Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 151 PM EST Mon Jan 29 2018 Valid Jan 29/1200 UTC thru Feb 02/0000 UTC ..See NOUS42 KWNO (ADMNFD) for upper air ingest status... 12Z final model evaluation with preferences/confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Evolving long wave trough over the Eastern U.S. by Tuesday Surface low evolution offshore the Mid-Atlantic/New England ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 29/12Z GFS/UKMET...29/00Z EC Mean Confidence: Average Some subtle yet still important differences linger over the surface response out over the western North Atlantic and the resulting impacts along the coast. The 29/00Z ECMWF ensemble members were more amplified and a bit faster than the GEFS and the operational ECMWF/GFS with the first piece of energy moving through the northern stream trough by 30/12Z...and then holds the trough back a bit more as a second piece of shortwave energy moves through some 12 to 18 hours later. Given satellite presentation and raob sampling...think that the second piece of shortwave energy may be handled better by the 29/12Z GFS/UKMET and 29/00Z ECMWF ensemble mean. The operational Canadian and the NAEFs still looked to be too weak with the wave amplitude by 30/12Z. While these differences exist...the overall clustering has improved over the past few runs. Low over Canada moving eastward and impacts in northern U.S. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 29/12Z ECMWF/GFS blend Confidence: Average The GFS has had a tendency to wrap up the system too much as it moves across Canada over the past few runs. The 12Z run also looked to be too strong...deepening the surface low to 981 mb which was some 4 to 7 mb deeper than other operational and ensemble forecasts valid at 30/21Z. The result was lower surface pressures along the international border. The GFS placement was pretty well supported. Given good run to run consistency for the UKMET and ECMWF at 12Z...a blend of the 12Z ECMWF and GFS should work for position...although hedging somewhat towards the ECMWF would help mitigate differences in strength at the surface and aloft. Spaghetti plots of mid level heights showed good clustering...with the exception of the NAEFs which ended up having a few members which were strong/fast outliers. Shortwave approaching the Pacific Northwest late tonight and movinng inland through Tuesday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model compromise Confidence: Above average A large area of low pressure...aloft and at the surface...near 50N 145W this morning will be filling as it approaches the west coast of North America later tonight or early Tuesday morning. Shortwave energy aloft accompanied by a surface cold front is expected to pivot around the southern periphery of the large upper low and affect the Pacific Northwest from later tonight into early Tuesday. Model agreement was good with the overall scenario. Think a general model compromise will take care of any minor differences pertaining to strength or position. Bann Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml