Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 240 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: 12z GEFS/NAM/UKMET blend Confidence: Slightly above 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. 19z update: The 12z ECMWF continues to be very slow lifting the initial coastal surface low north, even though greater agreement toward the faster/weaker solution continues to gain ground given UKMET/CMC shift. As the western portion of the trof re-orients to become the base of the positive to neutral tilt trof just offshore by 12z Wed, the ECMWF is also a bit more amplified here as well, but at least has shifted north toward the growing consensus. However, along with the CMC there is greater negative tilt/kick to the base of this s/w to progress the wave further east and deeper. The UKMET has shifted very close to the NAM and GEFS solutions. The GFS is close to this cluster, but given the better/slower GEFS mean solution, will incorporate it over the GFS in the blend with the NAM/UKMET, though a general model blend is very close to acceptable, the better clustering provides some additional confidence. ...Central/Southern Plains shortwave sliding into the lower MS valley Tues before stalling in NE Gulf thru Thurs... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model 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. 19z update: The UKMET remains the weakest/washed out of the global guidance but sharpened sufficiently to account for this small difference in the ensemble suite. The 12z CMC picked up pace to match the initial preference. With little change of the ECMWF, will support a general model 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: Slightly above 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. 19z update: Run to Run variation is shown with the 12z ECMWF (a tad south), UKMET, CMC and GEFS mean, but essentially continue to gravitate to a common solution. At this time from occurrence, will continue to support a general model blend at slightly increased confidence. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina