This week started with two very active days within the OUN CWA which allowed EWP forecasters to incorporate pseudo-GLM products into their warning operations.  Despite the dense radar coverage, forecasters used the total lightning products and provided some interesting insights.

Day One – Monday 23 May

Two storms developed in Northwest Oklahoma and exhibited very different lightning and radar signatures.  The northern storm formed in Major County, exhibited very large IC flash rates, and produced large hail.  Conversely, the flash densities were much smaller in the southern storm which produced a brief tornado.  This observation illustrated the variability between two storms that occurred in a similar environment and emphasizes the importance of continued research on the relationships between lightning and radar within individual storms.

The greatest pseudo-GLM densities (> 30 flashes min^{-1}) accompanied a large storm cluster which followed the merger of two strong storms.  The 3D-Var products indicated a strong updraft throughout the length of this storm cluster which helps explain the high flash rates.

Day Two – Tuesday 24 May

The high risk forecast and model-derived products all indicated a very active day was in store.  The CI products identified the initial convection 15-20 minutes prior to the first pseudo-GLM signatures.  Flash rates increased rapidly in the earliest convection, and the first tornadic storm occurred as two isolated storms merged near Weatherford, OK.  Flash rates spiked as the two storms merged, coincident with an increase in mid-level rotation.  These combined observations increased forecaster confidence as they issued the first tornado warning of the day.

The EWP forecasters observed that the greatest pseudo-GLM flash densities consistently tracked ahead of the main updraft and actually helped to identify changes in storm motion.  On several occasions the pseudo-GLM densities also indicated that the main center of rotation was shifting prior to the identification of new rotation tracks by the multi-radar multi-sensor algorithms.

Although lightning jumps preceded many of the tornados, forecasters commented that they would have liked to examine time trends for individual storms.  This has been a common theme during previous spring experiments, and was not fully accounted for by plotting swaths of the pseudo-GLM products.

-Scott Rudlosky (pGLM scientist week 3)

Forecasters conducted warning operations in the Sterling, VA and State College, PA CWAs, which allowed for analysis of the pseudo-GLM products (from the DCLMA). Although the earliest convection initiated along and just west of the Appalachian Mountains (out of range of the LMA), storms soon formed within range. Isolated storms initiated and developed rapidly ahead of the main line. The pseudo-GLM products detected IC flashes ~10 min prior to the first CG flashes in two of these storms. These storms continued to intensify and eventually merged into a line, further increasing the flash rates.

As the discrete cells merged into a line, flashes remained frequent, and the pseudo-GLM products helped confirm the strength of individual cells within the line. Greater flash rates also helped identify areas of new convection as they formed along the line.

Forecasters also observed that the pseudo-GLM swaths (i.e., 60 min sum of flashes) helped to illustrate persistent cells and identify the most intense portions of the line.

The above screen captures illustrate several four panel displays used to compare individual products in AWIPS. The pseudo-GLM products often were plotted alongside the 3-D Var updraft and vorticity tracks, as well as the multi-radar multi-sensor hail swaths and reflectivity at -10 C.

Scott Rudlosky (pGLM scientist, week 3)

We’ve changed to the State College domain, while the other team remains at Sterling. Already see a meso near the WV/MD border. Trying to interrogate products.

Previous forecast remains on track.  We have decided to begin at Sterling so we can interrogate lighting products even thought we think this will be at the southern end of the best severe storm area.

Mostly sunny skies in combination with relatively steep mid-level lapse rates have led to extremely unstable air with CAPE values in the 3-4K range over VT-NY-ern PA-wrn MD-N VA area with CIN removed.  A shortwave trough, perhaps convectively reinforced, was located over srn OH-ern KY moving east.  Effective shear values are increasing rapidly.

CI has already occured over ern WV.  We are in luck.

The majority of the forecasters stayed in the HWT to watch the storms as they approached the National Weather Center. Live data from the PAR along with area TDWRs and the KTLX radar showed an impressive evolution of two confirmed tornadic debris balls as the storms moved towards us.

The 3DVar products all handled the track and evolution of the storms very well and the combined radar products also have an excellent track of the tornadoes as well. Continuity was maintained as the storms moved into the cone of silence of the KTLX radar.

As the storms started to move into the metro OKC area, attention to the details/operations was lost as we watched live TV feeds and could see the hail falling outside the WFO window. The excitement rapidly turned to sorrow however as the live TV feeds showed homes and structures being ripped apart.

One last item that made it very clear how close we were to being impacted by the tornadoes directly; leaf and light matter debris was falling from the sky when several EWP members went up to the roof of the NWC to see the dissipation of the tornado moving south of Norman.

Back to operations…

-Jason Jordan

Everyone gone to the NWC tornado shelter.  Looks like the storms will miss us north and south, hopefully.

Rotational track shows up quite well for Marlow storm as SRM started to tighten up.

TOR warning for storm 10 miles west of Marlow, OK. Machine didn’t take it!

Pablo is issuing a SVR for storms near Byers and Ryan tracking northeast at 55mph. Nice MESH tracks on both of them. Ryan storm appears to be a left split. Too close together to write two boxes.

Other warning desk is now taking over responsibility for OUN CWA south of red river.