Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1237 AM EDT Tue May 29 2018 Valid May 29/0000 UTC through Jun 01/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z NAM/GFS evaluation with preliminary model preferences ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Any NAM/GFS initialization errors to not seem to degrade their short range forecasts. Shortwave moving across the Northwest late Tuesday Amplified trough moving into the West Thursday Downstream surface low pressure in the Plains ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Model blend; confidence above average The guidance handles these systems and resultant low pressure development in the Plains fairly similarly, within the noise of the ensemble guidance. A compromise of the 12z Canadian, 12z ECMWF, 00z NAM, 00z GFS, and 12z UKMET is preferred -- which helps deal with the UKMET's sharper upper trough -- with above average confidence. System moving across Plains/Great Lakes Tue-Thu ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-UKMET blend; confidence slightly above ave There are competing factors for this system's mid-level depth: A building upstream ridge (supporting a system on the stronger side of the guidance) and a building subtropical ridge rebounding to its south (which could lead to a weaker system). The 12z UKMET is most unique, merging this system with Alberto and creating a stronger system as a result. The 12z ECMWF uses convective feedback with Alberto to drag this upper trough more eastward than the other guidance, but at least it has the support of its 12z ensemble mean. A compromise of the 12z Canadian, 12z ECMWF, 00z GFS, and 00z NAM looks reasonable and is preferred with slightly above average confidence. Subtropical Tropical Depression Alberto ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-UKMET blend; see latest NHC advisory Beyond Wednesday evening, the 12z UKMET merges a few disturbances together to stall the combined system in Michigan, while the remainder of the guidance flies along, closer to the NHC forecast. Eventually the NAM outpaces the other guidance, but Alberto is well into Canada when this occurs. See the latest advisory from the National Hurricane Center for more about Alberto. Southwest to Plains shortwave late Tue-Thu ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: GFS/NAM/UKMET blend; confidence average The guidance brings a mid-level shortwave across the Southwest and develops a terrain-induced or a convectively-induced shortwave in the Rockies/central Plains Wednesday into Thursday. There is some timing spread, with the 00z GFS being quicker and 12z UKMET being slower. The 12z Canadian/12z ECMWF are the weakest with the system emerging into the Plains. With the degree of moisture and inflow available in the southern and central Plains, it appears that a stronger 700 hPa reflection would be preferred here, which is more along the lines of the 12z UKMET, 00z NAM, and 00z GFS. A compromise of those pieces of guidance is preferred with confidence no greater than average considering the lingering timing issues. See WPC Quantitative Precipitation Forecast discussions for more information on the precipitation forecast itself. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Roth