Saturday, May 28, 2011

"You Never Know What Path the Storm is Going To Take"


This report from KMOV TV aired yesterday illustrates the apparent gap between meteorologists and emergency managers on the topic of selectively warning of the path of tornadoes. Another example of the gap is here.

I don't ever wish to sound like I am "picking" on emergency managers. They have a difficult, "darned if you do, darned if you don't" job. That said, it does appear that there is a significant gap between meteorologists and emergency managers with regard to the the NWS "storm-based" (or path-based) warnings that became official more than five years ago.

Mr. Mark Diedrich, of St. Louis County Emergency Management, says in the report, "You never know what path the storm is going to take." That is simply not true. To illustrate, below is the storm-based warning (purple) issued by the National Weather Service on the St. Louis Good Friday Tornado when it was approaching Lambert Airport (an earlier warning covered the tornado prior to this time). I have added the location of the tornado at the time of the image (circled) and the path it actually took (arrow).
The tornado itself is just under the "rid" in Bridgeton Terrace and is
purple in color along I-70. 
Note that the polygon is far, far wider than the path of the tornado itself so that a margin of safety is built in. Even with sounding the siren only in the areas covered by the polygon the sirens would be sounding far to the south in Clayton and downtown St. Louis. I don't mind that because it is part of the "margin of safety" built-in by the National Weather Service. But to sound the sirens every time any part of a county (or adjacent county!) is threatened is unnecessary and breeds complacency.

3 comments:

  1. I will point you to the imagery and damage assessment information posted up by Washington University
    http://gis.wustl.edu/stl422.html
    and NOAA
    http://www.crh.noaa.gov/lsx/?n=survey1

    Notice there were multiple damaged buildings outside the warning area. The initial touchdown was designated in Earth City, with the tornado reaching EF-3 outside the warning area.
    In particular, this building on Josephine Marie Dr in Maryland Heights
    http://gisdev.srh.noaa.gov/FreeanceMobile/Media/?file=549020154-1303575201016.jpg
    was over 4000' feet outside the warning polygon.

    ReplyDelete
  2. Anonymous,

    In the above posting, I state, "To illustrate, below is the storm-based warning (purple) issued by the National Weather Service on the St. Louis Good Friday Tornado when it was approaching Lambert Airport (an earlier warning covered the tornado prior to this time)."

    Here is the first St. Louis county polygon as posted on this blog in real time:
    http://1.bp.blogspot.com/-NBlS4kZqM5Q/TbIaw_YwzDI/AAAAAAAADEU/zBepgX8JWt8/s1600/Picture+24.png

    And, now, the second: http://3.bp.blogspot.com/-PJxDxxBbNp4/TbImXaDfZ8I/AAAAAAAADE4/ya6BCuhNUuc/s1600/Picture+36.png

    The polygon in the above posting was the third for St. Louis Co. on Good Friday evening.

    As far as I can tell, the entire path of the tornado was mapped out, in advance, by the NWS's polygons.

    Mike

    ReplyDelete
  3. The house on Josephine Marine was located at 38.7352, -90.4592 (WGS84). It fell well east of the 1st polygon and more than a mile west of the 2nd polygon.

    Just on the NOAA survey alone, over 20 damaged structures fell in the gap area between the first polygon and the next two polygons.

    Creve Coeur Lake was the site of the first tornado damaged structure (a shed in Creve Coeur Lake Park), and the first severely damaged (yellow placard) structure was in Earth City (in the Rider Trail area), occurring 1.3 miles and 1.9 miles, respectively outside the closest warning area.

    ReplyDelete

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