Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1134 AM EST Fri Jan 26 2018 Valid Jan 26/1200 UTC thru Jan 30/0000 UTC ..See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z model evaluation along with preliminary preferences ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Mid-level shortwave weakening northeastward from the southern plains today... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model compromise Confidence: Above average The models handle the system similarly as it moves east and weakens with time. ...Large upper trough moving through the western/central U.S... ...Surface low near the U.S./Canadian border moving east with trailing cold front... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z NAM/GFS...26/00Z ECMWF Confidence: Average The 12Z runs of the NCEP guidance have adjusted towards a consensus solution suggested by the overnight ensembles and they clustered pretty well with other operational runs. The 26/00Z UKMET was on the flatter/faster side of the guidance but it was not nearly as fast/flat as it was on its Wednesday night/Thursday morning runs. This better clustering left the 00Z Canadian a bit out of phase. For the moment, will remove it from the preference pending arrival of the 12Z guidance. ...Low amplitude mid-level shortwave nearing the Pacific Northwest late tonight with accompanying surface low... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS and 26/00Z ECMWF blend Confidence: Slightly above average Ensemble scatter low plots still support a 12Z GFS and 26/00Z ECMWF/UKMET blend with the surface low as it...and the associated mid level wave...approaches the Pacific Northwest and then heads towards the southeast. The 12Z NAM was not quite as far south with the wave as it had been in previous runs...but it was still on the south side of the envelope of solutions and had a stronger vorticity center. The NAM has consistently been on the stronger and more southerly side of the guidance as the wave drops into the mean long wave trough. For the most part, the latitudinal differences are pretty small but increase late on day 3 when the NAM became slow/deep outlier compared with other model runs. ...Large closed low approaching British Columbia late Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non UKMET/Canadian model blend Confidence: Average The 26/00Z Canadian developed a double-barreled look to its mid/upper level system centered around 145W...which led to several periods where the Canadian was some 200 nmi north of other model guidance. The 26/00Z UKMET appeared to be an outlier with this system. Otherwise...the remaining operational model runs tended to cluster fairly tightly with the ensemble means from the GEFS and ECMWF. Despite some run to run adjustments, the 12Z NCEP runs and the 26/00Z ECMWF still formed a reasonably good consensus solution. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 MB forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml