Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1245 AM EDT Thu Jun 25 2020 Valid Jun 25/0000 UTC thru Jun 28/1200 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 00Z NAM/GFS Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Closed low over Ontario/Quebec Trough crossing the eastern U.S. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non 00Z NAM blend Confidence: Slightly above average The 00Z NAM/GFS are close to the consensus with the mid level closed low as it tracks from eastern Ontario into western Quebec, before slowing down and spinning over central Quebec through 28/12Z. However, the 00Z NAM appear to be too fast with its surface low crossing northern ME, while the 00Z GFS/12Z ECMWF show better clustering with the 12Z ECMWF ensemble mean (and the front that moves across the East Coast late in the period). Given the generally good clustering with the mid level and surface systems (outside of the 00Z NAM), forecast confidence is slightly above average. However, due to its faster surface solution, the 00Z NAM is not included in the preferred blend. Short wave crossing the Pacific Northwest and Plains/Midwest Long wave trough digging into the Southwest ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend for the northern stream short wave Non 12Z CMC for the long wave in the Southwest Confidence: Above average For the short wave energy tracking from the Pacific Northwest into the Northern Plains, the 00Z NAM/GFS are close to the consensus taking it across SD into IA/IL, as well as the surface low moving across Ontario. These solutions are close to their ensemble means, as well as the 12Z ECMWF Ensemble mean. Given the tight clustering, a general model blend is preferred. For the positively tilted long wave trough crossing CA after 26/00z, the 12Z CMC is too fast from the onset as it reaches the Southwest states by 28/12Z. Otherwise, there is good model clustering with this feature as well, so a non 12Z CMC blend is preferred with above average confidence. Strong shortwave trough over the Pacific Northwest this weekend ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average The 12Z NAM/GFS are close to the consensus taking short wave energy from the Gulf of AK across the British Columbia coast after 27/00z. Additional mid level energy dropping into the short wave position over British Columbia/Alberta causes the system to closed off over the Pacific Northwest toward the end of the period. By that time, the 00Z NAM/GFS are a bit faster than the consensus, but there is more spread in general throughout the model solutions. However, this cluster is not far from the 12Z ECMWF ensemble mean/GEFS mean, so the slightly faster solutions are not too fast not to include in a general model blend. Given the spread, though, forecast confidence is average. Lower MS Valley and Gulf Coast states ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average Though the 00Z GFS is a bit stronger with the short wave energy in the mid level flow across the region, it does have some support from the 12Z UKMET. Overall, there is fairly good clustering in the mid level flow (outside of weak impulses in the mid level flow that regional/global models cannot yet resolve) as heights fall across the Lower MS Valley and Gulf Coast states. Based on this, a general model blend is preferred, with slightly above average confidence. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hayes