Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1245 PM EDT Mon Mar 26 2018 Valid Mar 26/1200 UTC thru Mar 30/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z NAM/GFS evaluation...Including preliminary preferences ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ***Due to ongoing NCEP data issues data in NAWIPS was unavailable. The 12Z NAM/GFS were evaluated in AWIPS2 where the UKMET is only available through 36 hours, so data beyond this time is excluded from this evaluation.*** ...Southern stream portion of trough in the West, moving to the Plains by Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS/NAM and 00Z ECMWF blend Confidence: Average Generally good agreement for the upper low/positively tilted trough over the desert SW as it fills crossing the four corners region through Tuesday then as it becomes neutrally tilted and in line with the northern stream down the center of the CONUS on Wednesday. A 12Z GFS/NAM/UKMET and 00Z ECMWF blend will work for the southern stream portion of the upper trough over the West. The 00Z CMC is much slower than the consensus with movement of this trough. Issues with progression with the 00Z NAM seems to be improved with the 12Z run. Progression of this feature in the 00Z ECMWF is very similar to the 12Z NAM/GFS. A blend of the reasonably similar 12Z GFS/ECMWF/NAM is most fitting. ...Northern stream portion of the trough in the West, kicking east into the Great Lakes Tuesday and Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non CMC blend Confidence: Average Minor placement and strength differences exist with a weak surface low near the Great Lakes Tuesday. Aloft, the 00Z CMC remains slightly slower than the remaining deterministic guidance. Better agreement is seen in the 12Z NAM/GFS and 12Z UKMET through 36 hours as well as the 00Z ECMWF. ...Slow moving closed low setting up in the western Atlantic, south-southeast of Nova Scotia today into Tuesday... ...Accelerated development of a surface low in the vicinity of Bermuda... ...Associated strong surface high settling into New England... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS/NAM/UKMET and 00Z ECMWF Confidence: Average The Atlantic low pressure system and northeast CONUS surface ridge are handled quite similarly through 36 hours in all but the 00Z CMC. Differences are minor until Wednesday morning at which point some latitude and strength differences develop with the closed low. ...Shortwave rounding a Pacific ridge through the Gulf of Alaska on Monday and digging into the Northern Rockies Tuesday... ...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: GEFS/ECMWF Ensemble Blend Confidence: Below Average The greatest issues are with the shortwave trough moving off the Gulf of Alaska toward British Columbia. There are similarities with the 00Z ECMWF and 12Z NAM. However, there are enough placement and intensity differences to recommend an ensemble blend approach and await the 12Z ECMWF. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Jackson