Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 232 PM EDT Wed May 23 2018 Valid May 23/1200 UTC thru May 27/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation...with Final Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ---18Z UPDATE--- No change to the preliminary preference. The 12Z ECMWF has slowed the progression of the low in the Gulf further, as compared to its 00Z run, which was somewhat expected. The overall track did not change appreciably, though. The 12Z CMC and 12Z UKMET have moved into better agreement with the ECMWF elsewhere across the CONUS, with the GFS more distinctly different in the West -- still with a faster progression of the trough. ---PREVIOUS DISCUSSION (ISSUED 1252 PM EDT)--- ...Surface low development over the Gulf of Mexico by Saturday... Preference: Blend of 00Z ECMWF; 00Z ECMWF Ensemble Mean Confidence: Slightly below average The ECMWF appears to have trended in the right direction with respect to the timing of the surface low over the Gulf. Two model cycles ago (22.00Z run), it had a surface low approaching the mouth of the Mississippi River by Friday evening (26.06Z), but now delays that in its most recent 00Z run to about a day later (27.06Z). Given the lack of significant development thus far, would not be surprised by further trends in this direction. However, the overall progression indicated by the model appears more reasonable today. It is also fairly close in proximity to the ECMWF Ensemble Mean and a blend of the two is the preference for this system at this time. Did not include the 12Z GFS as it still appears to tie the surface low progression to a burst of convection, eventually tracking it across the Florida Peninsula. The 00Z UKMET is furthest south and southeast now and does not have a lot of other model support. The 12Z NAM and 00Z CMC are closer to the ECMWF, but the NAM is the furthest west (which also doesn't have a lot of support at the moment) and the CMC is faster and deeper with the surface low indicating a greater pace of development unsupported by observational data. ...All other areas and systems of interest... Preference: Blend of 00Z ECMWF; 00Z ECMWF Ensemble Mean Confidence: Average For the remainder of the CONUS over the next several days, models generally agree on the large scale features -- dominated by a trough and associated closed low progressing into the Great Basin this weekend, downstream ridging in the Plains, and low amplitude troughing evolving in the Great Lakes. The overall flow pattern remains fairly weak, so there are also a variety of embedded shortwaves (some perhaps convectively driven) that may also affect sensible weather. Model differences are not substantial, but are more noteworthy with the progression of the trough across the West. The 12Z GFS shows a typical bias for a faster trough (as does the GEFS Mean), with the 00Z UKMET the slowest and the 00Z ECMWF, 12Z NAM and 00Z CMC in the middle. The preference is to lean toward the ECMWF and its ensemble mean overall, but the NAM and CMC also seem to be close approximations that could be included in a blend as well. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Lamers