Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 245 PM EDT Sun May 20 2018 Valid May 20/1200 UTC thru May 24/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z model evaluation...with final preferences ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Shortwave troughs exiting the East today/tonight with cold front across the Northeast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models show similarly with this system. ...Weakening shortwave trough over the central Plains today and crossing the Midwest through Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non 12Z NAM blend Confidence: Average Decent model agreement begins to break down after 00Z/22 with the 12Z NAM appearing stronger with the mid-level shortwave and surface low near the Great Lakes Tuesday morning but with the latest ensemble guidance not showing much support for a low as it tracks east through the Great Lakes/Ohio valley. The 12Z NAM also ends up toward the faster side of the model spread with its cold front nearing the East Coast. Outside of the 12z NAM, the models show enough agreement for a blend. ...Closed low digging into the Southwest Monday and Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models continue to show similarly with this system, displaying only minor depth spread noted toward the end of the period. Will prefer a general model blend. ...Mid level trough over the eastern Gulf of Mexico... ...Lifting up across the Southeast on Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average Only minor differences exist with this system such that a general model blend can be used for this system. ...Shortwave energy/vorts lifting across the Plains Tuesday and Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS, 12Z UKMET and 00Z ECMWF Confidence: Average A complex evolution with weak height falls into the central and northern Plains makes for a challenging forecast. The 12Z NAM stands out with a more aggressive shortwave lifting into the northern Plains early Wednesday and a farther north warm front extending roughly northwest to southeast across the north-central U.S. The 12z GFS is also north with the 12Z ECMWF/UKMET south. The 12Z ECMWF adjusted south of most guidance with its warm front across the central to northern Plains but given little support for the front that far south, the 00Z ECMWF appears to be a better fit with a blended approach. The ensemble means support their parent models which leaves room for changes for future cycles. For now, given the GFS is within the ensemble spread and does not stand out enough to discount it from a blend, it will be included as part of the preference with the 00Z ECMWF/12Z UKMET near continuity. The CMC looks too quick with mid-level height falls into the Plains and will be excluded from the preference. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto