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We’ll plan on a 1pm start on Wed. The most likely areas for operation based on the day 2 SPC outlook and 21Z SREF probabilities are NE Colorado (best chance of supercells) and OK/W TX (for low-shear pulse storms in the Lightning Mapping Array)
– T. Smith, Week 4 coordinator
The storm we reported on in earlier posts is still ongoing. Below are the surface rotation track (upper left), midlevel rotation track (upper right) and MESH swatch (lower left). You can see the long track that this storm has had through the TFX CWA. Baseball sized hail was reported from this storm. We were also able to see a feed from a chaser cam trained on this storm. We finally got a public report of a tornado near Hobson at 5:41 MDT. This storm was clearly the star of the day! CL
So…after storms in MLB weakened early in our shift, we moved our domain to Tallahassee. We did issue a warning there, but it became apparent that the most interesting action today is in Montana, so we are on our third domain, Great Falls. This area was the best in the country as far as supercell potential, and we now have a strong storm for which I issued a TOR. Below is a selection of 3D-VAR products for this particular storm. The current SRM is on the bottom left. Top left is updraft helicity…that max is about 140 m/s^2. Top right is composite updraft maximum, which pegs this storm up to 19 m/s of upward motion. Finally, in the bottom right is maximum vorticity below 3 km. This scan only showed 13.4/s of vorticity, but the scan before had values as high as 27/s. Not a bad storm at all for this area of the country. We did get a golfball hail report out of this storm, but no tornado yet… CL
With limited areas favoring severe convection, we’ve moved to TFX to the lee of the Montana Rockies. Despite somewhat limited radar coverage, 3D-Var has performed very well with the supercells ongoing across the CWA. The right-most panels in the image above depict Max updraft and accumulated max updraft. The greatest magnitudes are co-located with a tornadic supercell in Judith Basin county. 3D-Var analyses appear to work relatively well even with sparse radar coverage.
After a significant period of marginal convection, the 3DVar data picked up on a stronger updraft, and subsequently, a very strong outflow boundary. It is very easy to pick out the strongest storm amongst the broken line of convection in the Max Updraft Composite imagery. Updraft values of 17 m/s noted at 2250z, with values as high as 23 m/s at 2230z in McClain County. Elsewhere, updrafts in the line were less than 10 m/s.
Zooming in, the 3DVar 1 km total wind vectors clearly pick up on the strong outflow winds at 2250z.
At 2305Z, it is clear that the spatial extent of the intense updraft is decreasing. 1 km winds are also decreasing which matches well with radar data. Thus will not extend severe thunderstorm warning.
The image below (Figure 1) illustrates the potential for convective initiation, using the UAH-CI tool. The high altitude jet routes overlaid with the CI and latest satellite data show the potential impacts to aviation. I expect that the CI tool will be very useful in operations – especially at the CWSUs.
TMU is always asking about timing and location of convective development. Things become problematic when routes need to be changed at the last second as a result of developing thunderstorms. If we have more tools to provide a larger lead time, TMU personnel can plan farther in advance – which leads to saving money and time…and stress!
Agitated cumulus on visible satellite noted over Childress County. UAH CI values currently at 53, but have been steadily increasing the last few volume scans. Outflow boundary from western Oklahoma storms continues to push southwestward. Watching to see if storms will develop if the boundary helps initiate convection. 21Z OUN WRF now showing a second line of convection developing along the southwest boundary. Stay tuned.
Latest run of the OUN WRF….
The MRMS algorithms have done well in depicting large hail and moderate storm rotation with supercells over the marine area. The first 4-panel image above depicts a cross-section through a supercell northeast of Jacksonville. A pronounced BWER is evident and correlates well with the MESH/rotation tracks panels in the bottom image.
The above image illustrates the use of 3d-Var as a potential enhancement in warning lead time. In assessing the Maximum updraft intensity in the upper right panel, we noticed a rapid increase in the magnitude of the storm updraft. MESH at this time was generally sub-severe…but an uptick in MESH is expected as analyses show increasing upward motion on the northern edge of the line segment. As an experiment, we opted to issue a severe warning based mostly in this increase in updraft speed. In retrospect, updrafts of similar magnitude have already produced hail to the size of quarters and larger, so we’re crossing our fingers.
One thing I’ve begun to wonder is will there be a loss of SA when a forecaster sees an area of “potential development”. The image below (Figure 1) illustrates the UAH-CI in the upper-left panel, while the upper-right panel shows the UW-CTC. My concern is that someone might see a CI area in the 60-70% confidence range and lose their sense of SA as they wait for further development…and the CTC algorithm to hopefully pick up on the developing storm.The UW-CTC product is designed to only pick up on the stronger development…which could easily lead to missing weaker convection. Not only that, but if any bit of the anvil goes near another developing cell…the algorithms will not pick up the newly developing thunderstorms…could end up to missing a warning.
