AMOSSG/4-SN No. 18

11/9/03

AERODROME METEOROLOGICAL OBSERVING SYSTEMS STUDY GROUP (AMOSSG)

FOURTH MEETING

Montreal, 15 to 18 September 2003

Agenda Item	7:	Aerodrome forecast requirements

OPERATIONALLY DESIRABLE ACCURACY OF FORECASTS

(Presented by Bryan Boase)

SUMMARY
A re-assessment of the operationally desirable accuracy of forecasts is suggested

in order to update the information provided in Attachment E to Annex 3.

1.	INTRODUCTION

1.1	It is recognized and agreed than an ongoing re-assessment of the operational accuracy of forecasts is essential. It is suggested that the complexity of this task requires input from a wide range of sources in order to adequately harmonise user requirements, scientific limitations and verification considerations.

2.	DISCUSSION

2.1	Forecast Accuracy Standards

2.1.1	One of the most highly desirable outcomes from improved observing systems is forecast accuracy. However, observing systems alone will not improve forecast accuracy. It is a combination of factors that include but is not restricted to, the strength of the science supporting forecast products, as well as the analytical skill levels of individual forecasters.

2.1.2	In developing forecast accuracy standards factors that must be considered include:

a)	the accuracy of verifying observations;

b)	the lead time of the forecast (i.e. is it valid or desirable to expect the last few hours of a TAF to be as accurate as the first few hours); and

c)	the interpretation of TAF elements and temporary change and probability groups given the non-deterministic nature of TAF.

2.1.3	It is therefore important that accuracy standards are developed with these and other factors in mind.

2.1.4	It is proposed that in order to develop meaningful, usable and valid forecast accuracy standards a separate focused working group/sub committee made up of experts from ICAO, IATA, WMO and States be established to address this issue.

3.	ACTION BY THE GROUP

3.1	The group is invited to consider the merit in establishing a separate working group or sub-committee to address the forecast accuracy issue.

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