Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1226 PM EDT Tue May 07 2019 Valid May 07/1200 UTC thru May 11/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Southern stream system starting in southwest today to the Plains Wed, Upper MS Valley and Upper Lakes Thu, with surface low crossing into Canada Fri... Preference: 00Z ECMWF/GEFS mean/12z NAM Conus Nest Confidence: Average The guidance takes a southern stream closed low 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 and attendant low will then cross the central Plains, Midwest and Great Lakes region through Thursday. The 12z NAM made a big adjustment in the track/intensity of the 700 mb low that resulted In a large change in QPF from the latter half of day 1 through day 2. Given the parent Nam on the 06z run cluster fairly well with the ECMWF/ECMWF Mean, the 06z run is preferred. The 12z Nam CONUS nest also clustered well with the aforementioned models/ensembles and had better continuity, so is preferred thru day 2 over the 12z parent NAM. The 06z GFS was a slow and weak outlier with the sfc-700 mb low track so is the least preferred. The 12z GFS has adjusted to move the low across the mid MS Valley to the upper lakes several hours faster and is now getting closer to the preferred cluster, so the 12z GFS is trending in the right direction. Given some of the spread in the details of the low track later in the period, confidence is still average. The guidance that best approximates the model consensus toward the end of the period is the 00Z ECMWF, the 00Z GEFS mean and the 00Z ECENS mean. ...Trough digging into the Intermountain West Tuesday and Wednesday and closed low 700-500 mb in CA Thu/Fri... Preference: General model blend Confidence: Slightly Above Average The models agree in developing a 700-500 mb wave as the trough moves south across CA/NV on Thu and then likely into a closed low Thu night and Fri in Ca, as the NAM/GFS/UKMET/Canadian/ECMWF all develop a closed 500 mb low, along with the ensemble means . The consensus has the 500 mb low just off the CA coast 00z Sat with minor timing and intensity differences. The 12z NAM was slightly deeper than the other solutions but is positions is well clustered position-wise with the other models. A blend of the models/ensemble means provides a good solutions given the good clustering overall. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Petersen