Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 238 PM EDT Sat Oct 19 2019 Valid Oct 19/1200 UTC thru Oct 23/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Northern stream shortwaves crossing the the West ejecting/deepening into the Plains and eventually into the Great Lakes... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend Weighting toward GEFS/ECENS/UKMET after 22.00z Confidence: Slightly above average thru 22.00z; average after 19z update: The 12z UKMET trended quite similar to the 06z/12z GEFS and 00z ECENS mean, making it a solid representative to the current thinking. The 12z CMC continues to be the slowest and well outside of the general overall consensus to suggest the initial preference remains solid. The 12z ECMWF, though much like the 12z NAM has the kicker shortwave entering the base of the trof and strengthening the triple point low lifting through the MS Valley Monday, but as it reaches the inner core of the upper low, the internal binary interaction; the NAM swings the core north, while the ECMWF swings it back west and then south, with a surface reflection well south of the initial preference (along with making it deeper). The overall mid to upper level mass fields look solid but this difference in the surface field after 22.00z makes it hard to blend it with the remaining guidance. At this point, will prefer to shift more to a GEFS/ECENS and UKMET focus/weighting in a non-CMC blend. Confidence remains average after 22.00z. ---Prior Discussion--- The lead height-falls that started the pattern change, continues to weaken and split with the northern stream shortwave/surface low well into Canada with a sharp but thinning frontal zone progressing across the Mississippi River Valley today while the southern stream vort center and continues to fade but also kick the extratropical circulation of Nestor eastward. The overall pattern for this wave continues to be solid with no disagreement to favor a general model blend for it. The next more potent wave has entered the Pacific Northwest as the left exit to the broad but strong 150+kt 250mb jet. This wave will continue amplify into the Wyoming Rockies, where along with vortical stretching coming out of terrain finds favorable upper level diffluence to rapidly develop a surface wave later today into Sunday morning. There has been a general trend toward a northern shift, which has been held best by the GFS/GEFS, NAM and UKMET; however, the 00z ECMWF has trended north as well and while still a bit slower than the GFS/NAM and less so the 00z UKMET, there is growing consensus and therefore confidence in this shift. The GFS remains faster and north than the GEFS mean but had trended a bit weaker overall too. The ECMWF remains slightly slower and south of the ECENS mean with both the GEFS/ECENS showing strong agreement at least initially through the Dakotas into the northern MS Valley. Much like the last few cycles the operational ECMWF shows greater departure from its mean than the GFS and its mean. The 12z NAM, showing a stronger secondary vort center rotating out of the CO Rockies, suggests a stronger triple point low moving north through into the Upper Midwest by Monday, this looks like typical Day 3 over amplification and so would favor lower weighting of the NAM by Day 3 in the blend. The CMC is very slow throughout the process and is a clear outlier at this point, so a Non-CMC blend is favored throughout the forecast period and will favor the mass fields centered near a GEFS/ECENS mean, which can be afforded by this non-CMC blend until 22.00z, when the NAM is to be weighted out of the preference as well. Confidence is slightly above average through 22.00z and then average thereafter. Third fast moving shortwave entering Northern US Rockies/MT High Plains late Tuesday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average to slightly below average 19z update: The 12z CMC slowed a bit, while the 12z ECMWF sped up; both matching each other but still a bit slower than the initial preference and 12z GFS/NAM and 12z UKMET. The 12z UKMET did temper a bit and is more useful to an overall blend. Given the harder predictability of a fast moving shortwave (especially emerging from reduced void of data in the North Pacific. As such, will support a general model blend at average to slightly below average confidence. ---Prior Discussion--- The 3rd more significant shortwave, will over-top the broad longwave ridge peaking around Vancouver Island and slip into the Northern US Rockies and MT High Plains. The 00z ECMWF is very slow even compared the CMC which has the downstream issues with the prior system. The CMC matches well with the amplitude/timing of the 12z GFS and NAM as well as the 00z UKMET. However, the UKMET is much strong particularly in the leading height falls supporting a deeper surface reflection. As such will favor a 12z GFS/NAM and 00z CMC blend though given the speed of the shortwave in the flow as well as complications with the exiting shortwave, this clipper system confidence in the blend is average to slightly below average. Post-tropical Storm Nestor ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: See latest NHC advisory Best Proxy: 00z UKMET or 12z UKMET/ECMWF/CMC blend 19z update: The 00z UKMET continues to be the best proxy for this system, though the 12z ECMWF/CMC are much closer in timing track, especially the ECMWF after 21.00z when the 12z UKMET/CMC both lift a bit north of the official NHC forecast. All in all, best proxy to 15z remains 00z UKMET or a 12z UKMET/CMC and ECMWF blend ---Prior Discussion--- Nestor has lost the majority of near center convection, and with the 15z advisory, NHC has declared Nestor to be extra-tropical. This is held consistent with nearly all of the global guidance as well. The 12z NAM continues to be the largest outlier favoring a northwestward shift of the track of the cyclone through the Carolinas into the NW Atlantic. The 12z GFS and 00z CMC are along track, until lifting north under influence of approaching northern stream strong cyclone in the Plains/Great Lakes, as well as a weaker surface/low level ridge across New England compared to the UKMET/ECMWF. The official NHC track follows the ECMWF/UKMET closest, though toward the end of the forecast period over the open waters, the ECMWF is faster than the official forecast, making the UKMET the best proxy for the 15z official forecast. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Gallina