Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 127 PM EDT Sun Aug 02 2020 Valid Aug 02/1200 UTC thru Aug 06/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z NAM/GFS Evaluation Including Preliminary Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Mid-level shortwave lifting from the Lower Great Lakes into southeastern Canada through tonight with accompanying surface low... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models show similarly with this system. ...Tropical Storm Isaias... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 03Z NHC advisory package Best model proxy: through 12Z/04: 12Z GFS, 00Z ECMWF, 00Z CMC blend 00Z/05 - 12Z/05: 00Z ECMWF/UKMET/CMC blend 00Z/06: near the 00Z ECMWF The 15Z NHC forecast track of Tropical Storm Isaias is overall closest now to a multi-model blend consisting of the 12Z GFS, 00Z ECMWF, 00Z UKMET and 00Z CMC. The model's proximity to NHC varies over the course of the next 3 days, but the 12Z NAM stands out the greatest with a timing that is 6 to 12 hours slower than the NHC track through Wednesday morning. Individual model timing varies considerably compared to the NHC track, where some models that are initially slower than NHC (00Z UKMET), speed up their timing to be faster than NHC by Wednesday afternoon. However, all of the models support the system rapidly lifting through New England by the end of the period. Please consult the latest NHC forecast advisory package for more details. ...Northern stream trough setting up over the Great Lakes on Monday/Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 06Z GEFS/00Z ECENS blend, or nearest to the 12Z NAM, 12Z GFS and 00Z UKMET Confidence: Average Northern stream energy will be digging down across the Great Lakes through Sunday with likely development of an elongated closed low a bit farther north over Ontario by Monday and Tuesday. The 00Z ECMWF/UKMET and 00Z CMC differ with the handling of two main vorticity maxima within the larger scale trough. The 00Z ECMWF stands out the greatest from the deterministic/ensemble guidance but there is growing support for a solution edging in the direction of the 00Z ECMWF noted by its mean and the 00Z UKMET/CMC. However, a blended approach near the 12Z NAM, 12Z GFS and 00Z UKMET is nearest to the preference of the ensemble means at this point, with the ensemble means considered best. ...Upper low/trough crossing the Pacific Northwest tonight... ...Energy dropping down over the Northern Plains/Midwest for Tuesday/Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z NAM, 12Z GFS, 00Z ECMWF Confidence: Slightly below average An upper trough will cross in through British Columbia and the Pacific Northwest tonight and then track well inland through Monday and Tuesday with the main focus of the height falls remaining across western and central Canada. However, the guidance supports some energy in the base of the trough separating out across the far northern Rockies and then advancing southeast by Wednesday across the northern Plains and Midwest. The 12Z NAM/GFS remain on the stronger side of the guidance with this energy over the northern U.S. Monday night through Tuesday...as is the 00Z CMC. This is reflected in the latest ensemble spaghetti plots which indicate the NAM/GFS/CMC on the edges of the latest member distribution. However, the 00Z ECMWF/UKMET are weaker and faster with this system tracking near the U.S./Canadian border. The 00Z UKMET and 00Z CMC are on the edges of the latest deterministic guidance, and so the preference is to equally weight the 12Z NAM, 12Z GFS and 00Z ECMWF. The thinking here is that a blended approach of these models will be closest to verification, lying in the middle of the model spread and near the middle ground considering trends. ...Southern stream trough moving into CA by Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models show similary with this system. ...Mid-upper level trough nearing the Pacific Northwest late Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average Only minor timing differences were noted, but agreement is fairly good for a day 3 forecast. 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