Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1230 PM EDT Tue Jun 19 2018 Valid Jun 19/1200 UTC thru Jun 23/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z model evaluation...including preferences and confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Large scale troughing over the Northeast this period...shortwave and coastal surface low by Thurs morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Above average The 12z NAM depicts a slightly further north shortwave axis/deformation connecting the exiting larger scale trof across the Northeast and the approaching shortwave feature out of the Great Lakes on Wed into Thurs. Here the NAM focuses convection along the deformation zone north of the other guidance that is closer the sfc boundary and warm sector. This leads to a deeper/northward shift in the coastal low development. The remaining guidance looks to have the placement of the shortwave and frontal zone fairly well, but the UKMET may be a bit quick with the sfc wave itself exiting the Mid-Atlantic coastal Atlantic. As such a Non-NAM blend is supported, but weighted toward the middle ground solutions of the 12z GFS and 00z ECMWF ...Mid level low center/surface trough over Texas... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z NAM/00z ECWMF with some low weighting to 12z GFS Confidence: Slightly below average The 00z UKMET remains the only significant compact outlier with respect to the system across S TX. The 12z GFS continues to be the weakest solution, quickly dissipating the energy across S TX, but also it the best aligned initially with the elongated shortwave energy shearing into the northern stream (tilted SW-NE across E AR, rather than more N-S over the Ozarks), so there is something to take into account and keep in the blend. The 00z CMC continues to suggest deep/compact energy lifting north across the ARKLATEX region, and weakening out the remaining energy in S TX. The ECMWF appears a better middle ground solution with good continuity and supported by the 12z NAM. As such will favor a blend of the 12z NAM and 00z ECMWF but inject some lower GFS weighting especially across AR into the northern stream. Moderate spread and uncertainty related to convective process and its upscale feedback, provide slightly below average confidence in this blend. ...Closed low over the West, dropping down across the Mid MS Valley by Friday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-UKMET blend Confidence: Slightly above average The 00z UKMET appears north and generally weak with the wave crossing out of the High Plains into the Lower MO valley, not spurring a strong occluded low like the GFS/CMC and lesser so the ECMWF. This may be related to reduced injection of shortwave energy from the inverted trof/closed low in the NW Gulf/S TX region, which seems unlikely given current observational The 12z GFS continues to be the most aggressive with this deeper occluded remaining on the western side of the ensemble suite. The 12z NAM is uncharacteristically weak with the surface wave depicting no occlusion but more of stationary center in the MS River valley waiting until Fri to shift eastward, within the ensemble suite, it is not ideal but also not well out of the realm of possibility to keep it in the blend. As such a Non-UKMET blend is preferred at slightly above average confidence. ...Shortwave crossing through mean large scale ridge in Northwest Thurs/Friday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Average Here the 12z NAM enters the Pacific NW late Wed, a bit north but with reduced ridging downstream and begins to amplify into E WA a bit too aggressively and retains this amplification through MT. Likewise the UKMET is stronger but remains in the same general belt of latitude as the remaining consensus of the 12z GFS/00z ECMWF/CMC and the overall ensemble suite; the UKMET though reduces some amplification toward Friday matching up with the 00z ECMWF in MT. The 12z GFS after crossing the mean ridge into MT, becomes compact and slows relative to the ECMWF/UKMET, but remains in the realm of possibility. As such a Non-NAM blend is supported though confidence is average in this blend given uncertainty of a shortwave crossing through a large-scale ridge where small timing differences can lead to larger/compounding downstream spread as noted in the remaining guidance in the blend. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina