SATELLITE 
INTERPRETATION  DISCUSSION

NOAA NESDIS  Regional and Mesoscale Meteorology Team Cooperative Institute for Research in the Atmosphere (CIRA)  Colorado State University  Fort Collins, Colorado

March 2, 1999

Fifteen-minute Intervals  Loop 1 Five-minute Intervals  Loop 2

This satellite interpretation discussion serves as a reminder to NWS offices that they may request 7 ½ minute interval (8/hour) satellite imagery, called Rapid Scan Operations or RSO, and to present an example of why such imagery is beneficial during severe weather outbreaks.  The following imagery was taken on April 7, 1998, during the GOES-10 checkout period.  Although the satellite was imaging every 5 minutes instead of every 7 ½ minutes, as would be the case during an RSO, the arguments for the more frequent imaging can still be made. The included loops compare six images at 15 minute intervals (Loop1) and fourteen images at 5 minute intervals (Loop 2) in capturing the intersection between two low level thunderstorm outflow boundaries and its subsequent evolution into a thunderstorm which produced a tornado during the central Illinois outbreak of April 7, 1998.  In both loops, the 2145 UTC image shows the two low level thunderstorm outflows whose intersection is monitored at 5 and 15 minute intervals up to 2300 UTC, five minutes before the report of a tornado 2.5 miles west of Mt. Pulaski, IL.  Comparison of the two sets reveals that although both sets record the developing thunderstorm, the five minute data contain, as would be expected, information that is not seen at the 15 minute interval.

With the fifteen minute imagery, the approach and intersection of the two outflows is not as obvious, and one needs to wait for the 2230 UTC image to confirm the growth of the cloud.  The continued development of the thunderstorm to just before the time of the reported tornado is better monitored by the 5 minute data.

Such interactions between low level thunderstorm outflow boundaries have been shown to be important in convective processes.  In this case, the interaction resulted in a tornadic thunderstorm.  With 5 minute data (or 7 ½ minute data), these interactions are better monitored than with the conventional 15 minute data, and provide important complementary data to radar analyses.  AWIPS equipped NWS offices can (today) receive and view the RSO data 1-3 minutes after scan time.