Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1220 PM EST Thu Jan 30 2020 Valid Jan 30/1200 UTC thru Feb 03/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Preliminary Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Evolution of Trough over Eastern Half of the U.S. into Sunday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~ Preference: 12Z GFS/NAM and 00Z ECMWF/UKMET Confidence: Average A full-latitude trough down the center of the CONUS into northern Mexico is being dug by a primary low currently over northwest Mexico with a secondary, reinforcing trough pushing down the northern High Plains. The secondary trough shifts south into northern Mexico through Friday, keeping the southern end of the trough positively tilted across the Gulf Coast through Saturday before shifting east of FL Saturday night. Embedded impulses in this trough vary among guidance, but there is now decent agreement on position and movement of these features outside of the 00Z CMC. The northern portion of the trough axis is expected to push though the Midwest Saturday as the southern trough axis moves across the Southeast. At the surface, low development occurs Friday night along the NC coast in the left exit of a strong southwesterly jet stream. Interaction of these two features in the upper levels is delayed until Saturday night along the southern Mid-Atlantic coast with the surface low well off New England at that time when it rapidly develops. There is excellent agreement in Day 2 QPF over the Carolinas, Mid-Atlantic coast and far southeast New England among the 12Z NAM (more so the 3km NAM)/GFS and 00Z UKMET/ECMWF. The tilt of the southern portion is more positive than previous runs which slows the cold frontal progression over the FL peninsula Friday night and results in a west to east QPF swath over the FL peninsula on Day 2. The only differences in the 12Z NAM/GFS and 00Z ECMWF/UKMET are latitudinal positioning of this swath somewhere around Lake Okeechobee. The 00Z CMC is an outlier in that it brings the northern and southern portions together sooner and farther south (late Saturday over the Southeast) and weaker than the consensus, so it is not preferred. ...Pacific Northwest Atmospheric River Leading a Longwave Trough Pushing into the West on Sunday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS/NAM and 00Z UKMET/ECMWF Confidence: Average An atmospheric river reaches the WA coast later today and waivers north/south through Friday night before shifting south down the OR coast Saturday in advance of a longwave trough that reaches to central CA as it pushes inland Sunday. The dilemma come with the exact QPF axis on Day 2 and the timing of the trough that moves ashore on Day 3. The 00Z ECMWF remains a steady 6 to 12 hours behind the rest of the guidance with the trough axis, so it has QPF less inland on Day 3. The 12Z GFS remains farther north with the forcing on the north side of the moisture plume with the Day 2 QPF focus on southern Vancouver Island. Both operational models are in line with their ensemble means. The Day 2 QPF axis has northern solutions with the 12Z NAM/GFS and southern in the 00Z ECMWF/UKMET which are focused on the northern Olympic Peninsula with the 00Z CMC in between. Day 3 QPF is in good agreement among the 12Z NAM/GFS and 00Z UKMET. The 00Z CMC is the fastest solution the slowest solution with the trough axis on Day 3 and is not preferred. The 00Z ECMWF should have the least weight on Day 3 given its slow progression. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Jackson