Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1239 AM EDT Thu Mar 15 2018 Valid Mar 15/0000 UTC thru Mar 18/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation including model preferences and forecast confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Evolution of deep cyclone over the Northeast U.S. and eastern Canada breaking down Sat as digging shortwaves from Hudson Bay Region wrapping through south side of the vortex Thurs/Fri with the last on Saturday becoming dominant within the vortex shifting east finally on Sun... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General Model Blend Confidence: Above Average thru 16/06z...Average thereafter Current setup depicts older center filling across the St. Lawrence Seaway as the newer deep center rotates out of New England with the new coastal surface low toward eastern Nova Scotia midday Thurs and becoming the dominant center over far E Quebec by early Friday. Models are in excellent agreement with this evolution enough to support above average confidence in a general model blend through 54hrs (06z Friday). This agreement includes a broad shortwave emerging from the Hudson Bay region crossing Northeastern US Thurs and Fri. Model consensus thereafter begins to break down a bit with the approach of strong Arctic stream shortwave energy which ushers in cold air advection across James Bay Sat and into far northern New England late Sat into Sun. The main difference is related to the timing and breadth of the wavelength itself. The 12z ECMWF/UKMET both a bit faster and broader with the wave as a whole; while the 00z NAM/GFS are lagging a bit more consolidated...leading to the focus of the cold air to be a bit further north than the ECMWF/UKMET respectfully. The 12z CMC favors the timing of the GFS/NAM though is a bit weaker overall. The Ensemble suite is not particularly helpful in determining a preference as each suite supports its operational run. Given the model spread is modest after 54hrs in New England...will favor a general model blend with slight increased weighting toward the GFS/GEFS and slightly reduced confidence to average overall. ...Amplified Trough Along the West Coast with Closed Low Pushing into the Northern Intermountain West by Saturday and breaking down into smaller peripheral waves by Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z GFS/12z ECWMF blend Confidence: Slightly Above Average Goes-WV mosaic depicts a large scale vortex dominating the northeastern Pacific into the West Coast and Intermountain West. The base of the trof will continue to sharpen and go negative tilt breaking from the mean trof by Fri. This wave is discussed in detail in section below; with the remaining internal shortwaves and slow weakening of the mean vortex covered in this section. WV loop shows the leading height falls currently over S ID heading toward N ID/W MT along with the main inner core/closed low just west of Vancouver island near 134W. The deterministic guidance has been trending toward a common evolution/strength and timing with both features nearing the ensemble mean trends as well. The 00z NAM continues to be slightly stronger with both features but the lead shortwave in particular continues to be a stark outlier in depth which continues as the wave begins to rotate back west over the main pivot of the vortex toward S BC/Vancouver Island by Sat. becoming the dominant feature in the remaining vortex by Sun. The 00z GFS/12z UKMET both support a stronger manifestation of this energy compared to a weakening ECMWF/ECENS solution. The inner core descends along the central West Coast Fri with the base unfolding south by early Sat which eventually shifts east with a developing surface wave through NV into central UT by Sunday. Here the 12z UKMET shows some slightly faster but more importantly much deeper manifestation than the ensemble suite and GFS/ECMWF. Timing of the 00z GFS was a bit slower and more amplified than the 18z run, and while deeper than the ECMWF and becomes better timed with it. The 12z CMC is generally broader and more symmetric with the vortex as a whole on Fri/Sat and as the vortex begins to break down into the outer periphery waves the timing of these waves are much slower overall and become clear departures from the rest of the guidance. As such will favor a 00z GFS and 12z ECMWF blend to best represent the ensembles and continuity. Confidence is slightly above average given the solid agreement even though it is such a large system with internal smaller scale differences. ...Negative tilt shortwave ejecting into the central Plains by Friday with associated strong Plains surface cyclogenesis...Deamplifying through Ohio Valley by Saturday and Mid-Atlantic/Carolinas late Sat/early Sun... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z GFS and 12z ECMWF/UKMET blend Confidence: Average Goes-WV mosaic depicts a large scale vortex dominating the northeastern Pacific into the West Coast and Intermountain West. While a strong vort rotates north through ID/W MT tonight into tomorrow...the focus shifts to the trailing s/w energy starting to reach the base of the trof over S CA at this time. This wave presses east across S UT/CO into early Fri with a solid negative tilt. This spurs rapid surface cyclogenesis across SE CO into KS Fri...rapidly occluding in the process. Here the 12z CMC has broken away from the general consensus focusing the inner core of the deeper vortex further northwest...which continues to keep it slow and lagging as the mid-level wave elongates/shears through the base of the larger scale ridge into the Ohio River Valley by Sat. Through the shearing process into the Ohio Valley, the 00z NAM and GFS both continue to be slightly more progressive than the UKMET/ECMWF...manifesting more toward later periods, in the Mid-Atlantic/Carolinas. Also the 00z NAM continues to be a bit stronger as well...perhaps a bit too much given the overall pattern. Still the spread/timing and strength are fairly tight with these 4 models respective of the ensemble suite and moving through the base of the ridge itself. A blend of the 00z GFS along with the 12z ECMWF/UKMET seems a prudent solution with increasing confidence though it remains average 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 Gallina