Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1159 AM EST Fri Jan 03 2020 Valid Jan 03/1200 UTC thru Jan 07/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z NAM/GFS Evaluation with Preliminary Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Amplifying longwave trough across the central U.S.... ...Surface low tracking from the Ohio Valley to offshore New England... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z NAM and 00Z ECMWF blend Confidence: Average Model spread concerning the interaction between two pieces of energy within a longwave trough shifting eastward has diminished considerably compared to previous days. However, some minor timing differences remain with the 500 mb trough axis which results in differing placements of the corresponding surface low to track east-northeastward just south of New England on Saturday. The 12Z GFS appears a bit fast compared to the latest deterministic/ensemble spread. The GEFS/EC ensemble means also support a slower track than the 12Z GFS with the 12Z NAM and 00Z ECMWF closest to what is considered best for this system. ...Shortwave trough/low impacting the Pacific Northwest... ...Energy ejecting out across the Plains/Midwest by Sat/Sun... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non 00Z CMC blend Confidence: Average The models are in fairly good agreement with the shortwave tracking from the Pacific Northwest Friday night toward the Great Lakes region Sunday night. The 12Z NAM/GFS are oriented farther north with the negatively tilted trough axis extending from the Upper Mississippi Valley to the Upper Ohio Valley Sunday evening compared to the 00Z ECMWF/UKMET/CMC. The 00Z CMC is slowest and farthest south, so it will be discounted given better agreement for a blend between the NAM/GFS and ECMWF/UKMET forecasts. ...Split flow trough near the Pacific Northwest by Sun... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non 00Z CMC blend Confidence: Average Similar to the above system, model spread is small with the mid-level trough axis reaching the Pacific Northwest on Sunday. However, the 00Z CMC stands out as slow compared to the remaining available guidance by late Monday. Therefore, while differences are relatively minor, a non 00Z CMC blend will be preferred for this system. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto