Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1231 AM EDT Fri Jun 12 2020 Valid Jun 12/0000 UTC thru Jun 15/1200 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 00Z Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Trough amplifying across the East... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average A the start of the forecast period, a fairly dry average long-wave trof sits across Ontario/Quebec with the moisture stream/frontal zone displaced along the Coastal Carolinas. As the trof matures and the core moves off toward the Labrador Sea, the positive tilt base will swing through the Northeast under little fanfare/model difference. Upstream jet energy/shortwave will dig through the Great Lakes on Sat into the Upper Ohio Valley/Central Appalachians, eventually building to the greater model uncertainty; aligned with typical model biases. The 00z GFS/NAM and lesser so, 12z UKMET are faster toward evolution and a more compact/symmetric closed low by late Sunday, while the slower to evolve ECMWF/CMC are flatter and progress Southeast of the higher terrain toward the lingering frontal zone/moisture axis through the Piedmont region of the Carolinas/Virginia. The latter, being weaker but closer to the moisture, produce convection a but east relative to the stronger but more distant drawing of the GFS/NAM. A compromise between the camps is preferred as both seem established in their inherent biases. Confidence is average given no one solution provides the ideal placement of the forcing/instability and moisture elements and a blend of all the models will smear the sensible weather elements. ...Longwave trough off the West Coast and shortwave lifting onshore California by the weekend... ...Closed low developing across the Northern Rockies Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-GFS blend Confidence: Slightly above average GOES-W WV suite depicts a closed low to the NW of Vancouver Island pressing east with a shortwave feature lengthening the long-wave trof southward as it approaches the SW/OR/N CA coast. The shortwave will move full-bodily into N CA tomorrow, with the closed low drifting east. The models are in good agreement in the evolution and timing of the closed low, but the 00z GFS continues to snap the base shortwave northward through the US Rockies into the S Canadian Rockies much to fast. This leads the developing surface wave to be tucked tight to the terrain and well west of the best overall ensemble cluster, including the bulk of the GEFS members. The faster evolution also allows for the wave to be favorably located in the upper level jet pattern, to further deepen/strength relative to the other guidance. Eventually, the inner core of the upper-low will swing through the Pacific Northwest under the preceding shortwave, even though the GFS is not solid with the preceding wave, the core is still ok as it swings negative tilt through the Northern High Plains early Monday, providing confidence in the overall progression. As such a non-GFS blend is preferred at slightly above average confidence. ...Approaching closed low to the Pacific Northwest by early Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~ Preference: 00z NAM/12z ECMWF blend Confidence: Average On the heels of the binary interaction across the Pacific Northwest/Northern Rockies in the late weekend, another shortwave will progress along the Aleutian chain into the Gulf of AK by Sunday. The 00z GFS and 12z UKMET are in typical faster positions within the guidance suite, which eventually leads to earlier and therefore further west positioning of the wave as it becomes a closed low late Sunday into Monday. The NAM/ECWMF and CMC all press eastward and slower to occlude, leading to the model spread. Overall, it is not large (with exception to the placement of the surface low), but the onshore flow/moisture flux is fairly agreeable with the exception of the CMC which is uncharacteristically wet across the West Coast by the end of the short-term forecast period (84hrs). Think the timing issues favor the the slower evolution, so will favor a 12z ECMWF/00z NAM blend though some incorporation of the GFS/UKMET seems plausible to account for some of the remaining uncertainty, but generally avoided the CMC in QPF. Confidence is average in this blend Gallina Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml