Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 244 PM EDT Thu Aug 01 2019 Valid Aug 01/1200 UTC thru Aug 05/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation and Preferences/Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Central U.S... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Average The main forecast issue for this time period is the shortwave energy riding over the top of the mid-level ridge that retrogrades slowly westward across the Four Corners area through Saturday. The models show the energy dropping down across SD/NE tonight through midday on Friday and then across eastern KS Friday night and early Saturday. The 12Z UKMET is the weakest of all of the guidance with the energy as it drops down the east side of the ridge axis, but the 12Z NAM is by far the most intense and appears notably too strong in relation to not only the global models, but also the consensus of the 12Z hires guidance, although the 12Z NAM-conest does edge stronger than the remaining hires models (ARW, ARW2, NMMB) by early Saturday. The NAM-conest though at least is a more modest version of NAM itself. The NAM tracks its mid-level energy and a supporting wave of low pressure well east of all of the global models going through Saturday and into Sunday, which also leads the NAM to be much wetter farther off to the east involving parts of the middle and lower MS Valleys (MO/AR/MS)versus the global models. Accounting for the NAM being such a strong outlier, and with the remaining guidance at least clustering better on a track of the mid-level energy and surface details, a non-NAM blend will be preferred. ...Northeast U.S./Southeast Canada... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Across the Northeast and Quebec, there is generally good model agreement with the evolution of the mid-level closed low and larger scale trough axis, so a general model blend is preferred here, as operational models cluster well with the ensemble means. ...Pacific Northwest/Southwest Canada... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z CMC/UKMET/ECMWF Confidence: Average The guidance agrees in taking a positively tilted longwave trough across portions of the Pacific Northwest and British Columbia off to the east toward central and southern Canada going into the weekend. The 12Z NAM becomes a stronger outlier with shortwave energy amplifying into the base of the trough by Sunday. The 12Z GFS is weaker with the shortwave energy, but has a stronger closed mid-level low over central Canada by the end of the period. The 12Z non-NCEP models are in between the NAM and GFS camps. The latest ensemble means per the GEFS mean and ECENS mean are supportive of the non-NCEP guidance, and thus a blend of the 12Z CMC/UKMET/ECMWF solutions will be preferred. ...Upper low/trough off the Pacific Northwest by Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Above average The models take a portion of the energy traversing southwest Canada and pinch off a new trough/closed low just offshore of WA/OR by Sunday. The 12Z NAM is farthest east with this energy, with the remaining global models now well clustered together a bit farther west and supported by the latest ensemble means. Will prefer a non-NAM blend as a result. ...Upper trough over the Gulf Coast/Southeast... ...Wave axis impacting Florida... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z CMC/UKMET/ECMWF solutions Confidence: Slightly below average A broad upper trough over the Gulf Coast states and adjacent areas of the Southeast will be interacting with a surface trough impacting the east coast of Florida over the next couple of days. The 12Z NAM and 12Z GFS tend to be a tad stronger than the non-NCEP guidance with this troughing, although the NAM becomes the bigger outlier as a result of its apparent mishandling of the energy dropping down from the central Plains into the lower MS Valley. Regarding the surface trough impacting Florida, the guidance is gradually supporting development of a weak low center along this as it lifts northeast up off the Southeast coastline this weekend. The 12Z UKMET becomes the strongest solution, with the 12Z NAM and 12Z CMC a tad weaker. The 12Z GFS and 12Z ECMWF are the weakest solutions, but still support a low center. The GFS is farthest west of all the guidance with the track. The NAM and GFS are generally considered more outlier solutions compared to the other global models and the ensemble means, so will prefer a non-NCEP model blend at this point. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Orrison