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from: Geoff DiMego, NCEP EMC has received much feedback this spring on a high bias in 2-meter dew point temperatures in the operational NAM (Eta) model. This is most likely attributable to a bug in the land-surface physics portion of the NAM. I pointed this out to the regional SSD's in early January soon after we found it but I wanted to reiterate it again following the recent feedback. This bug leads to excess surface evaporation over land and results in higher 2-meter dew points, particularly during the warm season in vegetated regions and in warm sectors. Because of this high bias, forecasters may choose to view the dew points at the first model level above ground to get more reasonable values, e.g. from the actual gridded data (if available), also plotted at: http://www.emc.ncep.noaa.gov/mmb/namsvrfcst/. The land-surface physics bug in the operational NAM was discovered late in 2005, but a decision was made not to fix it since at the time NAMX (WRF-NMM) implementation was planned for March 2006 (still the relatively cool season), and a proper NAM fix would have involved further testing. With limited resources, the focus remained on the WRF-NMM running in the parallel NAMX (which has no such bug). The good news is that the near-surface dew point temperatures look much better in NAMX. The NAMX is currently scheduled to be implemented operationally on 13 June 2006. For further information, please see: "http://www.emc.ncep.noaa.gov/mmb/research/FAQ-eta.html";, under "WRF Model", click on: "OPERATIONAL NAM-ETA VS NAMX/WRF-NMM: LOW-LEVEL DEW POINT TEMPERATURES". ---------------------------------------------------------------- Thanks to Mike Ek and Geoff Manikin for their assistance in this matter. ============================================================================== To unsubscribe nws-changes, visit: http://www.unidata.ucar.edu/mailing-list-delete-form.html ==============================================================================
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