Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 317 PM EDT Tue May 29 2018 Valid May 29/1200 UTC thru Jun 02/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z model preferences with confidence intervals ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ NAM/GFS initialization errors to not seem to degrade their short range forecasts. System moving across Plains Tonight to the upper Great Lakes Thu ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Model blend of the 12z NAM/12Z ECMWF/12z Canadian global; confidence average The models forecast a 700 mb trough over the northern to central Plains tonight to move slowly east out of the Plains and become negatively tilted as it moves into the upper MS Valley Wed night and upper Great Lakes Thu, when it merges with the remnants of Alberto. The NAM/GFS/Canadian and ECMWF have a similar amplitude with the 00/12z UKMET forecasting surface low pressure developing further north than the other models. This makes confidence in the 00z/12z UKMET lowest. Timing and phasing difference develop Wed night - Thu, with the GFS low pressure the slowest to move out of the upper MS Valley across Lake Superior. The 12z GFS trended a bit faster so it is closing the gap with the other solutions. Prefer a compromise of the 12z ECMWF, 12z NAM and 12z Canadian Global with average confidence. Subtropical Depression Alberto ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z NAM/HMON Hurricane Model/Hurricane WRF; confidence slightly above average The 06-12 NAM are tracking the circulation center well. The models are in decent agreement tonight into Wed. On Thu the GFS weakens and moves the low further west than other models. The Hurricane WRF and HMON hurricane model track nicely with the NAM, while the ECMWF and UKMET have a similar track, but a few hours slower. Given the 12 NAM agrees well with both continuity and the 2 hurricane models, more weighting can be given to the 06-12z NAM runs than other models. See the latest advisory from the Weather Prediction Center for more forecast information about Alberto. Amplified trough moving into the West Thursday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12z ECMWF/12z NAM/12z UKMET; confidence slightly above average The models forecast the next 700 mb wave to come onshore in the Pacific northwest around 00z Wed, with the trough drifting slowly inland and splitting on Fri, with the northern stream portion crossing the northern Rockies on to the northern Plains. The models handle these systems and resultant low pressure development in the Plains fairly similarly, with typical timing/phasing differences developing Fri. A compromise of the 12z ECMWF, 12z NAM, and 12z UKMET is preferred with slightly above average confidence. The 12z gfs is a few hours slower with both the 700 mb wave moving east from the Rockies and low pressure developing over the northern Plains Fri. The southern stream portion digs south across CA and may even slightly retrograde into the Pacific Ocean west of southern CA. The model agreement is good here, lending the situation to a consensus based approach. The 12z UKMET became an outlier by moving the 700 mb circulation faster west by 00z Sat. Central and Southern Plains to mid MS Valley potential shortwave Wed-Thu ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z ECMWF/12z UKMET/12 GFS Model blend; confidence slightly above average The models differ on the evolution of a potential wave that forms in the lee of the CO/NM Rockies and then moves east. The NAM has a higher amplitude 700 mb wave than the GFS/UKMET/Canadian Thu, likely as a result of latest heat release from convection as the wave crossing NE/KS into MO. The NAM is also faster than the model/SREF Mean majority so has the lowest confidence. A compromise of the 12z UKMET, 12z ECMWF, 12z GFS and 12z Canadian is preferred for mass fields with slightly above average confidence. See WPC Quantitative Precipitation Forecast discussions for information on the precipitation forecast. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Petersen