Azimuthal Shear Noise Behind Convective Line/ProbSevere Analysis

Posted in News on by Michael Bowlan.

Dealiasing problems in northwest Arkansas and southwest Missouri carried over to the operational version of the azimuthal shear rotation tracks.  The azimuthal shear in the lower left panel uses a new dealiasing suppression algorithm, which effectively eliminated the noise. Fortunately, the noise with the current operational version of azimuthal shear was in a stratiform area of precipitation well behind the convective line, making it easy to ignore this data.  Sampled winds in the region of the erroneous rotation tracks were very high — up to 80+ kts.

By focusing my attention on the azimuthal shear associated with the leading edge of the QLCS, and analyzing Probsevere data and trends, I was able to anticipate a strengthening of the line.  The Probwind component was only 32% at 1934Z, then steadily increased, reaching 89% at 2012Z.  At 2030Z there was a LSR of trees and power lines down in Mountain Home,  Arkansas. Probtor increased to 65% at 2014Z, and as this storm shifted north into southern Missouri, there was a report of a blown out store front in Hartville, MO.  It has not been confirmed whether or not there was a tornado. However, the increasing Probtor values increased my confidence for severe straight line winds that are often associated with strong mesovorticies.  Depending on the event, Probtor trends and values could be used as a confidence builder to increase my warning wind speeds from 60 to 70 mph or 70 to 80 mph. Roy

 

 

Difficult Warning Decision as Storms Enter LSX CWA

Posted in AllSky, GLM, HWT, ProbSevere on by Michael Bowlan.

The northern extent of a line of storms that has produced sporadic wind damage is approaching the LSX CWA from the south. One of these storms has good reflectivity structure with a tight front reflectivity gradient and a rear inflow notch. However, these storms appear to be entering a more stable airmass. This is reflected in the ProbSevere probabilities of the storm in question compared with one just a bit further north:

The northernmost storm with the cool contours has only a 22% ProbWind and is in an environment of only 715 J/kg MLCAPE (per the sampling feature). Meanwhile the storm in question to the south in the warmer contours has a 90% ProbWind with 1220 J/kg MLCAPE. These storms are moving to the northeast toward the more stable air. Incidentally, the All-Sky LAP CAPE does not depict as sharp of a gradient in the CAPE compared with the RAP-derived ProbSevere values:

I am not sure which is more accurate but I suspect the model-derived values are more accurate in this situation.

Furthermore, a weakening trend in the Flash Extent Density is observed on the northern end of the line:

This storm still deserves a warning, but we will see how quickly it weakens.

Ron Dayne

GLM Storm Intensification

Posted in GLM, HWT on by Michael Bowlan.

Storms are trending sub-severe across most of our CWA at this hour, but 1 cell behind the initial line started getting its act together. Here is the GLM Flash Extent Density (top left), GLM Minimum Flash Area (top right), GLM Total Optical Energy (bottom left), and KLZK base reflectivity (bottom right) before the cell started intensifying:

The large FED and MFA bullseye imply the updraft is intensifying on this storm. This proved to be a useful proxy because this was the result 8 minutes later:

This suite of products has a lot of utility for pulse severe events and DSS on-site weather events. -Atlanta Braves

Lightning Jump in GLM Products

Posted in News on by Michael Bowlan.

GLM flash extent density product did a good job showing a jump in lightning activity over north central Kansas Tuesday afternoon. The flash extent density (upper right) increased some 10-15 minutes before the strongest reflectivity (upper left) was seen at the surface, showing that the lightning jump could have been used to get a lead time on potential hazards such as hail, etc. Also of note, there is no easily discernible change in the total optical energy (bottom right) product despite the detected increase in lightning activity. The average flash area product (bottom left) also exhibited little change.

Dave Grohl

Precipitable Water Comparisons

Posted in AllSky, HWT on by Michael Bowlan.

The Blended TPW product (top left) shows promise in creating an all-observations precipitable water product in AWIPS. The polar-orbiter PW data in cloudy areas produces artificial gradients and inaccurate values compared to modeled fields (GFS top right and HRRR bottom left), but its attempt to generate an all-observational PW product is successful. I am unsure of how to suggest improvements in the cloudy areas but would encourage these model-free fields continue to be developed.

