Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1157 PM EST Thu Jan 23 2020 Valid Jan 24/0000 UTC thru Jan 27/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Preliminary Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Shortwave trough moving from the Pacific Northwest to the Missouri Valley by Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM or UKMET blend Confidence: Average Shortwave lifting onshore the Pacific Northwest Friday morning will move into the Northern Plains Saturday and then dig southeast around a big closed low over New England by Sunday. The guidance is nearly unanimous is intensifying this feature as it shifts out of the Plains, but differ considerably with timing and strength. The NAM is showing a general strong bias across the CONUS with its 00Z/24 run, including this shortwave closing off prior to the global consensus. It also shifts this feature very quickly into a short-wavelength but high amplitude shortwave ridge which develops upwind of the close low over New England. This seems unlikely due to the strength of this latter feature. The UKMET looks reasonable and is within the consensus envelope through 48 hours, but then races the shortwave off to the southeast such that by D3 is it nearly 5 degrees of longitude east of preferred consensus, so is not usable at the extended timerange. ...Next shortwave trough moving onshore the West Coast Sun... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS/12Z ECENS and limited weight on 12Z ECMWF Confidence: Slightly below average A vorticity lobe shedding eastward around a deep trough in the Gulf of Alaska will shift onshore Sunday and then dive towards the Four Corners Sunday night while amplifying. The degree of this amplification is the biggest question mark as far as the guidance, since the positioning and speed at which the shortwave advects eastward is well supported by the global consensus. The intensity of this shortwave then creates differences in the placement of the attendant surface low, especially just beyond this forecast period. The GFS and ECENS mean are in good agreement, while the ECMWF has shown less run-to-run continuity. ...Closed mid level low tracking from the Central Plains across Ohio Valley Sat into the Northeast Sun... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM or CMC blend Confidence: Slightly above average The global models have come into much better agreement both with the evolution of the large closed low, as well as timing and position of vorticity impulses rotating around it. The mid-level feature should be over eastern MO Friday morning, NW Ohio by Saturday morning, and then lifting across Upstate New York Sunday morning. Waves of vorticity rotating around this feature will produce swaths of snowfall and QPF in the Ohio Valley and Great Lakes, but more significant QPF will be associated with the leading shortwave above a triple point in the Mid-Atlantic which will spawn secondary surface low cyclogenesis Saturday. The biggest differences in the guidance involve these more subtle features, and not the primary mid-level cyclone. The NAM is generally a bit NW of the consensus, and also swings a robust vorticity impulse atop the Chicago area, while the remaining guidance focuses this energy further north. Further to the east, the CMC swings the vort lobe responsible for secondary surface low development further east and faster than the remaining guidance. From a mass fields perspective, these are the only two notable differences. However, the GFS has a QPF maxima that is not representative of the consensus, with high values across the Mid-Atlantic that are outside the envelope and seem too robust based on the speed of the feature. This suggests a UKMET/EC/ECENS/GEFS solution is most reasonable for D2 and beyond. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Weiss