Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 100 PM EDT Mon Apr 08 2019 Valid Apr 08/1200 UTC thru Apr 12/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Overall Pattern Across the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Exclusions: No 08/00Z NAM or 08/12Z NAM after 10/18z in Plains. Confidence: Slightly above to above average Deterministic and ensemble guidance continue to converge on a common solution in most of the streams/systems across North America, although the 08/12Z NAM continues to struggle with the evolution of the Plains system and the approach of more energy on Day 3. ...Great Lakes/New England (northern stream shortwaves)... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ GOES WV suite still denotes a highly arched shortwave trof with strong zonal jet beginning to bisect the wave. The 08/12Z NCEP numerical guidance continued the earlier trend with the left circulation stalling over Western Ontario through Tuesday before swinging through the Great Lakes into New England by Wednesday. Given the earlier move by the Canadian, a general model compromise is preferred at above average confidence for this stream/systems without excluding any model. ...Southeast (southern stream closed low)... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ GOES WV suite depicts a mature cyclone over parts of Louisian which has started to show signs that the weaken/filling process has begun. Guidance is agreement with slow stretching of the cyclone across the Lower MS Valley into Central Appalachians late Tues into Wed under influence of digging northern stream trof and increasingly progressive flow across the CONUS in the higher upper-levels. Given an overall convergence in the solution...in part due to the shift made by the Canadian overnight...felt a overall model compromise in terms of position will work, although the UKMET may be too strong. ...Approaching Western trof Mon/Tues, amplifying through Intermountain West by Wed spurring deep Plains cyclone, Wed into Thurs... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Guidance continues to show very good agreement in the timing of the shortwave that brings the end to the prolonged AR event across OR/N CA by midday Tuesday. As the shortwave, translates southeast, the ECMWF/CMC are generally a bit weaker though the CMC is a tad stronger further north than other guidance, which negatively plays into its evolution thereafter but does not affect the ECMWF evolution as much. The 08/12Z NAM/GFS and 08/00Z UKMET, in line with their usual bias, are a bit faster and earlier aloft to amplify the wave late Wed. The 08/12Z NAM trended a bit farther south than its previous run at the mid/upper levels, although the shift was not as much as the 08/12Z GFS. The shift of the GFS got it into somewhat better agreement with the 08/00Z ECMWF in terms of longitude but still a bit to the north of the 08/00Z ECMWF. A quick look at the 08/12Z run of the GFS FV3 showed to to be a decent compromise in both areas and had managed to capture the idea of a precipitation band over parts of Nebraska behind the surface low which the operational GFS did not show but was suggested by the 08/00Z ECMWF and 08/12Z NAM. ...Wed/Thurs Closed Low entering Pacific Northwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Closed low over the Northern Gulf of AK has been consistently progressive though with ensemble trends toward a stronger downstream ridge. Additionally, the approach of the next very strong jet further suggests a flattening/shearing of the shortwave energy through coastal BC into the Pacific Northwest by late Wed into early Thursday. Only the 08/00Z ECMWF was opposed to the magnitude of shearing, retaining a stronger/more concentric mid-level shortwave under-cutting the ridge. The 08/12Z NCEP runs had latched on to the flattening/shearing scenario. So still suggest excluding the ECMWF/CMC in this blend. Condifence here is average. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Bann