Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1226 AM EDT Sun May 05 2019 Valid May 05/0000 UTC thru May 08/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Low pressure waves over the Southeast/Mid-Atlantic... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Two shortwave impulses, one currently approaching the Mid-Atlantic region, and one over the TN Valley will both focus waves of low pressure through early Sunday as they lift off to the northeast. Gradually, the models support the waves of low pressure consolidating near the Delmarva by late Sunday, and then support a gradually strengthening low that ejects well offshore of the East Coast on Monday. The guidance is in rather good agreement with the details of both shortwaves and evolution of the waves of low pressure, so a general model blend will be preferred. ...Southern stream closed low approaching CA... ...Moving into the Southwest by Tuesday... ...High Plains cyclogenesis by Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 60 hours 00Z GFS/12Z ECMWF blend...after 60 hours Confidence: Above average The guidance allows for a southern stream closed low to approach central/southern CA by late Saturday and into Sunday. On Monday and Tuesday, the closed low will advance into the Southwest and then cross the Four Corners region, before then beginning to eject out into the central/southern High Plains by Wednesday. As the energy reaches the High Plains, all of the models support a well-defined area of leeside cyclogenesis focusing over the junction point of southeast CO, northeast NM, the OK/TX panhandles and southwest KS. The models are in very good agreement through about 60 hours with the height falls, but thereafter, the 00Z NAM begins to become a modestly stronger outlier solution. The NAM is also well south of the global models with its leeside low center by the end of the period. Also, the 12Z UKMET begins to outpace the remaining guidance with the progression of the upper trough by the end of the period. The best model clustering after 60 hours resides with the 00Z GFS and 12Z ECMWF with the energy aloft, and with the leeside cyclogenesis and frontal placement. So, will prefer a general model blend through 60 hours, followed by a blend of the GFS and ECMWF thereafter. ...Series of shortwaves over the Northern U.S... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 48 hours 18Z GEFS mean/12Z ECENS mean blend...after 36 hours Confidence: Slightly above average A series of northern stream shortwaves will be traversing southern Canada and portions of the northern Rockies, the northern Plains, the upper Midwest, and the Great Lakes region through the period. Model spread is modest through about 48 hours, and then there gets to be some smaller scale timing and depth differences with the shortwave energy crossing through southern Canada and the northern U.S. thereafter. Will prefer a general model blend through 48 hours, and then favor a blend of the 18Z GEFS mean and 12Z ECENS mean to smooth out some of the modest timing/depth differences seen toward the latter part of the period over southern Canada in particular. ...Trough digging into the Intermountain West Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS/12Z ECMWF blend Confidence: Slightly above average The models agree in digging a northern stream shortwave down from southwest Canada and into the Intermountain West by Tuesday. The 12Z UKMET is the fastest solution with this energy. Meanwhile, the 12Z CMC is the least defined and the weakest. The better model clustering and ensemble support resides with the 00Z GFS and 12Z ECMWF, so a blend of these solutions will be preferred. ...Trough reaching the southern Plains Monday/Tuesday... ...Reaching the lower MS Valley by Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS/12Z ECMWF blend Confidence: Average The models agree in bringing a southern stream trough northeastward out of Mexico by Monday and across Texas by Tuesday. The energy will reach the lower MS Valley by Wednesday. The 12Z CMC is somewhat of a stronger outlier with the trough, with the 12Z UKMET being the weakest. The 00Z NAM/GFS and 12Z ECMWF split the difference, but the better overall model clustering supports the 00Z GFS and 12Z ECMWF, which is closest to the model consensus, and so a blend of these solutions will be preferred. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Orrison