Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1213 PM EDT Mon Jun 04 2018 Valid Jun 04/1200 UTC thru Jun 08/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z model evaluation including preferences and forecast confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Closed low forming over southern Ontario/Quebec today sliding thru the Northeast Tues with associated surface low moving through southern Quebec today into Tues and redeveloping over SE New England on Tues... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 06z GEFS Confidence: Average Ensemble run to run trend has been shifting toward faster solutions, however, the overall fastest solutions (typically NCEP guidance, GFS/NAM) have been too fast to the overall trend. The ECMWF and more so the 00z ECENS mean/CMC are much too slow (even compared to the slightly faster 00z CMCE. The 06z GEFS seem a very nice compromise, hedging toward the faster solutions but still slower than the 12z GFS/NAM which is in line with current WPC thinking. As such will favor the 06z GEFS at average confidence. ...Central/Southern Plains shortwave sliding into the lower MS valley Tues before stalling in NE Gulf thru Thurs... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z GFS/NAM and 00z ECMWF blend Confidence: Slightly above average Decaying MCS across N TX along with slightly higher scale S/W over KS has slipped through the mean large scale ridge and will descend in latitude toward the lower MS valley. Here model guidance is fairly good in timing/orientation but as the trof settles to the eastern Gulf. The 12Z NAM is a bit deeper, but this seems to be consistent with higher resolution than any particular negative feedback and is fairly on par with the 00z ECMWF. The 12z GFS is shallower but very tight in the mean axis. The 00z UKMET is most washed out, perhaps too much. the 00z CMC is a clear outlier as the trof axis is displaced/slow and perhaps a bit too broad respectively. All considered a 12z GFS/NAM and 00z ECMWF blend at slightly above average confidence. ...Upper level troughing along the West Coast through Tuesday with embedded shortwaves and surface low reaching North Dakota/south-central Canada Tuesday night and through upper Midwest by Thurs.. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average A complex large scale pattern with numerous shortwaves moving through the mean base across the Pacific NW will dominate the forecast period, eventually expanding the large scale mean ridge further NW into the Rockies as the upper low focuses in the SE Gulf of AK Thurs/Fri. Lead height falls today into tomorrow clip the NW into MT, but help to deepen/shift the closed low over N Alberta further east in preparation for the more significant wave Wed. This second wave, using the flattening flow upstream, accelerates over the top of the ridge into the Dakotas by midday Wed supporting a south central Canadian surface low with an inverted surface trof/frontal zone crossing the Dakotas into the Upper Midwest by Thurs. While there are subtle but typical differences... 12z GFS a bit fast, the 00z CMC a bit slow, the affects across the US are minor in comparison. Here a general model blend is likely sufficient for moderate confidence...though would hedge toward the middle ground solutions (UKMET/NAM/ECMWF). The lingering trailing shortwave amplifies a bit just offshore central CA early Wed with little fanfare, but as it slides into the Intermountain West, allows for increased upslope flow regime and increased diffluence over the northern High Plains. The 00z GFS/NAM are faster and earlier to convect compared to the ECMWF, but given mesoscale influence...choosing one model or specific run over another is likely a bit foolhardy and given the large scale agreement, will continue to favor a general model blend for the mass fields with this portion of the forecast as well. Confidence remains average in the day 3 blend as well. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina