Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 303 PM EDT Fri Jun 12 2020 Valid Jun 12/1200 UTC thru Jun 16/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Final Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Trough amplifying across the East... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC with light weight on the 12Z NAM Confidence: Average 19Z Update: The 12Z ECMWF came much more in line with the consensus and previous blend with its evolution of the more compact shortwave forming into the upper low D3. The closed low position at the end of D3 is a bit further south on the ECMWF than consensus, but within the expected spread for D3 so can be added back into the blend. Only the CMC is much different with the leading shortwave, making it the dominant and driving weaker troughing across the east by D3. Otherwise, the globals can all be included in the preference. Previous Discussion: Multiple shortwaves digging across the east will amplify a longwave trough which will likely close off near the TN VLY by Monday. The lead shortwave which will rotate across upstate NY and then northeast into Canada Saturday night has generally good model agreement with its amplitude and evolution. The only exception is the 00Z/CMC which closes off this feature and makes it the dominant shortwave, closing it off near New England. This is unlikely and has no ensemble support, so is removed from the blend. Thereafter, only the 00Z/ECMWF is vastly different as it rotates two distinct perturbations through the longwave trough, while the remaining guidance depicts one more consolidated impulse. The consolidated idea has had the most continuity the past few days, so that combined with the better agreement suggests this is more likely. Due to the separate impulses, the ECMWF becomes out of phase with its shortwave ridge/trough pattern, and eventually closes off a low over the OH VLY, west and more slowly than the remaining consensus. On D3, the NAM trough axis is a bit west of the others, and closes off the low slightly further south which could impact QPF lifting into the Carolinas/Mid-Atlantic. Despite the spread being within the typical D3 envelope, the enhanced QPF as a result causes it to have a lighter weight in the preferences. ...Longwave trough off the West Coast and shortwave lifting onshore California by the weekend... ...Closed low developing across the Northern Rockies Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z Non-NCEP and 12Z NAM Confidence: Slightly above average Through 48 hours, Sunday morning, the global suite is very well aligned with the overall evolution of the shortwave lifting onshore CA and ejecting northeast as a longwave trough shifts towards the coast. After 48 hours, the GFS once again becomes strong and fast with this feature, likely in response to better ventilation aloft through the LFQ of a more robust just streak lifting around a closed low moving onshore WA state. This leads to a stronger surface low, higher QPF, and a more northerly closed low near the Canadian Rockies on Monday, which is well removed the deterministic consensus, and even well north of the GEFS mean placement. While there remains some uncertainty into how interaction with the shortwave lifting up from CA, and the weakening closed low advecting onshore WA will occur, the non-NCEP suite indicates the latter will remain dominant and lead to a weaker negatively tilted trough across the NW/Northern Rockies with zonal flow undercutting the feature to the east. While the NAM is a bit further north and more amplified with the end result, its evolution to get to that point looks otherwise within a reasonable spread and close to the GEFS mean, and can be included in the blend. This will also allow for some potential for a subtly more northern trough Monday should the leading shortwave out of CA be stronger than current progs suggest. Weiss Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml