We received the following problem report from the Met Office
concerning assimilated data for the autumn of 1998. This affected 
analyses produced for the period from September 1998 to mid-December
1998:

4th December 1998

Introduction of a new observation processing system in September
has caused problems with the assimilation of satellite data above 
10mb. These have resulted in temperatures at higher levels becoming 
too low. The problem has now been corrected and temperatures are 
returning to realistic values. The intervening period will be re-run.