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[aprssig] FINDU Pressure Display

Robert Kirk isobar at bcpl.net
Tue Feb 28 18:28:19 UTC 2006


My email  a while ago about 3 digit pressure encoding reminds me that the 
current display scale on FINDU makes it tough to interpret pressure 
tendencies. The scale runs about  0950 to 1080mb which mostly makes a one 
day view of pressure nearly flat.  Since a look at pressure tendency is 
much more important than the absolute pressure itself, and a change of only 
2mb an hour is a warning signal and lesser changes are important, the 
display is less useful than a good look at the needed inflection points and 
slope  which are now so hard to read.

 From memory, world pressure records go from about 875mb to 1065mb but  I'd 
guess that 99.9% are between 900 and 1050. Katrina got as low as 904mb at 
sea and 920 something when it hit; and Camille  was about the same. "Most" 
hurricanes are well above 970 when they hit land where our stations sit and 
few of us have stations in the tundra to see 950mb pressures (Forgive me 
any Albertians present.) Deep winter storms rarely go below 984 and Alberta 
Clippers rarely exceed  1040mb.

  Again I'd guess that 95% of all pressure readings fall between 980 and 
1040mb. FINDU already clips on the low end (Its 950 min would have clipped 
Katrina & Camille.)

A range of 980-1040mb would more than double the vertical resolution and 
the usefulness of the pressure plot at a trivial loss at the extremes.

Bob Kirk
N3OZB





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