Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 245 PM EDT Sun May 24 2020 Valid May 24/1200 UTC thru May 28/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation Including Final Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Shortwave trough crossing the Great Lakes through Sunday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: High A mid-level crossing the northern Great Lakes this evening will be advancing across northern New England on Monday along the northern periphery of the building East Coast ridge. The models are in good agreement with this system, and so a general model blend will be preferred. Shortwave over the northern Plains through Monday night ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z ECMWF/NAM/UKMET Confidence: Moderate-High A closed low initially over Wyoming and eastern Montana is forecast to evolve into an open wave as it reaches the western Dakotas by Monday afternoon. By Tuesday this disturbance should become absorbed by the westerlies across southern Canada. The 12Z GFS is stronger and a little faster with the trough as it crosses the Dakotas, and the CMC is the weakest solution and farther east with the surface low over the Upper Midwest. A blend of the 12Z ECMWF/NAM/UKMET works well as a starting point in the forecast. Synoptic scale trough over the West evolving into closed low over southern Plains ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z ECMWF/GFS/GEFS mean/00Z EC mean Confidence: Moderate A synoptic scale upper trough initially over the Intermountain West is forecast to emerge over the central and southern Plains over the next couple of days, and then evolve into a cut-off upper low situated over Texas and Oklahoma by the middle of the week. There will be a couple of smaller shortwaves pivoting around the southern periphery of the trough emerging from the Rockies, and these will lift northeastward across the southern Plains and serve to enhance convection across that region. The 12Z GFS is more amplified with these shortwaves and is also stronger with the developing closed low over the Red River Valley. By Wednesday morning, the NAM is farther to the west with the low compared to the other models, and the UKMET is slightly farther south. Both the 12Z GFS and ECMWF have good ensemble support, and thus a blend of these models along with their ensemble means will suffice. Mid-level trough and weak surface low impacting Florida early in the week ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z NAM/GFS/ECMWF blend Confidence: Moderate An upper level ridge will be building across the Southeast and the East Coast through the beginning of the week. South of the upper ridge will be a low-mid level trough axis that will gradually lift northward to the eastern Gulf of Mexico, with a weak surface wave of low pressure likely developing along it by Monday. Although this does not appear particularly impressive in terms of mass fields, it will be significant for QPF purposes. The 12Z UKMET remains a little more suppressed with the 700 mb trough across Cuba and the Florida Straits, and this keeps the heaviest rainfall farther south than the relatively well clustered NAM/GFS/ECMWF. The 12Z CMC, albeit to a lesser degree, also appears farther south with its QPF axis through Day 2 across South Florida. An initial blend consisting of the 12Z NAM/GFS/ECMWF should work well and maintains good continuity with earlier preferences. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hamrick