've got a jump.'
- 'In my opinion forecasters won't like that you have [use the lightning moving trace tool] manually.'
- 'In real time I can see [the moving trace tool] being a little clunky to use, a little labor intensive, but for analysis of an event it would be awesome to see that trending information.'
- 'It would helpful to see the lightning data plotted with the hail/MESH information.'
- 'We didn't hardly get any lightning with the Oklahoma bow echo... perhaps this could be an indicator that it wasn't going to be as strong of an MCS.'
- 'I paid attention to the lightning cores and where it was increasing significantly. This seemed to be a good indication of a strong storm.'

GOES-R CI
- 'There were a couple of times where the CI gave us an 80/90% value that developed/initiated into a deep convective core.'
- 'Values were overall low yesterday in TX, but where it pinpointed the higher values it did a good job of indicating strong initiation.'
- 'I thought it did extremely well. We were looking at a decent sized cu field and it seemed to pinpoint on specific cu very well.'
- 'Yesterday there was enough of a difference in the CI values where you could pick out the more significant initiation, but on other days it seems to be far more confetti-like.'
- 'THe Montague storm had a CI value of 60%. An hour later it initiated. Thirty minutes later we had baseball sized hail. Fifteen minutes after that we had a strong tornado.'
- 'It seemed to do well with the clusters of strong updrafts, but had trouble in higher terrain. This may be an elevation/snow effect.'

CTC
- We had good CTC rates on a number of storms that ended up falling apart. It ended up that the storms had good initiation but were moving into an environment not conducive to further growth.'
- 'The CTC did a good job yesterday, but it's still very important to know your environment. We saw strong signals, but not all initiated because of other environmental factors not seen in the CTC.'
- 'The CTC gave consistent lead time of at least 20-30 minutes for severe storms on multiple occasions [in Texas].'

Our last day of operations this week doesn't look to be nearly as exciting as yesterday. We're currently in the Goodland, KS, and North Platte, NE CWA's where things have already began to initiate, and may move further south later in the evening. Stayed tuned for further updates as the day progresses...

Flash Density Trace for Tornadic Storm near Leon, OK

A tornado was reported at 0022Z near the town of Leon in OK. The associated flash extent density trace from the parent storm is below. Focus on the time frame between 00Z and 0031Z. Notice a consistent trend upward in flash extent rate…with a peak value of 48 at 0021Z. Unfortunately…the trace was not created soon enough to capture the flash rate as the storm was intensifying prior to 00Z but the upward trend in flash rate correlated well with the pre-tornadic organization phase.

Here is a look at the storm near Leon at the time of the tornado report. Rotation tracks peaked at 11 s-1, MESH was maximized at 0.47″ and the vertically integrated ice peaked at 16 kg/m-2.

PGLM and Warnings in OUN

Loaded the one minute SPoRT Flash Extent Density product and used the editable Moving Trace tool. The moving trace circle had to be expanded for each frame; forecasters won’t like this because it doesn’t have a “apply to all” feature for this. It is also not intuitively obvious to forecasters that have been using other tools such as the warngen pathcast tool and distance/speed tool in AWIPS. The trace tool makes a graph showing “Flash Extent Density”, which showed trends in lightning for the selected storm.

1914 UTC Flash Extent Density. This product could be useful for NWS event support to describe specific lightning threats to outdoor activities. It could also be useful to identify strengthening updrafts that could produce large hail. One storm that showed a quick spike in Flash Extent Density above 50 Lma at 1912 UTC went on to drop 1 inch hail at 1926 UTC, for a 14 minute lead time. See Becca’s blog entry on this storm.

There were several bad one-minute data samples caused by loss of input data into the Oklahoma LMA. Two of them are illustrated below.

One minute Flash Extent Density showing the sharp drop that was apparently the result of a temporary loss of input data into the Oklahoma LMA. This occurred again at 1948 UTC see the trace graph below.

- Ostuno

PGLM and Rotation Tracks Associated with Weak Bow Echo

Rapidly developing convection showed a rapid increase in flash extent rates in the low teens to the mid 30s with a few pixels spiking in the 40s. This activity rapidly morphed into a bow echo that raced across south central Oklahoma. The SRM velocity gradient along the front end of the bow was very tight…and the rotation tracks product showed an interesting progression of bow-like rotation signatures from north to south. There were gaps between each line (seen in the graphic below) unlike a single storm track which is fairly continuous.

At the north end of the bow…the values of the rotation tracks were strongest which is to be expected in the region of the northern bookend vortex. The flash extent rate was relatively weak with the bow…along with weak sfc velocities estimated to be around 20 kts from mesonet observations. So although the reflectivity structure looked as if it could be an intense bow echo with moderate midlevel convergence…and rotation tracks were depicting embedded circulations within the line…no reports of severe wind or damage were reported or observed.

The highest values for sfc rotation tracks around 23s-1 were in the vicinity of the bow where smaller cells were merging with the main line near the northern bookend vortex. The best velocity couplet depicted on SRM went between Byng and Francis around 2349Z and was just southeast of the highest values for the sfc rotation tracks.

RJM

Nearcasting and High Based Thunderstorms

As mentioned a bit earlier in a post, the NRE product showed enhanced chances for convection all the way to the Lubbock area. Especially the theta-e difference product placed the tongue of mid-level unstable air just where high based thunderstorms finally evolved. Surface dewpoints in the mid 30s and temperatures in the low 90s point to elevated and high based thunderstorms with a distinct downburst/ heatburst? risk. The product helped a lot to focus on the anticipated area of initiation. LAPS also did a great job in developing the elevated thunderstorm activity both in space and time.

051513 2300 UTC Vertical Theta-E Difference (top left), Sustained Convection Index (top right), CAPE (bottom left),  and Visible Imagery (top right)

Helge