Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 245 AM EDT Tue May 07 2019 Valid May 07/0000 UTC thru May 10/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Southern stream closed low over southern CA... ...Crossing the Four Corners on Tuesday... ...Energy/low lifting across the Plains/Midwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 36 hours 00Z ECMWF/GEFS mean and 12Z ECENS mean blend...after 36 hours Confidence: Average The guidance takes a southern stream closed low over southern CA off to the east 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 models are in very good agreement through about 36 hours, but thereafter the 00Z NAM begins to accelerate the surface low and attendant front a bit faster off to the east compared to the global models. Regarding the global models, there is some timing and latitudinal spread noted with the low track. The 00Z GFS gradually becomes the slowest solution with the low center as it moves through the Midwest and toward the Great Lakes. The non-NCEP guidance is all faster, but not as fast as the NAM. The 00Z UKMET/CMC solutions both also tend to track their lows farther north, and overall a bit to the left of the model consensus. The UKMET also tends to be a bit stronger than all of the remaining guidance. Given some of the spread in the details of the low track later in the period, confidence is a bit lower for this PMDHMD issuance. The guidance that best approximates the model consensus toward the end of the period is the 00Z ECMWF, the 00Z GEFS mean and the 12Z ECENS mean. So, will prefer a general model blend through 36 hours, followed by a blend of the ECMWF and the latest GEFS/ECENS means. ...Series of shortwaves over the Northern U.S... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average A series of northern stream shortwaves will be traversing southern Canada and portions of the northern Plains, the upper Midwest, and the Great Lakes region through the period. Model spread is modest through most of the period, and so a general model blend will be preferred to resolve any smaller scale timing/depth differences. ...Trough digging into the Intermountain West Tuesday and Wednesday... ...Height falls over the Southwest by Thursday/Friday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~ Preference: General model blend Confidence: Above Average The models agree in digging a northern stream shortwave down from southwest Canada and into the Intermountain West by Tuesday and Wednesday. Some of this energy will then eject east out across the Plains, but there will be a portion of it that breaks away and retrogrades down to the southwest and interacts with a new southern stream closed low feature approaching the Baja Peninsula by the end of the period. This will lead to an elongated trough over much of the Southwest U.S. with a rather broad closed low feature over CA by the end of the period. The guidance is reasonably well clustered at this point, so a general model blend will be preferred. ...MCV over southeast TX moving to the lower MS Valley... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average A MCV moving through southeast TX will lift northeast up across the lower MS Valley and gradually shear out over the next day or so. Model spread with this is modest and so a general model blend 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