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Real-time posts made during testbed nowcast and warning operations.
The synthetic IR/WV forecast did a good job in placing strongest activity over Florida along the W coast, where eastward moving sea breeze probably caused strongest convergence in easterly wind regime. Pulsating storms featured reflectivity peaks in excess of 50 dBz.
Helge
A few interesting storms across WFO DMX this afternoon. Several were severe, with one storm producing hail and quite a bit of damage in and just S-SE of Waterloo. In this post, however, we will focus on a storm that was a little closer to the radar that did not as of yet produce any severe reports. Let’s look at a 4-panel of 3DVAR data:
We are interested in the storm that moved from southern Marion County into and through Mahaska County. Notice the Max Updraft and Vorticity Tracks (lower panels). These fields stay fairly constant over time along the path of the storm. This storm did develop some weak low to mid level rotation. Not the updraft helicity values in the top right that peaked near 100m2/s2 indicative of this.–Gordon Strassberg for WFO DMX.
The 3DVAR output showed strong increases in storm top divergence, updraft helicity, and maximum updraft speed in the 2245z image associated with a thunderstorm in Buchanan County in northwest Missouri. Subsequent to these increases the thunderstorm updraft split (left mover died quickly) and the storm turned to the right over the next several images, as shown in this image of the maximum updraft composite. The brightest image represents the current image while a history of previous images is shown in subdued colors.
A line with strong to severe storms continues to push rapidly to the east. The environment is favorable for rapid storm organization, given 60 kt deep layer shear and tongue of 2000 plus J/kg SBCAPE sneaking in from the SW.
At 2237Z, the composite reflectivity image was added (upper right) with core refl. aoa 70 dBz just where 3DVAR indeed had the most severe cell development along that line over NW Missouri.
Helge
The following CTC image led to the issuance of a warning at 2028Z. Severe hail signatures were noted with storm at 2112Z and severe hail was reported at 2130Z. 
MESH appears to have given us as much as 20 minute lead time before the 1.00 in. hail report. Decatur County is along the northern swath of hail.
HIRSCH
Thunderstorms continue to build rapidly to the SW along the cold front with initiation underway around 2145 Z over NE Kansas. It is amazing how well the OUN WRF captured the initiation:
Timing was excellent with placement just slightly off to the south. This model forecast would have helped forecasters a lot to pinpoint area of initiation well ahead.
Helge
The 3DVAR products indicated strengthening of this thunderstorm with both the updraft helicity and maximum updraft values spiking on the 2140z image. This thunderstorm had previously caused wind damage (downed power poles) across southern FIllmore county. The values at 2140z were higher than those previously (as shown by underlaid history tracks) so a severe thunderstorm warning was issued for the potential for strong damaging winds. 
UPDATE: Emergency managers reported widespread tree damage within the community of Winona, in the northern portion of the warned area, a lead time of 17 minutes. Dime sized hail was also reported within the warned area in southeastern Winona County.
Severe convection currently evolves along the cold front over C Iowa with Cld top cooling product showing impressive cooling rates below -65 K/15 min e.g. over Warren and Polk counties.
Helge
About 2100 UTC we gave up on lightning in the east coast domains (saw a max of 2 flashes / min during our time there) and re-localized to Des Moines, IA (McKinney & Kleinsasser) & La Crosse, WI (Strassberg & Hirsch) with our observers working Pleasant Hill, MO.
Storms are already ongoing with CTC rates as low as -50 C for multiple storms and we expect some SVR warnings shortly.
-K. Calhoun, Week 3 Coordinator
