Hello,

I am trying to locate the observation interval (averaging interval) for
the National Weather Service Weather Roundup (RWR) that provides
routine, standardized hourly observations for a sub-state region, an
entire state, or a multi-state region. I have reviewed all of the
relevant NWS directives and the federal meterological handbook but I am
unable to locate this information.

Specificially, I would like to know what time interval the weather
observations represent (for example I think that wind speed is a
2-minute average that occurred within the 15 minutes previous to the
hourly roundup), but does temperature represent an instantaneous value
observed at the actual time of the observation or does it represent a
15-minute average, or is it the average value for the entire hourly
observation? Similarly, what about other parameters such as humidity,
pressure, etc.?

Any help you can provide is greatly appreciated.

Thank you,
Fred Corey.

Fred Corey wrote:
Hello,

I am trying to locate the observation interval (averaging interval) for
the National Weather Service Weather Roundup (RWR) that provides
routine, standardized hourly observations for a sub-state region, an
entire state, or a multi-state region. I have reviewed all of the
relevant NWS directives and the federal meterological handbook but I am
unable to locate this information.

Specificially, I would like to know what time interval the weather
observations represent (for example I think that wind speed is a
2-minute average that occurred within the 15 minutes previous to the
hourly roundup), but does temperature represent an instantaneous value
observed at the actual time of the observation or does it represent a
15-minute average, or is it the average value for the entire hourly
observation? Similarly, what about other parameters such as humidity,
pressure, etc.?

Any help you can provide is greatly appreciated.

Thank you,
Fred Corey.

Fred,
Most such observations are made by the ASOS (Automated Surface
Observing System). There are also AWOS and manual sites, but what
follows below applies to the majority of observations you see in the
RWR.

Wind: Wind observations are updated at 5- second intervals, then
averaged over 2 minutes' worth of samplings. ASOS also looks for
gusts in exceedance of 10 minutes' worth of sampling by a value of 5
knots or more and records this value as a gust.

Visibility: Visibility measurements are made every minute, then
averaged over a 10- minute period.

Precipitation: Reported precipitation is updated once per minute.

Cloud cover: The ASOS reports a single cloud cover estimate based on
an analysis of clouds detected at the zenith over a period of 30
minutes. The observation is weighted toward the most recent 10 minutes
of data. The ASOS is not capable of reliably detecting clouds above
12,000 feet.

Altimeter: A new pressure value is computed every minute.

Temperature/Dewpoint: The temperature/dewpoint update cycle is once per
minute.

=====
Raymond C. Martin, Jr.
Associate Meteorologist, AccuWeather Inc.- http://www.accuweather.com/
New Jersey Expressways and Tollways - http://www.njfreeways.com/
Ray's Winter Storm Archive - http://www.njfreeways.com/weather/

"Fred Corey" wrote in message
oups.com...
[snip]
Specificially, I would like to know what time interval the weather
observations represent (for example I think that wind speed is a
2-minute average that occurred within the 15 minutes previous to the
hourly roundup), but does temperature represent an instantaneous value
observed at the actual time of the observation or does it represent a
15-minute average, or is it the average value for the entire hourly
observation? Similarly, what about other parameters such as humidity,
pressure, etc.?


Wind and cloud elements have values averaged over an interval, but IIRC, T,
Td and P are instananeous at the time of the report. Humidity is derived
from T and Td.

Absolute authority:
http://www.ofcm.gov/fmh-1/fmh1.htm

Thank you for the replies. The environmental program that I work for
has a air quality / met station (www.fraxinus.us) and with the
exception of wind, hourly values (reports) represent hourly averages,
not instanteous values recorded at the top of the hour. This may be
the way it is done by EPA for air quality monitoring but it seems less
useful when you want to know what the actual current conditions are.

A co-worker of mine thought that NWS uses 15-minute averages for all
parameters (except for precipitation), but based on comparing NWS
values with our values, I suspected that 1-minute or less averages are
used for the RWR.

Thank you again for taking the time to answer my questions,
Fred Corey


Fred Corey wrote:
Hello,

I am trying to locate the observation interval (averaging interval) for
the National Weather Service Weather Roundup (RWR) that provides
routine, standardized hourly observations for a sub-state region, an
entire state, or a multi-state region. I have reviewed all of the
relevant NWS directives and the federal meterological handbook but I am
unable to locate this information.

Specificially, I would like to know what time interval the weather
observations represent (for example I think that wind speed is a
2-minute average that occurred within the 15 minutes previous to the
hourly roundup), but does temperature represent an instantaneous value
observed at the actual time of the observation or does it represent a
15-minute average, or is it the average value for the entire hourly
observation? Similarly, what about other parameters such as humidity,
pressure, etc.?

Any help you can provide is greatly appreciated.

Thank you,
Fred Corey.