Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 158 PM EST Sun Feb 04 2018 Valid Feb 04/1200 UTC thru Feb 08/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... ...12Z model evaluation with final preferences... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Shortwave tracking from the upper Mississippi valley into the Ohio valley today... ...Surface low tracking northeast from the southeastern U.S. today, strengthening along the New England coast through early Monday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models have converged since yesterday to a common idea with only minor differences noted in the latest guidance. A general model blend is preferred to smooth out any remaining differences. ...Weak 700 mb shortwave tracking across the central Plains into the Midwest on Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-12Z NAM blend Confidence: Above average The 12Z NAM is slightly sharper/deeper/slower with the 700 mb shortwave as it reaches the Mississippi valley near 00Z/06. The remaining deterministic/ensemble consensus supports a non-12Z NAM blend for this system. The remaining 12Z guidance continues to support a non-12Z NAM blend for this system. ...Mid-level shortwave crossing the Northwest today, with additional energy amplifying across the Four Corners region Tuesday evening and into the Plains on Wednesday... ...Northern stream shortwave crossing the upper Mississippi valley on Wed with ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z NAM / 12Z GFS / 12Z ECMWF blend Confidence: Average The 00Z/12Z UKMET is faster with the northern and southern stream shortwaves associated with this system, noted as early as Tuesday morning. The effect is for the front in the southern Plains to be displaced farther south in the 00Z/12Z UKMET compared to the remaining guidance. The 12Z CMC 850 mb low is less developed and displaced westward by 12Z/07. The 12Z NAM/12Z GFS and 12Z ECMWF are in reasonable agreement and are supported by the latest ensemble means. The 12Z ECMWF did shift faster with the northern stream wave and slowed with the southern stream wave relative to its previous run but the 12Z ECMWF is within the relatively tight ensemble spread which is minor aloft. Ensemble spread is modest at the surface. ...Shortwave approaching the Pacific Northwest late Wednesday night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z ECMWF/UKMET/CMC blend Confidence: Average The ensemble means are in good agreement and show the 00Z CMC is too fast with the shortwave forecast to near the Pacific Northwest 00Z/08 but the 12Z run slowed toward the better consensus. The 12Z ECMWF/UKMET/CMC are closest to the ensemble means while the 12Z NAM and 12Z GFS are slower. However, ensemble spaghetti height spread is large so confidence in this preference is only average given the 3 day time frame and potential for future changes in the guidance. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto