[aprssig] FINDU Pressure Display

Robert Kirk isobar at bcpl.net
Sun Mar 5 15:27:51 CST 2006

Ray... Thanks for the info on the extremes.
I'd go for the 95% range I suggested below: 980 on the low end because as 
you say, the strong Pacific lows often hit in the 980s, but it's not common 
to down even to 976 once ashore. On the high end, I've seen a couple of low 
940s in Canada this year; rare, but I wouldn't quibble with your 950.

Bob Kirk

At 11:42 AM 2/28/06 -0800, Ray McKnight wrote:
> >From Wikipedia:
>"The highest recorded atmospheric pressure, 108.6 kPa (1086 mbar or 32.06
>inches of mercury), occurred at Tosontsengel, Mongolia, 19 December 20012.
>The lowest recorded non-tornadic atmospheric pressure, 87.0 kPa (870 mbar or
>25.69 inHg), occurred in the Western Pacific during Typhoon Tip on 12
>October 19792. The record for the Atlantic ocean was 88.2 kPa (882 mbar or
>26.04 inHg) during Hurricane Wilma on 19 October 2005."
>I believe the record for the Gulf of Mexico was set during Hurricane Wilma
>(2005), if not a record for the northern hemisphere as well.  FYI Wilma also
>produced the largest recorded wave height of 90 ft, which managed to bend
>structural steel I-beams on several large offshore oil platforms 35 degree
>due to taking the full force of broadside waves.
>As far as a more useful range for daily measurements, most "full sized"
>barographs have a chart range of 955-1060mb.  I regularly see dips below 990
>during strong Alaskan lows.  "Standard" barographs will have an expanded
>scale but not by much.  No consumer grade weather stations will be useful in
>measuring anything outside the range of a quality barograph.  I'd say that
>setting our range to 950-1050 would be reasonable for 99% or more of the
>time.  If I see anthing lower than that I'm bugging out to watch from the
>comfort of a distant hotel on the Wx Channel...
>----- Original Message -----
>From: "Robert Kirk" <isobar at bcpl.net>
>To: "TAPR APRS Mailing List" <aprssig at lists.tapr.org>
>Sent: Tuesday, February 28, 2006 10:28
>Subject: [aprssig] FINDU Pressure Display
> > 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
> > 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
> > slope  which are now so hard to read.
> >
> >  From memory, world pressure records go from about 875mb to 1065mb but
> > 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
> > 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
> > 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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