Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 113 AM EDT Tue Mar 27 2018 Valid Mar 27/0000 UTC thru Mar 30/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z NAM/GFS evaluation...including preliminary preferences ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Southern stream portion of trough in the West, moving to the Plains by Wednesday... ...Surface low tracking from the middle Mississippi valley Thursday morning to the Northeast Friday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS/12Z ECMWF/12Z UKMET blend Confidence: Average Synoptic scale trends with the shortwave have been generally a bit slower compared to yesterday through Thursday, but the 12Z CMC looks slowest and has the least ensemble support. The 00Z NAM is fastest to move the shortwave out to the east, with the 00Z GFS, 12Z ECMWF and 12Z UKMET in between the slower/faster models. The 00Z GFS has been consistent but faster, while the 00Z ECMWF has also been consistent but slower. The UKMET has been less consistent and jumping around between the faster and slower solutions. At the surface, ensemble scatter low plots are widely scattered and show hardly any support for the 00Z GFS surface low as it tracks into the Northeast, but little support for the 12Z ECMWF and 12Z UKMET as well. Given the broad support of the 00Z GFS, 12Z ECMWF and 12Z UKMET in the middle of the ensemble spread regarding 500 mb heights, a GFS/ECMWF/UKMET blend is the preference for now. ...Northern stream trough currently over the north-central U.S., lifting northeastward into eastern Canada by Wednesday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average The models show similarly with this system. ...Closed upper level low and associated surface low in the western Atlantic, located south-southeast of Nova Scotia today... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non-12Z CMC blend Confidence: Average Some minor differences remain with the mid-level height evolution of this system by late Wednesday and ensemble scatter lot plot spread remains large from south to north, trends since yesterday with the surface low have been north. Only the 12Z CMC remains south, so given trends and better deterministic agreement, a non-12Z CMC blend is preferred for this system. Differences are largely offshore into the Atlantic. ...Shortwave digging into the Northern Rockies Tuesday and the northern Great Plains Wednesday... ...Surface low developing over Alberta and Saskatchewan Tuesday with trailing cold front reaching the north-central U.S. Tuesday Night and Great Lakes Thursday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model Blend Confidence: Slightly above average The models show similarly with this system. ...Mid-level shortwave forecast to move into the Northwest late Thursday or Friday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS...12Z CMC blend Confidence: Below average Ensemble spread is large and run to run continuity is poor from the deterministic guidance which lowers confidence. However, trends have been faster and trying to stay in the middle of the latest spread is nearest the 00Z GFS and 12Z CMC. The 00Z NAM is much flatter and faster with the shortwave, while the 12Z ECMWF is slower and sharper, with these two models roughly representing the ends of the spectrum. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto