As would be expected, 3D-VAR struggles at greater distances from the radar.  A fairly large supercell thunderstorm that had a history of producing brief tornadoes was at 12-15kft AGL on BIS 88-D’s lowest slice.  It could be implied from base radar products that this storm had a powerful updraft, modest to strong mid-level rotation and strong storm-top divergence.  However, since the storm was too far from the radar, 3D-VAR products such as max updraft composite, updraft helicity, updraft vorticity and max convergence above 8km appeared much weaker than what was likely reality.

Several severe hail-producing supercells formed early this evening across northern South Dakota.  Reports of up to golfball size hail were received.  Here, we will focus on some 3DVAR products.

We want to draw your attention to the lower panels (the image was at 00Z).  The panel on the left clearly shows three distinct updrafts associated with each of the supercells.  The panel on the right shows the magnitude of the vorticity associated with each updraft very distinctly.  Let’s look at the next image, 0015Z:

Look at the bottom panels again.  You can clearly see the middle and southern storms have merged into one homogenous cell, especially in the updraft image on the left.–Gordon Strassberg for WFO ABR.

An outflow boundary from earlier coastal convection is intersecting instability in north-central Florida, leading to new development in the far southern portion of the JAX CWA and far northern portion of the MLB CWA. Updraft strength, updraft helicity, and even 10km divergence (not in this image) have all become very interesting across Marion, Lake, and Volusia Counties.

These data have prompted the issuance of SVRs for parts of Marion and Volusia county, and special marine warnings have been issued off the coast.  The JAX team has split into half-JAX, half-MLB to address the evolving threats.

Another severe thunderstorm warning was issued near the Florida-Georgia border based on strong dual-pol radar and MRMS signatures.  3DVAR hasn’t been as interesting (perhaps the storms are too close to the KJAX radar), but the simulated reflectivity product is picking up on an impressive outflow boundary crossing the state line.

The first severe thunderstorm warning for the day for WFO JAX comes along the JAX-CHS CWA line in Glynn County, GA.  The 3DVAR analysis indicates some of the strongest indicators seen this week.

The 1-km U/V winds indicate 30-40 knot winds (perhaps a rear-inflow jet) nearing the coast, 19 m/s composite updraft strength, 159 m/s^2, and 10km divergence of 10.72 s^1.  These values (particularly the updraft) are among the stronger storms we’ve seen this week.  After some AWIPS 2 problems, a severe thunderstorm warning was issued after confirming these data with the KJAX radar.

Late in the afternoon, as convection continued along the southern fringe of BTV’s county warning area, a storm cell began pulsing up and down.  This series of images shows how the max reflectivity on radar and the maximum updraft output from 3D-VAR began oscillating.  Maximum updraft strength from 3D-VAR would precede a peak in radar reflectivity by about 20 minutes.  We issued a warning for a southern BTV county, based on the Max Updraft data.  The storm produced 3/4 inch hail.

2205z.  Reflectivity is maximizing from a previous pulse, and current Max updraft values are less than 10 m/s.

2235z. Maximum Updraft values around 14 m/s. Max Reflectivity around 56 dbz.

2300z. Max Reflectivity back up to 60 dbz, while Max Updraft Strength continues around 18 m/s.

Dankers/Kearney