Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 149 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 Model Evaluation with Final 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: General model blend Confidence: Above average ...07Z update... With the 00Z UKMET slowing down its shortwave trough progression close to the remaining and consistent model consensus, a general model blend will be preferred for this system. ...previous discussion follows... 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: 00Z ECMWF/UKMET/CMC blend Confidence: Average ...07Z update... The 00Z CMC adjusted south from its previous 12Z cycle and has been included as part of the preference. Meanwhile, the 00Z ECMWF/UKMET remain fairly similar to their previous 12Z cycles. While the 00Z CMC is slightly less closed off with the mid-level energy, this is okay when blended with the 00Z ECMWF/UKMET which may be too far south. ...previous discussion follows... 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 12/00Z 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: 00Z ECMWF/UKMET/NAM blend Confidence: Slightly above average ...07Z update... The preference is to be between the faster and slower guidance, in line with the stronger ensemble clustering. The latest 00Z ECMWF/UKMET/CMC all trended slightly faster, but still with the 00Z GFS a fast outlier. The 00Z UKMET has been added to the preference with the relatively consistent ECMWF from 00Z and the 00Z NAM. ...previous discussion follows... 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: 00Z ECMWF/NAM/UKMET blend Confidence: Average ...07Z update... Adjustments made by the 00Z ECMWF/UKMET/CMC compared to their previous 12Z cycles were in the direction of the previous preference, or slightly south with the base of the trough/closed low approaching the Northwest. However, the 00Z CMC remains displaced too far north and slightly slower compared to the better model clustering observed in the ensemble and remaining deterministic guidance. ...previous discussion follows... 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