Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1156 AM EST Sun Jan 05 2020 Valid Jan 05/1200 UTC thru Jan 09/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z NAM/GFS Evaluation with Preliminary Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Shortwave trough tracking across the Great Lakes/Northeast through late Mon... ...Weak surface low moving through southern Canada... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models show similarly with this system. ...Split-flow trough near the Pacific Northwest today... ...Energy reaching the Great Lakes/Northeast Tue/Wed... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z NAM, 00Z ECMWF and 00Z UKMET blend Confidence: Slightly above average As shortwave energy makes its way east into the Great Lakes region on Tuesday, There are differences with the handling of the 500 mb trough. The 12Z GFS is displaced north with the core of the base of the trough in the vicinity of western Ontario noted mid-day Tuesday. The 00Z CMC is displaced slightly south and slower than the remaining consensus. Fairly good agreement in the ensembles exists for a blend near the 12Z NAM, 00Z ECMWF and 00 UKMET. ...Southern stream trough/low near the TN Valley by Tue... ...Surface low impacting the Mid-Atlantic/Northeast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z NAM and 00Z ECMWF Confidence: Average While model differences are rather minor with this system, a modest amount of spread remains in the ensembles and run to run consistency in the guidance has not been great. The 12Z GFS stands out first with a faster 500 mb trough progression toward the East Coast, perhaps due to more separation in the flow with the northern component of the larger scale trough axis tracking through southern Canada. Among the non 12Z GFS guidance, specifically concerning the 850 mb low, from late Tuesday into Wednesday, the 12Z NAM is on the south side of the deterministic guidance while the 00Z ECMWF/UKMET/CMC are north. The 12Z GFS is also south like the NAM, but again is faster than ideal. A blend between the 12Z NAM and 00Z ECMWF is considered best for this system at this time, but adjustments in future cycles appear possible given the changes seen leading to today's runs. ...Shortwave/fronts approaching the Pacific Northwest Mon and Tue... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non 00Z UKMET blend Confidence: Slightly above average Yet another in a series of shortwave troughs will arrive across the Pacific Northwest late Monday into Tuesday. Initially a warm front will cross the region ahead of this energy, with the main trough crossing by late Tuesday. Model agreement with the warm front is now good, but the 00Z UKMET is faster with the mid-level shortwave along the West Coast. The faster timing of the 00Z UKMET carries over downstream into interior portions of the West and is a notable faster solution in the spaghetti ensemble plots through Wednesday. While not a complete outlier, prefer to stick nearer to the better ensemble/deterministic clustering away from the 00Z UKMET. Timing differences among the non 00Z UKMET guidance are present (00Z ECMWF a bit faster) but are relatively minor. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto