A long line of severe storms impacted a broad region extending from Texas to Wisconsin on 21 October 2017. The destructive storms developed along a cold front in association with a high amplitude large-scale trough advancing out of the Rocky Mountain region. Ahead of the cold front, strong southerly flow drove anomalously high levels of moisture north, and combined with warm temperatures, led to a long corridor of high instability. Deep layer shear under strong flow aloft also supported the development and maintenance of robust updrafts.
The strongest of storms were centered in Oklahoma where the greatest instability developed, necessitating an SPC Enhanced Risk for Severe Thunderstorms. Initial, large-hail-producing supercell thunderstorms transitioned to linear modes and a damaging wind threat as the cold front pushed southeast. Given the severe risk, a GOES-16 1-min Mesoscale Domain Sector (MDS) centered over Oklahoma was requested by the Storm Prediction Center.
GOES-16 imagery and products provided forecasters with valuable information even before the first storms develop. Water vapor imagery revealed the progression and amplification of the upper-level trough through the Rocky Mountain Region during the previous evening and morning hours (Fig 1). Prior to initiation, increasing moisture and instability was analyzed in GOES-16 TPW and CAPE fields (Fig. 2). Strengthening deep layer shear could be diagnosed in Oklahoma using the Derived Motion Winds (DMWs) and surface observations (Fig. 3).
Figure 1: 21 October 2017 GOES-16 UL WV, ML WV, IRW, LLW (cw starting upper right). Full res
Figure 2: 21 October 2017 GOES-16 IR, CAPE. Full res
Figure 3: 21 October 2017 GOES-16 DMWs and VIS. Full res
Careful analysis of GOES-16 1-min visible imagery reveals areas where the atmosphere is destabilizing and convective initiation is becoming imminent (Fig X). Ahead of the cold front, transition of low stratus stable wave clouds (perpendicular to low-level flow) to cumulus cloud streets (parallel to low-level flow) indicated destabilization was taking place, but that the atmosphere was still capped. The exact location and progression of the cold front was easily tracked in the visible imagery among the abundant high and low clouds. Convective initiation appeared more and more likely as cumulus clouds along the front exhibited increasingly vertical growth.
Figure 4: 21 October 2017 GOES-16 5-min VIS. Full res
1-min imagery from GOES-16 is the first indicator that convective initiation is about to occur or is occurring. As can be seen in Figure 5, convection developed quickly along and ahead of the cold front during the mid afternoon hours.
Figure 5: 21 October 2017 GOES-16 1-min VIS. Full res
Creative displays allow forecasters to extract the maximum amount of useful information from GOES-16, quickly. The VIS/IR image sandwich combo combines the high resolution VIS with the quantitative information from IR into one display (Fig. 6). This image combo allows a forecasters to effectively monitor the health and evolution of a storm through the analysis of relevant storm top features and processes such as overshooting tops, enhanced V’s, cloud top cooling, and cloud top warming.
Figure 6: 21 October 2017 GOES-16 1-min VIS/IR sandwich combo. Full res
GOES-16 IR window channel shows convection develop and quickly organize into a quasi-linear convective system along the cold front (Fig. 7).
Figure 7: 21 October 2017 GOES-16 5-min 10.35 um IR window channel, warning polygons. Full res
The TPW, CAPE, and DMW products should continue to be monitored for information about the environment into which mature storms are moving.
-Bill Line, NWS
“The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing. Users bear all responsibility for inspecting the data prior to use and for the manner in which the data are utilized.”