Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1225 AM EST Thu Mar 07 2019 Valid Mar 07/0000 UTC thru Mar 10/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z NAM/GFS Evaluation Including Preliminary Preference and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Mid-level shortwave energy moving through the central U.S. ridging Thursday night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z NAM...00Z GFS...12Z CMC blend Confidence: Slightly above average The 12Z ECMWF is slightly slower/weaker with shortwave energy across the Midwest, while the 12Z UKMET is a bit slower than the consensus. The ensemble means show good agreement with one another and the 00Z NAM, 00Z GFS and 12Z CMC. ...Closed low in Pacific the Northwest, breaking into two with eastward progression... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 00Z/09 Near the 12Z ECMWF/UKMET after 00Z/09 Confidence: Average Differences with a closed low in the Pacific Northwest begin to appear near 00Z/09 with the 12Z UKMET and 00Z GFS slightly quicker with the northern portion of this system tracking through southern Alberta/Saskatchewan. The 00Z NAM is a bit of an outlier with the southern portion of the closed low being more progressive. The ensemble means are in good agreement and near the 12Z ECMWF and the 12Z UKMET by 00Z/10 while the 00Z GFS ends up quicker. Overall, while there is the potential for changes due to complex interactions of the upper level features, a solution near the 12Z ECMWF/UKMET and ensemble means is preferred at this time. ...Upper Midwest Deepening Surface Low This Weekend... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z NAM/12Z ECMWF blend through 12Z/09 near the 12Z ECMWF 12Z/09-12Z/10 Confidence: Slightly below average A positively tilted shortwave will enter the Southwest Thursday night and will track across the southern Rockies late Friday, emerging as a negatively tilted shortwave in the Central Plains for Saturday with a developing surface low. Overall trends in the deterministic and ensemble guidance have been faster since the 12Z cycle on Tuesday with the ECMWF making the smallest run to run changes. The 00Z GFS is the fastest and lies toward the fastest edge of the ensemble guidance. Despite the trends, the GFS is not supported by other deterministic guidance at this time which is a negative for using the 00Z GFS. The 12Z UKMET differs with its handling of shortwave energy in the base of the upper trough in the Southwest on Friday with a sharper/stronger mid-level shortwave which continues its track into west Texas and Oklahoma Saturday morning. The difference in the 12Z UKMET's handling of shortwave energy aloft affects its surface low track with a more southern/faster low compared to the remaining model consensus. The 12Z ECMWF and 00Z NAM appear best until about 12Z/09 when the 00Z NAM becomes a bit faster with the leading edge of the shortwave trough. The 12Z CMC could be used as a second option to the 12Z ECMWF for Saturday into Sunday. ...Next Pacific trough and surface low nearing Central West Coast Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z NAM, 00Z GFS, 12Z ECMWF blend Confidence: Slightly above average Another upper trough is expected to reach California by Sunday morning with some timing differences noted in the latest guidance. The 00Z NAM/GFS are faster with the 12Z UKMET/CMC slowest. Ensemble guidance from Wednesday supported a slightly faster trend leaving the 12Z UKMET/CMC toward the slower side of the guidance. The 12Z ECMWF is near the middle to slower side of the ensemble spaghetti heights but when blended with the 00Z NAM/GFS, a reasonable compromise is reached. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto