Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 137 PM EST Mon Feb 26 2018 Valid Feb 26/1200 UTC thru Mar 02/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... ...12Z model evaluation along with final preferences... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Departing weak positively tilted shortwave exiting the eastern U.S. today... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model compromise Confidence: Above average The models show similarly with this system. ...Northern Stream shortwave crossing the northern Plains through Wednesday night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z NAM/ECMWF/UKMET blend Confidence: Average Both the 12Z NAM/GFS are quicker with this shortwave compared to the 00Z ECMWF/UKMET/CMC, but the 12Z GFS becomes one of the fastest compared to the ensemble spread Wednesday night and beyond. Ensemble means support a blend closer to a 12Z NAM/00Z ECMWF blend with the 12Z NAM slightly quicker and 00Z ECMWF slower than the means. ...Closed low forming over the California coast tonight...becoming an open wave as it tracks into the southern Plains late Wednesday... ...Resultant surface cyclone into the Ohio valley on Thursday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z ECMWF/UKMET blend Confidence: Average Similar to the above referenced system, the 12Z GFS becomes faster than the remaining model consensus with this feature, and while not an outlier with respect to the spaghetti ensemble distribution of 500 mb height contours, the 12Z GFS has little deterministic support. There is some possible interaction with the northern stream shortwave referenced above with the southern stream wave referenced here, but the resulting surface cyclone shows reasonably well in the past few ensemble cycles regarding the surface low by 12Z/01 in the Ohio valley. While scatter low plots from the 00Z/26 ensembles support a solution closer to the 00Z ECMWF, the faster 12Z NAM/GFS could be on to a trend so a blend of the somewhat quicker 12Z NAM and 00Z ECMWF is preferred for this system. In fact, the 12Z ECMWF/UKMET both shifted east a bit, but not to the degree of the 12Z GFS. Worth noting, the 12Z NAM 500 mb low appears too weak from 12Z/01 - 00Z/02 which may result in the surface low from the 12Z NAM being too weak. The 12Z ECMWF/UKMET appear more reasonable here, with the ECMWF a bit slower/stronger aloft, and the 12Z UKMET a bit weaker/faster aloft. ...Large closed low off of the Pacific Northwest by Thursday evening... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 2/3 12Z ECMWF, 1/3 12Z GFS blend Confidence: Average Ensembles have shown the GEFS/GFS models to be consistently quicker with the evolution of the closed low off of the Pacific Northwest by Thursday evening. The 12Z NAM is also quicker. Given the consistent signal noted in the ensembles, a blend weighted toward the middle is preferred. The middle is best represented by a 12Z GFS/12Z ECMWF blend, but with more weight toward the ECMWF. Only minor changes were noted in the 12Z ECMWF/UKMET/CMC compared to their 00Z cycles regarding this system. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto