Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 148 PM EST Thu Jan 25 2018 Valid Jan 25/1200 UTC thru Jan 29/0000 UTC ..See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... ...12Z model evaluation along with final preferences... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Mid-level shortwave weakening northeastward from West Texas today/tonight... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model compromise Confidence: Above average The models show similarly with this system. ...Large upper trough moving through the western U.S. today... ...Surface low near the U.S./Canadian border moving east with trailing cold front Friday through the weekend... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z NAM / 12Z ECMWF / 12Z CMC blend Confidence: Average The 12Z GFS continues to appear faster than the model consensus with the progression of the 500 mb trough moving across the upper Mississippi valley early Saturday morning and with energy in the base of the trough near Kansas and Missouri. While the 12Z UKMET trended toward the consensus, certainly compared to its 00Z cycle, it is a bit slower than ideal with the trough progression across the Mississippi valley. A 12Z NAM/ECMWF/CMC blend appears most favorable with this system. This preference also applies across the Gulf Coast where the 12Z GFS is less aggressive with moisture return into the central Gulf Coast region on Saturday. A frontal wave in the Gulf of Mexico appears to be represented in the deterministic guidance by Sunday morning. However, the 12Z GFS is faster with this feature and is stronger than the remaining deterministic guidance and only weakly supported in the ensemble data. Therefore, a 12Z NAM/ECMWF/CMC blend appears a better fit for this entire system, from Canada to the Gulf Coast. ...Low amplitude mid-level shortwave nearing the Pacific Northwest late Friday night with accompanying surface low... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS / 12Z ECMWF blend Confidence: Slightly above average Ensemble scatter low plots support a 12Z GFS, 12Z ECMWF, 12Z CMC and 12Z UKMET blend with the surface low as it approaches the Pacific Northwest. There is moderately good agreement in the ensemble data to support this preference. The 12Z NAM is farther south while the 00Z UKMET is stronger and northward. As the shortwave moves inland, the 12Z GFS/ECMWF appear reasonably well clustered with the ensemble means. ...Large closed low approaching British Columbia late Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average Ensemble data is reasonably clustered with this next system to impact the West Coast, but the 00Z UKMET appears a low probability solution given its placement on the slow edge of GEFS/ECMWF/CMC ensemble members. The 12Z ECMWF/UKMET/CMC adjusted slightly, with the 12Z UKMET close now enough to the consensus to include in the preference. Confidence is only average considering the longer, 84 hour forecast range. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 MB forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto