We (NCEP and FSL) have found the problem, and it's about to get fixed.

There was a flaw in the RUC code reading in METAR BUFR data which assumed that altimeter settings would always be present. That was almost always true, that is, until last Thursday when a new set of ~40 Canadian METAR stations was added to the METAR data provided to the RUC, all missing altimeter settings. The missing flag, 99999 Pa was converted to 999.99 mb and thus, 1000 mb obs were being put in for all of these stations. Since there were a number of them, they corroborated each other in the RUC QC buddy check where they happened to occur in clusters and changed the RUC SLP analysis to near 1000 mb. There was, in turn, a modification of RUC heights by a corresponding number of meters aloft.

An emergency fix is being prepared now, and it is hoped that it will be put in within a couple of hours.

Stan Benjamin