Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1214 AM EDT Thu Jul 16 2020 Valid Jul 16/0000 UTC thru Jul 19/1200 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 00Z Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Long wave trough crossing the north central US through Thu with an accompanying surface cold front... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average The 00z GFS trended a bit weaker with the wave crossing the Great Lakes tonight and falls well within the overall tight packing in the model mass fields. This continues as it progresses across New England. The 00z NAM is a bit deeper, retains some amplification as it flattens, relative to the remaining guidance suite but not enough to remove it from the preference. As such, will maintain a general model blend with confidence remaining slightly above average. ...Cut off low west of California by Thursday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The 00z NAM/GFS continue to be close the 12z UKMET/ECMWF/CMC runs with the weakness between the zonal/broad subtropical ridge across the Southeast to the Southwest and the stronger East/Central Pacific Ridge. The wave continues to shear/retrograde under the Pacific ridge with some energy shifting into the Pacific NW with little fanfare. As such, a general model blend will continue to be preferred with this system at above average confidence. ...Long wave trough crossing the Pacific Northwest Thu, moving into south central Canada by Sat, clipping the Northern Plains into Upper Great Lakes by Sun... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend, reduce NAM weighting after 19.00z Confidence: Slightly above average The leading edge of height-falls clips the Pacific Northwest on Thursday as the core of the upper level-long wave trof tracks east across Northern BC/Alberta. The wave descends in latitude after crossing the Canadian Rockies, which will help drop a frontal zone across the Northern Tier. Here, the mass fields are in fairly good agreement in timing; only the 12z CMC appears a bit out of place eventually moving out of tolerance (generally a bit south with the surface low in Canada and north across the Central High Plains) by 72hrs. The 00z NAM, perhaps due to higher grid scale, suggests a stronger, higher convective clustering/QPF result across the upper Midwest as the front presses through. This falls in line with typical end of Day 3 bias, but is not dramatic enough to suggest it is not in the realm of probability. As such will support a Non-CMC blend overall at slightly above average confidence, but reducing influence of the NAM after 19.00z. 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 Gallina