Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1119 AM EST Sat Jan 27 2018 Valid Jan 27/1200 UTC thru Jan 31/0000 UTC ..See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z model evaluation along with latest model preferences/confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Weakening shortwave crossing the western Gulf Coast today... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models handle the system similarly today through tonight as it moves east and dampens out with time. ...Shortwave trough/cold front over the Great Lakes/Midwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models show a northern stream shortwave trough crossing portions of the northern Plains and the upper Midwest through tonight and then crossing the Great Lakes region through Sunday. Model spread is rather minimal with this system, and so a general model blend will be preferred. ...Evolving longwave trough over the Eastern U.S. by Tuesday... ...Surface low evolution offshore the Mid-Atlantic/New England... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-ECMWF consensus Confidence: Average The models take a relatively weak southern stream trough out of the southern Plains and allow it to cross the Gulf Coast states through Sunday which will help to drive an area of low pressure along a cold front advancing into the Eastern U.S. Meanwhile there will be an intrusion of northern stream shortwave energy crossing the Midwest that will be digging southeast through the Ohio and Tennessee Valleys through Monday. The two streams will attempt to phase along the East Coast by later Monday and will likely lead to the development of a longwave trough over the Eastern U.S. that will take on a neutral to negative tilt. The aforementioned low pressure wave which will be over the Gulf Coast states should lift northeast and redevelopment over the Mid-Atlantic coastal plain Sunday night and then move offshore the Delmarva before then intensifying east of New England Monday night. The 00Z ECMWF and its ensemble mean are both well south of the model consensus offshore the East Coast. The 12Z NAM, 12Z GFS, 00Z CMC and 00Z UKMET are clustered north by comparison. Generally the ECMWF cluster is an outlier and will be dismissed for now. Thus a non-ECMWF consensus will be preferred. ...Large upper trough/closed low impacting the Northwest... ...Surface low near the U.S./Canadian border moving east... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS and 00Z ECMWF Confidence: Above average The models bring a robust upper trough into the Pacific Northwest by later Monday and Tuesday as a strong closed low wraps up over the Gulf of Alaska. The upper trough and associated cold front will move inland and cross the northern Rockies before then ejecting east across the northern Plains. A strong area of low pressure with this system will traverse southern Canada just to the north of the U.S./Canadian border. The 00Z UKMET appears to be just a tad too progressive, with the 12Z NAM and 00Z CMC a bit too slow. The 12Z GFS and 00Z ECMWF best approximate the model consensus and are well clustered, so will prefer a blend of these two solutions. ...Shortwave approaching the Pacific Northwest late Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM consensus Confidence: Above average The models allow another shortwave to approach the Pacific Northwest and adjacent areas of British Columbia by late Tuesday. The 12Z NAM is somewhat of a stronger outlier as the energy approaches British Columbia, with the remaining models pretty well clustered with timing and depth. Thus a non-NAM consensus will be preferred at this time. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 MB forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison