Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1217 PM EDT Sat May 12 2018 Valid May 12/1200 UTC thru May 16/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z model evaluation including preferences and forecast confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Stationary closed low in Great Basin slowly fills through Tues ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Closed low is parked over northern Great Basin and remains there slowly filling through Tues before nearly evaporating in the flow by 00z Wed in southern ID. There is small variation with precise depth/location by Wed, but overall this is very strong agreement to have above average confidence in a general model blend. Developing closed low with weak surface inflection across Eastern Gulf of Mexico by Sunday and drifting toward MS/AL coast by late Tues ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z NAM/GFS and 00z ECMWF blend Confidence: Slightly above average Currently surface easterly wave is producing convection well west of current guidance suggestions but mid-level wave/axis appears well placed with the overall scheme. The 12z NAM depicts this bi-model development/low level mass response a bit better in placement but likely a bit too aggressive with the convective response. Similarly the 00z ECMWF is a south and west member within the ECENS suite but adjusts with time toward the north and east...while the GFS and GEFS solutions are near the ECENS means. The GFS shows favor toward increased convection along the eastern side of FL with limited low level mass response compared to a similar convective development seen in the UKMET which does respond with a SW to NE oriented troughing; though the UKMET mass looks out of phase with the ensembles. The 00z CMC while initially well placed with the overall cluster, responds to greater height falls over the Southern Plains by Tuesday and lifts NW a bit too fast in the ensemble suite and cycle to cycle ensemble spaghetti analysis trend. Overall, a NAM/GFS and ECMWF blend look a good compromise to this trend and overall ensemble clustering. Confidence is slightly above average given fairly tight spread but influence of convection that is likely to evolve with enough variance to the mass fields to have full confidence in this blend coming to fruition. Persistent stationary front from Central Plains, N Ohio Valley to Mid-Atlantic with near daily weak surface waves before becoming less defined toward late Monday into Tuesday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average through Monday...Average afterward. Broad global scale closed low centered in Hudson Bay and closed low spitting out shortwave features into the Central Plains on a daily basis move into gentle confluent flow across the Midwest and Northern Ohio Valley into the Mid-Atlantic. Initial surface responses to the waves are stronger with a better well defined quasi-stationary surface front with daily (centered near convective maxima) surface wave rolling along the boundary maintaining convective clusters/MCS feed back to the larger scale synoptic mass fields and keep a fairly stable/consistent low level surface pattern for the next few days. However, as the closed low fills in the West, the shortwaves ejected become equally weak and ill-defined...and along with tightening mid-level ridging across the Lower Ohio (due to the approach of the closed low in the Gulf), the mass field response is very messy and becomes influenced more at the convective/outflow scales making model choices near impossible. Still, a general model blend will retain the larger scale synoptic/stationary front pattern at some moderate confidence, though that significantly reduces by the end of the forecast period. Please refer to QPFPFD for additional model preferences, given the importance of convective placement/strength to the mass fields. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina