The GOES-R Overshooting Top (OT) Detection algorithm (applied to current GOES) was utilized during the very early morning hours of June 23 across the Texas panhandle and western Oklahoma. This algorithm, which automatically detects the location of OT’s using the GOES IR window channel, has proven to be especially valuable in monitoring the evolution of mature convection, especially overnight in the absence of the higher resolution visible imagery. As has been mentioned in previous posts, OT’s indicate the presence of strong updrafts within a convective system, and likely areas of hazardous weather. The algorithm provides forecasters with a tool to quickly spot, in the imagery, where OT’s are present as well as trends in the feature.
By 0400Z on the 23rd, an MCS was propagating across the Texas panhandle/western Oklahoma, producing heavy rainfall and severe winds across the region. An SPC forecaster on shift viewing the OT product utilized it to help monitor trends in the strongest updrafts and areas most likely to be experiencing hazardous weather. The forecaster mentions in a 0723Z SPC Watch Update Mesoscale Discussion (MD,Fig. 1): “TRENDS IN 7 KM AND 9 KM CAPPI AND GOES-R OVERSHOOTING TOP PRODUCT INDICATED THE MORE PERSISTENT UPDRAFTS SINCE AT LEAST 0530z HAVE BEEN FROM THE SRN TX PANHANDLE INTO WRN OK…WITH FORWARD MOVEMENT OF THIS ACTIVITY AT 35-40 KT TOWARD THE SSE.”
Figure 2 is an animation of GOES-East IR imagery with overshooting tops and SPC storm reports overlayed during the time of and in the vicinity of the MD. Notice the cluster of persistent Overshooting Tops within the large cloud shield across the Texas panhandle between 0415 and 0530Z. This is where the highest concentration of severe weather (and heavy rainfall) was reported. Between 0530 and 0730 UTC, the MCS continued to propagate to the SSE as the overshooting tops became more spread out along the leading edge of the system from the southern Texas panhandle into western Oklahoma, as was mentioned in the MD. A few wind reports and heavy rainfall were reported in the vicinity of the persistent OT’s. After 1000Z, the OT’s dropped off completely as the MCS began to weaken.
Fig. 2: June 23, 2014 0415-1345 UTC GOES-East IR imagery, Overshooting Top Magnitude, SPC storm reports.
The storms that ravaged the southern United States this past week not only produced deadly severe weather, but also incredible flooding. Figure 1 shows parts of the Florida Panhandle and southern Alabama received in excess of 10 inches of rain on Tuesday, April 29 alone!
Figure 1: April 29 12Z to April 30 12Z precipitation analysis. More negative values indicate stronger OT’s
A previous blog post introduced the Overshooting Top Detection product and explained its utility in severe weather situations. Overshooting tops are also indicators of where heavy rainfall may be occurring. Furthermore, the constant presence of overshooting tops over a particular location over an extended period of time may indicate a prolonged period of heavy rainfall, which could lead to flooding.
The animation in Figure 2 shows GOES-East IR imagery with overshooting top detection’s overlaid from the afternoon of the April 29 into the early morning hours of the April 30. During much of this period, GOES-East was in Rapid Scan Mode, meaning images were often available every 5-10 minutes (instead of 15). Notice the persistence of overshooting tops centered over the Mobile area throughout the period, where copious amounts of rainfall were recorded. By about 09Z, a downward trend in overshooting top detection’s had begun as the storm system shifted eastward and weakened. The Overshooting Top Detection product provides a day/night capability for forecasters to easily identify where within a convective system the strongest updrafts are occurring, and where severe weather and/or heavy rainfall may be occurring given other meteorological factors.
Figure 2: April 29 22Z – April 30 10Z GOES-East IR with Overshooting Top Magnitude overlaid.
Figure 3 shows this same system during the early morning hours of April 30 at much higher resolution. This is a 375 m IR image taken with the Suomi NPP VIIRS instrument. Notice the visibility of features that aren’t easily seen in current GOES IR imagery such as gravity waves and overshooting tops.