Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 241 AM EDT Fri Mar 16 2018 Valid Mar 16/0000 UTC thru Mar 19/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation including model preferences and forecast confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Deep cyclone over the Northeast U.S. and eastern Canada with digging shortwaves from Hudson Bay region wrapping through south side of the cyclone with gradual shift to the east By Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend Confidence: Above Average Deep, occluded currently centered near Ile d'Anticosti will continue to fill and wobble northward as a weak shortwave moves through the base of the broader cyclone across the Mid-Atlantic today. Eventually, a strong pool of cold air and northwesterly flow over eastern Nunavut plunges south with a strong shortwave eventually replacing the center/focus of the larger scale vortex over SE Canada (clipping northern New England) Sunday. Model guidance as come into stronger agreement in timing/shape of this upstream stronger wave with exception of the 12z CMC. The 12z CMC while better than prior runs remains a less intense with higher heights and is slightly displaced to the north and west to the otherwise very tight clustering presented by the 00z GFS/NAM and 12z ECMWF/UKMET and their counterpart ensemble suite. As such will favor a non-CMC blend at Above average confidence. 07z update: The 00z CMC trended slightly toward consensus but remains enough of an outlier that it's removal strengthens confidence in the blend. As such a non-CMC blend is preference at above average confidence. ...Negative-tilt shortwave ejecting into the Central Plains by Friday with associated strong surface cyclogenesis...Deamplifying through Ohio Valley and Carolinas this weekend... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z GFS/ECMWF/UKMET blend Confidence: Slightly Above to Above Average Goes-W WV depicts a strong shortwave at the base of the larger scale western trof beginning to take more of a negative-tilt orientation as it tracks through the four-corners currently. A lee cyclone is beginning to rapidly deepen across SE CO/SW KS at this moment as well. Guidance continues to evolve this wave into a compact banded stacked system under the upper-level diffluent pattern aloft across KS by midday today. Eventually, riding into the larger scale ridge over the MS River Valley, the system quickly breaks down and shears into the westerly flow. Guidance has been trending toward a common solution with a lead weak piece of energy leading the main core through the Ohio Valley and eventually Mid-Atlantic/Carolinas Sat. The NAM which had been a faster solution has slowed with the 00z run, however, typical negative bias of the NAM shows a more robust vorticity center with the remaining inner core/upstream wave through the Ohio Valley Sat. This leads it to delay even further than the slowest other solutions (12z CMC). The 00z GFS continues to converge with the 12z UKMET/ECMWF solutions with respect to the wave elongation as well as the depth/timing and placement of the surface wave; enough so to continue a 00z GFS and 12z ECMWF/UKMET blend. Confidence remains slightly above average as well in this blend preference. 07z update: The 00z CMC remains generally weaker than the UKMET/ECMWF (which show little change from the 12z runs) or the GFS. It's inclusion would offset the stronger 00z NAM...so either a general model blend OR blending the 00z GFS/ECMWF/UKMET should suffice at slightly above to above average confidence overall. ...Northern peripheral shortwave across S Canadian Rockies that rotates to Vancouver Island late Saturday and then consolidates and stalls just off WA/OR coast Sun/Mon... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z NAM/UKMET and *12z* ECMWF blend Confidence: Slightly Below average Goes-WV and Radar Mosaic depict center of elongating shortwave feature across S Alberta at this time. Guidance is fairly confident in a retrograde across central BC over the next day or so around the northern periphery of the larger scale vortex. By late Sat into Sunday, the wave will consolidate again near/along the western coast of Vancouver island and settle south toward the WA coast. The 12z CMC is a bit more aggressive in drawing the wave south with stronger ridging developing to the north. The model spread begins to increase as the main vortex breaks down as well as the approach of a stronger/more compact closed low from the Central Pacific advances east; and by midday Sun the system either begins to shift south or begins to elongate E-W in between the two systems. The 12z ECMWF/00z NAM are a bit more progressive south while the GFS and the UKMET hang back and stretch. Ensembles support there respective operational runs, however ensembles supporting a slightly slower central Pacific wave would shift favor slightly to the progressive solutions. As such an 12z ECMWF and 00z NAM blend is favored slightly over a general model blend; confidence is average in this preference over the general model blend. 07z update: The 00z ECMWF made a sizable shift/change, dramatically slowing on Sunday and becoming more influenced by the approach of the central Pacific closed low, shearing toward it on Monday well north of even the GFS. While it is supported closely by the recent 00z CMC, the reason for this shift appears to be related to an over amplification of a vorticity center well north of Vancouver island emerging from the central BC coast. This seems a one-off error well separated from the 12z ECENS members. The 00z UKMET offsets this shift by trending faster as a compromise between the faster NAM and middle ground (GEFS supported) 00z GFS. Will continue to favor a 00z NAM/UKMET blend with the 12z ECMWF included for this feature. Confidence is reduced to slightly below average. ...Core of large scale deep layered cyclone off OR coast enters CA/NV Sat/early Sunday before swinging strong height-falls into negative tilt trof through central Rockies with associated strong lee sfc cyclone early Mon in Southern Plains... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General Model Blend Confidence: Above average Goes-W WV depicts a deep layered cyclone centered off the OR coast at this time with an upstream shortwave near the Queen Charlotte Islands. This pair will go through a binary interaction...with the main center slowly drifting across N CA into NV by Sat with the upstream s/w descending in latitude paralleling the coast. As the main center translates east into the Great Basin, it weakens slowly deferring to the strengthening s/w rounding its base Sun into the four corners region. The wave then goes negative tilt early Monday and spurs strong lee cyclogenesis in SE CO shifting to OK by the end of the period. The 00z trended ever so slightly slower and while still a tad stronger in depth through the evolution joins the remarkably strong clustering in timing and evolution of the system anchored by the 12z ECMWF/UKMET and CMC as well as the 00z GFS and its prior run(s). While the NAM is agreeable in mass fields there are issues with respect to the placement of convective initiation and QPF (please refer to QPFPFD for additional details). Still all considering above average confidence could be afforded in a general model blend. 07z update: Little variation from the 00z non-NCEP guidance, as well as the 00z GEFS Mean...as such will keep highest confidence in initial preference. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina