Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 132 AM EST Wed Dec 04 2019 Valid Dec 04/0000 UTC thru Dec 07/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Upper low arriving California on Wednesday... ...Energy then crossing the southern U.S. through Friday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-UKMET blend Confidence: Above average Overall there is good agreement with the evolution of the upper low offshore the West Coast and its associated surface reflection which will advance inland across central/southern CA on Wednesday, and then move progressively east across the Four Corners and southern Plains through Thursday. The system will be gradually weakening with time, and especially as it crosses from the southern Plains to the Southeast by the end of the week. The 00Z UKMET still appears somewhat questionable with its mass fields as it has its closed low feature a little north of the remaining guidance cluster as the energy crosses the Southwest. Once the system ejects from the southern Plains eastward, the UKMET ends up being a little slower than the remaining guidance. A non-UKMET blend will be preferred with this system. ...Amplifying trough across the Northeast through Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z GFS/UKMET/ECMWF Confidence: Above average The models amplify a shortwave trough into the Northeast U.S. through Wednesday. The 00Z NAM is a tad stronger than the global models with this system. Although, of the global models, the 00Z CMC appears to be a little too weak. The ensemble mean clusters per the GEFS and ECENS, and the latest HREF cluster, favor a solution toward the 00Z GFS/ECMWF/UKMET camp, and thus a blend of these solutions will still be preferred. ...Weak shortwave/low clipping the Northern Plains Wednesday... ...Crossing the Great Lakes/Northeast through Thursday/Friday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z GFS/UKMET/ECMWF Confidence: Above average The models support a weak shortwave and associated surface low/front clipping the northern Plains late Wednesday and quickly reaching the Great Lakes region by late Thursday before arriving across the Northeast on Friday. The 00Z NAM and to a lesser extent the 00Z CMC both end up being stronger outliers with this system as it crosses the Great Lakes and Northeast. There is better ensemble support for the modestly weaker 00Z GFS/UKMET/ECMWF cluster, along with the 00Z ARW/NMMB hires model solutions (at least through 48 hours). Will maintain the GFS/UKMET/ECMWF consensus preference for the time being. ...Deep closed low offshore the West Coast by Friday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z NAM/UKMET/ECMWF Confidence: Average The models support another very deep closed low evolving offshore of the West Coast by Friday. The 00Z GFS edges the closed low a bit closer to the coast versus the remaining suite of guidance. The 00Z CMC tends to be farther east, and a bit weaker as well. There is some support from the latest GEFS cluster for this slightly more progressive GFS solution, but the majority cluster of guidance is a little slower and farther offshore at the end of the period, so a non-GFS and non-CMC blend will be preferred with a focus on the 00Z NAM/UKMET/ECMWF solutions. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison