Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 244 PM EDT Sun Jun 21 2020 Valid Jun 21/1200 UTC thru Jun 25/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ MCV over the Red River Valley approaching the Arklatex ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z ARW/ARW2/NMMB/HRRR Confidence: Average A well-defined MCV over the Red River Valley of the South will be moving slowly off to the east this afternoon and will cross the Arklatex and adjacent areas of the lower MS Valley going through tonight. The global models currently still have a poor handle on the strength of this energy, especially with their resulting QPF signal going through tonight. The hires CAM guidance is doing much better with strong exception to the 12Z NAM-conest which appears to be dampening out its energy too quickly this afternoon and evening. Will prefer a blend of the hires guidance with this energy led by the 12Z ARW/ARW2/NMMB/HRRR solutions. MCV/trough over the OH Valley approaching the Mid-Atlantic ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average A larger MCV/trough that is traversing the lower OH Valley will lift northeast and cross areas of the central Appalachians and the northern Mid-Atlantic region going through Monday. The global models and hires CAM guidance show a rather sharp leeside trough developing over south-central Pennsylvania, western Maryland, eastern West Virginia and western Virginia by midday which then shifts slowly eastward by evening to near or just east of the Blue Ridge. The 12Z GFS/NAM/NAM-conest solutions are a tad stronger with the leeside trough than the 12Z non-NCEP models along with the remaining 12Z hires CAM suite of guidance, but there is very good agreement on the placement of it. A general model blend will be preferred for the time being. Closed low over Manitoba/Ontario Shortwaves crossing the Great Plains and Midwest ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS/UKMET/ARW/ARW2 blend...Plains energy Non-NAM blend...broader closed low/trough Confidence: Average The large closed low currently over Manitoba will remain the dominant weather driver over the Plains and Midwest as multiple shortwave troughs round the base of it and interact with existing fronts across the region. The models in particular drive one shortwave trough down across the central Plains tonight and early Monday which will likely lead to a significant convective outbreak and threat of excessive rainfall. The 12Z NAM appears to be a tad too strong with this energy, with the global models reasonably well clustered. The 12Z ECMWF though appears to be one exception as it looks too weak. Of the hires CAM guidance, the 12Z NMMB appears to be too weak as well. Based on the latest model clustering, a blend of the 12Z GFS, 12Z UKMET, 12Z ARW and 12Z ARW2 will be preferred with this shortwave. Regarding the upper low, the global models are relatively well clustered with timing and depth through the period as it moves east. Toward the end of the period, the 12Z NAM places its upper low a tad north of the multi-model consensus, and also has stronger shortwave energy rounding the base of it involving the Great Lakes and the OH Valley. A non-NAM blend will be preferred with the broader closed low and troughing evolution as a result. Troughs approaching British Columbia and Pacific Northwest ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-GFS blend Confidence: Slightly above average A pair of shortwave troughs will impact the Pacific Northwest and adjacent areas of British Columbia going through the middle of the week as energy rounds the base of the deep Gulf of Alaska closed low. The first shortwave will arrive mainly across British Columbia by late Monday. The 12Z GFS is a slower and stronger outlier solution with this energy versus the remaining well clustered guidance which agrees on a relatively flatter and more progressive evolution. A second shortwave will be arriving and tending to amplify a bit over the Pacific Northwest on Wednesday. The 12Z GFS and to some extent the 12Z UKMET are also seen as being a tad deeper with this energy compared to the remaining models. The latest ensemble guidance yields poor support for the GFS, and therefore a non-GFS blend will be preferred given this and the clustering of solutions away from it. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison