Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 111 PM EDT Thu Jul 30 2020 Valid Jul 30/1200 UTC thru Aug 03/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z NAM/GFS Evaluation Including Preliminary Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Mid-upper level troughing over the Northeast to the Ohio Valley and Mid Atlantic through Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average The models show similarly with this system. ...Mid-level energy advancing south from the Plains today to the lower MS Valley Fri and Ohio Valley Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of 12Z GFS/00Z ECMWF Confidence: Average Mid-level energy emanating from the Central Plains will advance through the Ozarks tonight before amplifying into larger scale troughing along the MS River Valley by Saturday/Sunday morning. Associated with the upper trough, the models develop surface low pressure in the lower MS River Valley Fri night to early Sat before the low advances toward the OH Valley. There remain timing differences with the 12Z NAM/12Z GFS fastest, although the 12Z NAM is fastest. The 00Z UKMET trended back toward a slower/stronger solution aloft with the UKMET flip flopping back and forth between its 00Z (slower/stronger) and 12Z (quicker/slightly weaker) cycles. Meanwhile, the 00Z CMC is weaker with the trough overall, but not as fast as the 12Z NAM. The 00Z ECMWF is slower than the 12Z GFS but slightly faster than its ensemble mean, with a middle ground favored. The closest blend for a middle of the road approach is between the 12Z GFS and 00Z ECMWF. ...Tropical Storm Isaias... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: closest proxy to 15Z NHC Advisory... Through 12Z/01: 12Z NAM, 12Z GFS, 00Z ECMWF blend 12Z/01 - 00Z/03: 12Z NAM/12Z GFS blend Confidence: Refer to NHC products The models have significant differences on the track of Tropical Storm Isaias, with the 00Z ECMWF/UKMET/CMC generally south and west of the 15Z NHC advisory. Meanwhile the 12Z GFS is north and east of the 15Z NHC advisory. The 00Z UKMET/CMC are consistently displaced south and/or slow with the track of Isaias compared to NHC. Through Saturday morning, before model differences expand, a blend of the 12Z NAM, 12Z GFS and 00Z ECMWF is closest to the NHC track. From Saturday morning through Sunday evening, a 50/50 blend of the 12Z NAM and 12Z GFS positions is closest to the NHC track. It should be noted that the 12Z GFS shows a stronger system when compared to the NHC advisory and remaining deterministic guidance by Sunday afternoon. ...Cold front moving through the north-central U.S. Friday and Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average There is relatively good agreement for the trough axis and related cold front impacting the north-central U.S. through Saturday. While minor timing differences are evident, a general model blend appears reasonable given the differences are small enough at this time. ...Upper low/trough approaching the Pacific Northwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average Fairly good agreement continues in the models for this system with only minor timing differences noted. Run to run consistency has been good and ensemble spread is relatively small. Therefore confidence is slightly higher than average for this system. 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