Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1250 PM EDT Mon May 06 2019 Valid May 06/1200 UTC thru May 10/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Preliminary Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Southern stream closed low crossing southern CA... ...Crossing the Four Corners on Tuesday... ...Ejecting out into the Plains by Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 48 hours 06/00Z ECMWF/ECENS mean blend...after 48 hours Confidence: Average...becoming below average The guidance allows for a southern stream closed low to cross southern CA through this afternoon and then advance across the Four Corners region on Tuesday. The height falls will induce leeside cyclogenesis over the central High Plains by early Wednesday, and the supporting energy will then begin lifting northeast toward the Midwest by late Wednesday and into Thursday. The models are in very good agreement through about 48 hours with the height falls, and with the initial placement and evolution of low pressure over the central High Plains, but thereafter, the guidance diverges with respect to the timing of low pressure as it advances toward the Midwest. The 12Z NAM remains a more progressive outlier solution on Day 3. The previous CMC and ECMWF were also on the slow side of the guidance. Regarding the attendant front draped across the region, there are some concerns that the GFS may be a bit too far north with its frontal placement between 48 and 60 hours, along with its low center. Given the spread of low positions by the end of the period, and lowering of confidence in the details, the preference will be to maintain the previous model choice which is a general model blend into Day 2, followed by a blend of the 00Z ECMWF/ECENS mean thereafter. ...Series of shortwaves over the Northern U.S... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through much of Day 2 Non-NAM blend...end of Day 2 and all of Day 3 Confidence: 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 most of the period, with exception of the 12Z NAM across the northern Plains and upper Midwest after about 54 hours when it becomes more amplified than the global models with mid-level troughing digging across this region. Eventually, the operational GFS and even the ECMNF begin to catch up with the Will prefer a general model blend through 54 hours, and then a non-NAM blend thereafter still looks acceptable. ...Trough digging into the Intermountain West Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z GFS/UKMET/ECMWF Confidence: Slightly above average The models agree in digging a northern stream shortwave down from southwest Canada and into the Intermountain West by Tuesday. There is some increase in model spread with the depth of troughing over the Intermountain West on Wednesday, as the 00Z NAM becomes a bit deeper than the model consensus and the 00Z CMC on the weaker side. Better clustering and ensemble support resides with the 12Z GFS, 00Z UKMET and 00Z ECMWF, so a blend of these solutions will be preferred. ...Trough reaching the southern Plains Later Today and Tuesday... ...Reaching the lower MS Valley by Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-GFS blend Confidence: Average The models agree in bringing a southern stream trough northeastward out of Mexico later today and across Texas by Tuesday. The energy will reach the lower MS Valley by Wednesday. Overall, the 12Z GFS remains on the weaker side of the envelope of solutions with this energy after it crosses the Rio Grande Valley and moves across TX. Generally, the remaining guidance...both operational runs and ensembles...is rather well clustered with the mass field details. Given that the GFS is the bigger outlier solution, a non-GFS blend will be preferred with this system. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Bann