Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1216 AM EDT Mon May 21 2018 Valid May 21/0000 UTC thru May 24/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z model evaluation...with preferences and confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Weakening shortwave energy over the Midwest... ...Surface wave crossing the OH Valley/Lower Great Lakes... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Above average There is good model agreement in general with the shortwave energy currently moving across the Midwest which will move downstream and gradually shear out across the OH Valley through Tuesday. The energy though will be strong enough to foster a wave of low pressure across the OH valley and lower Great lakes region through Tuesday which will move into the Northeast Tuesday night. The 00Z NAM is perhaps a little too strong with the energy as it moves downstream. The global models are rather well clustered surface and aloft, so will suggest a non-NAM blend at this time. ...Trough digging across the Northeast by Tuesday/Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Above average The guidance depicts an amplification of a northern stream shortwave trough across the Northeast by Tuesday and Wednesday. The 00Z NAM edges toward the stronger side of the model suite, with the global models all a little less amplified. Will prefer a non-NAM blend with this evolution for now. ...Large scale trough/closed low impacting the West... ...Energy crossing the northern High Plains by Thursday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z GFS, 12Z UKMET, and 12Z ECMWF Confidence: Average The models are in excellent agreement in digging height falls across the West over the next couple of days which includes a well-defined closed low that digs in across the Southwest through Tuesday. On Wednesday, this closed low feature will begin to lift off to the northeast, and the energy should open up into a progressive trough by Thursday that will be ejecting up across the northern High Plains. The 00Z NAM in general looks a little too deep with the troughing across the Intermountain West, and the 12Z CMC is the most progressive by the end of the period to eject its height falls out across the High Plains. The 00Z GFS, 12Z UKMET and 12Z ECMWF are well clustered with their respective timing and depth details, and given good ensemble support, a blend of these solutions will be preferred. ...Mid level trough/closed low lifting up across the Southeast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The guidance is in very good mass field agreement with this system, so a general model blend will be preferred. ...Shortwave energy/vorts lifting across the Plains Tuesday and Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z UKMET and 12Z CMC Confidence: Average Multiple shortwave impulses are expected to lift northeast out of the base of the Western U.S. trough and across the Plains on Tuesday and Wednesday, but the guidance is rather well clustered on at least a very well-defined and convectively enhanced vort that will cross over southeast NM and far west TX early Tuesday before lifting up across the High Plains. Generally speaking, the 00Z NAM and 00Z GFS look a bit too amplified, and the GFS definitely has some convective feedback concerns at least briefly over southeast NM and west TX. The 12Z ECMWF though does not look strong enough which is also reflected in its QPF fields. A compromise toward the 12Z UKMET and 12Z CMC will be preferred which supports a solution in between stronger and weaker camps. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison