Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 303 PM EDT Sat Aug 01 2020 Valid Aug 01/1200 UTC thru Aug 05/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation Including Final Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Mid-level trough digging across the Mid-MS/TN/OH Valleys... ...Surface low crossing the OH Valley/Lower Great Lakes... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z NAM/12Z GFS/12Z ECMWF Confidence: Slightly above average ...19Z update... The 12Z UKMET/CMC adjusted closer in line with the consistent NAM/GFS/ECMWF, with enough adjustment to allow for a general model blend. ...previous discussion follows... Mid-level energy in place over the Lower Ohio Valley Saturday afternoon will drive a surface low north-northeastward from southern IL/IN into southern Ontario/Quebec late Sunday. The shortwave embedded within a longwave trough axis will lift northeastward into Canada as well before shearing out across eastern Canada in southwesterly mid-level flow. The 12Z NAM/GFS continue to show good agreement with each other and the 00Z ECMWF. The 00Z ECMWF remains a tad quicker while the 00Z UKMET is slower. Overall, these differences are relatively minor but quicker trends and the even slower/weaker 00Z CMC stand out enough from the group to discount the 00Z UKMET/CMC. A blend of the 12Z NAM/12Z GFS and 00Z ECMWF look best at this time ...Hurricane Isaias... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 03Z NHC advisory package Best model proxy: near the 12Z GFS ...19Z update... No major adjustments were seen in the 12Z non-NCEP guidance, but given the 12Z CMC increased its forward speed on Tuesday along the East Coast, the CMC was removed from the preference. The 12Z ECMWF/UKMET remain as slow/slower (respectively) compared to their previously 00Z cycles. ...previous discussion follows... The 15Z NHC forecast track of Hurricane Isaias does not match any single model or model blend consistently throughout the 84 hour short range period. However, the 12Z GFS is fairly close to the NHC track, but the GFS is closer to the coast compared to NHC through Tuesday. By Monday evening, the 00Z CMC (which was west or south of the NHC track early on) catches up and actually outpaces the NHC track by a little while the 12Z GFS falls behind slightly in timing compared to NHC. Therefore, the closest model guidance to NHC is the 12Z GFS through 00Z/04, but a blend of the 12Z GFS and 00Z CMC from 00Z/04 to 00Z/05. Again, no single model or model blend matches exactly with the NHC track so consult the latest NHC forecast advisory/discussion for more details. ...Northern stream trough setting up over the Great Lakes... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average ...19Z update... The 12Z UKMET and 12Z CMC continued to trend toward the agreeable NAM/GFS/ECMWF, such that they can now be included as part of a general model blend. ...previous discussion follows... Northern stream energy will be digging down across the Great Lakes region this weekend with suggestion of an elongated closed low developing a bit farther north over Ontario by Monday and Tuesday. The latest guidance is in fair agreement but the 00Z UKMET/CMC become a little west or deeper than the remaining model consensus by Tuesday morning. ...Upper low/trough approaching the Pacific Northwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z NAM, 12Z GFS, 12Z UKMET blend Confidence: Average ...19Z update... The 12Z ECMWF made a significant adjustment in that it shows greater amplification of a northern shortwave and greater interaction/phasing with the southern shortwave entering into British Columbia Sunday night. The interaction of the two pieces of energy seen in the ECMWF results in a weaker surface reflection across southern Saskatchewan compared to the remaining model consensus. The 12Z CMC remains excluded from the preference due to its faster timing of the southern shortwave along the U.S./Canadian border. ...previous discussion follows... Timing differences show up with the trough axis as it nears British Columbia and the Pacific Northwest late on Sunday and then advances inland across the far northern Rockies and adjacent areas of southwest Canada on Monday. The 00Z CMC ends up being on the weaker and more progressive side of the guidance as the energy advances inland. While minor timing differences remain among the non 00Z CMC guidance, agreement is good enough to support a general model blend (excluding the 00Z CMC) at this time. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml This product will terminate August 15, 2020: www.weather.gov/media/notification/pdf2/scn20-58pmdhmd_termination. pdf Otto