Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 233 PM EDT Tue May 05 2020 Valid May 05/1200 UTC thru May 09/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Model Evaluation Including Final Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...700 mb low tracking across the northern mid Atlantic to southeast New England Wed evening and into the offshore waters Wed night night-Thu... ...Surface low development over North Carolina Tue night and off the mid Atlantic coast Wed... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 06z GFS/12z ECMWF/12 NAM/00z Canadian global Confidence: Slightly above average The models show a 500 mb trough cross the Great Lakes and Oh Valley, with a triple point low developing over North Carolina and gradually strengthening as it moves off the mid Atlantic coast and just southeast of the 40n 70w benchmark. The 12z NAM/06z GFS/12z ECMWF cluster well so a blend of these solutions is preferred. The lowest confidence is in the 12z UKMET, as its 700-500 mb wave is not as amplified as the majority model/ensemble cluster, with even the ensemble means more amplified. ...Mid-level shortwave moving from Pacific Northwest Coast Tuesday night across the northern Rockies Wednesday night, northern Plains Thursday, then the MS Valley to Ohio Valley Friday... ...Cold front dropping southward through the Great Plains on Thursday and low pressure developing on the front in the OH Valley Fri... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 06Z GFS, 12z NAM, 09Z SREF Mean blend Confidence: Average The models indicate a deep layer trough moves onshore and cross the Pacific northwest, with an embedded 700 mb circulation that develops, moves across MT and then SD, then moves downstream into the mid MS Valley and Ohio Valley. The 12z UKMET and 12z ECMWF trended towards a slightly more amplified wave, in the direction of the NAM and SREF Mean. The models have good timing agreement as the 700 mb wave cross es the MS Valley and Oh Valley, but the NAM and particularly 12z GFS have a higher amplitude/shorter wavelength trough than the ECMWF/UKMET/Canadian global. The models occasionally have a bias of weakening closed lows too fast, so I would not dismiss the stronger NAM/GFS. Given the 12z GFS produces the strongest low pressure along the front in the Ohio Valley, preference is given to the slightly weaker 06z GFS run, which clusters better with the NAM. Since the Canadian/ECMWF/UKMET all trended towards the Nam and 06z GFS, those solutions were given more weighting. Petersen Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml