Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 230 PM EDT Mon Sep 02 2019 Valid Sep 02/1200 UTC thru Sep 06/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Final Model Evaluation, Confidence, and Preferences ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Overall Pattern Across the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 54/60hrs 12z GFS/NAM/ECMWF thereafter Confidence: Above average through 60hrs Average thereafter esp in northern stream 19z update: The 00z ECMWF/CMC were slow to break down the initial Pacific shortwave, but the 12z runs do, still a bit slower than the GFS/UKMET but more in line with typical smaller timing differences/biases. However, this also allows for greater upstream amplification by 84hrs over Central Canada, more like the CMC. The 12z ECMWF/CMC are slower than the UKMET which is timed with the GFS/NAM but still much deeper. So overall, the spread is reduced in placement of the waves along the north side of the 3H jet (which are starting to agree in strength), for greater agreement. Still, favor the less amplified solutions of the NAM/GFS and ECMWF but with increased confidence to average after 60hrs. ---Prior Discussion--- Deep inner core/closed low across southern Hudson will continue to shift northeast with strong surface cyclone across the Northeast US/Southeast Canada today, with frontal zone that will drape southward across the Mid-Atlantic through early Tuesday. A strong short-wave currently in central Alberta will drive southwest ushering in strong Northwesterly flow into the Great Lakes, supporting a surface wave in the Great Lakes by late Tuesday/early Wed with strong model agreement, pressing the cold front in the central Appalachians by Wed night. Through this time (54-60hrs, a general model blend can be supported a above average confidence. Thereafter, a compact shortwave just off WA coast will slide into the northwest flow and cross the northern tier, but into fairly flat to global scale weak ridging and weakens quickly. Though this wave will have importance to timing/placement of baroclinic enhancement to the jet and drawing Dorian northward. However, there is strong model agreement that Pacific jet energy will starting over topping the ridge in the Canadian Rockies and spur deeper shortwave development at its nose into the Northern Tier, with additional left rotor shortwaves strung out into boreal Saskatchewan. The strength and timing of the jet are uncertain with moderate to large model spread across Canada into the Great Lakes region. The typically slower guidance, of the ECMWF/CMC are slower to weaken the initial Pacific shortwave, though the CMC is much stronger with the jet, allowing for a greater amplified upstream wave. The UKMET/NAM/GFS are faster to weaken the initial wave, but the UKMET is very strong with the jet but further north bringing it into Manitoba with a very amplified wave. The NAM/GFS are less strong and therefore are flatter, much like the ECMWF. Given the initial setup and orientation to the Pacific stream, a flatter, slightly weaker 3H jet seem more plausible and fit with the longer-term ensemble trend. While the NAM/GFS are more progressive than the ECMWF...a blend of them seems a more stable yet lower confidence solution at this time. (60-84hrs from Northern Tier/Central Canada, through the Great Lakes. This timing and therefore phasing with Dorian fades into the medium range, so please refer to WPC PMDEPD for greater detail/preference. ...Tropical Wave nearing Mexican East Coast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-Nam blend Confidence: Slightly above average 19z update: No significant departure from the 00z UKMET/CMC/ECMWF to the 12z runs...the UKMET remains north paired with the GFS, but still well displaced from the NAM to keep initial preference/confidence. ---Prior Discussion--- The 12z NAM continues to be quite amplified to the NNW with the wave which longer term ensemble trends and current flow per WV suite, suggest would continue SW for the short-term period. While the 12z GFS and 00z UKMET are slightly more amplified than the 00z ECMWF/CMC, a blend of the four is fairly tight providing slightly above average confidence in a non-NAM blend for this system. ...Hurricane Dorian... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Please refer to the official National Hurricane Center forecast track 19z update: The 12z UKMET slowed sufficiently to not be as close as the 12z GFS to the 15z NHC forecast, so best proxy to 15z forecast is going to be the 12z GFS/GEFS (00z UKMET). The ECMWF, remained the slowest and SW compared to the GEFS/GFS...but still has the CMC and now the UKMET paired with it. ---Prior Discussion--- A blend of the 12z GFS/06z GEFS and closest to the 00z UKMET provide the best proxy to the official 15z NHC forecast track for Dorian with respect to mass fields, all being slightly faster than the 00z ECMWF/CMC that remain slow to lift north. The CMC has stronger northward forcing for QPF due to proximity to the right entrance to the strong northern stream jet...so is out of place even compared to the close surface agreement with the ECMWF. The 12z NAM remains out of phase with the remaining guidance and is further east and eventually further northeast of the otherwise tighter packing of other solutions and is disregarded in QPF/mass preference/proxy. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Gallina