Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 227 AM EDT Mon Oct 07 2019 Valid Oct 07/0000 UTC thru Oct 10/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Upper trough crossing the Great Lakes through Monday with progressive cold front... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average 07z update: The 00z ECMWF trended faster, but remains slightly slower than the remaining guidance. Suggest the ECMWF's inclusion to the blend at this point, but perhaps at lower weighting given the otherwise very strong agreement. ---Prior Discussion--- The models show very good agreement with the details of the upper trough and associated shortwave energy that will be crossing the upper Midwest and Great Lakes region through Monday. However, the 12Z ECMWF shows some slow bias breaking from the remaining consensus exiting the Great Lakes a bit slower than the other guidance Monday; delaying the progress on Tuesday through New England. The 12z ECENS mean has some supporting members, but that number is well below half; so it seems prudent to keep the Non-ECMWF blend preference with this system. Note: this appears to negatively affect the lingering trof in the Appalachians and northward track of the tropical wave (see below). ...Lingering shortwave energy amplifying over Central Appalachians into the Mid-Atlantic... ...Deepening surface low pressure off the East Coast within elongated coastal trof back to FL... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z GEFS/GFS/NAM and UKMET blend Confidence: Slightly below average 07z update: With a slightly faster exit of the northern stream shortwave, the placement/timing of the remaining shortwave in the Appalachians and orientation of the tropical moisture stream/surface stream closer to the coast with the new 00z ECMWF. It is still a bit slower with the embedded shortwave energy in the tropical stream relative to the GFS/NAM/CMC, so cyclogenesis remains south of those guidance members but the shift is much better toward the centroid of GEFS/CMCE and ECENS ensemble solutions, but still south of the initial preference. The CMC trended north as well as the UKMET. This placed the CMC well north of the overall guidance/ensemble suite and a shade deeper and the UKMET very close to the NAM. The 00z GEFS was very similar to the 18z run and so is still the most preferable solution. Confidence is increased a bit in the overall forecast to slightly below average in a GEFS/GFS/NAM/UKMET blend. ---Prior Discussion--- Continued uncertainty remains with the evolution of combining streams along the Eastern US Coast. As mentioned above, the 12z ECMWF is slow exiting with the main northern stream wave; this allows the lingering base of the trof to be tugged eastward a bit more than other guidance suggests. This may increase some ridging just off shore, as the operational ECMWF is the only main deterministic guidance member to deflect the tropical return warm conveyor belt, along the western periphery of the subtropical ridge, out to sea farther. As the tropical wave and surface cyclogenesis lifts north and is enhanced by the baroclinic flow aloft, the ECMWF presses the wave south into an anticyclonic loop and is on the eastern-southern side of the ECENS guidance solutions. While the ECENS solutions are still further south than GEFS/CMCE members, the operational solution is on the outside periphery of the guidance. The 12z UKMET is very weak across the Cumberland Plateau into the central Appalachians, and favors a slower emergence of the tropical-stream cyclogenesis, in the center of the ECENS cluster. The 00z NAM/GFS and 12z CMC, much like the UKMET/ECMWF are starting to favor stronger shortwave energy emerging along the warm conveyor belt along the east coast surface trof. So while, there is a trend toward a weakening or smaller lingering shortwave out of the Central Appalachians helping to build some weak form of Rex Block in the Northeast, there is reduction of baroclinic influences relative to the tropical surge. The cool conveyor remains strong and active south of Long Island, but the surface cyclogenesis is a bit further south and east with the 00z runs relative to the 12z/18z solutions. This places the 00z GFS very close to a favorable 18z GEFS solution. The 00z NAM is very aggressive with tropical energy lifting north, and as it intersects with the forming cool conveyor, very strong response/cyclogenesis occurs. The CMC has been similar and more consistent overall toward this solution. So while there is remaining high uncertainty (given small timing/depth difference lead to large evolution outcome differences, WPC is favoring something closer to the 18z GEFS/00z GFS with some 12z CMC and 00z NAM weighting and even lower 12z ECENS mean input to account for this uncertainty. Confidence and more inclusion of the ECMWF/UKMET into preference occurs toward Florida/Bahamas, given less model spread and better consistency of the moisture/flow regime axes. ...Deep upper trough/closed low amplifying over the West... ...High Plains cyclogenesis... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Broad large scale trough currently over AK and the northern Gulf of AK will drop southeast and support strong cold air surge down both sides of the terrain. This will support a sharper, but elongating positive tilt trough to dominate the Northwestern CONUS to Northern Canada by late Tuesday. The trof will support a strong compact shortwave shifting east through Boreal Canada as the southwestern portion starts to take shape and spur Central High Plains cyclogenesis by Wed with cold front extending through the Northern Plains ahead of the cold surge. Guidance is remarkably in good agreement with the evolution of the entire trough, with only small depth issues near the centers of each developing internal cores. The 00z NAM shows this the most in a typical late day 3, over-deepening solution. This helps to sharpen the northeastward extending deformation zone and QPF axis relative to other guidance as well as greater convective development in the warm sector from NE KS to MN. The UKMET/ECMWF are on this more aggressive side compared to the slightly weaker 00z GFS. However, this is fairly minor and in line with typical biases that are accounted for in a general model blend. As such the general model blend remains WPC preference at above average confidence. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Gallina