Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 247 AM EDT Sat May 04 2019 Valid May 04/0000 UTC thru May 07/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Southern stream trough/wave activity over the South... ...Energy lifting northeast toward the Mid-Atlantic... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z UKMET/ECMWF blend Confidence: Slightly above average A series of southern stream shortwave impulses/MCVs will continue to lift northeast from the southern Plains up across the OH/TN Valleys and into the Mid-Atlantic region going into the weekend. This will allow multiple waves of low pressure to lift up along a frontal zone draped across the region. Gradually, there will be a consolidation of low pressure over the central Mid-Atlantic region through Saturday, and then a gradual intensification of this low pressure on Sunday as it advances offshore along with the dominant shortwave trough. The 00Z NAM is likely too amplified with its shortwave trough over the Mid-Atlantic on Sunday and definitely is a deeper outlier offshore the East Coast. The 00Z GFS after about 36 hours again becomes more progressive than the remaining guidance with the exiting low. Meanwhile, the 00Z CMC tends to lag the remaining guidance with the low progression as it advances offshore. The best model clustering at this point is with the 00Z UKMET and 00Z ECMWF, and this will be the preference, as these solutions have overall the best support from the 00Z GEFS mean and 12Z ECENS mean. ...Southern stream closed low approaching CA... ...Moving into the Southwest by Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend 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. The model spread with this feature is quite modest, so a general model blend will be preferred. ...Series of shortwaves over the Northern U.S... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 36 hours 00Z GEFS mean/12Z ECENS mean blend...after 36 hours Confidence: Average A series of northern stream troughs will impact areas 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. There is some spread with the details of additional shortwave energy and possibly a small closed low dropping down across Saskatchewan by the end of the period, with all of the models showing a stronger feature here with exception of the 00Z ECMWF. The 00Z NAM/UKMET and 00Z CMC are the strongest solutions. The 00Z GEFS mean and 12Z ECENS mean offer a nice mass field compromise that smooths out some of the smaller scale differences seen in the guidance. Will prefer a general model blend through 36 hours, followed by a blend of the GEFS/ECENS means thereafter. ...Trough reaching the southern Plains Monday/Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z UKMET/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 00Z GFS is a strong outlier with this system and actually supports a closed low to mid-level low center over central to northeast TX. The 00Z NAM supports this as well but is not as deep. The 00Z non-NCEP models generally favor a more open trough axis, although the 00Z CMC hints at a closed low feature and is also on the slower side of the guidance. Will prefer a blend of the 00Z UKMET/ECMWF solutions for now which tend to have better support from the latest GEFS/ECENS means. ...Front over the central Plains/Midwest Monday/Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z ECMWF/12Z ECENS mean Confidence: Slightly above average The series of northern stream shortwaves traversing the northern U.S. and southern Canada Sunday and Monday will allow a cold front to gradually drop down toward the central Plains and Midwest by Tuesday. The preference with this frontal timing and placement will be toward the 00Z ECMWF and 12Z ECENS mean which is a tad more suppressed compared to the 00Z GFS. The 00Z NAM and 00Z UKMET tend to support a more suppressed solution as well. Given concerns about the GFS mass fields just to the south over the southern Plains by Monday and Tuesday, and with the strength of northern stream high pressure nosing down across the northern Plains by this period, a more suppressed frontal evolution 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