Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 116 PM EDT Thu Jun 11 2020 Valid Jun 11/1200 UTC thru Jun 15/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Preliminary Model Evaluation Including Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Trough amplifying across the East... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Average Three distinct shortwaves will dig into the East from Canada, each one reinforcing the trough which is likely to become anomalously deep by Monday. Through the first 60 hours, the spread in intensity and position of these shortwaves is minimal, so a general blend seems reasonable. However, late D2 into D3, Saturday into Sunday, the most robust shortwave begins to slide southeast and will eventually close off atop the Ohio Valley. The NAM is a clear outlier during this evolution as it sharpens the trough well west of the global consensus leading to a closed low too far west, and enhancing QPF into the Appalachians. While there is some east-west spread in the position of the trough axis and closed low by D3, notably the ensemble means being a bit east of the deterministic solutions, the spread for D3 seems within tolerance and the remaining guidance can be included in the preference. ...Longwave trough off the West Coast and shortwave lifting onshore California by the weekend... ...Closed low developing across the Northern Rockies Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM through 48 hours, ECMWF/ECENS/GEFS/UKMET thereafter Confidence: Slightly Below Average Closed low positioned off British Columbia will spin nearly in place through Friday, while a shortwave rounding the base of the longwave trough extending south from the BC closed low will lift onshore CA late Friday. The NAM is by far a slow outlier with the eastward ejection of this shortwave, lagging the consensus and all other available guidance too much to be included in the blend. Thereafter, the evolution becomes messy. The shortwave lifting from CA into the Great Basin will encounter progressively greater shear as the BC low begins to dig southeastward towards WA state. The NAM, which was already slow, is much too strong with this feature so continues to be removed from the blend. By late D2 into D3, the GFS produces a pronounced jet streak rotating around the BC low. While a jet streak development seems likely, the strength of this feature is much stronger on the GFS than any other guidance, which allows for better upper ventilation and a stronger surface low, mid-level impulse, and heavier QPF. The GFS then closes off a low well north of the CONUS border, vastly different from the non-NCEP camp, and much further north than its own ensemble mean. While there are some discrepancies into the amplitude of the trough in the NW into D3, the remnants of the opening BC low, the non-NCEP guidance is well clustered overall to the ECENS/GEFS means. The CMC may be a bit strong with the remaining energy, so after D2 the preference changes to the 06Z GEFS with the 00Z ECENS/ECMWF/UKMET. Weiss Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml