Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 100 AM EDT Sat May 02 2020 Valid May 02/0000 UTC thru May 05/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z NAM/GFS Evaluation Including Preliminary Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Shortwave/surface low tracking near the U.S./Canadian border through Sunday, frontal zone through Ohio Valley; Northeast reinforcement/surface redevelopment Sunday to Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non 00Z GFS blend, led by 00Z NAM/12Z ECMWF Confidence: Average The models are in fair agreement with timing, but the 00Z GFS becomes faster with the shortwave as it nears the Northeast. This is reflected in ensemble spaghetti plots and comparisons of the 00Z GFS to the latest deterministic consensus. While there are some differences with frontal placement across the MS Valley and to the west...with the 12Z UKMET slower in the Southern Plains, a non-00Z GFS blend of guidance appears reasonable at this point in time. ...Deep trough offshore the West Coast today with remnant shortwave energy moving through the Northern Rockies Sunday morning, northern High Plains surface low... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z ECMWF/CMC/ECMWF mean Confidence: Below average Large spread and poor run to run consistency make for below average forecast confidence. Initially, there is good agreement with the upper trough axis reaching Washington and Oregon but differences grow through Sunday with the remnant shortwave as it moves inland across the Northern Rockies and southwestern Canada. There are also embedded shortwaves within zonal flow across the Intermountain West with poor model agreement. The preference is to stay near the middle, away from outliers, while considering trends. This takes out the 00Z NAM and 00Z GFS which are faster with the upper trough into southern Alberta/Saskatchewan. The 12Z ECMWF is slightly more elongated with the trough axis toward the east by Monday morning, but the 12Z ECMWF mean is more in line with a middle ground. The 12Z UKMET is also middle ground but it lacks a more robust shortwave to the south as seen in the ensembles. The 12Z CMC is also a reasonable solution near the ECMWF and its mean. ...Next embedded shortwave in Gulf of AK gyre, clipping NW Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z ECMWF/ECMWF mean Confidence: Slightly below average Ensemble spaghetti heights show the 12Z UKMET as a fast outlier with the trough axis clipping the Pacific Northwest Monday night. The 12Z CMC also appears a bit fast while the 00Z NAM/GFS appear slow. Overall trends in the ensembles over their past four 12/00Z cycles support some slowing valid Tuesday morning which would leave the faster guidance out of the preference. While there is some potential for further slowing, prefer to stay toward the middle or the 12Z ECMWF/ECMWF mean. This solution is also consistent with other systems downstream across the CONUS. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto