Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1213 AM EST Sun Jan 19 2020 Valid Jan 19/0000 UTC thru Jan 22/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z NAM/GFS Evaluation with Preliminary Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Surface low/trailing cold front exiting the Northeast early today... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models show similarly with this system. ...Shortwave/front clipping the Pacific Northwest by Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non 12Z UKMET blend Confidence: Above average The guidance mostly agrees well with a quick moving Pacific shortwave trough early Monday whose impacts will be greater into British Columbia than Washington. Only the 12Z UKMET (which trended faster than previous cycles) stands out with a faster timing than the remaining strong consensus. ...Amplifying shortwave crossing the Midwest Sunday/Monday... ...Closed low evolution over the Southeast by Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z ECMWF/UKMET blend Confidence: Average Timing differences with this progressive, but vigorous, northern stream shortwave begin to show up in the latest model guidance on Monday. However, its related impacts are likely felt more by Tuesday across the coast of the Southeast as a potential closed low develops. The ensembles have shown good agreement with the timing over their past 4 1200Z cycles, but waver with north/south placement of the vorticity max. The 00Z NAM is the most aggressive with a slower and rather strong surface reflection just off of the Southeast coast. The 00Z GFS was notably faster than the remaining model consensus and the 12Z CMC was on the north side with the closed low. Somewhere near the 12Z ECMWF/UKMET is considered best at this time given placement toward the middle of the spread. ...Southern stream shortwave crossing California by Monday... ...Energy crossing the Southwest on Tuesday and reaching the Great Plains on Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z ECMWF/00Z NAM blend Confidence: Slightly above average Southern stream shortwave energy will be crossing southern areas of California on Monday ahead of a deep upper trough/closed low offshore of the Pacific Northwest. This energy will then eject quickly down across the Southwest on Tuesday. The 12Z UKMET ends up being slower and deeper than the remaining suite by Tuesday while the 00Z GFS becomes a clear, fast outlier when compared to ensemble guidance and the remaining deterministic guidance. While some latitude differences exist between the 12Z ECMWF and 00Z NAM, a blend of these two appears to be closest to the favored middle ground of the latest ensemble means. ...Deep upper trough/closed low arriving across the Pacific Northwest by Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z ECMWF/00Z NAM blend Confidence: Average While timing of this system is in relatively good agreement, with only the 12Z CMC showing somewhat slower, there are latitude differences with the center of the closed low and related surface low. Ensemble low plots have clustered closer to one another compared to previous cycles, but moderate differences remain. The 00Z GFS appears to be too far south however, and will not be included as part of the preference. The 00Z NAM appears reasonable but should be blended with the 12Z ECMWF given the placement of the ECMWF mean. A 12Z ECMWF/00Z NAM blend will fit best at this time with ensemble member clustering for this system impacting the western U.S. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto