Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 309 PM EDT Wed May 30 2018 Valid May 30/1200 UTC thru Jun 03/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z model evaluation including preferences and forecast confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...System moving across upper MS Valley tonight to the upper Great Lakes Thu. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z GFS/NAM/ECMWF blend Confidence: Slightly above average Upper trough crossing the northern Plain today moves east across the upper MS Valley tonight into the upper Great Lakes and then into Ontario Thu, when it merges with post tropical Alberto (see section below). There are slight timing and phasing differences but better clustering than there was yesterday. Agreement is good on the frontal wave gradually strengthening as it moves northeast across Ontario. As a result of the improved clustering a consensus based approach can be taken to resolve remaining differences in low pressure/frontal timing/intensity. ...post tropical Alberto... ~~~~~~~~~~~~~~~~~~ Preference: Non-UKMET model blend Confidence: Above average The 12z UKMET remains a bit deeper and slower than the 12z GFS/NAM/ECMWF/09z SREF Mean in tracking the post tropical Alberto circulation across MI into Ontario. The ECMWF/GFS/NAM cluster well so a blend among these solutions would resolve small detail differences. The circulation is forecast to merge with a frontal wave up in Ontario. The trailing cold front crosses the Great Lakes and Ohio Valley, with the section below discussing the future evolution. ...Shortwave crossing the Great Lakes/Ohio Valley Thu to the lower Lakes Fri/central Appalachians Fri and to Mid-Atlantic into Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 09z SREF Mean/12z GEFS Mean/UKMET blend Confidence: Average A broad 700 mb northern stream trough crosses out of the MS River Valley on Thurs and across the upper Great Lakes and Ohio Valley Thu night and lower Lakes and central Appalachians Fri. The models have generally good agreement with weak areas of low pressure within a wavy front centered in the Ohio Valley Fri. The models are signaling that east of the Appalachians a closed low forms at 700 mb and possibly a wave on the surface front becomes a closed low. The NAM and GFS are further north with the development. The previously further south ECMWF has trended north towards the NCEP models, so there was a lessening of the spread. The ECMWF/Canadian solutions have the low a little further offshore by 00z Sun. Confidence has become average given the lessening of the overall spread/ensemble uncertainties. ...Mesoscale Convective System across KS/MO/OK Wed into Thurs... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z GFS/12z GEFS Mean/12z ECMWF blend Confidence: Average A lee trough in the high plains from eastern CO and NM that crosses KS/OK/TX tonight into MO Thu is responsible for convective development tonight into Thu. The 12z CMC has amplified the wave to better match the other models/ ensemble means. The NAM seems to retain a stronger wave into the mid-MS valley which is likely part of a later time frame negative NAM bias. A blend of the 12z GFS and 12z ECMWF/12z GEFS Mean blend will be favored. ...Amplified trough moving into the West Thursday, ejecting into the Plains with surface waves in the Northern High Plains/Dakotas & E CO/KS late Fri into Canada Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z NAM/12z GEFS Mean/09z SREF Mean/12z ECMWF blend Confidence: Average A 500 mb trough moves onshore this afternoon in the Pacific northwest and inland Thu into the northern Rockies , followed by the northern Plains Fri night and Saturday. Surface low pressure develops in ID in response to the wave and moves into MT. A second low develops near the MT/WY border and then moves across the Dakotas Fri night, with a consolidated low center moving north into Canada Saturday. The 12z GFS shows a more amplified and slower moving trough aloft and thus the surface low pressure is a few hours slower. The 12Z GEFS Mean matches closely with the 09z SREF Mean/12z UKMET/12z NAM. The 12z ECMWF slowed down the low pace a few hours with the timing of low pressure moving north in Canada, and now clusters better with other models. Given better clustering among the 09z SREF/12z GEFS/12z ECMWF/NAM, a blend of this group is recommended. Further south, the models are in good agreement in developing another area of low pressure further south in the central Plains Fri night and moving this wave east towards the MS Valley Sat. Slight timing/phasing differences aloft lead to differences in the sea level adjusted pressure field. The UKMET is more progressive with the wave and is least favored. A blend of the 12z NAM/GFS/12z ECMWF/12z Canadian global would work given clustering of the frontal timing/development of surface low pressure with these solutions. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Petersen