Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 214 AM EST Mon Jan 27 2020 Valid Jan 27/0000 UTC thru Jan 30/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Final Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Shortwave diving across the Plains to off the North Carolina coast tonight... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Above average Guidance is in good agreement in spatial and intensity evolution of this feature as it shears off to the east today and tonight. The NAM is a bit strong but also a bit fast with this energy when compared to the other guidance and the consensus. Although the differences are minimal, since the remaining suite is in lock step, chose to remove the NAM from the preferred blend. ...Split flow trough crossing the Mountain West today and reaching the Southeast Wednesday night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: GEFS/GFS/ECMWF/ECENS Confidence: Below average 07Z Update: Trend in the guidance has been for a deeper 500/700mb trough digging into the Southern Plains early D2, but still considerable spread exists by D3 as the two mid-level impulses try to interact across the Southeast. While the D2 period is beginning to favor a deeper solution, which brings the 00Z GFS back into the blend, the longitudinal separation of the northern and southern stream on D3 is increasing, suggesting less interaction across that region. Progressive split flow trough moving across the Mountain West this morning will move across the CONUS as the southern stream becomes dominant, with a closed low likely developing across the Southern Plains and into the Southeast by the middle of the week. The northern stream portion will not dissipate, however, and the guidance diverges by D3 into how much interaction will occur with the two impulses. The UKMET continues to be a shallow and fast outlier, but is showing some signs of deepening towards the global consensus in its last few runs. Still, it is outside the ensemble envelope with its position and intensity. The NAM remains slow overall as the feature deepens, which makes significant QPF differences (heavier further north and west) into the Southern Plains D2. The GFS is a bit stronger than the mean with the southern energy, and keeps the amount of interaction, especially by D3, of the two features to a minimum. This agrees with the CMC, although the CMC appears to be too fast with the southern stream impulse which is why the level of interaction is so weak. This leaves the ECMWF/ECENS/GEFS which are in good agreement with the timing and depth of the southern stream energy, and provide a little more impetus for interaction by D3 across the Southeast. ...Progressive upper trough over the Pacific Northwest and amplifying into the Southern Plains Wednesday. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: ECENS/GEFS means with some weight of the 00Z/27 NAM Confidence: Slightly below average Yet another in a series of Pacific shortwave troughs will arrive on Tuesday across the Pacific Northwest, and then dig into the West on Wednesday, with the gradual development of a closed low over the Southwest late Wednesday. There is good agreement in the broad scale, but finer resolution differences in the timing of the low closing off, as well as to what latitude this will occur are considerable. The ECMWF is fast to close off the upper low over Mexico, and is also the furthest south of the global models. It is well south of its mean as well, which is well collocated with the NAM and GEFS mean. The CMC and UKMET are much further east with the trough axis by D3, likely too progressive due to being weaker. A blend of the ECENS/GEFS mean seems most appropriate, but some NAM would help with the finer details of QPF in the terrain as its mass fields are reasonable. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Weiss