Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1240 AM EDT Mon May 06 2019 Valid May 06/0000 UTC thru May 09/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with 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 12Z ECMWF/ECENS mean blend...after 48 hours Confidence: Average The guidance allows for a southern stream closed low to cross southern CA through Monday 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 UKMET begins to become a bit of a stronger outlier with the height falls and is also slower/deeper than the remaining guidance with the ejecting surface low. The 00Z NAM for its part becomes the most progressive solution, and especially by the end of the period. The 12Z CMC/ECMWF and 00Z GFS all split the difference with respect to timing, but the GFS does outpace the CMC/ECMWF solutions a bit as the low center crosses the Midwest. The 18Z GEFS mean is actually even faster than the deterministic GFS, while the 12Z ECENS mean favors the slower CMC/ECMWF camp. 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 60 and 72 hours, along with its low center. This is time period where the ECMWF and the ECENS mean appear to be more reasonable. So, based on the above mentioned spread and clustering, a general model blend will be preferred through 48 hours, followed by a blend of the 12Z ECMWF/ECENS mean thereafter, although it possible that this consensus could be a tad too slow at the end of the period given the GFS and GEFS mean solutions. ...Series of shortwaves over the Northern U.S... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 60 hours Non-NAM blend...after 60 hours 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 00Z NAM across the northern Plains and upper Midwest after about 60 hours when it becomes more amplified than the global models with mid-level troughing digging across this region. Will prefer a general model blend through 60 hours, and then a non-NAM blend thereafter. ...Trough digging into the Intermountain West Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z GFS/12Z 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 12Z CMC on the weaker side. Better 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: Non-GFS blend Confidence: Average The models agree in bringing a southern stream trough northeastward out of Mexico on Monday and across Texas by Tuesday. The energy will reach the lower MS Valley by Wednesday. Overall, the 00Z GFS becomes the weakest solution with this energy after it crosses the Rio Grande Valley and moves across TX. Generally, the remaining guidance for now is rather well clustered with the mass field details, although the 00Z NAM may be a little too sharp with its energy as it moves into the lower MS Valley. 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 Orrison