Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1213 AM EDT Mon May 28 2018 Valid May 28/0000 UTC thru May 31/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z model evaluation including final preferences and confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Subtropical Storm Alberto... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: See NHC Forecast Nearest Guidance: 00z GFS or GFS/UKMET/ECMWF blend Much tighter clustering exists for Alberto including lifting north through AL, eventually the 00z NAM accelerates toward deeper height falls across the upper Midwest. The 12z ECMWF/ECENS mean are a shade east of the forecast track but the best proxy. The 00z GFS shifted a bit west and now appears to match the NHC forecast best through 72hrs; interestingly, this continues to make it the eastern-most within the GEFS solutions. The UKMET, while ideally on track is a few hours slower than the GFS and official forecast. The CMC is generally weaker and favors a westward track through the TN and Mid-MS River valley influenced by the western trof. ...Approaching northern stream shortwave and frontal zone across northern Great Lakes into New England Mon to Tues... ...Developing surface low southeast of Long Island by early Mon... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend Confidence: Above average The CMC continues to delay surface cyclogenesis off shore on Mon and aloft is reduced spacing between the northern stream digging trof and frontal zone clipping New England on late Mon/early Tues. As such would favor a non-CMC blend at above average confidence. ...Western U.S. closed low lifting into the northern Plains by Wed...associated lee cyclones/trof with eventual consolidation across MT/ND by Wed... ...Shortwave ejecting east across the central Plains into the lower Missouri Valley with surface wave in... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z GFS/12z ECMWF blend Confidence: Above average shifting to average by 30/12z. The guidance continues to show excellent agreement with the upper low as it begins to emerge from the Rockies on Tuesday into Wed. Convective upscale feedback seems to doom the 00z NAM a bit as the wave rotates around the parent circulation then accelerate east into the Central Plains and low MO river Valley too quick and much stronger than the remaining guidance. The 00z CMC is in a typical slowest position, and emerges at peak heating late Tuesday into Wed, leading to upscale growth as well leading it to be a bit more compact and show less connection to a much weaker Alberto circulation lifting north. These combining streams are more aligned in the UKMET/ECMWF and 00z GFS, though the UKMET may be a bit too weak with the remaining energy into the Northern Red River valley by late Wed into Thursday. While the overall differences may be small enough to support a general model blend, a 00z GFS and 12z ECMWF/UKMET blend is preferred at this time at above average confidence early but shifting to average toward Wed/Thursday when there is more uncertainty with combining streams. ...Longwave trof amplifying south into Pacific Northwest by Wed, reinforced near OR/CA border Thurs... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z GFS/12z ECMWF blend Confidence: Average Cycle to cycle ensemble spaghetti analysis shows an agreed upon trend toward earlier height falls across northern Vancouver Island late Monday into Tuesday which broadens the trof and leads to earlier yet sharper wavelength generally going negative tilt into the Pacific Northwest by Wed. The 00z NAM is even faster with the lead height falls compared to remaining guidance/ensembles supporting a deeper broader trof along the West Coast by Thursday but also retains the compact inner core of the upper low over N Vancouver Island...which would fall into typical late period NAM negative bias. The 00z GFS and 12z ECMWF show similar evolution and match the overall trends noted in the ensemble suite, including the interaction with the subtropical feed at the base of the digging trof which has been a point of disagreement at times. The 12z UKMET looks similar and has good timing but as is typical may be a bit more amplified toward a closed low/concentric circulation at the base of the trof on Thursday. The 12z CMC is too slow in the northern stream and much too strong across BC/Alberta by Thursday as well to include it. As such will favor a 00z GFS and 12z ECMWF blend at 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 Gallina