Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 133 PM EST Sat Feb 29 2020 Valid Feb 29/1200 UTC thru Mar 04/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Latest Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Deep upper trough exiting the Northeast today... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The latest guidance shows very good agreement with the details of the deep trough exiting the Northeast later today and tonight. The 12Z NAM is a tad stronger than the global models as it clips southern Newfoundland by early Monday, but a general model blend otherwise be preferred. ...Shortwave crossing the Upper Midwest/Great Lakes by Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-GFS blend Confidence: Above average A shortwave and associated cold front will cross the Upper Midwest and Great Lakes region Sunday night through Monday. The 12Z GFS is a tad stronger than the remaining model guidance with the upper trough and also its surface low reflection as it crosses southern Canada. Given the reasonably good model clustering/agreement seen away from the GFS, a non-GFS blend will be preferred. ...Shortwave over the northern Plains/Midwest by Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-GFS blend Confidence: Above average A new northern stream shortwave trough and associated cold front will drop across southern Canada and dig across the northern Plains and Midwest by Tuesday. A surface low center with this system will cross southern Canada through the period. The 12Z GFS is generally a tad more amplified with the upper trough, and also has its surface low track on the south side of the model spread on Tuesday. Overall, the GFS is a bit of an outlier relative to the remaining guidance which is rather well clustered, so a non-GFS blend will be preferred with this system as well. ...Possible shortwave near the Pacific Northwest on Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z CMC/UKMET/ECMWF Confidence: Average The guidance suggests a shortwave embedded within fast upstream Pacific flow will be near or approaching the Pacific Northwest on Tuesday. The 12Z non-NCEP models per the UKMET, CMC and ECMWF have all clustered toward a more progressive solution with energy arriving across British Columbia and Washington State by late Tuesday. The 12Z NAM is quite slow, with the 12Z GFS faster but slower than the non-NCEP models. Given the fast and relatively zonal upstream Pacific flow, a blend of the more progressive non-NCEP models will be preferred. ...Deep trough amplifying into the Southwest Sunday/Monday... ...Energy ejecting east across the southern Plains Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend...through 60 hours 12Z GEFS/00Z ECENS mean blend...after 60 hours Confidence: Above average...becoming average after 60 hours The models amplify a shortwave trough crossing the Pacific Northwest today and support a closed low dropping south down across coastal areas of California on Sunday. Thereafter, the energy is expected to advance east across northern Mexico and then eject out across the Rio Grande Valley and adjacent areas of the southern Plains on Tuesday. The 12Z NAM is overall somewhat of a stronger outlier with this system through the period, including as it takes the system out over the southern Plains. The 12Z GFS has trended a little slower than its previous run, but is still the most progressive solution as the energy arrives across the Rio Grande Valley on Tuesday. The 12Z non-NCEP models are now all tightly clustered on a slower solution of the closed low toward the end of the period, with the UKMET and especially the CMC both trending slower with this run to match the ECMWF. The 00Z ECENS mean strongly supports this slower camp. The 12Z GEFS mean is quite consistent with its previous run in being faster than the non-NCEP model consensus, but slower than the GFS. Given the overall slower trend seen with the model consensus compared to the previous couple of model cycles, a blend of the latest GEFS mean and ECENS mean will be preferred by the end of the period, which will yield a slight edge to the slower consensus of guidance and thus a dismissal of the GFS by that point. Model clustering is good for a non-NAM blend to be preferred through about 60 hours as the system crosses down near the West Coast and into Southwest, with a GEFS/ECENS mean blend preferred thereafter as it approaches the Rio Grande Valley. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison