**Observer Quality Control of NWS Upper-air Soundings**

WSH, May 29, 2008

Observers must make every effort to quality control their rawinsonde
observations prior to dissemination to data users. Transmitting poor
quality soundings can lessen the accuracy of weather forecasts and
warnings.

Here are guidelines for ensuring high quality upper air observations:

1 ***Inflate the balloon correctly***. Observers must strive for an
average balloon ascension rate between 275 and 350 meters/minute from
surface to flight termination for each sounding. Stations should have no
more than 5% of their flights per month with ascent rates below 275
meters/minute or above 350 meters/minute. Average ascension rates below
275 meters/minute reduce ventilation of the temperature and RH sensors
and can cause loss of valuable wind data. Ascension rates above 350
meters/minute increase gas costs per flight and typically result in
lower burst heights. **Lastly, observers must not under inflate balloons
in the hope that they will reach higher altitudes and result in a higher
station performance score.**

2\. ***Prepare the radiosonde in accordance with the instructions.*** To
ensure the radiosonde functions correctly the instrument preparation
instructions **[must]{.underline}** be followed exactly as stated. The
radiosonde sensor boom or other components **[must not]{.underline}** be
manipulated in a manner not in accordance with the radiosonde
preparation instructions. With good intent, some observers bend the
sensor boom differently from that noted in the instructions and believe
it will provide better data or do no harm. In most cases these changes
don\'t work and cause very erroneous data. Following all the radiosonde
preparation instructions will help ensure a problem free sounding.

3\. ***Do not use flight trains less than 25 meters in length.*** The
balloon skin, especially when exposed to sunshine, is significantly
warmer than the surrounding air. When a short flight train is used heat
from the balloon reaches the temperature sensor, contaminating the
measurements.

4\. ***Examine MicroART and RRS data plots and take action on all check
and status messages*.** MicroART and RRS will alert the observer to
possible data errors. If check messages are displayed (examples: ART
orientation errors, super-adiabatic lapse rates, duplicate pressure
levels, erratic angles, pressure jumps, and RH sensor failure) observers
should make every effort to edit the data accordingly and/or notify the
Electronics Technician to get the ground equipment repaired. If
observers have questions about how to handle specific data problems not
covered in the MicroART or RRS Training Guide, they should take the
initiative to contact the Regional Office for assistance.

5 ***Do not excessively smooth out bad data in a sounding.*** Sometimes
radiosonde or ground equipment problems result in MicroART or RRS
reporting many (10 or more) super-adiabatic or other "Check Messages"
that relate to problems with the pressure, temperature, relative
humidity, or winds data. To solve this problem, some observers
arbitrarily delete up to 9/10\'s of every minute of data for much of the
flight so that software will fill in the missing data with interpolated
values. The same holds true for the position data. **[THIS MUST NOT BE
DONE!]{.underline}** Editing this much data only creates an overly
smoothed sounding that is not representative of the true atmosphere. The
best course of action when this situation occurs is to terminate the
flight at the point where the problems began. (see item 6 below for more
information). Moreover, if the same kinds of data check messages appear
from one flight to the next for several weeks or more then the ground
tracking equipment and RSOIS should be examined by the station
electronics technician.

6\. ***Terminate a sounding early if necessary**.* NWS uses about 75,000
radiosondes each year and a small percentage will not function
correctly. Sometimes a radiosonde will provide clearly erroneous
temperature or pressure data from the start or later in the flight and
many data check messages will be displayed. In such cases the sounding
must be terminated at the point where the bad data started. If the RH
and wind data are erroneous the flight does not need to be terminated.
Delete the bad RH and/or winds from the point where the problem occurred
to flight termination.

