The NWS approximation explains it

Message posted by JB737 on May 25, 2007 at 20:06:38 PST:

It is looking more and more as if the National Weather Service used their own approximation of density altitude that ignores water vapor.

For the weather conditions in the report, if their simplified method gives 6900 ft density altitude, then the more exact method (accounting for water vapor) shows 7162.

The corresponding field elevation would be 4497 ft.

The Groom Lake runways, according to Google Earth, are between 4438 and 4482 ft elevation.


Groom Lake is well within any reasonable accuracy range of measuring the input parameters, darned near dead center.

Unless I find out that the automated weather stations use a different method, then this is enough to satisfy me that the forecast was for Groom Lake, and that there is no deceptive data transmitted.

Just a documented NWS approximation, which is worst at high elevation, high temperature, and high humidity. August in Nevada qualifies, at least on that day when the dewpoint was 17C (62.6F) rather than being a subfreezing number as I am sure it sometimes must be out there.


In Reply to: New/Improved "Groom Lake VOR" calcs posted by JB737 on May 25, 2007 at 18:58:37 PST:


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