Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 142 PM 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 model evaluation with final 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: 12Z ECMWF/UKMET blend Confidence: Average Although the 12Z ECMWF?UKMET/CMC trended faster with their 12Z runs, trends had been slower previously and the 12Z GFS remains the fastest with the 500 mb trough moving into the northern Mid-Atlantic and Northeast U.S. early Friday morning. While the 12Z GFS is quickest, any lingering 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/12Z ECMWF, but the GEFS and CMC members are sparse and spaced out. The 12Z UKMET trended near the ECMWF but lies a little north of it, a more supported solution compared to the 00Z UKMET. The 12Z CMC is a bit more developed and south with the surface low early on Friday, holding little support. Therefore, a 12Z ECMWF/UKMET 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: 12Z ECMWF/UKMET/CMC blend Confidence: Average Through 00Z/03, models trended toward the consistent GFS/ECMWF solution compared to Tuesday's runs. However, ensemble trends show toward a bit more amplified with the shortwave as it reaches the Intermountain West on 12Z/03. The 12Z GFS is 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/UKMET/CMC blend. While there is a decent amount of consistency for the 12Z ECMWF/UKMET/CMC idea, there is still enough spread in the ensemble guidance and run to run changes to only keep confidence average. ...Weak low level wave tracking through the upper Midwest early Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS / 12Z 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 12Z 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 12Z ECMWF and 12Z UKMET, like their 00Z cycles, remain less developed with the low level wave and do not drop the cold front extending west of the low far as quickly to the south when compared to the remaining deterministic guidance. However, the 12Z ECMWF/UKMET did trend toward the remaining quicker model consensus. Ensemble means are similar versions of their deterministic counterparts and show reasonably close agreement by 00Z/04, and the 12Z ECMWF is now closer to the 00Z ECMWF ensemble mean with the cold front and low level wave. Therefore, a 50/50 blend of the 12Z ECMWF and 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