Tornado outbreak in Iowa
GOES-16 (GOES-East) Upper-level Water Vapor (6.2 µm), Mid-level Water Vapor (6.9 µm), Low-level Water Vapor (7.3 µm) and “Red” Visible (0.64 µm) images (above) revealed the well-defined signature of a mid-tropospheric lobe of vorticity moving from southeastern South Dakota across Iowa during the day on 19 July 2018 — this feature provided synoptic-scale forcing for ascent which aided in the development of severe thunderstorms in central and eastern Iowa. A number of tornadoes were reported, along with some large hail and damaging winds (SPC storm reports). A closer look using 1-minute Mesoscale Domain Sector GOES-16 “Red” Visible (0.64 µm) images (above) showed the line of thunderstorms as they developed in advance of an approaching cold/occluded front (surface analyses). Two larger storms were dominant, which produced tornadoes causing significant damage and injuries in Pella KPEA and Marshalltown KMIW — above-anvil cirrus plumes were evident with both of these supercells. In addition, early in the animation a few orphan anvils could be seen along the southern end of the line (southeast and east of Des Moines KDSM).The corresponding GOES-16 “Clean” Infrared Window (10.3 µm) images (below) showed cloud-top infrared brightness temperatures of -65ºC to -70ºC with the larger Pella storm, and around -55ºC with the smaller Marshalltown storm to the north.
The NOAA/CIMSS ProbSevere model (viewed using RealEarth) had a ProbTor value of 74% at 2055 UTC for the Pella storm (above) and 83% at 2130 UTC for the Marshalltown storm (below). GOES-derived Cloud-top glaciation rate (from infrared imagery) is one of the predictors used in the model. ProbSevere time series plots for the Pella and Marshalltown cells are shown below. They indicated that the Pella storm was long-lived, persisting past 0300 UTC — and that ProbTor ramped up quickly and then down quickly, bracketing the time of the tornado in Marshalltown. A toggle between 375-meter resolution Suomi NPP VIIRS Visible (0.64 µm) and Infrared Window (11.45 µm) images at 1946 UTC (below) provided a look at the early stage of development of tornado-producing convection. Additional satellite imagery and analysis of this event can be found on the Satellite Liaison Blog.The EF-3 damage at the Vermeer Plant in Pella. Preliminary estimated peak winds of 144 mph and a max tornado width of 400 yards. Tornado end time and path length still TBD. #iawx pic.twitter.com/aMMmhdn21N
— NWS Des Moines (@NWSDesMoines) July 21, 2018
Preliminary damage survey…Lennox Warehouse in Marshalltown where the EF-3 damage occurred caused by 144 mph estimated peak winds. #iawx pic.twitter.com/egcNJqBSOE
— NWS Des Moines (@NWSDesMoines) July 21, 2018
As of 4:09 CDT, a tornado debris signature was about 3 miles NE of Pella, IA moving southeast. Radar and webcam shot from @akrherz. #iawx pic.twitter.com/y8erooTml7
— U.S. Tornadoes (@USTornadoes) July 19, 2018
Tornado Emergency for Marshalltown, IA. A damaging tornado is now making it’s way through Marshalltown. Debris from the tornado is being seen by the radar up to 11,000 ft. Indicating a strong tornado is ongoing! #iawx pic.twitter.com/2eKqFlpe2N
— U.S. Tornadoes (@USTornadoes) July 19, 2018