Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 245 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 model evaluation...including final 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/00Z ECMWF/00Z UKMET blend Confidence: Average Synoptic scale trends with the shortwave have been generally a bit slower compared to yesterday through Thursday, but the 00Z CMC continues to look too slow despite trending faster from its 12Z cycle. The 00Z NAM is fastest to move the shortwave out to the east, with the 00Z GFS, 00Z ECMWF and 00Z UKMET in between the slower/faster models. The 00Z GFS has been consistent and slower than the 00Z ECMWF which has trended faster compared to its past 3 cycles. The UKMET has shown better consistency with its 00Z and 12Z cycle nearly the same. 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 00Z ECMWF and 00Z UKMET as well, with perhaps the 00Z ECMWF closest to the better low clustering. Given the broad support of the 00Z GFS, 00Z ECMWF and 00Z UKMET in the middle of the ensemble spread regarding 500 mb heights, a GFS/ECMWF/UKMET blend is the preference at this time. ...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-00Z 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. The 00Z CMC has trended north with its surface low but remains toward the south of the other guidance. Given trends and better deterministic agreement, a non-00Z 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...00Z 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 00Z CMC. The 00Z NAM is much flatter and faster with the shortwave, while the 00Z UKMET is slower and sharper, with these two models roughly representing the ends of the spectrum. The 00Z ECMWF trended a tad faster compared to its previous cycle which appears to be a good move, but the 00Z UKMET trended in the opposite direction. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto