Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 243 AM EDT Fri May 01 2020 Valid May 01/0000 UTC thru May 04/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation Including Final Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Deep trough/closed low impacting the East through Friday and early Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average ...07Z update... Only minor timing differences remain with this system but agreement is now sufficient to support a general model blend. ...Shortwave/surface low tracking near the U.S./Canadian border through Sunday night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS/ECMWF/UKMET blend Confidence: Slightly above average ...07Z update... The 00Z ECMWF/UKMET did not make significant adjustments, but the 00Z CMC adjusted south. Therefore, the GFS/ECMWF/UKMET continue to be the favored middle ground. ...previous discussion follows... The 00Z GFS has backed away from its previous (12 & 18Z cycles) runs showing a more amplified 500 mb shortwave over Manitoba/Ontario Friday night. However, the 00Z NAM appears to be a northern outlier with the shortwave and surface low, with the ensemble scatter low plots supporting a non-00Z NAM blend. Regarding timing, the 00Z NAM/GFS are quicker to progress an associated cold front toward the south and east while the 12Z ECMWF/UKMET/CMC are slower. A blended approach is recommend at this time with differences becoming smaller by Sunday. ...700-500 mb shortwave reaching the central Plains Saturday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z NAM/ECMWF/UKMET blend Confidence: Slightly below average ...07Z update... No major changes noted with the 00Z ECMWF/UKMET/CMC compared to their 12Z cycles but the 00Z UKMET did adjust a bit stronger with the shortwave. The 00Z CMC remains weaker and will not be included in the preference. ...previous discussion follows... The 00Z GFS continues to look too amplilfied with this feature exiting the Rockies into the Great Plains on Saturday. Since yesterday, the latest ensemble guidance has trended toward the middle of the deeper GFS and flatter non-NCEP camp. Currenlty the middle ground is favored and that is between the 00Z NAM and 12Z ECMWF. The faster 00Z NAM may not be wrong given the zonal flow that sets up across the lower 48 in the wake of the departing East Coast trough axis. Convective uncertainty continues to lower confidence with this feature. ...Deep trough offshore the West Coast today and Saturday with remnant shortwave energy moving through the Northwest Sunday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non 00Z CMC blend Confidence: Average ...07Z update... Model differences are small enough through 00Z/04 to recommend a general model blend. However, the 00Z CMC adjusted south with the remnant shortwave trough across western Canada through 12Z/04 and stands out from the remaining deterministic/ensemble consensus. ...Potential mid-level shortwave reaching the West Coast on Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z NAM/12Z ECMWF mean/12Z UKMET blend Confidence: Below average ...07Z update... Some adjustments by the 00Z ECMWF/UKMET/CMC compared to their previous 12Z cycles with this feature included the UKMET trending slower/south. The 00Z NAM/12Z ECMWF mean and 12Z UKMET are considered the best compromise that favors a middle ground approach. ...previous discussion follows... While there are some differences among the deterministic guidance, most agree that a 500 mb shortwave will reach the northern CA coast Sunday afternoon or early evening. The 00Z GFS appears too fast and deep compared to the remaining available deterministic/ensemble guidance. The 12Z ECMWF and 12Z CMC are flat with this feature while the 12Z UKMET is faster/weaker and north. Ensemble means support somewhere between the somewhat stronger 00Z NAM and flatter ECMWF/CMC. Therefore, a blend of the 12Z ECMWF mean and 00Z NAM is preferred through the end of the short range period (12Z/04). Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto