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Name: Ron K.
Status: educator
Age: 50s
Location: N/A
Country: N/A
Date: 12/10/2002


Question:
How do I obtain the current sea level barometric pressure for my area? (NE Pennsylvania) The instructions for the weather station in my classroom requires that information to set it up.


Replies:
Ron -

You need to know the altitude of the instrument in feet above sea level. You can get the elevation of the ground from a geodetic chart and add to it the height of the instrument above the ground. For every 1000 feet, you need to correct the local barometric pressure by adding 1 inch of mercury or fraction thereof. It makes sense... the air pressure at sea level would be greater. This method would likely serve your purpose.

As an alternative, the National Weather Service or an FAA Flight Service Station can provide you with the SLP for many airport with reporting stations. They are reported hourly.

Larry Krengel


Dear Ron-

You can visit this site, and find the nearest observing location to your school. Just click on the map, and then select a city. The sea level pressure is one of the values that is reported on a weather observation.

http://www.wunderground.com

Wendell Bechtold, meteorologist
Forecaster, National Weather Service
Weather Forecast Office, St. Louis, MO


Ron,

I am puzzled by the terms "sea level bp" and "bp for my area." In the answer that follows, I shall assume you want the current local bp.

Almost any local TV station's weatherperson could provide the information you seek. You might also check with the national weather service listed in your phone book. The information you get should be sufficient to set up your weather station.

It will not (need not) correspond exactly with local conditions because sometimes local conditions can change so quickly that it is impossible to get an exact match between your station and the reference station. What you really want to illustrate to your students is relative change in barometric pressure over the course of a day or other longer time span.

If you are a real stickler for exactitude, reference your station against an accurately calibrated and zeroed mercurial barometer. One might be available in a local college or high school science lab.

Regards,
ProfHoff 547


Ron,

What you are looking for is the MSL (Mean Sea Level) pressure, which you can get from your local NWS (National Weather Service) radio station or from the NOAA site on the web. Go to weather.gov and select "Surface Weather" under "Observations" from the list on the left. On the next page to come up, "Select State" in the "ASOS" box. On the next page to come up, "Select a Location" in the "Current Weather Conditions" box. The next page to come up shows MSL pressure in inches and hPa (hectaPascals) as well as many other observations.

You could calculate MSL, but it is a complicated calculation involving altitude, temperature lapse rate, and dewpoint. It is much easier to get it from one of the sources above.

David R. Cook
Atmospheric Research Section
Environmental Research Division
Argonne National Laboratory


I do not have a direct source but you can start your search at either of the following web sites. Each also provides a direct link to the agency web master, who I am sure could give you a resource for your specific data: http://www.nws.noaa.gov/om/osd/portal.shtml http://www.daily-tangents.com/refsheet/weather/

Vince Calder


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