Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 304 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 Model Evaluation Including Final 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. No significant changes were noted in the 12Z ECMWF/UKMET/CMC compared to their previous 00Z cycles, other than a slight nudge faster with the exiting trough axis. ...Mid-level energy advancing south from the Plains today to the lower MS Valley Fri and Ohio Valley Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Near the 12Z NAM/GFS/UKMET 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/ECMWF fastest and 12Z UKMET slowest. While the 12Z CMC remains weaker/flatter with the trough axis, the 12Z ECMWF/UKMET trended quicker. The models, especially the UKMET, have been flip flopping back and forth between slower/stronger (00Z) and quicker/slightly weaker (12Z) cycles. The preference is to be near the middle of the past few cycles of deterministic/ensemble guidance, or near the 12Z NAM/GFS/UKMET which is a slight nudge faster than the previous preference. The 12Z ECMWF may have utility earlier in the forecast, but the 12Z CMC appears to have the lowest likelihood of verifying. ...Tropical Storm Isaias... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: closest proxy to 15Z NHC Advisory... Through 12Z/02: 12Z ECMWF 12Z/02 - 00Z/03: 12Z NAM/12Z GFS blend Confidence: Refer to NHC products The models have significant differences on the track and speed of Tropical Storm Isaias for the weekend, with the 12Z ECMWF/UKMET/CMC generally south and west or slower than the 15Z NHC advisory. Meanwhile the 12Z GFS is faster, north and east of the 15Z NHC advisory. The CMC has been consistently displaced south and/or slow with the track of Isaias compared to NHC for several cycles. Through Saturday night, before model differences expand, the 12Z ECMWF is fairly close to the 15Z advisory for the track of Isaias. A blend of a blend of the 12Z NAM and 12Z GFS also gets fairly close to the NHC track. By Sunday evening however, the 12Z ECMWF slows relative to the NHC advisory with a 50/50 blend of the 12Z NAM/GFS looking reasonably close to the forecast NHC position. The 12Z UKMET is also fairly close to the NHC track but becomes increasingly slower through Saturday and Sunday. 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: Slightly above 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. No significant changes were noted in the 12Z ECMWF/UKMET/CMC compared to their previous 00Z cycles. ...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. No significant changes were noted in the 12Z ECMWF/UKMET/CMC compared to their previous 00Z cycles. 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