Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 228 AM EDT Sun Aug 25 2019 Valid Aug 25/0000 UTC thru Aug 28/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Strong Closed Low Tracking Across Northern Tier/Southern Canada... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend weighted toward 00z ECMWF/GFS/CMC Confidence: Above average becoming slightly above average by Day 3 07z update: The 00z UKMET showed significant improvement shifting north; however, it is a deeper solution and therefore tucked west with the surface wave relative to the ECMWF/GFS. This is a minor difference that would be fine blending out and supporting a general model blend weighted to the new 00z ECMWF/CMC and the GFS. ---Prior Discussion--- The tightly packet deterministic guidance that had been consistent for the past few days with the large/high-amplitude northern stream trof digging across the Plains into Lower MS Valley has become a bit less agreeable, more typical of the spread given the pattern, especially at intersections with other streams (like out of the Western Gulf), where phasing/timing is tricky. The disagreement in the northern most portion of the trof, with the closed low, in Southern Canada and the northern Tier, continues to be mostly a displacement south of the UKMET. The 18z GFS joined the UKMET, but the 00z GFS shifted back north until the low becomes quite mature into late Tues/Wed. The ECMWF/ECENS are well north of the GFS but still show best consistency and agreement, though the 18z GEFS showed some more similarities to suggest the GFS/ECMWF and their ensembles, as well as inclusion of the 00z NAM is preferred for this portion of the system. ...Shortwave Crossing KS, Lifting through Great Lakes and Pressing Cold Front into Upper Ohio Valley... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average 07z update: The issues with CMC have become better resolved, while still presenting a stronger triple point (like the UKMET), it does not appear to have a negative result on the sensible weather, so a general model blend could be employed for this portion of the wave. This also includes the slowly sinking tail end to the cold front and QPF axis across the Central then Southern Plains (Red River) by 12z Wed. ---Prior Discussion--- Further south, through the Central Plains, as the MCV/shortwave currently in KS starts to shear and lift back through IL into the Great Lakes late Monday into Tuesday; the 12z CMC shows some negative over amplification bias as the system deepens through the Great Lakes and even dominates the closed low further west, shifting the whole cyclone east, well departed from the ensemble suite/remaining guidance. The 00z NAM is a bit stronger and delays the frontal zone push eastward relative to the other guidance but not significantly and blended with the typical fast bias of the GFS suggests, a non-CMC blend is preferable here. ...Western Gulf Tropical Wave/Phasing with Base of Northern Stream Trof... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend weight slightly more to 00z GFS Confidence: Average 07z update: The 00z ECMWF trended a bit less active with the tropical wave and therefore is much weaker. While it is still a bit deeper than the GFS/NAM and CMC, it has a partner in the UKMET which seems equally plausible. The timing of the ECMWF with the other guidance pressing the phased trof through the southeast fits well with a general model blend, but still favoring the GFS a bit more in the blend overall. ---Prior Discussion--- The base of the trof, shows the greatest spread in its interaction with the tropical wave lifting through the Western Gulf into LA later today. The 12z ECMWF, shows very strong convective development of the wave even with a surface inflection that lifts north into TN/Cumberland Plateau, which is too intense and depicts a very strong QPF response that is overdone as well. The 00z NAM along with the 12z UKMET and CMC support greater strength in the sheared trof along the Gulf Coast as the two streams meld by Tuesday. The 00z GFS also trended this direction but are weaker than the NAM/UKMET. Continuity and trends would favor the GFS slightly in a non-ECMWF blend for this tropical wave. ...Tropical/Subtropical Wave off Florida, lifting along Gulf Stream... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Average 07z update: The 00z ECMWF trended a bit slower and weaker and looks very similar to the GFS even depicting a slight westward jog toward 12z Wed due to the approaching height falls and connecting to the old frontal zone. The 00z UKMET and CMC both start a bit east of the GFS/ECMWF and meander similar to the GFS/ECWMF pair but slightly east through each forecast step, with the UKMET a bit faster than the CMC. A GFS/ECMWF blend could be employed but to cover the modest spread a non-NAM solution is preferred at average confidence. ---Prior Discussion--- Along FL east coast through the Gulf Stream, the tropical invest area continues to show solid continuity of a deepening surface wave, however, the depth of the wave continues to trend slightly weaker and slower lifting east-northeast. The 00z GFS matches placement and timing with prior run, along with the weaker UKMET/CMC, but the 12z ECMWF is clearly still fastest and eventually deeper by 12z Wed too. The 00z NAM also continues to be very slow...so would prefer a 00z GFS/UKMET/CMC blend for this wave at average confidence. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Gallina