AMOSSG/5-SN No. 17

18/3/05

AERODROME METEOROLOGICAL OBSERVING SYSTEMS STUDY GROUP (AMOSSG)

FIFTH MEETING

Montreal, 11 to 14 April 2005

Agenda Item	5:	Aerodrome observation requirements
5.1:	Reporting requirements and criteria

CHARACTERISTICS OF UNIDENTIFIED PRECIPITATION

(Presented by Dennis Hart)

SUMMARY
Edition 15 of ICAO Annex 3 introduced the possibility to report unidentified precipitation (UP), when the type of precipitation cannot be detected by an automatic observing system. This paper suggest changes to the Annex 3; to make it possible to add the characteristic of the unidentified precipitation.

1.	INTRODUCTION

1.1	Since the introduction of edition 15 of ICAO Annex 3 automatic observing systems can be used during non-operational hours of an aerodrome. Relevant provisions were introduced to overcome some special characteristics of these type of observations. One of this provisions is to introduce the possibility to report "unidentified precipitation" (UP), when the type of precipitation cannot be detected by an automatic observing system.

1.2	No provisions were made to identify the possible characteristics of the precipitation of the unidentified type. The addition of characteristics to unidentified precipitation could be of value for aeronautical users.

2.	DISCUSSION

2.1	To report UP is something to avoid when using automatic observation systems. But the nature of some systems and incorporated algorithms does not always prevent this to happen when precipitation is detected by automatic systems. Information on the exact type of precipitation is highly appreciated by users. But information on precipitation without knowing the exact type, can also be of great value for users of aeronautical observations. Especially in combination with other observed and reported parameters.

2.2	Information on the characteristics of weather phenomena like thunder and shower is also of importance for aeronautical users. Therefore it is still considered to be a requirement for automated observational reports to report Thunderstorm (TS) and Shower (SH). Even when the type of precipitation is unknown, the information itself, if it is a shower or thunderstorm, can be of great help in identifying the possible hazards for aviation.

2.3	Some of the current automatic observing systems are capable to identify the characteristics of weather phenomena and precipitation in particular without identifying the exact type of weather. So from a technical perspective, it is possible to observe the characteristics of the precipitation, even when it's of an unidentified type; characteristics like TS and SH can be detected and reported in combination with UP.

2.4	It is therefore proposed to introduce the possibility to report unidentified precipitation in combination with the characteristic Thunderstorm and Shower; TSUP and SHUP shall be introduced as a recommended weather phenomena to report.

2.5	Consequently, the associated recent weather phenomena should be introduced; RETSUP and RESHUP shall be introduced as a recommended recent weather phenomena to report.

3.	ACTION BY THE GROUP

3.1	The AMOSSG is invited to:

a)	note the content of this paper;

b)	agree on the proposal stated in paragraph 2.4;

c)	agree on the proposal stated in paragraph 2.5; and

d)	undertake any further action, if necessary.

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