The AllSky PW product (bottom right) looks really good. The inclusion of GFS data in cloudy areas is a neat idea and the partly cloudy areas seem to be well-computed. This is a tool I will definitely use for situational awareness. -Atlanta Braves

Azimuthal Shear in SGF CWA

Posted in News on by Michael Bowlan.

The mid level azimuthal shear product is doing a good job pinpointing the strongest updrafts along the line in southern Missouri, while the low level azimuthal shear product shows a lot of elongated shear zones, which one would expect. One issue i noticed is the low level azimuthal shear product seems to leave certain features in place over a period of several minutes while at the same time propagating these features downstream, thus resulting in the same feature being plotted twice in two different places. See the loop at the bottom for an example

-64BoggsLites

Increase in lightning activity across SGF CWA

Posted in News on by Michael Bowlan.

GLM flash extent density (top left) and flash event density (top right) have shown increasing trends over the last 20-30 minutes across southern Missouri, within the broken line approaching the LSX CWA. Both of these products help to identify locations within a linear feature where updrafts are maximized. Additionally, the total optical energy product seems to be matching up well with respect to trends when compared to the ENTLN cloud flashes and CG strikes.

-64BoggsLites

Allsky, TPW, and NUCAPS Moisture and Instability Profiles

Posted in News on by Michael Bowlan.

Radar image of a severe QLCS in NW Arkansas at 1923Z.  This line has been producing wind damage and a few spin up tornadoes. Next I’m going to diagnose column moisture and instability downstream, across north-central Arkansas using satellite and satellite-model merged products.

The GOES-16 AllskyLAP showed a deep plume of moisture extending from the Gulf of Mexico northward into Arkansas and Missouri.  Specifically, in north-central Arkansas, sampled PWATs were around 1.60 inches and MUCAPE was near 700-800 J/kg. Skies were mainly clear in this area, which resulted in a relatively smooth appearance in the PWAT and CAPE plots. Interestingly, and not plotted here, the 700-300mb AllskyLAP PWAT had lower values or drier conditions to the east of the approaching QLCS. This presence of mid-level dry air may be conducive for severe weather over north-central and northeast Arkansas over the next 1-3 hours — especially for damaging winds.

Merged TPW data at 19Z estimated PWATs near 1.50 inches into north-central Arkansas. However, there was a sharp discontinuity from 1.50 to 1.00 into the northwest part of the state where widespread cloud cover was present and the data originated from polar orbiting satellites (some of which could have been advected in). The SPC mesoanalysis did not display a sharp gradient in PWATs in this area, but rather had a gradual decrease to 1.30 inches.

Not the best satellite pass with my area of concern on the far western fringe of the NUCAPS data. Surprisingly, the sounding data on the edge in northern Arkansas was nearly identical to the SPC mesoanalysis data with values near 1200 J/kg! It likely helped that skies were mainly clear at the time of the pass. The GOES-16 AllskyLAP data was underdone in comparison.  As mentioned, only up to 700-800 J/kg.

NUCAPS 700-500mb lapse rates in northern Arkansas are close to model forecasts. The NUCAPS in this pass was indicating lapse rates around 6.2 C/km. Model data was generally a little bit lower around 5.8 C/km.  The SPC mesoanalysis was on the high end near 6.5 C/km. Roy

AllSky Overview – Big Help

Posted in AllSky, HWT on by Michael Bowlan.

The AllSky products seem to do a really good job of providing timely and relevant environmental data with higher spatiotemporal resolution than other means. Representative model soundings and the SPC Mesoanalysis page are nice tools, but the AllSky products add a helpful third point to interrogate environmental evolution. Perhaps the most helpful application is tracking of fronts and boundaries. As the dry line advances it is easy to see its eastward extent. In addition, the extent of the warm air is very clear as it pushes into Missouri.

This 4 panel display with cloud type in the lower right is a useful tool for identifying potential causes for inconsistent data from pixel to pixel. I like these products and look forward to their operational implementation at the end of this month! -Atlanta Braves

AzShear and QLCS

Posted in News on by Thea.

A little later in the day on March 3, 2019, a complex QLCS was seen on KMXX.

The base reflectivity at 0.5 degrees (left) shows several different features along the complex that need investigation given the favorable environment for tornadoes. The corresponding base velocity product (upper right) show several locations where shear is present. However, the single radar AzShear product highlights the portions along the line that look the most threatening.

Thorcaster