7\. ***Edit the position data as stated in the MicroART training
guide**.* It's rare that the ART system will lock-on the radiosonde
immediately at release. When plots of the position angles versus time
are displayed, it's clear from the erratic data in the plots that the
actual lock-on time was later in the flight. ***If a layer of position
data is bad, then delete ALL the position data in the layer.*** Say it
takes a couple of minutes to lock onto the radiosonde at release.
Examination of the azimuth and elevation angles plots shows that the
angles are erratic until 2.1 minutes into the flight. In such a case,
**[ALL]{.underline}** the position data up to 2.1 minutes into the
flight must be deleted. No effort must be made to determine which points
to keep or delete. If angles become erratic later in the flight, this
procedure must also be followed. The correct procedures to follow are
covered in the MicroART Training Guide.

8\. ***Examine MicroART plots of elevation and azimuth angles versus
time.*** Rapid oscillation in the elevation and azimuth angle plots or
data spikes indicate that the group equipment is operating below
standards. When this problem is occurring, MicroART will typically post
frequent "Check Messages" noting erratic angles and rapid changes in
wind speed and direction aloft. Observers must edit the position data
accordingly, inform the electronics technician staff about the problem,
and make sure it is documented into EMRS.

9\. ***Don't delete good data.*** WSH has seen soundings where the
observer deleted data for no apparent reason. Some observers arbitrarily
delete up to 9/10\'s of every minute of data for much of the flight so
that software will fill in the missing data during the minute period
with interpolated values. The same holds true for the position data.
**[THIS MUST NOT BE DONE!]{.underline}** Editing good data only creates
an overly smoothed sounding that is not representative of the true
atmosphere. Again, refer to the MicroART or RRS training guide for the
correct data editing procedures.

10\. **Make sure the surface weather observation taken for the sounding
is accurate.** The surface weather observation of station pressure,
temperature, RH, and wind are used as critical "tie points" for the
sounding and must be accurate. Likewise, the surface observation of
clouds and weather are also of importance and must be accurate. These
data **[must never]{.underline}** be edited or corrected to make them
fit with the sounding data aloft. If the surface weather equipment
(e.g., RSOIS) appears to be out of calibration, it must be serviced as
soon as possible.

12\. ***NEVER release a radiosonde into or near a thunderstorm.*** If a
thunderstorm is occurring at the time of balloon release, then the
observer **MUST** wait (15 minutes from the last clap of thunder) until
the storm passes before releasing the balloon.

Here\'s why,

> \(a\) The observer increases the likelihood of being killed by a
> lightning strike as he or she proceeds to release the balloon. During
> a storm, the flight train basically becomes a lightning rod with the
> observer holding the lower end.
>
> \(b\) The data collected inside or near thunderstorms are mostly
> garbage and are not useful for weather forecasts. The sounding does
> not represent the synoptic scale environment and NCEP does not use
> such soundings for ingestion into numerical weather prediction models.
> See Figures 1 and 2 below that show Skew-T plots of radiosonde data
> collected inside thunderstorms.
>
> \(c\) Thunderstorms typically terminate a flight early owing to
> balloon icing or strong downdrafts.
>
> If the storm persists during the entire release time window, then the
> observation will be logged as missed.

13 ***Examine ALL data quality reports issued by WSH, NCEP, and NCDC to
identify data problems**.* Data quality reports are issued monthly and
are available here: <http://www.ua.nws.noaa.gov/dataqc.htm> . If station
staff notice prolonged, data quality problems that persist from month to
month, they must contact their Regional Office Upper air program manager
to help find the cause and troubleshoot the problem.

![](media/image1.png){width="4.0472222222222225in"
height="3.6034722222222224in"}

**Figure 1.** Sounding taken inside a thunderstorm with very erratic
temperature data. Sounding plot provided courtesy of the University of
Wyoming.

![](media/image2.png){width="4.05in" height="3.6881944444444446in"}

**Figure 2.** Another example of a sounding taken inside a thunderstorm.
This observation was terminated early owing to balloon icing or strong
storm downdrafts. Sounding plot provided courtesy of the University of
Wyoming.