Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1155 AM EST Wed Jan 31 2018 Valid Jan 31/1200 UTC thru Feb 04/0000 UTC ..See NOUS42 KWNO (ADMNFD) for upper air ingest status... ...12Z NAM/GFS evaluation with preliminary preferences... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Cold front moving through the Great Lakes today and the lower Mississippi valley to the Mid-Atlantic Thursday night... ...Possible surface low development along front over southeastern Quebec early Friday morning with impacts to northern New England... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z ECMWF/CMC blend Confidence: Average Except for the GFS, the deterministic guidance has been trending slower with leading edge of the 500 mb trough moving into the northern Mid-Atlantic and Northeast U.S. early Friday morning. The 12Z NAM/GFS remain a bit faster than the 00Z ECMWF/UKMET/CMC with the timing of the cold front to the East Coast, but these timing differences are somewhat minor. Regarding possible surface low development over eastern Quebec between 00Z-12Z Feb 2, ECMWF ensemble members are well clustered near the 00Z ECMWF, but the GEFS and CMC members are sparse and spaced out. The 00Z UKMET appears on its own with a surface low farther south over northern Maine by 12Z02, but this idea is mostly unsupported in the ensemble guidance. Therefore, a 00Z ECMWF/CMC blend is best fitted to the trends and ensemble clustering. ...Weakening mid-level shortwave approaching the Northwest on Friday along with preceding onshore flow... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z ECMWF/CMC blend Confidence: Average Through 00Z/03, models trended toward the consistent GFS/ECMWF solution. However, ensemble trends show toward a bit more amplified with the shortwave as it reaches the Intermountain West on 12Z/03. The 12Z GFS and 00Z UKMET are on the more amplified side of the ensemble spread, while the 12Z NAM is much flatter/weaker with this feature. The ensemble means support a middle ground idea, best supported by a 00Z ECMWF/CMC blend. ...Weak low level wave tracking through the upper Midwest early Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 70% 12Z GFS / 30% 00Z ECMWF blend Confidence: Average Differences are rather significant with the amplitude of a weak low level wave forecast to translate across the middle to upper Mississippi valley on Saturday. The 00Z CMC is unsupported with a rather developed wave approaching the southern Ontario/Quebec border by 00Z04, with ensemble scatter low plots extending from near James Bay to eastern Nebraska. The 00Z ECMWF and 00Z UKMET are less developed with the low level wave and do not drop the cold front extending west of the low far to the south. Ensemble means are similar versions of their deterministic counterparts and show reasonably close agreement by 00Z/04, but the 00Z ECMWF ensemble mean is more amplified than the 00Z ECMWF. Therefore, a blend of the 00Z ECMWF and 12Z GFS, weighted more to the 12Z GFS appears best. The 12Z NAM is on the more amplified/slower side for what it's worth. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto