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NCEP Service Center Evaluations SPC Steve Weiss
Since no access to PFC soundings from the parallel runs, SPC cannot comment on the vertical profile of low level moisture. However, there was a noticeable enough difference between the BL dewpoint values in the two runs coupled with the apparent increased moisture bias of the parallel run to raise questions about possible causes of the enhanced moisture return (advection, land-surface processes, etc.). We hope EMC will explore this aspect of NAM performance and identify processes contributing to the forecasts of increased low level moisture.
There is a chance that in operational return flow situations the higher values of moisture/instability in the parallel version could lead to an erroneous early introduction of severe potential if forecasters are unaware of the possible bias in the NAM model forecasts. However, SPC forecasters will continue to consult the SREF and GFS guidance in their decision-making process, and pay close attention to evolving NAM model characteristics through the warm season and convey any new observations to EMC.