Severe storms produced large hail (including significant) and tornados across Wyoming and Colorado on 29 July 2018. Strong northwest flow over a moist airmass led to very favorable shear and instability across the region, and a SPC Enhanced Risk for severe was in place. GOES-16 1-min imagery was available to support NWS forecasters during the event. Storms early on produced overshooting tops and above anvil cirrus plumes, a signature indicative of severe and significant severe potential. The plumes appear as smooth cirrus cloud features emanating from the overshooting top and downstream over the storm anvil. Cumulus clouds are also analyzed being drawn into the southern regions of the storms, indicative of strong inflow winds.
Figure 1: 29 July 2018 GOES-16 1-min VIS. Full res
A little later over east-central Colorado, a severe storm developed that produced a measured wind gust of 83 mph, along with hail at least 2.75″ in diameter (baseball). GOES-16 1-min imagery of this storm showed a large and persistent overshooting top and an above anvil cirrus plume (VIS, Fig 2). The corresponding 1-min IRW imagery (Fig 3) shows a large overshooting top (round region of coldest pixels) along with a relatively cooler area immediately downstream of the overshooting top (completing the thermal couplet) and a relatively cool region extending downstream above the anvil (above anvil cirrus plume). Overlaying a semi-transparent IRW on the VIS, we get the sandwich image combination (Fig 4). Radar imagery of the storm showed reflectivity over 80 dBz along with significant beam attenuation, indicating a lot of hail (Fig 5).
Figure 2: 29 July 2018 GOES-16 1-min VIS. Full res
Figure 3: 29 July 2018 GOES-16 1-min IRW. Full res
Figure 4: 29 July 2018 GOES-16 1-min IRW. Full res
Figure 5: 29 July 2018 KPUX 0.5 degree radar reflectivity. Full res
A cluster of thunderstorms made a long trek south through the southeast Colorado plains Thursday night into early Friday morning. The storms produced heavy rainfall and gusty winds, including a 45 knot measured gust at La Junta. Additionally, the storm produced frequent lightning as evidenced by GOES-16 GLM and NLDN CG data. To the west of the storm, low clouds developed along the I-25 corridor in the anomalously moist atmosphere. Low ceilings brought IFR conditions to KCOS and MVFR to KPUB.
Cloud top brightness temperature trends from ABI IR and GLM total lightning trends were analyzed through the night in order to monitor the health of the storm cluster. Given the 45 knot wind report and constant cold IR temperatures and total lightning, SPS’s were issued for the duration of the storm. The 4-panel animation shows several long flashes extending into the anvil stratiform region of the system, from which several CGs were measured by NLDN.
Figure 1: 27 July 2018 GOES-16 FED (TL), AFA (TR), TOE (BR), and KPUX base reflectivity and NLDN CGs (BL). Full res
As the storm advanced south, low clouds spread west to the I-25 corridor. The Nighttime Microphyics RGB was utilized to track the progression of the low clouds and amend/update TAFs. The image combination below shows the nighttime microphysics RGB with IR brightness temperatures overlaid (gray-scale) for the coldest temperatures. GLM Flash Extent Density is also overlaid. In the RGB, recall that during the warm season, the ~aqua colors represent warm liquid water clouds, the ~tan colors are cooler water clouds, and the red colors are cold ice clouds (overlaid with IR in the animation below).
Figure 2: 27 July 2018 GOES-16 5-min Nighttime Microphysics RGB (color underlay) with IR brightness temperatures overlaid (grayscale) and GLM Flash Extent Density overlaid. Full res
A long-lived, prolific above anvil cirrus plume (AACP) generating storm produced large hail and heavy rainfall as it tracked southeast along the Sangre de Cristo mountains in south-central Colorado on Tuesday. The largest hail report from the storm was 1.75″, 12 miles south of Westcliffe. The storm tracked over two burn scars, leading to flash flooding. The AACP signature indicates a particularly strong updraft and increased likelihood of a severe storm.
Figure 1: 25 July 2018 GOES-16 5-min visible satellite imagery. Severe thunderstorm (yellow) and flash flood (green) warnings and storm reports also included. Burn scars outlined in red. Full res
Severe thunderstorms developed across central Iowa during the afternoon of 19 July 2018, producing multiple tornados. Fortunately, 1-minute imagery from GOES-16 was available over the region to aid forecasters during the event.
GOES-16 derived motion winds in the area of tornadic development indicated enhanced low-level and deep layer shear just prior to initiation. With surface winds of 12 knots from 160 degrees and GOES-16 DMWs indicating ~1 km winds of 16-20 knots from around 220 degrees, 0-1 km shear was around 16 knots, which is favorable for supercell tornados (Fig 1). DMWs around 6 km were 40-50 knots from 275 degrees, which yields a 0-6 km shear vector of around 49 knots, favorable for supercell development. Figure 2 combines the mesoscale and CONUS winds to show the abundance of winds vertically and horizontally that can be available from GOES-16. Numbers from the nearby DMX VAD wind profiles are similar.
GOES-16 CAPE showed convection develop on the western edge of a CAPE max. As has been found in previous experiments, although CAPE derived from GOES may often be lower than other sources, the gradients in the moisture/instability fields are captured well.
NUCAPS profiles from Suomi-NPP were available ahead of the line of the line of storms around the time of initiation (Figure 4). Considering central Iowa does not have a balloon launch, temperature and moisture profiles from polar orbiting satellites have exceptional value. The surface conditions of the profiles need to be modified to match nearby obs. After doing so, the profiles near Des Moines indicated around 2,000 j/kg of MLCAPE and up to 4,000 j/kg of SBCAPE, supportive of strong updrafts (Figure 5). Further, the mid/upper levels of the profiles were dry above moist low levels, indicating favorable convective instability.
GOES-16 1-min imagery revealed progressively enhanced cumulus development and clumping northwest of Des Moines between 1800 UTC and 1900 UTC. Initiation took place shortly thereafter, confirmed by the first GLM total lightning detections at 1926 UTC (Figure 6). The first tornado was reported around 1950 UTC, just as GLM FED values began to rapidly increase. A max of 3 flashes/5-min was detected at 1940 UTC, and a max of 23 flashes/5-min was detected at 1950 UTC. At 2000 UTC, a max of 100 flashes/5-min was detected with this storm as it continued to produce a tornado. The updraft weakened briefly thereafter, before strengthening again from 64 flashes/5-min at 2037 UTC to 142 flashes/5-min at 2112 UTC when 1.5″ hail was reported.
Further south, severe thunderstorms produced widespread damaging winds, including a reportedly fatal storm that capsized boats on Table Rock Lake. GOES-16 1-min visible imagery showed rapid updraft growth with this storm through old anvil clouds up to the tropopause, quickly producing overshooting tops and an above anvil cirrus plume, the latter of which is a sign of a particularity strong storm.