Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 131 PM EST Mon Dec 16 2019 Valid Dec 16/1200 UTC thru Dec 20/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Preference and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Eastern CONUS... ~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average 19z update: The 12z UKMET solution shifted slower and therefore well within the mean spread to suggest a full suite blend, particularly with little variation in the 12z GEFS/ECMWF or CMC. Confidence is above average. ---Prior Discussion--- Large scale synoptic stretching of the shortwave currently emerging into the Southern Plains, is in full affect by late Tuesday in a long positive tilt orientation from New England to Central TX and is fairly well placed in timing/strength. A compact Arctic shortwave breaks from the global scale vortex over the NW Territories by midday Tuesday as it rolls just north of the Great Lakes Wed. The interaction shows the 00z UKMET a tad faster/weaker than ECMWF/CMC more compact, slightly slower and a tad south relative with the 12z GFS/NAM in between hedging toward the slower ECMWF/CMC. This is very minor differences from a synoptic perspective, but would suggest lesser weighting to the UKMET in a general model blend. Confidence is slightly above to above average even with the tail end of the trof as it skirts through the Southeast by Fri. ...Western CONUS into Central Plains Fri... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend (greatest weighting toward GEFS mean) Confidence: Slightly above average 19z update: The 12z UKMET slowed significantly in the northern stream and while it still outpaces the remaining guidance it is just a tad faster than the GFS and looks quite similar including in the southern stream. The 12z CMC is a bit slower in the northern stream but again matches the ECMWF fairly well. So timing will be the remaining problem as the evolution of the features look quite similar. This timing issue will continue to affect the QPF most, given the timing of the moisture return north and which section of the West Coast it hits before the AR starts in earnest at the very end of the forecast period. The 12z GEFS continues to be the most middle ground solution, so will support a general model blend but weight heaviest to the GEFS followed by the ECMWF then GFS/UKMET. The NAM, particularly in the southern stream into the Great Basin/Four Corners is most out of phase (though not dramatically so). Confidence remains slightly above average for the mass fields...but average for QPF. ---Prior Discussion--- An elongated, narrowing trof will approach the West Coast Tuesday which is expected to fully sever and re-consolidate into a closed low along the CA coast by 00z Wednesday, with some remaining energy providing DPVA at the leading nose of the developing Westerly jet by Thursday. The 00z UKMET is strongest with the remaining vorticity strip at the nose of a tighter/faster jet stream which accelerates the northern stream across the Rockies well faster than the remaining guidance and ensemble suite (including its trends). This in turn, slows the southern stream closed low through the Four Corners at the anticyclonic rotor. The 12z NAM, which tends to be stronger by Day 3, is very similar just a bit slower in the northern stream, more in line with the GEFS suite. The 12z GFS removed some of the stronger vorticity strip but with a slightly faster evolution is able to tap a more southerly warm advection along the west coast/OR consolidating moisture flux comparative to the ECMWF. While the ECMWF, is weak with the low flow and the digging shortwave relative to the GFS/NAM allowing for a broader QPF swath (or delayed focus for heavy rain). The 00z CMC,will favor the CMC but matches the mass field well with the GFS/GEFS too, providing average to slightly above average confidence in the evolution overall. This places the GEFS mean as a nice middle ground overall, and so will glean the greatest weight in a non-UKMET blend. Confidence is slightly above average in the mass fields, but reduces with the moisture/QPF axis to average. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina