Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 133 AM EST Fri Jan 17 2020 Valid Jan 17/0000 UTC thru Jan 20/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Central to Eastern US system... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 48hrs 00z GFS/ECMWF blend afterward Confidence: Slightly above average 07z update: The ECMWF continues with continuity/tight clustering to the GFS and while the UKMET remains a tad north in the mass fields/surface low, it does continue to provide overall confidence toward the GFS/ECMWF blend with some inclusion (particularly in convective areas for QPF). As such will keep with initial preference and confidence throughout. As for the Arctic shortwave, the ECMWF trended back to match the NAM/GFS while the UKMET slowed and is weaker it still outpaces the best agreement for that wave (even if dry). ---Prior Discussion--- Subtropical shortwave and overrunning precip shield evident across the Southern Plains, with a sharp northern stream trof pressing eastward across Central CA at this time. The guidance has come into much stronger agreement in the combined systems' track and interaction across the Upper Midwest to Mid-Mississippi Valley Sat. There are some small differences but the affects are fairly minimal. However, by Sunday (and afterward) the binary interaction has lead to an elongated closed low extending from the Upper Great Lakes through the Northeast; however, internal shortwaves/jet speed maxes are not showing much congruity with the 00z NAM becoming very strong upstream and eventually curling back into a strong/compact closed low through the Canadian Maritime. The 12z CMC is fracturing the shortwave into two smaller components, while the 00z GFS, 12z UKMET and 12z ECMWF are more middle ground showing less vortex roll-up. However, the UKMET axis of rotation is a tad further north, off-setting the best mass fields and associated surface low track, even more so than the weaker CMC. So would be favoring a 00z GFS/12z ECMWF blend with some inclusion of the UKMET, particularly in QPF/moisture flux convergence across the Southern MS Valley back into the Western Gulf, where the GFS and even so the ECMWF seem to be very dry. All in all, these model differences are quite nit-picky, and a general model blend could be employed at least through 48hrs, as the greatest mass differences evolve across the Northeast afterward; but if a tighter, higher fidelity blend is desired, would favor a 00z GFS/12z ECMWF blend at slightly above average confidence. Of note: A very sharp Arctic shortwave descends at the nose of a weakening/closed warm ridge that has been over N AK into the NW Territories reaching the Great Lakes/Northern Plains by Mon. This is rapidly weakening with the exception of the UKMET, which has a very strong shortwave that is similar to the ECMWF/CMC in placement by the end of the short range. It is very dry, but would help to enhance forcing on any ongoing lake effect plumes Monday. The GFS/NAM are both slower and are really just weaker extensions of the old shortwave/vorticity strip north of the polar jet axis. All in all, it is more of a reason to exclude the UKMET particularly late in the forecast period for this area, but is not a major player overall. ...Pacific Northwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 20.00z Non-CMC blend afterward Confidence: Above average prior to 20.00z Below average afterward 07z update: The model suite particularly messy with the shortwave between larger/ahead of deeper compact wave, though the ECMWF trended a bit further north closer to the UKMET/GFS/NAM keeping the CMC as a southern outlier. So will keep with initial preference. ---Prior Discussion--- The next compact shortwave/closed low continues to show very strong agreement through the ensemble/deterministic suite approaching Haida Gwaii mid-day Saturday directing the tail end of the trof/moisture plume into the Olympic peninsula before directing a stronger Atmospheric river into the Vancouver Island through Monday. It is by Monday that the next shortwave starts to advance past 140W. There is a very large spread in the wavelength of this trough and its timing mainly dependent on a very strong (or not) upstream kicker shortwave. The GFS/NAM and UKMET present it as very strong/very compact and therefore shorten the preceding wavelength and kick it faster compared to the ECMWF/CMC. The CMC is much stronger and extends southward more compared to the ECMWF. The affects through day 3 seems to be quite minimal, especially in the QPF, with the exception of the typical day 3 timing issues of the GFS fast, ECMWF slow. Ensemble trends may suggest the GFS/UKMET are on to something but the ECMWF is fairly consistent and tends to have better performance with these Pacific systems, so the uncertainty/confidence is quite low. But would favor more ECMWF/UKMET with respect to QPF, but perhaps more GFS/UKMET in terms of mass fields. So will prefer a Non-CMC blend after 20.00z, though mostly in timing (slowing the UKMET/NAM/GFS and speeding up the ECMWF). For more details for the upstream shortwave, please refer to WPC PMDEPD for preferences. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina