An Example of How GOES-14 Super Rapid Scan Operations for GOES-R Helped During Warning Operations at NWS WFO Raleigh, NC on 18 August 2014

GOES-14 Super Rapid Scan Operations for GOES-R (SRSOR) was operating over North Carolina on Monday August 19th during severe weather operations at WFO Raleigh. During the event, there were several instances where having the increased temporal resolution was very advantageous during radar interrogation and warning operations. At around 2000 UTC a multi-cellular broken line of showers and thunderstorms approached the Greensboro and Winston-Salem area from the northwest (Fig. 1).

KRAX 1951 UTC 18 AUG 2014

Figure 1. KRAX reflectivity data from 1951 UTC 18 Aug 2014 showing a multi-cellular line of convection moving into the Triad. A perceived boundary is indicated on the image.

 

 

 

 

 

 

 

 

 

 

 

 

 

Based on differential heating patterns, surface observations, and the linear structure to the convective pattern, it was clear that there was some kind of boundary in the area, but it was not clearly defined by surface observations (too far apart) or by radar observations (large gaps between cells). By looking at the one-minute Super Rapid Scan data, the boundary was clear and continuous in the cloud pattern, stretching from Iredell County northeastward to Orange County (Highlighted on Fig. 2).

GOES-14 Visible Imagery 1953 UTC 18 August 2014

Figure 2. GOES-14 visible image from 1953 UTC 18 AUG 2014 showing a boundary across the northwest Piedmont region of NC. An overshooting top of a storm producing a waterspout can also be seen over the Pamlico Sound.

 

An overshooting top can clearly be seen over Alamance County indicating a developing storm prior to it showing any severe characteristics on radar. This overshooting top seen at 1953 UTC would identified 45 minutes before a severe thunderstorm warning was issued on the same cell. In addition, the location of a meso-low was also clear as lower altitude clouds were seen traveling northward to the east of the storm, and southward to the west of the storm, indicating the counterclockwise motion seen with a low pressure system. Also of note in figure 2 is the special marine warning over the Pamlico Sound. Here an overshooting top can also be seen from a storm producing a waterspout at the time in the Newport/Morehead City, NC county warning area.

The motion of the boundary was easily traceable with subsequent one-minute visible images and were used to anticipate where future convection might occur. A bit later in the event, it was clear that the western side of this boundary began to accelerate to the southeast. Meanwhile, the eastern side remained fairly slow moving and toward the south. A small meso-low could be seen moving through the boundary with an area of strong low-level convergence over northern Alamance County (Fig. 3).

GOES-14 Visible image from 2038 UTC 18 AUG 2014

Figure 3. GOES-14 Visible image from 2038 UTC 18 AUG 2014 showing progression of a boundary along with a surface meso-low near Greensboro, NC.

The result was a strong thunderstorm that was deemed worthy of a severe thunderstorm warning with radar reflectivity presentation of a large 65 dBz reflectivity core up to 20 kft, indicative of potential severe hail (Fig. 4).

4.0 degree KRAX Reflectivity from 2039 UTC 18 AUG 2014

Figure 4. KRAX 4.0 degree reflectivity image from 2039 UTC 18 AUG 2014, showing a 65 dBz hail core near 20 kft over Northern Alamance County, NC.

So how did having the Super Rapid Scan Operations for GOES-R impact our warning operations here at WFO RAH? First, knowing where the boundary was at all times, how fast it was moving, and in what direction allowed us to narrow down our area of focus for potential severe convection. This boundary was also a catalyst for some weak low level rotation within several small cells along the NC/VA border. Knowing how the boundary was evolving led us to begin to see small features in the flow, such as the meso-low pressure and associated area of low-level convergence on the east side of the low which led to the growth of the storm over Northern Alamance County.

Did having the Super Rapid Scan push us over the edge to warn on a storm before radar indications of its severity? No, but warning operations involve so much more than that one warn/no warn decision point. So much of warning operations hinges on forecaster confidence in their decision and evidence leading up to the issuance of a warning. While the greater temporal resolution of the satellite imagery did not ultimately make us warn based on that data alone, it certainly increased our confidence in our warning decisions and ultimately made the process more efficient because that evidence was coming in quicker than ever before. That alone made having the Super Rapid Scan data very valuable and very worthwhile, and something that should be able to be built into everyday operations at NWS weather forecast offices around the country.

To see SRSOR data from other cases please visit http://cimss.ssec.wisc.edu/goes/srsor2014/GOES-14_SRSOR.html.

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About Ryan Ellis - WFO Raleigh, NC

Meteorologist, NWS WFO Raleigh, NC B.S. University of Miami 2004 M.S. University of Hawai'i 2008
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