Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 231 AM EDT Sat Jun 13 2020 Valid Jun 13/0000 UTC thru Jun 16/1200 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 00Z Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Exiting trough across Mid-Atlantic to Northeast... ...Closed low developing in Southern Appalachians Mon/Tues... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-GFS blend Confidence: Slightly above average 07z update: The 00z ECMWF trended a bit weaker and therefore east, while the CMC/UKMET trended a bit west to further tighten agreement between this lot; and remaining south of the GFS and now a bit east of the NAM. So will keep with the initial preference of non-GFS at slightly above average confidence. ---Prior Discussion--- Lingering shortwave energy over the Lower Great Lakes will consolidate in the mid-levels later today into early Sunday and start to slide northeast into SE Canada by Monday, with little fanfare or model differences. The trailing edge of the longer wave pattern upstream across the Upper Great Lakes with a small 90kt NW-SE oriented jet will amplify into a small but compact wave through the Midwest later today and drop into the central Ohio Valley. Guidance has finally come into strong agreement with the placement/magnitude of the wave through 48hrs as it pivots/stalls in S OH/E KY/W WV, enough to have above average confidence in a general model blend through this period. Afterwards, the models spread as the wave exits the tight loop expanding into a broader closed low across the Southern Appalachians into the Coastal Plain of GA/SC. The 00z GFS is slowest to wobble out and draws stronger energy from the northern stream to delay this further, leading to an overall northward orientation to the rest of the global/ensemble suite. The 18z GEFS shows some closeness initially but by 84hrs is further south and closer to the ECMWF/NAM. The 12z UKMET/CMC are a bit east of the ECMWF/NAM but the evolution/placement and shape all suggest a non-GFS blend is preferable at slightly above average confidence. It should be noted that the 00z NAM is a bit strong with retrograding a low level wave through the Carolinas and tightening the overall low level flow for a strong QPF signal...this is likely over-inflated but given the model resolution and capability for resolving some mesoscale moisture/instability better than the global guidance...it should be incorporated but with some caution given the bias to over-strengthen systems especially in the late Day 2 to Day 3 period. ...Longwave trough off the West Coast and shortwave lifting onshore California by the weekend, interacting through Northern Rockies/SW-Central Canada Sunday-Tues... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-Nam blend, weight heavier to ECMWF/UKMET/CMC Confidence: Slightly above average 07z update: While the GFS remains on the western fringe of the solutions, all three non-NCEP guidance members trended closer to it, and left the more sheared, slower NAM out to the east. The 00z GEFS seems to split the difference between the GFS and the ECENS mean, providing more confidence toward a non-NAM blend. As such, will support a non-NAM blend but still weighting toward the non-NCEP guidance. ---Prior Discussion--- A tight shortwave is lifting north through CA at this time, along the eastern side of a closed low near Vancouver Island. The 00z GFS continues to be slightly faster lifting into SW Canada relative to the other guidance and in doing so finds a more favorable environment/position relative to the upstream closed low to rapidly deepen and become the dominant circulation in the binary interaction relative to the rest of the global guidance suite. T This doesn't seem to negatively affect the timing/strength of the remainder of the closed low as it swing around the base of the larger scale closed low, as well as, the eastward progression of the frontal zone into the Northern Plains where spread is small. Still the GFS is not generally favored outside of the CONUS, where a more elongated West to E sheared trof is preferred from the UKMET/ECMWF/NAM than the more compact CMC, but only in weighting within a non-GFS blend. Confidence is slightly above average. ...Next closed low/embedded shortwaves entering Pacific NW Mon-Tues... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average 07z update: The alluded shift toward a faster solution, depicted in the GFS/UKMET/NAM was followed by the ECMWF and lesser so the CMC. As such a general model blend can be preferred with equal weighting and increased confidence to slightly above average. ---Prior Discussion--- Upstream, a closed low is developing in the western Gulf of AK later today into Sunday, though remains fairly progressive in nature. There is a forecast slow down as the deeper cyclone occludes/wobbles west of Haida Gwaii/Charlotte Island. This will also allow for return subtropical shortwave energy to press eastward and bring solid DPVA into the Pacific NW by midday helping to broaden the larger scale pattern into a dual lobe global scale gyre from the eastern Gulf of AK through much of Western Canada (see system in above section). The typically faster solutions of the GFS/UKMET and NAM continue to trend faster but now suggest the main body of the wave will drop through the mouth of the Columbia River at 84hrs. This is opposed by the ECMWF/CMC which continue to lag and favor more of an amplification of the subtropical shortwave relatively speaking to the GFS/UKMET/NAM. The effects on QPF are actually minimal, though the mass fields are showing increased spread leading to increased confidence there, but lesser so on the mass field side. The faster trend has been noted through multiple cycles of the ensembles, yet this faster solution is also aligned with the general negative bias of these models relative to the ECMWF/CMC. So at this time will keep with more continuity over the trend, and prefer a higher weighting to the ECMWF/CMC; however, leaving the door open towards a potential shift with the new 00z ECMWF/CMC solutions. As such a general model blend is preferred but weighted more heavily toward continuity/ECMWF/CMC. Gallina Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml