Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 234 PM EDT Fri Oct 18 2019 Valid Oct 18/1200 UTC thru Oct 22/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Northern stream shortwaves entering the West ejecting into Northern and Southern Plains... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 54 hours; 12z UKMET/ECMWF/GEFS and 00z ECENS mean blend thereafter Confidence: Slightly above average to above average for lead wave Average after 54hrs 19z update: No change on the leading shortwave(s) in either stream and continuation with general model blend remains. For the developing Plains low on Day 3, the 12z UKMET slowed a tad, toward the 06z GEFS and with the 12z GEFS shifting a bit faster than the 06z GEFS, there is still solid agreement to keep better confidence away from the faster NAM/operational GFS. This was further enhanced as the 12z ECMWF trended faster and very close to the 00z ECENS. So there is evidence, both of these operational guidance members along with the ensemble means will be fruitful as preference bringing confidence back to average after 54hrs. For note: the 12z CMC remained slow and looks like a clear outlier now without its ECMWF pair. ---Prior Discussion--- GOES-WV suite denotes a sharp and deep latitude trough advancing from SW Saskatchewan south through UT/AZ advancing with modest pace. A surface trof with multiple waves across S Canada and the Dakotas will sharpen/focus to the north as the northern portion of the trof breaks from the southern. Aloft the CMC, more so than the ECMWF, are in a typical slower position and so are a bit more amplified lifting through the Great Lakes but with limited sensible weather affects to break from a general model blend for this portion of the wave. As the southern portion of the trof emerges, early Saturday, The frontal zone will press eastward into AR/E TX by late evening with the GFS a bit faster than the ECMWF but not to tremendous negative effect given how weak the remaining forcing is relative to north. Still the upper level shortwave will help to kick out the combined baroclinic/Potential TC 16 with general weakening through the TN Valley. So like the north, a general model blend can be supported for this wave. Upstream, however, the next stronger shortwave along the cyclonic rotor of a very strong/broad Pacific jet, is already pressing height-falls with increased wavy nature to the pattern entering the Upper Snake River/Central Rockies by 20.00z. Typical timing issues are already starting to manifest by this time, with the 12z GFS and 00z UKMET outpacing the 00z ECMWF/CMC. However, the GEFS members are slower than the operational and the ECENS are faster and this will be key as the nose of the diffluent pattern ahead of the trof reaches the Front Ranges of the Rockies. Vortical stretching combined with the favorable upper pattern leads to rapid surface cyclogenesis in the faster solutions of the GFS, but the slightly slower NAM, UKMET are a bit more reasonable relative to the GEFS than the operational GFS. By 21.00z, the ECMWF is well too slow and emerges more elongated north south due to broader zone of vorticity stretching out of the terrain. This leads to about a 6hr delay even compared to yesterday's 12z ECMWF run and two most recent ECENS means; a typical negative sign for the operational ECMWF. Though it is paired with the CMC, will be favoring a GEFS/ECENS mean blend after 20.18z with slightly below average confidence due to the larger than normal timing differences and their effects on the cyclone development. Tropical Storm Nestor (former PTC Sixteen) ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: See latest NHC advisory Best Proxy: 12Z UKMET/ECMWF 19z update: The ECMWF and CMC both have latched onto the convective center of Nestor near the UKMET, as the system goes extratropical crossing the Southeast, the GFS breaks a bit fast comparatively, and when the UKMET/ECMWF slow to match the 15z NHC forecast best. So now, best proxy is a 12z UKMET/ECMWF blend, though only the NAM is a significant outlier from the deterministic guidance suite. ---Prior Discussion--- 12z NAM/06z GFS and 00z ECMWF/CMC along with a plethora of WRF Hi-Res CAMs appear to be favoring the baroclinic development of the convective environment (stronger thunderstorms/clustering along the northern Gulf frontal zone) over the convective complex/confluent surface trof/effective cold front south of the developing surface low. This is opposed by the UKMET and the 12z HRRR/Exp. HRRR. The latter appear to have a more realistic depiction of the current convective environment as well as the instability field over the former solutions even though they are less numerous in the overall suite. Yet, the surface circulation/center continues to struggle to come together (hence still PTC) which is is counter to initialization of most of the guidance which has formed a consistent surface low, tracking it northeast. The 12z GFS appears to be coming to a compromise now initially favoring the deeper convection that is ongoing at initialization relative to the 06z run. So even though the clustering is tightening in the guidance, the evolution path is quite uncertain so close monitoring/changes in observations may key to determining the best solution. Currently, the 15z NHC forecast track best proxy appears to be something closer to a blend of the 06z GFS and the 00z ECMWF, though the 12z GFS remains a bit faster initially and looks a bit better to blend with the 00z ECWMF as a proxy to the 15z forecast than the 06z especially after crossing the Southeast into the Western Atlantic. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Gallina