Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 148 PM EST Sun Jan 20 2019 Valid Jan 20/1200 UTC thru Jan 24/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12z Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Eastern U.S... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The deep cyclone will continue the track through New England today into SE Canada. As expected, the 12z NAM/GFS both show little variation and continued strong overall agreement in the model guidance suite. As such will continue to support a general model blend at above average confidence. ...Western/Central U.S... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z ECENS mean/ECMWF and 12z ECMWF/CMC blend Confidence: Average 19z update: Increasing spread continues, as the 12z ECMWF slowed/deepen even further with a stronger more defined deformation band across the Midwest. The 12z UKMET slowed too, but unlike the ECMWF/CMC, it was suppressed much in line with the 12z NAM...this places the GFS out too fast looking more like a typical negative bias. The good news was the 12z CMC shifted south and looks more on par with the initial preference. As such will support some slower trending but favor the 12z ECMWF/CMC or near the 00z ECENS mean/00z ECMWF solution. Confidence is average. ---Prior Discussion--- The apex of a broad trof enters the Pacific Northwest Sunday with the strong energy across the base of the trof in Central CA/Great Basin. As the wave emerges into the Plains and the strong energy starts to stretch northeast into the Midwest by Tuesday, there remains increased spread in evolution that continues to spread further with the 12z cycle. The 12z NAM is fast stretching the energy/jet north but still keeps the bulk of energy/cold air filtering southward which leads to the wave inflection across MO into Central IL, which rolls up into a more compact system through the southern Great Lakes by Wed. This is a fairly solid break from the other guidance and continuity to not be favored at this time. The 12z GFS continues a slow trend to slightly faster and much more elongated/stretched shortwave feature across the Midwest into the Great Lakes; while not as fast and stretched out as the 00z UKMET, the 12z run is trending away from the continuity, preferred solution over the last few days. The 00z ECMWF are slower, typical of bias, and also support a stronger compact leading wave supporting a deeper surface cyclone/stronger deformation band across E NEB, IA into S WI... This is the same axis as the GFS but is obviously slower. The CMC is nearly the same but about half a state north, keeping this bias north through the duration of the forecast period (which is consistent internally to the CMC, but not generally preferred). As such will support a 12z GFS/00z ECMWF blend which also keeps with continuity/central ensemble suite over the last few cycles. Confidence remains average given the timing and north/south axis placement near the surface wave, at least the cold front across the lower MS valley is a bit better in its agreement. ...Pacific Northwest on Day 3... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z ECMWF/CMC blend Confidence: Slightly below average 19z update: The 12z ECMWF/CMC trended more favorably toward a slower, more compact solution, as did the UKMET. However, the UKMET was clearly fast and actually quite prolific with QPF...so not inclined to support such a dramatic shift in preference toward this solution. The ECMWF/CMC were further south and slightly weaker than some of the initial over-intense concerns noted with the 12z NAM/GFS. As such will adjust preference toward the 12z CMC/ECMWF blend but still be slightly below average in confidence. ---Prior Discussion--- In wake of the broad trof early in the week, solid broad ridging builds across the Eastern Pacific as far north as Vancouver Island by late Tuesday. The next system rides the ridge toward the BC coast, but differences in timing and strength/compact nature of the wave nearing the apex of the ridge, leads to significant differences in the mass fields as it rolls into the Pac NW by Wed. The 12z NAM/GFS continue to be most robust/compact with the wave though the CMC/ECMWF being weaker are a bit faster at least with the apex of the shortwave allowing for a similar timing of warm advection precip across the NW Tues into Wed. However, given the ECMWF/CMC are weaker the trailing trof energy is stronger and slower bringing a surge of increased QPF in by the end of Wed toward 00z Thursday. The UKMET is generally middle ground on both solutions (more compact with the leading shortwave, but still stronger with the trailing shortwave energy too), but is clearly well north of the track/placement of the wave/QPF compared to either of the two solutions. Ensemble/run to run ensemble continuity favors the stronger compact wave as well as the ECENS solutions shifting more toward the GFS/NAM than the GEFS members shifting the other way. As such, will favor a blend of the 12z NAM/GFS but will include the ECENS/GEFS mean to the blend to help handle some of the uncertainty. Confidence is slightly below average in this blend. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina