Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 134 AM EST Thu Jan 09 2020 Valid Jan 09/0000 UTC thru Jan 12/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Shortwave entering OR/CA tonight, amplifying across the Four Corners/High Plains Fri and through MS Valley into Great Lakes late Sat into Sun... ...Deepening surface low over the Lower MS Valley Fri/Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z GFS/ECWMF blend Confidence: Slightly above average 07z update: The 00z ECMWF showed very little variation and remains quite close to the GFS, just a tad weaker. The 00z UKMET was on that weaker trend, perhaps a bit too much allowing it to lift through the Great Lakes a bit too fast with the surface low tracking a bit south with less westward wobble in the occlusion phase like the initial preference. The 00z CMC, trended away from weaker and went toward a more typical slow bias, and is now generally west of the otherwise tighter agreement of the GFS/ECMWF. The overall differences are very small but with overall good agreement and within tightening ensemble suite, will support a 00z GFS/ECMWF blend at slightly above average confidence, but still increasing. ---Prior Discussion--- GOES-West WV denotes sharpening shortwave nearing SW OR at this time, this wave digs through CA today before bottoming out over far northern Old Mexico early Friday. Concurrently, the ill-formed northern portion of the longer wave meridional trof sharpens and accelerates along the S Canadian Prairies under stronger anticyclonic jet streak crossing the Canadian Rockies, eventually decoupling with the southern portion of the wave. The base slowing and having a favorable jet entrance associated with the exiting northern stream, amplify ins a closed low across the Lower MS valley with very strong moisture flux supporting convection that will feed the increasingly diffluent upper level pattern (feeding back on cyclogenesis). The 00z NAM shows very consistent but also substantially deeper solution nearly 40-60 dm so at 5H which may be related to finer resolution of convection and latent heat release supporting stronger jet both aloft and in the low levels, which is a typical negative bias toward Day 3; though the mass field placement and track of the surface cyclone are solidly in the center of the ensemble suite...there is some concern of stronger blending into any preference. The 00z GFS showed the most significant change mainly in a slightly slower/sharper base to the trof, delaying its ejection into the Southern Plains, this brought it into very strong agreement with the very consistent ECENS mean solution providing greater confidence overall. The 12z ECMWF/UKMET have some very small internal differences/placement of convection relative to the GFS, but a blend between these 3 are best especially with timing of the cold front pressing through the South, to account for fast/slow biases. The 12z CMC is much too weak and fast and with the slowing of the GFS it is dismissed. So overall a non-CMC blend is preferred though would weight the NAM lower in any blend, and perhaps eliminated in some locations were thermal profile may be a bit more compromised in precip phase. Confidence in this blend is raised slightly above average. ...Next upper trough over the Northwest by Sat shearing into longer wave trof over Intermountain West Sun... ...Phasing/sharpening third shortwave along BC coast into Pac NW late Sun... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Slightly above average 07z update: The CMC trended a bit slower with the cold air pocket and therefore the centroid of the closed low over NW Canada...so a Non-NAM blend will suffice through the short-term with both the initial shortwave (broadening into longer wavelength) as well as the approaching Gulf of AK system on Sunday. ---Prior Discussion--- In the wake of the larger meridional trof, a compact mid-wavelength shortwave/small closed low nears Vancouver Island into the Pacific Northwest. Downstream splitting of flow regime of the southern and northern portion of the trof allows for greater southern stream ridging, therefore allowing for a broadening of the trof as a whole breaking into smaller scale shortwave features along the periphery of the broadening trof through the Intermountain West by Sunday. With the exception of the 00z NAM that shows very strong/sharp shortwave energy sliding along the western side of the ID/MT Rockies, there is strong model agreement. So a non-NAM blend is favored through Sun. Another shortwave phasing with a lobe of very deep Arctic cold closed low slides down the BC Coast, here guidance is in good agreement, with exception of the 12z CMC which bleeds a much colder Arctic air mass through the northern Canadian Rockies displacing the interaction...so would favor removal of the CMC in any NW US/Western Canadian blends for Sunday. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina