Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1257 PM EDT Wed Jun 06 2018 Valid Jun 06/1200 UTC thru Jun 10/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z model evaluation including preferences and forecast confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Northeastern Gulf shortwave stalls through Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average The shortwave progressing through the eastern Gulf of Mexico has caught up to the tail end of the Eastern Seaboard mid-level trof. Some of the energy will continue to shed into the eastern US trof, but guidance continues to be quite strong on retaining some weak stalled shortwave energy in the eastern Gulf. While small differences in shortwave depth/placement exist, it is to be expected, but the overall pattern is well agreed upon with minor exception of the UKMET a bit further west. This seems minor in the grand scheme and suggest a general model blend but at slightly above average confidence due to this minor difference. ...Mid-level shortwave moving across southern Canada through Thursday with accompanying surface low/front eventually the Northeast Fri...Secondary shortwave/SE Canada trough reinforcement Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average through 9/00z... Average afterward 12z NAM/GFS continue to show good continuity with the well agreed upon evolution of the shortwave crossing southern Canada toward the Northeast Wed into Fri. As the shortwave reaches the broad base of a larger scale N Quebec closed low, small differences occur in amplification with the 12z NAM/00z UKMET a bit greater, but still well within a tight cluster. The spread increases into Sat as Northern, upstream jet/shortwave energy reinforces the trof, with the ECMWF a bit sharper with the feature and the CMC a bit slower. These are small perturbations that have varied from run to run enough to not have a tremendous confidence in going one over another and a general model blend should work given the wave differences are fairly small. Confidence is above average through Fri but reduce to average to account for the reinforcement differences. ...Weakly amplified shortwave off CA coast this morning...lifts through Intermountain West supporting "ridge-rider" MCSs in Northern/Central Plains Thurs night into Fri and sliding into Great Lakes/Ohio Valley by Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z GFS/06z GEFS with 00z ECMWF blend Confidence: Below average GOES-WV suite depict broad shortwave lifting into CA at this time, with broad diffluence expanding downstream over the Intermountain West. This evolution is fairly well agreed upon in timing/shape...model spread will increase when convective upscale influence starts late tonight into Wed and seems to be highly dependent on the cap strength. The 12z NAM and GFS continue to be fastest/earliest to develop this wave and retain it as the cap strength is a bit weaker. This is followed by the CMC and then ECMWF/UKMET. While the GFS has significantly backed off the grid scale feedback noted in the 06z run (with the very deep surface reflection)...it has faded back toward the GEFS mean. As the system evolves into Fri, the UKMET/ECMWF continue to depict the strongest Cap strength and focus convection toward the forcing across N IA/S MN into WI/central LP of MI. The thermal gradient/cap may be a bit too strong as the CMC and new GFS continue to support initiation a bit less focused and south. Given outflow boundaries and current soundings/observations with current boundaries... believe the UKMET/ECMWF may be a bit too aggressive and would favor something closer to the 06z GEFS solution, but cannot eliminate the possibility of the stronger cap (given the strength of the overall ridge as a whole). Additionally, the GFS does show some faster timing issues to fully be confident in that camp. Think a compromise of slower GEFS/GFS solution with some 00z ECMWF may be best but confidence is below average due to contingency of cap, strength of outflow boundaries, etc. ...Large closed low off of the British Columbia coast amplifying to the Central West Coast by the end of the week... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 09/00z 12z NAM and 00z ECMWF/UKMET blend thereafter Confidence: Above average before 09/00z Slightly above average after. Closed low over the Eastern Gulf of AK continues to be well behaved in the global guidance, this includes the magnitude/timing of a shortwave rotating around the base toward the Pacific Northwest late Fri into Sat. It is after about 12z Sat there is model spread related to the upstream jet streak and its strength/timing advecting the old occluded core southeast toward N CA/SW OR by late Sat. The 12z GFS has become weak and generally less sharp with the base of the trof, but with this weakness swings the base through into S OR/SW ID a bit faster by 00z Sun. The 00z ECMWF seems sharpest while the CMC lags starting about 09/00z enough to not be favored. The 12z NAM is a bit weaker/less sharp than the ECMWF but not to the degree of the GFS and would favor the ECMWF at the end of the forecast. All considered, will favor a general model blend up to 09/00z but shift to a 12z NAM and 00z UKMET/ECMWF blend thereafter. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina