Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1225 AM EDT Sat Oct 12 2019 Valid Oct 12/0000 UTC thru Oct 15/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Initial Model Evaluation with latest Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Subtropical Storm Melissa ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Subtropical Storm Melissa is now beginning to accelerate towards the east-northeast after remaining nearly stationary well to the south of Cape Cod, Massachusetts. The upper level ridge that had blocked the storm is now moving out of the way and the large scale circulation around the Upper Midwest low is increasing the steering flow and causing it to gain forward speed. Similar to the 12Z guidance on Friday, the latest guidance shows good agreement with the evolution and timing of this system and thus a general model blend is preferred. Deep Plains/Upper Midwest Cyclone ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through Sunday night, then GFS/ECMWF Confidence: Above average An impressive deep layer cyclone over the north-central U.S. has reached maximum intensity as of Friday night, and is now forecast to gradually weaken after remaining nearly stationary on Saturday. It should then track in a general eastward direction across Lake Superior and then northeastward across Ontario. The cold front trailing from the parent surface low will cross the Appalachians Saturday morning and then exit the East Coast by Saturday night, albeit not nearly as strong as it was over the Plains. A secondary cold front associated with the storm system will likely develop and cross the Midwest on Sunday and then move toward the East Coast on Monday. The models remain well clustered with the mass field evolution of this system through Sunday night. By Monday morning, the 12Z CMC has its closed low and mid level height fields slightly farther south than the other models as the energy crosses into southeast Canada. Therefore, a general model blend is best through 60 hours, followed by a GFS/ECMWF blend. Pacific Northwest to the Northern Plains ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: NAM/GFS/ECMWF Confidence: Above average The next feature of interest to affect the western U.S. will be a progressive upper-level trough and associated cold front that should reach the West Coast by early Sunday, and then advance inland across the northern Rockies on Monday. By Monday night, the height falls start arriving across the High Plains and induces lee-side cyclogenesis over the central Plains to Upper Midwest. The main difference noted with the models is that the 12Z UKMET is less amplified than the model consensus with the 500mb heights, and is slower with the front that develops across the Plains. There is enough agreement among the NAM, GFS, and ECMWF to merit a blend of these models. Southwestern U.S. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: ECMWF/UKMET/EC Mean Confidence: Near Average A southern stream shortwave perturbation is progged to reach California Sunday night and separates from the northern stream trough mentioned above. The CMC appears slightly more amplified in the mid to upper levels and the GFS becomes faster as the system crosses the Desert Southwest by Monday. The ECMWF and UKMET appear to fit the pattern best and have support from the EC mean. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Hamrick